Engineering Geology for Civil Engineers PDF

ENGINEERING GEOLOGY FOR CIVIL ENGINEERS 2019  TABLE OF CONTENTS CHAPTER 1: GENERAL GEOLOGY Geology in Civil Engineering 6 Branches of Geology 7 Earth struct...

ENGINEERING GEOLOGY FOR CIVIL ENGINEERS 2019  TABLE OF CONTENTS CHAPTER 1: GENERAL GEOLOGY Geology in Civil Engineering 6 Branches of Geology 7 Earth structure and Composition 15 Elementary knowledge on Continental drift and Plate tectonics 17 Earth Processes 25 Weathering 33 Work of rivers, wind and sea and their engineering importance 40 Origin, occurrence of earthquake 54 Mode of occurrence 63 Prospecting 65 Ground water 69 Importance of Civil Engineering 75 CHAPTER 2: MINERALOGY Elementary knowledge on symmetry elements of crystallographic systems 79 Physical properties of minerals 82  Study of following rock forming minerals  Quartz family, fieldspar family, augite, hornblende, biotte, muscovite, calcite, garnet Properties, process of formation of all minerals 110 Coal and Petroleum 114 Their origin and occurrence in India 118 2|P age  TABLE OF CONTENTS CHAPTER 3: PETROLOGGY Classification of Rocks 122 Distinction between Ingenious, Sedimentary and Metamorphic rocks 124 Description occurrence, properties and distribution of following rocks: a. Igneous Rocks 127 b. Sedimentary Rocks 132 c. Metamorphic Rocks 137 CHAPTER 4: STRUCTURAL GEOLOGY AND ROCK MECHANICS Attitude of Beds 143 Outcrops 150 Geological Maps 151 Study of Structures folds, faults and joints 157 Rock Mechanics 160 Physical properties and mechanicals properties of: 166 a. Rocks b. Porosity c. Permeability d. Density e. Strength f. Hardness g. Elasticity h. Plasticity 3|P age  TABLE OF CONTENTS Dynamic property of rocks 185 Types of waves theory 187 Factors influencing wave velocity 190 Static and dynamics moduli of elasticity 195 CHAPTER 5: GEOLOGICAL AND GEOPHYSICAL INVESTIGATION IN CIVIL ENGINEERING Site investigations 201 Geological methods 206 Geophysical methods 208 Seismic and electrical methods 210 Core boring 213 Logging of cores 231 Geological condition necessary for construction of: 255 a. Dams b. Funnels c. Building d. Road cutting REFERENCES 268 269 270 271 272 273 274 275 4|P age  CHAPTER 1: GENERAL GEOLOGY 5|P age LESSON 1: GEOLOGY IN CIVIL ENGINEERING Civil engineers who deals with foundations of a structure and works related to dams and tunnels stability of earth slopes etc. should be knowledgeable of geography, climate, type of soil and geology (rock formation) etc., of the place they are working in. But to be exact it is not the job of the civil engineer to the whole details of geography of all the places possible cause it is for professional geologist to do. It is important to know that in those projects like dams or foundation of a bridge where we are going to deal with rocks that the full geological details survey should be done by an engineering geologist, not by a civil engineer. But the civil engineer should understand the geologist’s report and the terms used. One of the most important point in the report is the geological history of the rock formation in the site. Hence in this chapter we will discuss historic geology to be familiarized with the terms and definitions as used in a geological report. Here is an example of a report where the construction site is describe. “The damsite consists of cretaceous rocks underlying miocene deposits which are overlain by quaternary deposits”. The geologist are not only concerned in lithological profile of the site, but also about its history. This chapter objective is to define historical terms used in reports. QUESTION: 1. How does geology helps in civil engineering? 2. Why is it important that the civil engineer should understand the geological details of the soil in their project? 3. What is the importance of learning geology in civil engineering? 6|P age LESSON 2: BRANCHES OF GEOLOGY Geology is the scientific study of the all constituents of planets, their internal and external forms and processes. More precisely, it is the study of nature, structure and history of the planet. Earth is the home to all life, well known to the humankind. Geology, itself, is a major part of The Earth and atmospheric sciences, which were born as twins. The subject of geology encompasses all aspects including the composition, structure, physical properties, and history of a planets'( like Earth's) interrelated components and the processes that are shaping the features on the surface. Geologists are the scientists who study the origin, occurrence, distribution and utilities of all materials (metallic, nonmetallic, inorganic, etc), minerals, rocks, sediments, soils, water, oil and all other inorganic natural resources. It is a very vast subject covering a wide spectrum of scientific principles and holding hundred and fifty plus scientific branches. This report enumerates and highlights most of them, in a nutshell, for all those who intends to know for planning their career path. Some more branches could be added as and when needed. The Subject of Geology: The word "Geology" is derived from the Greek word "geo" means globe and "logos" means logical discourse. Hence, geology is defined as the logical study of all of the globe. Today, geology does not restrict its domain to the study of the planet earth alone. It also includes the study of the other planets and moons of the entire solar system. Geology is a very vast subject. It has several branches. In the olden days, people divided it into two broad areas, as physical geology and historical geology. The subject of Physical geology deals with the study of Earth's materials, such as minerals and rocks, as well as the processes that are operating on and within the Earth and on its surface. The subject of Historical geology focuses on the origin and evolution of life on the Earth, its continents, oceans, atmosphere, and the life of all ecosystems. Historical geology is more than just concentrating on the past events in geological history. It is the study of the sequential changes that have happened and evolved continuously during the past 4.6 billion years on the planet. Geology is a grand parent subject comprising four levels of grand children branches. Main Branches Economic Geology Mineralogy General Geology Paleonotology Geotectonics Petrology Historical Geology Structural Geology Allied Branches Engineering Geology Geophysics Environmental Geology Hydro-geology Geochemistry Marine Geology 7|P age   ECONOMIC GEOLOGY Economic Geology is the scientific study of the Earth’s sources of mineral raw materials and the practical application of the acquired knowledge. Economic geology is primarily concerned with the earth's materials that are used for economic and/or industrial purposes. These materials include precious stones and base metals, nonmetallic minerals, construction-grade stones, petroleum minerals, coal, and water. These materials include precious and base metals, nonmetallic minerals, construction grade stone, petroleum minerals, coal, and water. Economic geology is a sub discipline of the 17 geosciences. It is “the application of geology”. It might also called as the scientific study of the Earth’s sources of mineral raw materials and the practical application of the acquired knowledge The term commonly refers to metallic mineral deposits and all other mineral resources. The techniques employed by other branches of earth sciences (such as geochemistry, mineralogy, geophysics, petrology and structural geology) are used to understand, describe, and exploit an ore deposit. Economic geology may be of interest to other professions such as engineers, environmental scientists, and conservationists because of the far-reaching impact that extractive industries have on society, the economy, and the environment. Economic geology focuses on the properties and characteristics of ores, ore minerals and gangue minerals, gives an outline of the processes of formation and classification of ore deposits, the mode of occurrence, origin, distribution (in India) and economic uses of gold, ores of iron, manganese, chromium, copper, aluminum, lead and zinc; mica, gypsum, magnesite and kyanite; diamond; coal and petroleum  ENGINEERING GEOLOGY Engineering geology is the application of the geology to engineering study for the purpose of assuring that the geological factors regarding the location, design, construction, operation and maintenance of engineering works are recognized and accounted for. Engineering geologists provide geological and geotechnical recommendations, analysis, and design associated with human development and various types of structures. The realm of the engineering geologist is essentially in the area of earth-structure interactions, or investigation of how the earth or earth processes impact human made structures and human activities. Engineering geology is the application of the geology to engineering study for the purpose of assuring that the geological factors regarding the location, design, construction, operation and maintenance of engineering works are recognized and accounted for. Engineering geology studies may be performed during the planning, environmental impact analysis, civil or structural engineering design, value engineering and construction phases of public and private works projects, and during post-construction and forensic phases of projects. Works completed by engineering geologists include; geological hazard assessments, geotechnical, material properties, landslide and slope stability, erosion, flooding, dewatering, and seismic investigations, etc. Engineering geology studies are performed by a geologist or engineering geologist that is educated, trained and has obtained experience related to the recognition and interpretation of natural processes, the understanding of how these processes impact 8|P age  human made structures (and vice versa), and knowledge of methods by which to mitigate against hazards resulting from adverse natural or human made conditions. The principal objective of the engineering geologist is the protection of life and property against damage caused by various geological conditions. The practice of engineering geology is also very closely related to the practice of geological engineering and geotechnical engineering. If there is a difference in the content of the disciplines, it mainly lies in the training or experience of the practitioner.  GEOTECTONICS Geotectonic has a special place among the geological disciplines. Geotectonic is a subject of earth science which deals with the phenomena of solid earth on a global scale and the timescale of the earth’s history. It is the subject relating to the shape, structure, and arrangement of the rock masses resulting from structural deformation of the earth's crust. It encompasses the aspects like radioactive dating, isotope analysis, and deformation mechanisms of fault rocks. The research methods are mainly concerned with the observations and measurements during field work, indoor analyses and experiments using rock samples, employing modeling and theories to support them. In trying to discover the deep-lying causes of tectonic processes, geotectonic has to unite the results of all the Earth sciences. This field also emphasis on the plate geometries, geodynamical processes, and sedimentary products. Origin and history of major tectonic elements of the earth, especially their interaction through time are discussed in detail. Geotectonic deals with solid earth phenomena on a global scale and the timescale of the earth’s history.  HISTORICAL GEOLOGY The planet earth has undergone several changes during each geologic period. Great mountain ranges have been folded up in one period and eroded away in the following one. Many of them have been uplifted more than once. Some of them often got washed off into the adjacent depressed zones like basins and seas. Historical geology is the discipline that uses the principles and techniques of geology to reconstruct and understand the past geological history of Earth. It is a major branch which deals with the records of events of earth history and with the historical sequence and evolution of plants and animals of past ages. Its object is to arrange the events of earth history in the regular chronological order of their occurrence and to interpret their significance. Fortunately, the historical records are preserved in the layered rocks of the crust. Historical Geology is , sometimes , called as Stratigraphical Geology. It brings together all collated details of other Branches of Geology like Paleontology, petrology and structural geology, pertaining to age-wise correlated beds.  MINERALOGY The history of mineralogy is as old as humankind. Minerals have been an important part of our society since the time of prehistoric man. Mineralogy is the branch of geology concerned with the study of minerals. The early writings on mineralogy were devoted to gemstones, mostly seen in the records of ancient Babylonia, the ancient Greco-Roman world, ancient and medieval China, and Sanskrit texts from ancient India 9|P age and the ancient Islamic World. The modern study of mineralogy was founded on the principles of crystallography. It is the scientific study of chemistry, crystal structure, and physical (including optical) properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization. There are several different branches to mineralogy  PALEONOTOLOGY Paleontology (US spelling) or palaeontology (UK spelling) is the scientific study of the developing history of life on earth. It is the study of ancient plants and animals based on their fossil record. It is a fact that the evidence of existence of all life on earth, since the origin, are mostly preserved in rocks. This includes the study of body fossils, tracks, burrows, cast off parts, fossilized faeces ("coprolites"), and chemical residues. Body fossils and trace fossils are the principal types of evidences that help to know about the ancient life. In addition, the geochemical evidences also help to decipher the evolution of primitive life existed before. The subject of Paleontology helps to determine the organisms' evolution and interactions with each other and their environments (their paleoecology). It also heavily relies on the two subjects such as biology and geology. It differs from archaeology in that it excludes the study of anatomically modern humans. It uses techniques drawn from a wide range of allied sciences like biochemistry, mathematics, and engineering. Use of all techniques from other sciences, has enabled paleontologists to discover much of the evolutionary history of life, almost all the way back to the origin of Earth. As the knowledge level has increased, paleontology became a specialised subject with more and more sub-divisions. Some of which focus on different types of fossil organisms , while the other branched out and orients towards the ecology and environmental history of ancient climates. On several fronts, paleontology overlaps with geology (the study of rocks and rock formations) as well as with botany, biology, zoology and ecology. Today, paleontology has become a very big subject with its own branches. These branches are unique in their applications. The major subdivisions of paleontology include paleozoology (animals), paleobotany (plants) and micropaleontology (microfossils) and palynology. Paleozoologists may specialise in invertebrate paleontology, which deals with animals without backbones or in vertebrate paleontology, dealing with fossils of animals with backbones, including fossil hominids (paleoanthropology). Micropaleontologists study microscopic fossils, including organic-walled microfossils whose study is called palynology. There are many developing specialties such as paleobiology, paleoecology, ichnology (the study of tracks and burrows) and taphonomy (the study of what happens to organisms after they expire). Major areas of study include the correlation of rock strata with their geologic ages and the study of evolution of life forms.  PETROLOGY Petrology is the scientific study of rocks, their composition, texture, and structure, their occurrence, distribution and origin in relation to physicochemical conditions and geologic processes of formation. It is concerned with all three major types of rocks— 10 | P a g e igneous, metamorphic, and sedimentary. Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. Petrologic, petrographic, and petrogenetic studies can be applied to igneous, metamorphic or sedimentary rocks. The classification of rocks is based on the information acquired during the petrographic analysis. Petrographic descriptions start with the field notes at the outcrop and include all macroscopic description of hand specimens. The most important tool for a petrographer is the petrographic microscope. The detailed analysis of minerals by optical mineralogy in thin section and the microtexture and structure are critical to understanding the origin of the rock. EPMA- Electron microprobe analysis of individual grains as well as the whole rock chemical analysis by atomic absorption, X-ray fluorescence, and laser-induced breakdown spectroscopy, are used for understanding the genesis and distribution. Analysis of microscopic fluid inclusions, within the mineral grains, with a heating stage on a petrographic microscope, provides clues to the temperature and pressure conditions existent during the mineral formation.  STRUCTURAL GEOLOGY Structural geology is the scientific study of the three-dimensional distribution of rock units with respect to their deformational genesis and histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover the information about their origin and history of deformation (strain) in the rocks. It helps to understand the stress field that resulted in the observed features of strain and geometries. This understanding can also be linked to important events in the geologic past. These can also help to find out the date of events. Once the nature of these rocks are determined, petroleum geologists can discover if petroleum, natural gas, or other natural resources that are trapped within the rocks. Deposits of gold, silver, copper, lead, zinc, and other metals, are commonly located in structurally complex areas. Structural Geology aims to characterise deformation structures (geometry), to characterize flow paths followed by particles during deformation (kinematics), and to infer the direction and magnitude of the forces involved in driving deformation (dynamics). This subject is a field-based discipline. Field Geology is a branch which requires the knowledge of Geomorphology, Petrology, Sedimentology and Stratigraphy, Structural Geology and GIS. Structural geology is an essential part of engineering geology, which is concerned with the physical and mechanical properties of natural rocks.  ENVIRONMENTAL GEOLOGY Environmental geology, like hydrogeology, is an applied science concerned with the practical application of the principles of geology in the solving of environmental problems. It is a multidisciplinary field that is closely related to engineering geology and, to a lesser extent, to environmental geography. Environmental geology, like hydrogeology, is an applied science concerned with the practical application of the principles of geology in the solving of environmental problems. It is a multidisciplinary field that is closely related to engineering geology and, to a lesser extent, to environmental geography. Each of these fields involves the study of the interaction of humans with the geologic environment, 11 | P a g e including the biosphere, the lithosphere, the hydrosphere, and to some extent the atmosphere. In other words, environmental geology is the application of geological information to solve conflicts, minimizing possible adverse environmental degradation or maximizing possible advantageous condition resulting from the use of natural and modified environment.  GEOCHEMISTRY Geochemistry is a branch that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the entire Solar System. This subject has made important contributions to the understanding of a number of processes including mantle convection, the formation of planets and the origins of all kinds of rocks, minerals, mineral fuels, soils and valuables. The mobility of all elements on in and out of a planet are fully studied under geochemistry. Today. geochemistry is a major branch of Earth Science that applies varieties of chemical principles to deepen the understanding of the planets. Geochemists consider the globe composed of discrete spheres — rocks, fluids, gases and biology — that exchange matter and energy over a range of time scales. An appreciation for rates of reactions and the range of physical conditions responsible for the chemical expressions of each sphere provides the significant framework to study the co-evolution of the solid Earth, its oceans, atmosphere, biosphere, and climate. Sub-disciplines of geochemistry include biogeochemistry, organic geochemistry, trace and elemental geochemistry, and metamorphic and igneous-rock geochemistry. The wings of geochemistry are, Organic Geochemistry, Inorganic Geochemistry, Stable Isotope Geochemistry, Light Stable Isotope Geochem, Metallic Element Stable Isotope Geochem, Actinide/Radionuclide Geochemistry, Petroleum Geochemistry, Aqueous Geochemistry, Environmental Geochemistry, Biogeochemistry, and Planetary Geochemistry. It involves thermodynamics, and analytical chemistry as major tools and techniques. The analytical instruments and their use are also a part of it. The instruments include inductively- coupled plasma and stable-isotope mass spectrometers, a chromFTIR lab, fully automated electron microprobe, X-ray diffractometer, laser Raman, SEM, and several other equipment facilities.  GEOPHYSICS Geophysics is a major subject of natural science. It is a core branch of geology. It is concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and composition; its dynamics and their surface expression in plate tectonics, the generation of magmas, volcanism and rock formation. The study includes the water cycle including snow and ice; fluid dynamics of the oceans and the atmosphere; electricity and magnetism in the ionosphere and magnetosphere and solar-terrestrial relations; and analogous problems associated with the Moon and other planets. Although geophysics was only recognized as a separate discipline in the 19th century, its origins date back to ancient times. The first magnetic 12 | P a g e compasses were made from lodestones, while more modern magnetic compasses played an important role in the history of navigation. The first seismic instrument was built in 132 BC. Isaac Newton applied his theory of mechanics to the tides and the precession of the equinox; and instruments were developed to measure the Earth's shape, density and gravity field, as well as the components of the water cycle. In the 20th century, geophysical methods were developed for remote exploration of the solid Earth and the ocean, and geophysics played an essential role in the development of the theory of plate tectonics. Today, Geophysics is applied to societal needs, such as mineral resources, mitigation of natural hazards and environmental protection. Geophysical survey data are used to analyze potential petroleum reservoirs and mineral deposits, locate groundwater, find archaeological relics, determine the thickness of glaciers and soils, and assess sites for environmental remediation. While there are many divisions of geophysics such as oceanography, atmospheric physics, climatology, and planetary geophysics, this brochure describes 25 three of the most popular The major branches of geophysics are: 1. Biogeophysics – study of how plants, microbial activity and other organisms alter geologic materials and affect geophysical signatures. 2. Exploration geophysics – the use of surface methods to detect concentrations of ore minerals and hydrocarbons. 3. Geophysical fluid dynamics – study of naturally occurring, large-scale flows on Earth and other planets. 4. Geodesy – measurement and representation of the Earth, including its gravitational field. 5. Geodynamics – study of modes of transport deformation within the Earth: rock deformation, mantle convection, heat flow, and lithosphere dynamics. 6. Geomagnetism – study of the Earth's magnetic field, including its origin, telluric currents driven by the magnetic field, the Van Allen belts, and the interaction between the magnetosphere and the solar wind. 7. Mathematical geophysics – development and applications of mathematical methods and techniques for the solution of geophysical problems. 8. Mineral physics – science of materials that compose the interior of planets, particularly the Earth. 9. Near-surface geophysics – the use of geophysical methods to investigate small-scale features in the shallow (tens of meters) subsurface. 10. Paleomagnetism – measurement of the orientation of the Earth's magnetic field over the geologic past. 11. Seismology – study of the structure and composition of the Earth through seismic waves, and of surface deformations during earthquakes and seismic hazards. 12. Tectonophysics – study of the physical processes that cause and result from plate tectonics. Branches of geophysics: Petroleum Geophysics and Environmental Geophysics. 13 | P a g e   HYDRO-GEOLOGY Hydrogeology is the study of the distribution and movement of water in aquifers and shallow porous media—that is, the porous layers of rock, sand, silt, and gravel below the Earth's surface. Hydrogeology examines the rate of diffusion of water through these media as the water moves down its energy gradient. The flow of water in the shallow subsurface is also pertinent to the fields of soil science, agriculture, and civil engineering. The flow of water and other fluids (hydrocarbons and geothermal fluids) in deeper formations is relevant to the fields of geology, geophysics, and petroleum geology. Geohydrology is the area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust. The term geohydrology is often used interchangeably.  MARINE GEOLOGY Marine geology or geological oceanography is the study of the history and structure of the ocean floor. It involves geophysical, geochemical, sedimentological and paleontological investigations of the ocean floor and coastal zone. Marine geology has strong ties to physical oceanography. Marine geology or geological oceanography is the study of the history and structure of the ocean floor. It involves geophysical, geochemical, sedimentological and paleontological investigations of the ocean floor and coastal zone. Marine geology has strong ties to geophysics and to physical oceanography. Marine geological studies were of extreme importance in providing the critical evidence for sea floor spreading and plate tectonics in the years following World War II. The deep ocean floor is the last essentially unexplored frontier and detailed mapping in support of both military (submarine) objectives and economic (petroleum and metal mining) objectives drives the research. QUESTION: 1. What are the most important branches of Geology? 2. Why does Geology is important to the field of Civil Engineering? 3. State the importance of Engineering Geology and Environmental Geology. 14 | P a g e LESSON 3: EARTH STRUCTURE AND COMPOSITION Core, mantle, and crust are divisions based on composition. The crust makes up less than 1 percent of Earth by mass, consisting of oceanic crust and continental crust is often more felsic rock. The mantle is hot and represents about 68 percent of Earth’s mass. Finally, the core is mostly iron metal. The core makes up about 31% of the Earth. Lithosphere and asthenosphere are divisions based on mechanical properties. The lithosphere is composed of both the crust and the portion of the upper mantle that behaves as a brittle, rigid solid. The asthenosphere is partially molten upper mantle material that behaves plastically and can flow.  Crust Earth’s outer surface is its crust; a cold, thin, brittle outer shell made of rock. The crust is very thin, relative to the radius of the planet. There are two very different types of crust, each with its own distinctive physical and chemical properties. Oceanic crust is composed of magma that erupts on the seafloor to create basalt lava flows or cools deeper down to create the intrusive igneous rock gabbro. Sediments, primarily muds and the shells of tiny sea creatures, coat the seafloor. Sediment is thickest near the shore where it comes off the continents in rivers and on wind currents. Continental crust is made up of many different types of igneous, metamorphic, and sedimentary rocks. The average composition is granite, which is much less dense than the mafic igneous rocks of the oceanic crust. Because it is thick and has relatively low density, continental crust rises higher on the mantle than oceanic crust, which sinks into the mantle to form basins. When filled with water, these basins form the planet’s oceans. The lithosphere is the outermost mechanical layer, which behaves as a brittle, rigid solid. The lithosphere is about 100 kilometers thick. The definition of the lithosphere is based on how earth materials behave, so it includes the crust and the uppermost mantle, which are both brittle. Since it is rigid and brittle, when stresses act on the lithosphere, it breaks. This is what we experience as an earthquake. Figure 1. EARTH STRUCTURE  Mantle The two most important things about the mantle are: (1) it is made of solid rock, and (2) it is hot. Scientists know that the mantle is made of rock based on evidence from 15 | P a g e seismic waves, heat flow, and meteorites. The properties fit the ultramafic rock peridotite, which is made of the iron- and magnesium-rich silicate minerals. Peridotite is rarely found at Earth’s surface.Scientists know that the mantle is extremely hot because of the heat flowing outward from it and because of its physical properties. Heat flows in two different ways within the Earth: conduction and convection. Conduction is defined as the heat transfer that occurs through rapid collisions of atoms, which can only happen if the material is solid. Heat flows from warmer to cooler places until all are the same temperature. The mantle is hot mostly because of heat conducted from the core. Convection is the process of a material that can move and flow may develop convection currents. Convection in the mantle is the same as convection in a pot of water on a stove. Convection currents within Earth’s mantle form as material near the core heats up. As the core heats the bottom layer of mantle material, particles move more rapidly, decreasing its density and causing it to rise. The rising material begins the convection current. When the warm material reaches the surface, it spreads horizontally. The material cools because it is no longer near the core. It eventually becomes cool and dense enough to sink back down into the mantle. At the bottom of the mantle, the material travels horizontally and is heated by the core. It reaches the location where warm mantle material rises, and the mantle convection cell is complete.  Core At the planet’s center lies a dense metallic core. Scientists know that the core is metal for a few reasons. The density of Earth’s surface layers is much less than the overall density of the planet, as calculated from the planet’s rotation. If the surface layers are less dense than average, then the interior must be denser than average. Calculations indicate that the core is about 85 percent iron metal with nickel metal making up much of the remaining 15 percent. Also, metallic meteorites are thought to be representative of the core. If Earth’s core were not metal, the planet would not have a magnetic field. Metals such as iron are magnetic, but rock, which makes up the mantle and crust, is not. Scientists know that the outer core is liquid and the inner core is solid because S-waves stop at the inner core. The strong magnetic field is caused by convection in the liquid outer core. Convection currents in the outer core are due to heat from the even hotter inner core. The heat that keeps the outer core from solidifying is produced by the breakdown of radioactive elements in the inner core. QUESTIONS: 1. What are the two types of crust and its properties? 2. What is the Earth’s core made up of? 3. Which layer make up the asthenosphere? 16 | P a g e LESSON 4: ELEMENTARY KNOWLEDGE ON CONTINENTAL DRIFT AND PLATE TECTONICS Several centuries ago, observers looking at global maps noticed the similarity in outline of the eastern coast of South America and the western coast of Africa (figure 3.1). In 1855, Antonio Snider went so far as to publish a sketch showing how the two continents could fit together, jigsaw-puzzle fashion. Such reconstructions gave rise to the bold suggestion that perhaps these continents had once been part of the same landmass, which had later broken up. Wegener began to publish his ideas in 1912 and continued to do so for nearly two decades. He proposed that all the continental landmasses had once formed a single supercontinent, Pangaea (Greek for “all lands”), which had then split apart, Figure 1. The jigsaw-puzzle fit of South the modern continents moving to their present America and Africa suggests that they positions via a process called continental drift. were once joined together and subsequently separated by continental drift. Several other prominent scientists found the idea intriguing. However, most people, scientists and nonscientists alike, had difficulty visualizing how something as massive as a continent could possibly “drift” around on a solid earth, or why it should do so. In other words, no mechanism for moving continents was apparent. There were obvious physical objections to solid continents plowing through solid ocean basins, and there was no evidence of the expected resultant damage in crushed and shattered rock on continents or sea floor. To a great many reputable scientists, these were insurmountable obstacles to accepting the idea of continental drift. As it turns out, additional relevant evidence was simply undiscovered or unrecognized at the time. Beginning in the 1960s, data of many different kinds began to accumulate that indicated that the continents have indeed moved. Continental drift turned out to be just one consequence of processes encompassed by a broader theory known as plate tectonics. Tectonics is the study of largescale movement and deformation of the earth’s outer layers. Plate tectonics relates such deformation to the existence and movement of rigid “plates” over a weaker, more plastic layer in the earth’s upper mantle.  Plate Tectonics—Underlying Concepts As already noted, a major obstacle to accepting the concept of continental drift was imagining solid continents moving over solid earth. However, the earth is not rigidly solid 17 | P a g e from the surface to the center of the core. In fact, a plastic zone lies relatively close to the surface. A thin shell of relatively rigid rock can move over this plastic layer below. The existence of plates, and the occurrence of earthquakes in them, reflect the way rocks respond to stress.  Stress and Strain in Geologic Materials An object is under stress when force is being applied to it. The stress may be compressive, tending to squeeze or compress the object, or it may be tensile, tending to pull the object apart. A shearing stress is one that tends to cause different parts of the object to move in different directions across a plane or to slide past one another, as when a deck of cards is spread out on a tabletop by a sideways sweep of the hand. Strain is deformation resulting from stress. It may be either temporary or permanent, depending on the amount and type of stress and on the physical properties of the material. If elastic deformation occurs, the amount of deformation is proportional to the stress applied, and the material returns to its original size and shape when the stress is removed. A gently stretched rubber band or squeezed tennis ball shows elastic behavior.  Lithosphere and Asthenosphere The earth’s crust and uppermost mantle are somewhat brittle and elastic. Together they make up the outer solid layer of the earth called the lithosphere, from the Greek word lithos, meaning “rock.” The lithosphere varies in thickness from place to place on the earth. It is thinnest underneath the oceans, where it extends to a depth of about 50 kilometers. The lithosphere under the continents is both thicker on average than is oceanic lithosphere, and more variable in thickness, extending in places to about 250 kilometers. The layer below the lithosphere is the asthenosphere, which derives its name from the Greek word asthenias, meaning “without strength.” The asthenosphere extends to an average depth of about 300 kilometers in the mantle. Its lack of strength or rigidity results from a combination of high temperatures and moderate confining pressures that allows the rock to flow plastically under stress. Below the asthenosphere, as pressures increase faster than temperatures with depth, the mantle again becomes more rigid and elastic. Figure 2. The outer zones of the earth. The terms crust and mantle have compositional The asthenosphere was discovered by studying implications lithosphere and asthenosphere describe physical properties. The lithosphere the behavior of seismic waves from earthquakes. includes the crust and uppermost mantle. The Its presence makes the concept of continental asthenosphere lies entirely within the upper mantle. Below it, the rest of the mantle is more drift more plausible. The relationships among rigidly solid again. crust, mantle, lithosphere, and asthenosphere are illustrated in figure 3. 18 | P a g e   Locating Plate Boundaries The distribution of earthquakes and volcanic eruptions indicates that these phenomena are far from uniformly distributed over the earth. They are, for the most part, concentrated in belts or linear chains. This is consistent with the idea that the rigid shell of lithosphere is cracked in places, broken up into pieces, or plates. The volcanoes and earthquakes are concentrated at the boundaries of these lithospheric plates, where plates jostle or scrape against each other.  Plate Tectonics—Accumulating Evidence Through the twentieth century, geologists continued to expand their knowledge of the earth, extending their observations into the ocean basins and applying new instruments and techniques, such as measuring magnetism in rocks, or studying the small variations in local gravitational pull that can provide information about geology below.  The Topography of the Sea Floor Those who first speculated about possible drifting continents could not examine the sea floor for any relevant evidence. Indeed, many assumed that the sea floor was simply a vast, monotonous plain on which sediments derived from the continents accumulated. Once topographic maps of the sea floor became available, however, several striking features were revealed (figure 3.3). There were long ridges, some thousands of kilometers long and rising as much as 2 kilometers (1.3 miles) above the surrounding plains, thus rivaling continental mountain ranges in scale. Examples can be seen along the western edge of South America, just south of the Aleutian Islands, and east of Japan. Studies of the ages and magnetic properties of seafloor rocks, as described below, provided the keys to the significance of the ocean ridges and trenches. Figure 3. Global relief map of the world, including seafloor topography. Note ridges and trenches on the sea floor. 19 | P a g e   Magnetism in Rocks—General The rocks of the ocean floors are rich in ferromagnesian minerals, and such minerals are abundant in many rocks on the continents as well. Most iron-bearing minerals are at least weakly magnetic at surface temperatures. Each magnetic mineral has a Curie temperature, the temperature below which it remains magnetic, but above which it loses its magnetic properties. The Curie temperature varies from mineral to mineral, but it is always below the mineral’s melting temperature. A hot magma is therefore not magnetic, but as it cools and solidifies, and iron-bearing magnetic minerals crystallize from it, those magnetic crystals tend to line up in the same direction. This is the basis for the study of paleomagnetism, “fossil magnetism” in rocks. The explanation for magnetic reversals must be related to the origin of the magnetic field. The outer core is a metallic fluid, consisting mainly of iron. Motions in an electrically conducting fluid can generate a magnetic field, and this is believed to be the origin of the earth’s field. (The simple presence of iron in the core is not enough to account for the magnetic field, as core temperatures are far above the Curie temperature of iron.) Perturbations or changes in the fluid motions, then, could account for reversals of the field. The details of the reversal process remain to be determined. Figure 5. Age distribution of the sea floor superimposed on a shaded relief map. (“B.P.” means “before present”). Note relative spreading rates of Mid-Atlantic Ridge (slower) and East Pacific Rise (faster), shown by wider color bands in the Pacific. -Atlantic Ridge (slower) and East Pacific Rise (faster), shown by wider color bands in the Pacific.  Age of the Ocean Floor The ages of seafloor basalts themselves lend further support to this model of seafloor spreading. Specially designed research ships can sample sediment from the deep-sea floor and drill into the basalt beneath. The time at which an igneous rock, such as basalt, crystallized from its magma can be determined by method. When this is done for many samples of seafloor basalt, a pattern emerges. The rocks of the sea floor are youngest close to the ocean ridges and become progressively older the farther away they are from the ridges on either side (see figure 3.4). Like the magnetic stripes, the age pattern is symmetric across each ridge. As seafloor spreading progresses, previously formed rocks are continually spread apart and moved 20 | P a g e farther from the ridge, while fresh magma rises from the asthenosphere to form new lithosphere at the ridge. The oldest rocks recovered from the sea floor, well away from active ridges, are about 200 million years old.  Polar-Wander Curves Evidence for plate movements does not come only from the sea floor. For reasons outlined later in the chapter, much older rocks are preserved on the continents than in the ocean—some continental samples are over 4 billion years old—so longer periods of earth history can be investigated through continental rocks. Studies of paleomagnetic orientations of continental rocks can span many hundreds of millions of years and yield quite complex data. Magnetized rocks of different ages on a single continent may point to very different apparent magnetic pole positions. The magnetic north and south poles may not simply be reversed but may be rotated or tilted from the present magnetic north and south. When the directions of magnetization and latitudes of many rocks of various ages from one continent are determined and plotted on a map, it appears that the magnetic poles have meandered far over the surface of the earth— if the position of the continent is assumed to have been fixed on the earth throughout time. The resulting curve, showing the apparent movement of the magnetic pole relative to the continent as a function of time, is called the polar wander curve. We know now, however, that it isn’t the poles that have “wandered” so much. How Far, How Fast, How Long, How Come? Past Motions, Present Velocities Rates and directions of plate movement have been determined in a variety of ways. As previously discussed, polar-wander curves from continental rocks can be used to determine how the continents have shifted. Seafloor spreading is another way of determining plate movement. Figure 6. Seismic tomography is a technique that uses seismic-wave velocities to locate areas of colder rock (blue) and warmer rock (red). The deep cold rocks in this cross section may be sunken slabs of cold subducted lithosphere; the warmer columns at right, mantle plumes. The direction of seafloor spreading is usually obvious: away from the ridge. Rates of seafloor spreading can be found very simply by dating rocks at different distances from the spreading ridge and dividing the distance moved by the rocks. 21 | P a g e Another way to monitor rates and directions of plate movement is by using mantle hot spots. These are isolated areas of volcanic activity usually not associated with plate boundaries. They are attributed to rising columns of warm mantle material ( plumes), perhaps originating at the base of the mantle. Reduction in pressure as the plume rises can lead to partial melting, and the resultant magma can rise through the overlying plate to create a volcano. If we assume that mantle hot spots remain fixed in position while the lithospheric plates move over them, the result should be a trail of volcanoes of differing ages with the youngest closest to the hot spot. Looking at many such determinations from all over the world, geologists find that average rates of plate motion are 2 to 3 centimeters per year. In a few places, movement at rates over 10 centimeters per year is observed, and, elsewhere, rates may be slower, but a few centimeters per year is typical. This seemingly trivial amount of motion does add up through geologic time. Movement of 2 centimeters per year for 100 million years means a shift of 2000 kilometers, or about 1250 miles! Why Do Plates Move? A driving force for plate tectonics has not been identified. For many years, the most widely accepted explanation was that the plates were moved by large convection cells slowly churning in the plastic asthenosphere. According to this model, hot material rises at the spreading ridges, some magma escapes to form new lithosphere, but the rest of the rising asthenosphere material spreads out sideways beneath the lithosphere, slowly cooling in the process. As it flows outward, it drags the overlying lithosphere outward with it, thus continuing to open the ridges. When it has cooled somewhat, the flowing material is dense enough to sink back deeper into the asthenosphere. Movements between Plates It is believed that the plates can move between themselves just like ice blocks floating on ice water in figure 1.7 producing various forces between the plates causing earthquakes. Figure 7. Movements of continental plates.  Plate Tectonics and the Rock Cycle In the previous chapter, we noted that all rocks may be considered related by the concept of the rock cycle. We can also look at the rock cycle in a plate-tectonic context, as illustrated in figure 8. New igneous rocks Figure 8. An ocean-continent convergence 22 | P a g e zone illustrates some of the many ways in which plate-tectonic activity transforms rocks. form from magmas rising out of the asthenosphere at spreading ridges or in subduction zones. The heat radiated by the cooling magmas can cause metamorphism, with recrystallization at an elevated temperature changing the texture and/or the mineralogy of the surrounding rocks. Some of these surrounding rocks may themselves melt to form new igneous rocks. The forces of plate collision at convergent margins also contribute to metamorphism by increasing the pressures acting on the rocks. Weathering and erosion on the continents wear down preexisting rocks of all kinds into sediment. Much of this sediment is eventually transported to the edges of the continents, where it is deposited in deep basins or trenches. Through burial under more layers of sediment, it may become solidified into sedimentary rock. Sedimentary rocks, in turn, may be metamorphosed or even melted by the stresses and the igneous activity at the plate margins. Some of these sedimentary or metamorphic materials may also be carried down with subducted oceanic lithosphere, to be melted and eventually recycled as igneous rock. Plate-tectonic processes thus play a large role in the formation of new rocks from old that proceeds continually on the earth. SUMMARY This chapter gives a short account of the rocks subjected to stress may behave either elastically or plastically. At low temperatures and confining pressures, they are more rigid, elastic, and often brittle. At higher temperatures and pressures, or in response to stress applied gradually over long periods, they tend more toward plastic behavior. The outermost solid layer of the earth is the 50- to 100- kilometer-thick lithosphere, which is broken up into a series of rigid plates. The lithosphere is underlain by a plastic layer of the mantle, the asthenosphere, over which the plates can move. This plate motion gives rise to earthquakes and volcanic activity at the plate boundaries. At seafloor spreading ridges, which are divergent plate boundaries, new sea floor is created from magma rising from the asthenosphere. The sea floor moves in conveyor belt fashion, ultimately to be destroyed in subduction zones, a type of convergent plate boundary, where oceanic lithosphere is carried down into the asthenosphere. It may eventually be remelted or sink as cold slabs down through the mantle. Magma rises through the overriding plate to form volcanoes above the subduction zone. Where continents ride the leading edges of converging plates, continent-continent collision may build high mountain ranges. Present rates of plate movement average a few centimeters a year. One possible driving force for plate tectonics is slow convection in the asthenosphere; another is gravity pulling cold, dense lithosphere down into the asthenosphere, dragging the asthenosphere along. Plate-tectonic processes appear to have been active for much of the earth’s history. They play an integral part in the rock cycle—building continents to weather into sediments, carrying rock and sediment into the warm mantle to be melted into magma that rises to create new igneous rock and metamorphoses the lithosphere through which it rises, subjecting rocks to the stress of collision— assisting in the making of new rocks from old. 23 | P a g e QUESTIONS 1. What causes strain in rocks? How do elastic and plastic materials differ in their behavior? 2. Define the terms lithosphere and asthenosphere. Where are the lithosphere and asthenosphere found? 3. Describe the rock cycle in terms of plate tectonics, making specific reference to the creation of new igneous, metamorphic, and sedimentary rocks. 24 | P a g e LESSON 5: EARTH PROCESSES Earth processes shape the Earth’s surface and the sedimentary deposits that record those processes link human timescales to geologic history. The dynamic environments at Earth’s surface reflect connections between biological, physical and chemical systems. The study of earth processes is based on number of fundamental principles, some of which are unique. The earths topographic features are a mixture of landforms being formed at the present time and others that have been shaped in the past by processes no longer active, it embraces the investigation of both the mechanics of modern processes and the historic influence of geologic time. The former includes an understanding of the physics and chemistry of surface processes that generate landforms, and all the latter adds the element of time to landforms that evolves over period of time too long to study in the context of modern processes. The origin of landforms can be related to a particular geologic process, or set of processes, and the landforms thus developed evolve with time through a sequence of forms having distinct characteristics at successive stages. (Davis, 1990) The surface processes responsible for most of the earth’s topographic features are weathering, mass wasting, running water, ground water, glaciers, waves, wind, tectonism, and volcanism. Considering the mechanics, and in some cases the chemistry, and of each of the processes, followed by the analysis of the landforms that they create and the evolution of such forms with time. The earth processes bestows distinctive features on the landscape and develops characteristics assemblages of landforms from which the origin of the forms can be identified. In the very same way that fingerprints can be used to identify a person. Earth’s surface is a dynamic interface across which the atmosphere, water, biota, and tectonics interact to transform rock into landscapes with distinctive features crucial to the function and existence of water resources, natural hazards, climate, biogeochemical cycles, and life. Interacting physical, chemical, biotic, and human processes “Earth surface processes” alter and reshape Earth’s surface on spatial scales that range from those of atomic particles to continents and over time scales that operate from nanoseconds to millions of years. The study of Earth surface processes and the landscapes they create is rich with open questions and opportunities to make fundamental scientific advances and to understand and predict the interactions, causes, and effects of these processes. Scientists who study Earth’s “surface processes” have a distinctive and novel ability to contribute to understanding how Earth’s surface changes with time and resolving important environmental challenges that may arise from these changes. Research in Earth surface processes has grown significantly in the last two decades, in response largely to two factors. First, scientists, policy makers, and the public have become increasingly aware of the impact of human activity and climate change on Earth’s surface. The changes to Earth’s surface affected by natural events and by humans, notably through land use, have altered the physical, chemical, and biological integrity of soils, mountains, prairies, rivers, coasts, and watersheds. Thus, society has heightened its demand for scientific guidance in making decisions concerning the future of Earth’s surface. Second, development of new analytical and computing tools has markedly 25 | P a g e increased our ability to examine Earth’s surface at high spatial and temporal resolution and to develop models that can help to understand the speed and magnitude over which surface processes interact and affect changes.  EVOLUTION OF LANDFORMS Landforms evolve with time through a continuous sequence of forms having typical features at successive stages of development, largely as a result of continuous changes in processes and rates as time goes on. Given example is the basin of Navation, formed under a permanent snowfield below the snowline, it enlarges until the snow and ice accumulate to form a glacier, which then develops a steep upper headwall and create a scoured basin. The changes in the landforms are progressive, and the forms evolve continuously.  MONITORING EARTH SURFACE PROCESSES AT HIGH RESOLUTION IN SPACE AND TIME The evolution and increasing availability of new measurement technologies has enabled many of the advances in Earth surface processes. Technological advances in remote sensing, geochemistry, geochronology, and computing have fostered great progress in the study of Earth’s surface. For example, recent advances in the areas of digital topography and geochronology enable scientists not just to conduct research faster or more accurately, but to make observations and interpretations that were not possible previously.  DIGITAL TOPOGRAPHY Throughout history, the creation of maps has been a means of recording observations that enable us to find and denote paths and patterns and to generate hypotheses about the controls on the spatial relationship of features. Topographic maps, depicting land elevation and displaying landforms, have been crucial to scientific inquiry about the Earth and have been central to land development. In the 1980s, a profound step was taken when line drawings of elevations on topographic maps were digitized and the landscape could be represented via digital elevation models on computers. This innovation launched thousands of scientific studies exploiting this new capability and ultimately gave rise to many new practical applications. In the last decade, technological advances have enabled the first airborne and satellite-mounted surveys of topography using radar (interferometric synthetic aperture radar, InSAR) and laser (light detection and ranging, or lidar) technology, giving unprecedented spatial resolution over large areas. This development has led to a second wave of digital topographic studies that are transforming not just research in Earth surface processes, but also the fields of agriculture, ecology, engineering, and planning. With regard to Earth surface processes, digital elevation data enable us to examine, for the first time, topographic features over broad areas using computer-automated techniques. This ability is leading to new insights and tools that link 26 | P a g e  landscapes to hydrology, geochemistry, tectonics, and climate. Although many digital elevation data are coarse in scale for studying the features, for example, of mountain belts with long, high hillslopes, the data have been truly revolutionary. The advances in the past decade are akin to those of the 1960s in the fields of seismology and geophysics, when accessibility to global seismic and paleomagnetic data and new tools to process such signals spurred the plate tectonics revolution and greater understanding of Earth’s subsurface processes. One of the most recent transformative phases in the measurement and characterization of landscape topography has been the ongoing development of laser surveying, both from the ground and from airborne instruments. This method is referred to as lidar, or airborne laser swath mapping (ALSM) in the case of aerial surveys. High-resolution swath bathymetry uses sonar for the same types of measurements in marine environments. With lidar, a laser pulse is sent from the instrument, and the time for its return from a reflected surface is detected and used to calculate distance. Current technology permits typical accuracies to about 5 to 10 centimeters vertically and 20 to 30 centimeters horizontally, with data returns every few decimeters. From these returns a point cloud of elevation data is created; various analytical methods are then used to distinguish vegetation from ground. Obtaining surveys over broad areas that document topography at the resolution at which transport, erosion, and deposition processes operate. Lidar data also capture important quantitative attributes of vegetation that can be used in studies. of ecohydrology and eco geomorphology. Landslide scars, channel banks, river terraces, floodplain features, fault traces, and other landforms can be detected, quantified, and used to advance theoretical and practical understanding. Repeat scans allow change detection as never previously possible. These techniques also permit improved understanding of the human impact on types and rates of geomorphic processes. Documenting topography at the resolution of transport and erosion processes. Area in red box on the digital air photo is the area covered by the upper lidar images. Image width of the digital air photo is 3 kilometers. Figure 9. TOPOGRAPHY SOURCE: National Center for Airborne Laser Mapping (NCALM), Bottom Image courtesy of Google Earth.  GEOLOGIC STRUCTURES Landforms are produced either by directly offsetting the land surface or by secondary erosion of rocks of differing resistance. Most of the earth’s major features, such as the mountain ranges and the configuration of the continents and the ocean formed basins which are the results of large-scale motion of crustal plates. Direct offsetting of the land surface is known as neotectonism, referring to very recent crustal activity. For example, an escarpment created by fault movement is a land form caused directly by tectonic movement. The etching out of the valleys and ridges by erosion of rocks of 27 | P a g e differing resistance whose spatial configuration is determined by the geologic structure. Recent erosions has etched out the weaker beds into valleys and the more resistant ones into ridges whose position and orientation are determined by the earlier crustal deformation. Usually the result of the powerful tectonic forces that occur within the earth. These forces fold and break rocks, form deep faults, and build mountains. Repeated applications of force the folding of already folded rocks or the faulting and offsetting of already faulted rocks can create a very complex geologic picture that is difficult to interpret. Most of these forces are related to plate tectonic activity. Some of the natural resources we depend on, such as metallic ores and petroleum, often form along or near geologic structures. Thus, understanding the origin of these structures is critical to discovering more reserves of our nonrenewable resources.  GEOMORPHIC SYSTEMS The understanding of surface processes and geomorphic systems involves application of a number of concepts common to all scientific disciplines. These concepts include uniformitarianism, equilibrium, and positive feedback.  EQUILIBRIUM SYSTEM An equilibrium system is one in which a delicate balance exists between opposing forces such that any change in the variables that control the system produces a change in one or more of the other variables to generate a new balance. In late 1884, Le Chatelier expressed the concept that a change in any variables governing the equilibrium of a chemical system will cause a compensating change among other variables that will establish stability in the system. The general equation is known as the equilibrium was anticipated seven years before Le Chatelier by American geomorphologist G.K. Gilbert. He applied the concept of negative feedback to explain streams that transport as much load as they are capable of carrying without either eroding or depositing any of it, a condition he called graded. If a graded stream has a steeper slope than that required to develop the velocity it needs for transporting the load, the increased velocity accompanying the steeper slope will lead to entrainment of more channel material, and erosion of the bed will lower the slope until the velocity is adjusted to just transport the load. A change in slope from steep to gentler will have the opposite effect – increasing the slope by deposition of material in the channel. In this way, a graded stream produces a smooth longitudinal profile of equilibrium. Every reach of graded stream is part of an equilibrium system, and any interruptions of the variables controlling the system will introduce waves of erosion and deposition that over through the system until a new equilibrium is produced. In geomorphic equilibrium, negative feedback processes counteract external changes to the system and stabilize the system by making adjustments within it. For the given example coarse of debris, beyond the capacity of the stream of transport, is introduced into a stream, deposition occurs in time, thereby it is needed to increase the sloping of the channel and the increasing of velocity of flow until it is sufficient to transport the newly added coarse material, at which time has a new steady state is attained. 28 | P a g e  The applied concept of Gilbert to hillslopes and pediments in the western part of the United States. He then identified equilibrium in stream channels, equilibrium of hillslopes, and equilibrium of control of pediments. Each of the systems responds to changes in controlling the variables by evoking a change in the system, which reestablishes new balance. Gilbert’s importance was recognized by Davis his work about the perception of equilibrium in streams and slopes. Davis incorporated them into his work concept which is the cycle of erosion. Mackin also placed great emphasis on the profile of equilibrium in his classic 1948 paper on the graded stream: according to Mackin “Its diagnostic characteristics is that any change in any of the controlling factors will cause a displacement of the equilibrium in a direction that will tend to absorb the effect of change.” Time is a critical element in geomorphic equilibrium because of most natural geomorphic systems are dynamic and equilibrium must be considered in a framework of long or short periods of geologic time. In his definition of a graded stream, Mackin wrestled with the problem of changes in as fluvial system “over a short period of years” in order to deal with changes in streams that occur hourly, daily, weekly and so on. Most of these short term changes balance out in the long run and do not really produce a lasting geologic effect. TYPES OF EQUILIBRIA A. STEADY STATE EQUILIBRIUM FIGURE A 29 | P a g e  B. DECLINING EQUILIBRIUM FIGURE B A. DYNAMIC EQULIBRIUM FIGURE C B. METASTABLE EQUILIBRIUM (EPISODIC EROSION) FIGURE D 30 | P a g e  C. DYNAMIC METASTABLE EQUILIBRIUM (EPISODIC EROSION) FIGURE E The steady state equilibrium has an under conditions that change very little with time. For example, an erosional surface of low relief in the latter stages of the cycle of erosion. The figure A illustrates the two variations of this type of equilibrium and that the conditions are constant. Figure B has small variations in forms oscillate about a constant average condition, and a short-term change offset one another, so that the overall trend does not deviate significantly. Declining Equilibrium occurs when the rate of change declines with time to successively lower the rate of change in figure C. A related type of equilibrium known as dynamic equilibrium, consists of small variations about a changing average condition. Short term oscillations do not entirely offset on another so that the average trend changes progressively. This type of equilibrium is characteristics of graded streams and graded slopes in the cycle of erosion where the rate of erosion of streams slowly changes as topographic relief of an area diminishes with time.  UNIFORMITARIANISM To understand the origin of relict landforms created by ancient processes, one must understand modern processes and use this knowledge to extrapolate into the past. Implicit the assumption of basic physical and chemical processes that apply to the present and equally to the past and the future, this concept was championed by Hutton and Lyell as uniformitarianism. This concept is often stated as, “The present is the key to past,” meaning that the clue to recognition of the origin of relict landform lies in studying present landforms. Care may be exercised in the application of uniformitarianism due to rate of surface processes may have actually existed in the past but may not be operative in the present. Given example is the difficulty of interpreting relict glacial landform if glaciers were not present today. However, in most cases, landforms may be understood by extrapolation of present processes backward in time.  POSITIVE FEEDBACK SYSTEM Positive feedback occurs when a change in the input variable causes magnification of change in the direction of the initial adjustment. The bend of the stream meander causes the water to enhance erosion on the outside of the bend, which cause the bend to enlarge, which in turn cause accelerated erosion on the outside of the bend, until finally 31 | P a g e two meanders intersect and destroy one another. Positive feedback system thus carry the source of their own destruction and eventually accelerate to self-elimination. QUESTIONS: 1. Explain your understanding about the three concepts of geomorphic systems. 2. What are the importance of earth processes? 3. What features are the topographic features responsible for the earth processes? 32 | P a g e LESSON 6: WEATHERING Weathering is the breakdown of rocks at the earth’s surface by the action of rainwater, extremes of temperature, and biological activity. It does not involve the removal of rock material. There are three types of weathering: physical, chemical and biological. The weathering of rocks due to the physical and chemical processes that take place in the rocks near the surface by the atmospheric agencies, which lead to its disintegration and decomposition, is called the surface weathering. Another form is the changes that take place deep down the rock, due to chemical action. Thus, there are two processes that constitute weathering of rocks. They are: 1. Mechanical Disintegration. In this process the rock is split into smaller pieces or even soils, but the character of the product of this type of weathering of a given rock is the same. An example is the conversation of rock into sand. 2. Chemical Weathering. In this process the rock (mineral assemblage) decomposes to other products. The weathered product and original rock grains need not be the same. An example is the conversion of rock into clay. The process of weathering represents an adjustment of the minerals of which a rock is composed to the conditions prevailing on the surface of the Earth. As such, weathering of rocks is brought about by physical disintegration, chemical decomposition and biological activity. It weakens the rock fabric and exaggerates any structural weaknesses, all of which further aid the breakdown processes. A rock may become more friable as a result of the development of fractures both between and within mineral grains. The agents of weathering, unlike those of erosion, do not themselves provide for the transportation of debris from the surface of a rock mass. Therefore, unless the rock waste is otherwise removed, it eventually acts as a protective cover, preventing further weathering. If weathering is to be continuous, fresh rock exposures must be constantly revealed, which means that the weathered debris must be removed by the action of gravity, running water, wind or moving ice. Weathering also is controlled by the presence of discontinuities in that they provide access into a rock mass for the agents of weathering. Some of the earliest effects of weathering are seen along discontinuity surfaces. Weathering then proceeds inwards so that the rock mass may develop a marked heterogeneity with corestones of relatively unweathered material within a highly weathered matrix. Ultimately, the whole of the rock mass can be reduced to a residual soil. Discontinuities in carbonate rock masses are enlarged by dissolution, leading to the development of sinkholes and cavities within the rock mass. The rate at which weathering proceeds depends not only on the vigour of the weathering agents but also on the durability of the rock mass concerned. This, in turn, is governed by the mineralogical composition, texture, porosity and strength of the rock on the one hand, and the incidence of discontinuities within the rock mass on the other. Hence, the response of a rock mass to weathering is directly related to its internal surface area and average pore size. Coarse-grained rocks generally weather more rapidly than fine-grained 33 | P a g e ones. The degree of interlocking between component minerals is also a particularly important textural factor, since the more strongly a rock is bonded together, the greater is its resistance to weathering. The closeness of the interlocking of grains governs the porosity of the rock. This, in turn, determines the amount of water it can hold, and hence, the more porous the rock, the more susceptible it is to chemical attack. Also, the amount of water that a rock contains influences mechanical breakdown, especially in terms of frost action. Nonetheless, deep-weathered profiles usually have been developed over lengthy periods of time. The type and rate of weathering varies from one climatic regime to another. In humid regions, chemical and chemico-biological processes are generally much more significant than those of mechanical disintegration. The degree and rate of weathering in humid regions depends primarily on the temperature and amount of moisture available. An increase in temperature causes an increase in weathering. If the temperature is high, then weathering is extremely active; an increase of 10∞C in humid regions more than doubles the rate of chemical reaction. On the other hand, in dry air, chemical decay of rocks takes place very slowly. Weathering leads to a decrease in density and strength, and to increasing deformability. An increase in the mass permeability frequently occurs during the initial stages of weathering due to the development of fractures, but if clay material is produced as minerals breakdown, then the permeability may be reduced. Widening of discontinuities in carbonate rock masses by dissolution leads to a progressive increase in permeability. Civil Engineers are interested in weathering of rocks as they meet with the products of weathering as well as the original rock itself in their construction.  Mechanical Weathering Mechanical or physical weathering is particularly effective in climatic regions that experience significant diurnal changes of temperature. This does not necessarily imply a large range of temperature, as frost and thaw action can proceed where the range is limited. Alternate freeze–thaw action causes cracks, fissures, joints and some pore spaces to be widened. As the process advances, angular rock debris is gradually broken from the parent body. Frost susceptibility depends on the expansion in volume that occurs when water moves into the ice phase, the degree of saturation of water in the pore system, the critical pore size, the amount of pore space, and the continuity of the pore system. In particular, the pore structure governs the degree of saturation and the magnitude of stresses that can be generated upon freezing (Bell, 1993). When water turns to ice, it increases in volume by up to 9%, thus giving rise to an increase in pressure within the pores it occupies. This action is further enhanced by the displacement of pore water away from the developing ice front. Once ice has formed, the ice pressures rapidly increase with decreasing temperature, so that at approximately -22 ∞C, ice can exert a pressure of up to 200 MPa. Usually, coarse-grained rocks withstand freezing better than fine-grained types. The critical pore size for freeze–thaw durability appears to be about 0.005 mm. In other words, rocks with larger mean pore diameters allow outward drainage and escape of fluid from the frontal advance of the ice line and, therefore, are less frost susceptible. Fine-grained rocks that have 5% sorbed water are often very susceptible to frost damage, whereas those 34 | P a g e containing less than 1% are very durable. Nonetheless, a rock may fail if it is completely saturated with pore water when it is frozen. Indeed, it appears that there is a critical moisture content, which tends to vary between 75 and 96% of the volume of the pores, above which porous rocks fail. The rapidity with which the critical moisture content is reached is governed by the initial degree of saturation. The mechanical effects of weathering are well displayed in hot deserts, where wide diurnal ranges of temperature cause rocks to expand and contract. Because rocks are poor conductors of heat, these effects are mainly localized in their outer layers where alternate expansion and contraction creates stresses that eventually rupture the rock. In this way, flakes of rock break away from the parent material, the process being termed exfoliation. The effects of exfoliation are concentrated at the corners and edges of rocks so that their outcrops gradually become rounded (Fig. 3.2). However, in hot semi-arid regions, exfoliation can take place on a large scale with large slabs becoming detached from the parent rock mass. Furthermore, minerals possess different coefficients of expansion, and differential expansion within a polymineralic rock fabric generates stresses at grain contacts and can lead to granular disintegration. There are three ways whereby salts within a rock can cause its mechanical breakdown: by pressure of crystallization, by hydration pressure, and by differential thermal expansion. Under certain conditions, some salts may crystallize or recrystallize to different hydrates that occupy a larger space (being less dense) and exert additional pressure, that is, hydration pressure. The crystallization pressure depends on the temperature and degree of supersaturation of the solution, whereas the hydration pressure depends on the ambient temperature and relative humidity. Calculated crystallization pressures provide an indication of the potential pressures that may develop during crystallization in narrow closed channels. Crystallization of freely soluble salts such as sodium chloride, sodium sulphate or sodium hydroxide often leads to the crumbling of the surface of a rock such as limestone or sandstone. Salt action can give rise to honeycomb weathering in porous limestone or sandstone possessing a calcareous cement. There are two types of mechanical weathering (a) Block disintegration (b) Granular disintegration. In both cases, the products remain the same as the original material. Only the size of the product changes. In block disintegration massive rock is broken up to large blocks. Granular disintegration results from the loss of cohesion between individual mineral grains. This takes place more on the coarser variety of rocks like granite. The agents of mechanical weathering are: 1. Temperature changes 2. Living things like trees and those that bore holes 3. Mechanical abrasion of wind and water We will examine how these influence the weathering of rocks. 1. Temperature Changes: All the rocks, especially igneous rocks have joints. In addition, rocks, especially igneous rocks, are made of minerals in very close contact. In sedimentary 35 | P a g e rocks, the formation is such that there will be a filling material between rock pieces that become sedimentary rocks. Rocks when heated, expands, but on cooling it does not come back to its original length. There is some residual strain which is very small. Imagine, this has been happening from last many millions of years. The exposed rock which has been heated and cooled can break up into blocks because of this reason. Another reason for the breaking up of igneous rocks is the difference in coefficients of expansion of the different minerals which are in close contact in these rocks. This can result in large strains in the rock on heating and resultant in cracking into blocks or even disintegration into small pieces. These changes affect rocks with large crystals like granite more than other rocks like basalt. This principle (effect of heat on rocks) has been used for quarrying granite in some countries. The conversion of a large mass of rocks into blocks at the surface along steep slopes leads to rock-falls in the mountains regions due to gravity. 2. Effects of living things: Growing of trees in joints of rocks can lead to disintegration of the rock. Similarly boring of holes by animals also affect weathering of rock. 3. Mechanical abrasion due to wind, flowing water etc.: The abrasive effect of wind and flowing water can also lead to the smaller amount of weathering, and the effect depends on the intensity of wind and flow of water.  Chemical Weathering In the chemical weathering, the product of weathering is different from the parent rock as it undergoes chemical changes. The changes that can happen are such as 1. Carbonation 2. Solution (as in limestones) 3. Hydration 4. Oxidation The atmosphere contains oxygen, nitrogen, carbon dioxide, several inert gases, moisture etc. In addition, the water that flows on the ground among decaying vegetation will contain many reactive chemical substances like carbon dioxide, organic acids etc. These contribute to chemical weathering. Many minerals are changed to other substances with different chemistry. This is known as chemical weathering. Among the processes specified above for making chemical changes carbonation and solution are the important ones. For example, the mineral orthoclase present in rocks, becomes kaolinite by carbonation. The weathering of granite to laterite is due to solution. The process of chemical disintegration 36 | P a g e affects basic rocks like basalt more than the other rocks, like granite. Where these two rocks basalt and granite, occur side by side, the place converts itself to valleys of basalt and ridges of granite due to excessive weathering of basalt. Igneous rocks are more susceptible to chemical weathering than sedimentary rocks as sedimentary rocks are produced from weathered products of igneous rocks.  Transport of Products of Weathering The weathered products can remain in place or they can be also transported by water or wind. If they remain in place, they become residual soils. They may be transported and may become sedimentary rocks or become alluvial soils. The agents that transport these materials are mainly: 1. Water in the forms of steams of rivers, and 2. Wind that blows soils from one place to the other, especially in the dry areas. 3. Glaciers in polar regions, the regolith. The mantle of unconsolidated material above bedrock consisting of (a) residual materials that remain in place where it has weathered. (b) transported material transported by gravity or water (rivers, lakes, sea etc.) and wind. Table shows the classification of regolith. (The soil formed out of the parent rock below and still remains in situ is called residual soil). Type Name Details Laterite, gravel, sand clay In situ materials (a) Residual deposits along with rocks Peat, organic soils, chemical (b) Cumulative deposits precipitates etc. Talus, materials from earth Transported materials (a) Gravity deposits due to creep etc. (b) Alluvial deposits Alluvial, swamp deposits (c) Aeolian deposits Dunes, loess (wind-blown) (d) Lacustine deposits Silt, clay, sand etc. (lake deposits) (e) Marine deposits Sand, clay etc. 37 | P a g e Note: The soil profile of a place depends on its history for the past 4500 million years of the earth’s life and the changes that have happened. We cannot accurately trace its history of a place by any means, except by taking samples from the place and identify them from their composition. Type of Regolith at a Place The layers of weathered rocks, soil etc. lying over bedrock is technically called regolith. Usually textbooks in geology deal only with rocks but civil engineers are interested in both the soil as well as the rock below the ground level. Even though it is difficult to predict the geological history and the nature of the soil deposit in a place, we will be able to guess from our experience of the deposits we have found in many other similar places, the type of deposit we are likely to meet in a given site. For this purpose of studying the geology of soil deposits we divide soil deposits into the following five groups: 1. River deposits 2. Lake deposits 3. Shore deposits 4. Sea deposits 5. Wind deposits The nature of soil strata that we usually find in each of these above deposits will be similar but different form each other. We will deal with them separately in the later chapters. All civil engineers dealing with foundation engineering should have a fair knowledge of the nature of deposits in each group. We will study it in the following chapters. Symbols Used to Describe the State of Weathering of Rocks The following symbols are sometimes used to describe the state of weathering of rocks in our geological field survey of a site. 1. Completely Weathered Rock Materials (CWRM) 2. Highly Weathered Rock Materials (HWRM) 3. Moderately Weathered Rock Materials (MWRM) 4. Partially Weathered Rock Materials (PWRM) 5. Hard Rock (HR) 38 | P a g e Summary Weathering is the disintegration or decomposition of the original rocks to form the regolith. In general there are many ways by which weathering of rocks take place. They are (1) Mechanical Weathering (2) Chemical Weathering (3) Weathering of rock by plants and animals. Geomorphology is a special subject. It is the study of landscape. The aerial photographs of landscape are very helpful for the preliminary investigations of large projects like building a reservoir. Even a preliminary study of geomorphology is quite interesting and rewarding. QUESTIONS: 1. In this process the rock is split into smaller pieces or even soils, but the character of the product of this type of weathering of a given rock is the same. 2. What will happen if the weathered products can be remain in place or can be also transported by water or wind? 3. It is the layers of weathered rocks, soil lying over bedrock. 4. Give the general ways by which weathering of rocks take place 39 | P a g e LESSON 7: WORKS OF RIVERS, WIND AND SEA AND THEIR ENGINEERING IMPORTANCE  RIVERS To a hydraulic engineer and an irrigation engineer the water that flows into the river is most important. From the geological point view, we look upon rivers as one among the means of distributing the products of weathering all over the earth surface. All the rivers have a beginning which is called the head. The place where a river ends in the sea or lake is called the mouth. In all the cases, the slope of the rivers at the head is high so that it can carry all the materials (the coarse and fine weathered products) from the parent rocks down. The slope slowly decreases and in the plains it is smaller. Thus the shape of the slope curve from the head to the mouth is concave (facing the sky). Thus concept of change in slope is very important in our study of deposits along the rivers.  PLAYFAIR’S LAW (Functions of a river) Very few people realize that the whole river system from its start to the finish (head to mouth) is a sensitive, lively system. This lively performance of rivers is described by the Playfair’s law which can be stated as follows. “Every river consists of a main trunk fed by the branches that run in valleys, proportioned to its size and all of them together forming a system of valleys communicating with each other and having such a nice adjustment of their toward slopes that none of them join the principal valley either at a too high or too low level, a circumstance which would be impossible if the valleys were not the work of the stream which flows in it”. This law indicates vibrant systems and explains how the deep valleys and other landforms have been formed. They are the work of the rivers to facilitate the smooth flow of water and sediments. These landforms have been formed by the three geologic functions of the rivers, namely:  EROSION The erosion is one of the most expressive features of river which is turbulent with currents in all directions. Most rivers carve the river valley by erosion. The higher the velocity and turbulence, the greater is the erosion. The river erosion can take place in the following four ways: (1) Corrasion (2) Corrosion (3) Attrition, and (4) Hydraulic action. These can be indicated as follows: Corrasion: This is the abrasive force or corrosive force, producing a mechanical erosion of rocks by the sediments the river carries. The abrasion of rock fragments depends on the three factors (1) If the transported material is hard in relation to the 40 | P a g e   bed, the bed gets affected and wears down (2) If both are hard then the bed gets polished (3) If the bed is harder the bed is not affected.  Corrosion: In this process the water dissolves particles of the river banks or bottom and carries them in solution.  Attrition: This is due to the rubbing of the particles being carried by the river when they are thrown at each other.  Hydraulic action: This is the force of the water of the fast flowing rivers that can dislodge materials from the river banks and river beds. Transportation of Eroded Materials The materials that have been eroded have to be transported down the river. There are three ways in which the river can transport the materials dislodged by it, they are: 1) Dissolved load 2) Suspended load: The fine particles of sand silt and clay can remain in suspension. 3) Bed load: The large-sized materials settle to the bed of the river and move along the bed by rolling, sliding or by sudden movement (saltation). This bottom load is also called the traction load. Deposition (Alluvial Deposits) When the velocity of water in river is not enough to carry the load of soil particles it has been carrying, it deposits the load at the places of low velocity. This usually happens in the regions where the slope of the river bed becomes gentle. As the slope of the river at the head of the river is large and towards the mouth it is small, the maximum size of deposits the river can carry is larger near the head and becomes smaller towards the mouth. Because of this reason, in the regions where the river had large slopes earlier and now small slopes, we may meet with coarse pebbles at the bottom with fine sand or silt at the top of the river bed. This is the soil profile of most of the rivers at mid reaches. These functions act on the following three physical processes involved in the formation of river valleys, namely: 1) Deepening of the river valley 2) Lengthening or shortening of the river valley, and 3) Widening the river valleys Carried or Deposited Particles by River Water Different particles of soil require different velocities (a) For them to be scoured by water (b) For them to be carried in water and (c) To be deposited on their path. For example, it requires a velocity of about 150cm/s for gravel pieces to be carried by rivers. Sand may require only 30 to 15 cm/s. It is also interesting to note that sand and gravel generally roll along the bed of the river, whereas silt and clay are carried in suspension. 41 | P a g e  Velocity curve of a stream with depth Figure 10. Fields of erosion, transportation and deposition of river sediments in the flow of Bed rivers.  Stream Cycle The stream cycle can be briefly described as follows. We have seen that a river is a live system. It passes through three stages in the same way as humans. These stages described herein below:  Juvenile or Youth Stage (Upper Course) This is the stage of high downward vertical erosion. It develops the following characteristic formations: a) V- shaped valleys b) Gorges and canyons c) Rapids and cataracts (Rapids of greater dimensions are known as cataracts) d) Waterfalls e) Holes f) Piracy (Capturing of a streamlet that flowed into one river another stream that flows into another river) 42 | P a g e   Maturity Stage (Middle Course) This is the middle course of a river where the gradient is gentler and the river valley becomes wide, leading to the following features: a) Meanders: (The term meander is derived from river Meanderz in Turkey, which flows in loops). In the wide plains the river may be made to bend and take a curve due to some obstructions. Then the velocity around the outside bend becomes very much higher and hence the river cuts down the river bank. As the velocity inside the bend being less, deposition of fine particles takes place which is shown. The clay deposits are found more on the inside of the river bends where the velocity is low. As erosion cuts away bank on one side and deposition takes place on the opposite side, the river migrates laterally and produces a meandering river. b) Flood plain: The flood plains occur in the middle course of the river that has formed its maturity. The valley characteristics are absent and the river flows along a wide and flatter region. Overflow of the banks and flooding happens during floods. This leaves behind deposits of silt on both sides. These are called flood plains. The following are the geomorphologic features of this region:  Levees: The natural embankments formed by the river in the flood plains are called levees. As the floodwate