Geology for Civil Engineers PDF

CIVI-231 Geology for Civil Engineers Biao Li, PhD, PEng Associate professor in Geotechnical Engineering Department of Building, Civil, & Environmental Engineering https://www.geo-mechanical.com/ B.Sc. And M.Sc. (Civil engineering, China University of Geos...

CIVI-231 Geology for Civil Engineers Biao Li, PhD, PEng Associate professor in Geotechnical Engineering Department of Building, Civil, & Environmental Engineering https://www.geo-mechanical.com/ B.Sc. And M.Sc. (Civil engineering, China University of Geosciences Beijing) Ph.D. (Geotechnical Engineering, University of Calgary)  why civil engineers need Geology? Tunnel Oil production Pipeline OR 2 With solid background in Geology? More opportunities in jobs! And… Course outline 3 Chapter 1: An Introduction to Geology and Plate Tectonics 4  The Science of Geology Geology (geo = earth; logos = discourse) Physical geology – studies Earth materials; seeks to understand processes that operate on and beneath its surface Historical geology – seeks to understand the origin of Earth and its development through time 5  The Science of Geology Geology, people, and the environment Relationships between people and the natural environment include: Natural hazards Resources World population growth Environmental issues 6  The Science of Geology Some historical notes about geology Catastrophism – 17th century, Earth’s landscapes were formed by sudden disasters Uniformitarianism - “The present is the key to the past”. Proposed in the 18th century by James Hutton, and states that the processes we observe on our planet today have been shaping our planet throughout time. 7  Geologic Time Scientists such as James Hutton knew Earth must be very old. Before the discovery of radioactivity, it was difficult to determine the age of Earth. Our current age-dating techniques are constantly being refined. Extinct about 66 million years ago 4.6 billion years 8  Geologic Time Relative dating and the geologic time scale Relative dating – Events are placed in their proper sequence or order without knowing their age in years Law of Superposition – Younger rock layers are deposited over older rock layers. Principle of Fossil Succession – Fossil organisms success each other in a determinable order. 9  Geologic Time The magnitude of geologic time Involves vast times – millions or billions of years The Earth is 4.6 billion years old! An appreciation for the magnitude of geologic time is important because many processes are very gradual How about 2 hours of class time 10 Geologic Time 11  Early Evolution of Earth Origin of Planet Earth Big Bang theory – Large explosion sent all matter in the universe flying outward at incredible speeds Nebular hypothesis – Bodies in solar system evolved from a rotating cloud called a solar nebula Protosun and protoplanets - Formed from a contracting, slowly spiraling nebula 12 Video 13  Early Evolution of Earth Formation of Earth’s Layered Structure Chemical segregation early in the formation of Earth by gravity Core – Inner layer: dense, iron-rich Crust – Outer layer: solid, thin Mantle – Largest layer between core and crust composed of iron, magnesium and oxygen- seeking elements 14  Plate Tectonics: A Geologic Paradigm Continental drift – Alfred Wegener (1915) proposed continents moved about the face of the planet Plate Tectonics – current understanding of how continents move 15  Continental Drift: An Idea Before its Time Evidence across the Atlantic Ocean: Fit of Continents – Fit together like a jigsaw puzzle. Fossil evidence – Same fossils found on separated continents. Rock type and Structural Similarities – Rocks on one continent match those on another continent. Paleo-climatic evidence – Evidence for ancient glacial ice explained by a super-continent. 16  Planet of Shifting Plates Plate Tectonics: The lithosphere is broken-up into pieces called “plates”. There are seven major plates. Lithospheric plates move relative to one another at very slow rates. Movement driven by convection in mantle. Averages about 5 cm / year. 17 Planet of Shifting Plates 18  Planet of Shifting Plates Plate boundaries Divergent boundary Two plates move apart, resulting in upwelling of material from the mantle to create new seafloor. Occurs mainly at mid-ocean ridges. Can occur under continents at rift valleys. 19  Planet of Shifting Plates Plate boundaries Convergent boundaries Two plates move towards each other. Continental settings: two continental plates collide. Oceanic settings: oceanic crust descends into mantle. This margin of crust consumption into the mantle is called a “subduction zone”. 20  Planet of Shifting Plates Plate boundaries Transform fault boundaries Plates slide past each other without either generating new lithosphere or consuming old lithosphere. These faults form in the same direction as plate movement. 21 Planet of Shifting Plates Mosaic of rigid plates that constitute Earth’s outer shell. 22  Earth’s Internal Structure Two Types of Defining Earth’s Internal Structure: Composition: Physical Properties: Crust Lithosphere Mantle Asthenosphere Mesosphere Core Inner Core Outer Core 23  Earth’s Internal Structure View of Earth’s layered Video structure 24  Earth’s Spheres Earth is a small, fragile and self-contained planet. Earth’s four interacting spheres: Hydrosphere Atmosphere Biosphere Geosphere These four spheres are constantly interacting with each other. 25  Earth’s Spheres The breathtaking beauty of Earth as seen by the Apollo astronauts in the 1960s and 1970s. 26  Earth’s Spheres Hydrosphere Includes: Oceans, freshwater, glacial ice Oceans account for almost 71% Atmosphere Thin layer producing weather, climate Biosphere Includes all living things on Earth Geosphere Includes rocks, landforms, Earth’s Interior 27  The Face of Earth Two principal divisions of Earth’s surface: 1. Continents Average elevation is 840 m above sea level 40% of Earth’s surface 2. Ocean basins Average depth is 3800 m below sea level 60% of Earth’s surface 28  The Face of Earth Continents Young mountain belts – most prominent Old mountain belts – more eroded Shields – very old, large, flat expanses of rock Ocean basins Oceanic ridge system – the most prominent topographic feature on Earth Trenches – can exceed depths of 11,000 m 29  Earth as a System Earth’s four spheres are linked as a system through their interactions. Earth’s system is powered by energy from the sun and heat from Earth’s interior. Humans are part of this system. Our actions produce often large-scale changes in all four spheres. 30  Earth as a System The Rock Cycle: Part of the Earth system The process by which one rock changes to another rock: metamorphic, igneous, sedimentary. Each rock type is linked to the other. 31  Earth as a System The Rock Cycle: Part of the Earth System Basic Cycle: Molten magma becomes igneous rock Weathering creates sediments Sediments lithify into sedimentary rock Burial and heat produce metamorphic rock Metamorphic rock can be heated to produce magma, or eroded to form sediments. 32  Earth as a System The Rock Cycle: Rocks constantly form, change, and re-form over Video longs spans of time 33 Example questions for quiz 1. The ____________ layer of the Earth is molten and metallic in composition. a. inner core b. lithosphere c. mantle d. outer core 2. The famous San Andreas Fault in California is a ____________ plate boundary. a. convergent b. emergent c. divergent d. transform Thanks for the attentions! 34 Chapter 2: Minerals: The Building Blocks of Rocks 2-1  Minerals: The Building Blocks of Rocks Definition of a mineral: Naturally occurring Inorganic Ice is a mineral? Glass is a mineral? Solid Ordered internal molecular structure Definite chemical composition Definition of a rock: A solid mass of minerals or mineral like matter that occurs naturally Smart Video: mineral VS rock 2-2 The Composition of Minerals Elements Basic building blocks of minerals 118 are known (90 naturally occurring) Atoms Smallest particles of matter Retains all the characteristics of an element 2-3 The Composition of Minerals Atomic structure Nucleus Central region of atom Consists of protons (positive charges) and neutrons (no electrical charges) Electrons Negatively charged particles that surround the nucleus Located in discrete energy levels called shells 2-4 The Composition of Minerals Atomic structure Atomic number – number of protons in the atom Atomic weight – approximately the total number of protons and neutrons in the nucleus Valence electrons – outer-most electrons in the shell 2-5 The Composition of Minerals Bonding Chemical bonds – Strong attractive force forms compounds Ionic bonds – One atom gives up electron(s), and another receives them. These now oppositely-charged atoms attract each other, bond, and become electrically neutral Covalent bonds – bonds that share electrons 2-6  The Composition of Minerals Ionic bonds Covalent bonds 2-7  The Structure of Minerals Mineral Consists of an ordered array of atoms chemically bonded to form a particular crystalline structure 2-8  The Structure of Minerals Polymorph Some elements can join in more than one geometric arrangement Deeply buried, high pressure Chemical composition stays the same Physical properties differ Example: diamond and graphite Shallowly buried, low pressure 2-9 Physical Properties of Minerals Crystal habit (shape) External expression of the orderly internal arrangement of atoms Crystal growth is often interrupted because of competition for space and rapid loss of heat 2-10 Physical Properties of Minerals Crystal habit (shape) Smart video: MineralScale 2-11 Physical Properties of Minerals Lustre Appearance of a mineral in reflected light Two basic categories: 1. Metallic 2. Non-metallic Other terms, such as vitreous, silky, or earthy, are used to further describe non- metallic lustre 2-12 Physical Properties of Minerals Colour Colour can be obvious (yellow, pink, etc.); but should not be the only diagnostic tool. Slight impurities can produce strong colour variations. Example: Quartz – can be clear, white, rose, smoky, purple, etc. 2-13 Physical Properties of Minerals Quartz (SiO2) exhibits a variety of colours as in the purple amethyst. Video: MineralColor 2-14 Physical Properties of Minerals Streak Colour of a mineral in its powdered form, when rubbed on an unglazed porcelain tile (streak plate) Hardness Resistance of a mineral to abrasion or scratching All minerals are compared to a standard scale called the Mohs scale of hardness 2-15 Physical Properties of Minerals Streak Colour of a mineral in its powdered form, when rubbed on an unglazed porcelain tile (streak plate) 2-16 Physical Properties of Minerals Hardness Resistance of a mineral to abrasion or scratching All minerals are compared to a standard scale called the Mohs scale of hardness Video: MohsScale 2-17 Physical Properties of Minerals [kə'rʌndəm] ['topæ z] 2-18 Physical Properties of Minerals Cleavage Tendency to break along planes of weak bonding Produces flat, shiny surfaces Cleavage is described as: Number of planes exhibited Angles between adjacent planes Video: IgneousCleavage 2-19 Physical Properties of Minerals Fracture Absence of cleavage when a mineral is broken Conchoidal fracture - breaks to form smooth curved surfaces like broken glass 2-20 Physical Properties of Minerals Specific gravity Ratio of the weight of a mineral to the weight of an equal volume of water Average value is approximately between 2.5 and 3 2-21 Physical Properties of Minerals Other (“special”) properties Magnetism Reaction to hydrochloric acid Malleability Double refraction Taste Smell Elasticity 2-22  Minerals Classes Approximately 4660 minerals have been identified Rock-forming minerals A handful of common minerals that make up most of the rocks of Earth’s crust Composed mainly of the 8 elements that make up over 98% of the continental crust In order of abundance: oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. 2-23  Mineral Classes The eight most abundant minerals in Earth’s continental crust 2-24  Mineral Classes The Silicates Most common mineral group Basic building block is the silicon-oxygen tetrahedron (SiO4)4- Four oxygen ions surrounding a much smaller silicon ion to form a more complex ion 2-25  Mineral Groups More complex Silicate structures Tetrahedra are linked together to form various structures including: Single chains Double chains Sheet structures 3D framework 2-26 Mineral Groups Types of silicate structures 2-27 Mineral Groups 2-28  Common Silicate Minerals Ferromagnesian (dark) silicates Minerals containing ions of iron and/or magnesium Most common are: Olivine Pyroxenes (most common is augite) Amphiboles (most common is hornblende) Biotite Garnet 2-29  Common Silicate Minerals Nonferromagnesian (light) silicates Minerals containing various amounts of aluminum, potassium, calcium, and sodium Most common are: Muscovite Feldspar Orthoclase (potassium feldspar) Plagioclase Quartz (silica) Clay (variety of complex minerals that have a sheet structure) (e.g., kaolinite) 2-30 Common Silicate Minerals 2-31  Mineral Classes Important non-silicate minerals Several major groups exist including Oxides Hydroxides Sulphides Sulphates Native Elements Halides Carbonates Phosphates 2-32 Mineral Classes 2-33  Gemstones Gemstones were once erroneously classified by colour. We now classify based on composition. 2-34  Chapter 3: Igneous Rocks Biao Li, Concordia. 3-1  Magma: The Parent Material of Igneous Rocks Igneous rocks Form as molten rock cools and solidifies Parent material of igneous rocks is magma Forms from partial melting of rocks inside Earth Magma that reaches the surface is called lava Biao Li, Concordia. 3-2  Magma: The Parent Material of Igneous Rocks Extrusive igneous rocks Form when magma solidifies at the surface Also called volcanic rocks Intrusive igneous rocks Form at depth from magma that crystallizes slowly. Also called plutonic rocks A body of plutonic rock is called a pluton Biao Li, Concordia. 3-3  Generating Magma from Solid Rock Most igneous activity occurs at divergent plate boundaries Role of heat Geothermal gradient – change in temperature with depth Rocks in lower crust and upper mantle are near their melting points Bulk of magma forms without additional heat Melting begins if confining pressure drops or if volatiles (fluids, gases) are introduced Biao Li, Concordia. 3-4  Generating Magma from Solid Rock Geothermal gradient 3-5  Generating Magma from Solid Rock Role of pressure Pressure increases with depth Melting occurs at higher temperatures at depth due to higher confining pressure When confining pressures drop, decompression melting occurs Biao Li, Concordia. 3-6  Magma Decompression melting INSERT FIG. 3.4 FROM 4CE Biao Li, Concordia. 3-7  Generating Magma from Solid Rock Role of volatiles Water and other volatiles (gases) cause rock to melt at lower temperatures Volatiles generate magma where the oceanic lithosphere descends into the mantle When mafic magma forms, it rises toward the surface In continents, mafic pooling melts crust and forms silica rich felsic magma Biao Li, Concordia. 3-8 Generating Magma from Solid Rock Role of volatiles 3-9  Generating Magma from Solid Rock Summary Magma can be generated by: 1. The addition of heat 2. A decrease in pressure (without added heat), causing decompression melting 3. The introduction of volatiles, which lowers the melting temperature Smart video IntrusiveVsExtrusive Biao Li, Concordia. 3-10  The Nature of Magma Magma Three distinct components: 1. Liquid portion (melt), composed of mobile ions 2. Solids, if any, are silicate minerals that have already crystallized from the melt 3. Volatiles (gases dissolved in the melt) include water vapour (H2O), carbon dioxide (CO2), and sulphur dioxide (SO2) Biao Li, Concordia. 3-11  From Magma to Crystalline Rock Crystallization Cooling magma results in the systematic arrangement of ions into crystal structures Silicon and oxygen atoms link together first to form silicate minerals Minerals formed first tend to have better developed crystal faces Biao Li, Concordia. 3-12  How Magmas Evolve Bowen’s reaction series One volcano can have lavas with different compositions. As magma cools, minerals crystallize in a systematic fashion based on their melting points During crystallization, the composition of the liquid portion of magma continually changes Due to removal of elements by earlier- forming minerals Silica component of the melt enriches as magma evolves Biao Li, Concordia. 3-13  How Magmas Evolve Biao Li, Concordia. 3-14  How Magmas Evolve Bowen’s reaction series Magmatic differentiation – Formation of one or more secondary magmas from a single parent magma During crystallization solid and liquid components can separate Magmatic differentiation and component separation at various stages produces different types of igneous rocks. Biao Li, Concordia. 3-15  How Magmas Evolve Bowen’s reaction series Assimilation - Changing a magma’s composition by the incorporation of foreign matter (surrounding rock bodies) into a magma Magma Mixing - Occurs when one magma body intrudes another Biao Li, Concordia. 3-16  How Magmas Evolve Partial melting and magma formation Incomplete melting of rocks is known as partial melting. Formation of a mafic (basaltic) magma Most originates from partial melting of peridotite in the mantle. Primary magmas – mafic magmas that originate from direct melting of mantle rock, and have not yet evolved. Biao Li, Concordia. 3-17  How Magmas Evolve Formation of Andesitic and Felsic Magmas Found only within, or adjacent to, the continental margins Evidence suggests interactions between mantle mafic magma and silica-rich crust generate these magmas Intermediate composition (between mafic and felsic) = andesite Biao Li, Concordia. 3-18  How Magmas Evolve Formation of Andesitic and Felsic Magmas Enriched silica magmas are evolved magmas called secondary magmas Felsic magmas are higher in silica and therefore more viscous (thicker) than other magmas Form at lower temperatures than mafic magmas Tend to produce large plutonic structures Biao Li, Concordia. 3-19  Igneous Compositions The composition of igneous rocks is ultimately determined by the composition of the magma from which is crystallized. Igneous rocks are composed primarily of two main groups of silicate minerals: dark silicates and light silicates. Biao Li, Concordia. 3-20  Igneous Compositions Dark (ferromagnesian) silicates Olivine Pyroxene Amphibole Biotite mica Light (non-ferromagnesian) silicates Quartz Muscovite mica Feldspars Biao Li, Concordia. 3-21  Igneous Compositions Felsic versus mafic compositions Classified by proportions of light and dark minerals Felsic (granitic composition) Composed of light-coloured silicates Rich in silica (SiO2) ≈ 70% Major constituents of continental crust Mafic (basaltic composition) Composed of dark silicates, Ca-rich feldspar More dense than granitic rocks Comprise the ocean floor, volcanic islands Biao Li, Concordia. 3-22  Igneous Compositions Other compositional groups Intermediate rocks - andesitic composition Contain at least 25% dark silicate minerals Associated with volcanic activity on continental margins Ultramafic composition - Peridotite Rare composition that is composed entirely of ferromagnesian silicates Biao Li, Concordia. 3-23  Igneous Compositions Silica content as an indicator of composition Silica (SiO2) content in crustal rocks exhibits a considerable range A low of 40% in ultramafic rocks Over 70% in felsic rocks Silica content influences magma behaviour Biao Li, Concordia. 3-24  Igneous Compositions Smart video Igneous Composition Classification Biao Li, Concordia. 3-25  Igneous Textures Texture Used to describe the overall appearance of an igneous rock based on the size, shape, and arrangement of interlocking crystals. Tells us about the environment in which the rock was formed. Geologists can make inferences about rock’s origin. Biao Li, Concordia. 3-26  Igneous Textures Three Factors affecting crystal size 1. Rate of cooling Slow rate promotes the growth of fewer, but larger crystals Fast rate forms many small crystals Very fast rate forms glass (unordered ions) 2. Amount of silica (SiO2) present 3. Amount of volatiles (dissolved gases) Biao Li, Concordia. 3-27  Igneous Textures Types of igneous textures Aphanitic texture Fine-grained texture Rapid rate of cooling of lava or magma Microscopic crystals May contain vesicles (holes from gas bubbles) and thus rocks that contain them have a vesicular texture Biao Li, Concordia. 3-28  Igneous Textures Types of igneous textures Phaneritic texture (coarse-grained) Slow cooling Crystals can be identified without a microscope Porphyritic texture (Porphyry rock) Minerals form at different temperatures and rates Large crystals (phenocrysts) embedded in a matrix of smaller crystals (groundmass) Biao Li, Concordia. 3-29 Igneous Textures 3-30  Igneous Textures Types of igneous textures Glassy texture Very rapid cooling of molten rock Resulting rock is called obsidian Pele’s hair – strands of volcanic glass Pyroclastic texture (fragmental) Various fragments ejected during a violent volcanic eruption Textures often appear more similar to sedimentary rocks Welded tuff – common pyroclastic rock Biao Li, Concordia. 3-31  Igneous Textures Types of igneous textures Pegmatitic texture (pegmatites) Exceptionally coarse-grained Form in late stages of crystallization of granitic magmas Common crystals of quartz, feldspar and muscovite are abnormally large Smart video Igneous Texture Biao Li, Concordia. 3-32  Naming Igneous Rocks Igneous rocks are classified by their texture and mineral composition. Various igneous textures result from different cooling histories. Two rocks may have similar compositions but different textures, thus different names Example: granite - rhyolite Biao Li, Concordia. 3-33 Naming Igneous Rocks 3-34 Naming Igneous Rocks 3-35  Naming Igneous Rocks Felsic (granitic) rocks Granite Phaneritic Composed of about 20% quartz and about 65% or more feldspar May exhibit a porphyritic texture The term granite covers a wide range of mineral compositions Biao Li, Concordia. 3-36  Naming Igneous Rocks Felsic (granitic) rocks Rhyolite Extrusive equivalent of granite Aphanitic texture May contain glass fragments and vesicles Less common and less voluminous than granite Biao Li, Concordia. 3-37  Naming Igneous Rocks Felsic (granitic) rocks Obsidian Dark-coloured, glassy rock Ions in the glass are unordered Pumice Volcanic rock with a frothy texture Forms when large amounts of gas escape through lava to form a gray mass. Biao Li, Concordia. 3-38  Naming Igneous Rocks Intermediate (andesitic) rocks Andesite Volcanic origin Medium gray colour, fine-grained Commonly exhibits porphyritic texture May resemble rhyolite, making identification more difficult without a microscope Biao Li, Concordia. 3-39  Naming Igneous Rocks Intermediate (andesitic) rocks Diorite Plutonic equivalent of andesite Coarse-grained Intrusive Composed mainly of intermediate feldspar and amphibole - salt and pepper appearance Biao Li, Concordia. 3-40  Naming Igneous Rocks Mafic (basaltic) rocks Basalt Volcanic origin Dark green to black in colour Composed mainly of pyroxene and calcium-rich plagioclase feldspar Most common extrusive igneous rock Biao Li, Concordia. 3-41  Naming Igneous Rocks Mafic (basaltic) rocks Gabbro Intrusive equivalent of basalt Dark green to black in colour Composed primarily of pyroxene and calcium-rich plagioclase Makes up a significant percentage of the oceanic crust Biao Li, Concordia. 3-42  Naming Igneous Rocks Mafic (basaltic) rocks Peridotite Dominates the upper mantle Ultra-mafic composition Primarily composed of olivine, pyroxene, and calcium-rich plagioclase feldspar Occurs as rare slivers of mantle rock pushed to Earth’s surface Biao Li, Concordia. 3-43  Naming Igneous Rocks Pyroclastic rocks Composed of fragments ejected during a volcanic eruption Varieties Tuff – ash-sized fragments Welded tuff – hot ash fused together Volcanic breccia – particles larger than ash Smart video Igneous Classification Biao Li, Concordia. 3-44  Chapter 4: Volcanoes and Volcanic Processes Biao Li, Concordia. 4-1  The Nature of Volcanic Eruptions Primary factors that determine eruption style: Composition of magma Temperature of magma Amount of dissolved gasses All of these factors affect the magma’s viscosity (the mobility of the magma) Biao Li, Concordia. 4-2  The Nature of Volcanic Eruptions Factors affecting viscosity Viscosity Directly related to its silica content. The higher the silica content, the greater the viscosity. Felsic (rhyolitic) lavas (>70% silica) form short, thick flows. Mafic (basaltic) lavas (about 50% silica) tend to be fluid and can travel long distances. Copyright © 2015 Pearson Canada Inc. 4-3  The Nature of Volcanic Eruptions Importance of dissolved gases Dissolved gases increase fluidity of magma. Gases provide force to propel magma from a vent, or conduit (opening). Dissolved gases migrate upward contributing to summit inflation. Highly viscous magmas expel jets of hot ash- laden gases that evolve into plumes called eruption columns. 4-4  The Nature of Volcanic Eruptions A summary of eruption types Fluid mafic lavas generally produce quiet eruptions, allowing the gases to migrate upward and escape with ease Example: Hawaiian volcanoes Highly viscous lavas (rhyolite or andesite) produce more explosive eruptions Example: Krakatoa 4-5  Materials Extruded During an Eruption Lava flows Mafic lavas are much more fluid and flow easily Types of mafic flows Pahoehoe flows (twisted or ropy texture) Aa flows (rough, jagged blocky texture) Pillow lavas - form when lava enters water Lava tubes – Cave-like tunnels below hardened lava that allow molten lava to continue flowing 4-6 Materials Extruded During an Eruption 4-7  Materials Extruded During an Eruption Gases 1-6% of a magma by weight Held in magma by confining pressure Mainly water vapour and carbon dioxide, but also nitrogen and sulphur dioxide. Volcanoes are a natural source of air pollution. 4-8  Materials Extruded During an Eruption Pyroclastic materials Ejected fragments from eruptions that range in size from dust to pieces several tonnes in weight. Hot ash falls and glassy shards fuse to form welded tuff 4-9  Materials Extruded During an Eruption Pyroclastic materials Types of pyroclastic debris by size Ash and dust - fine, glassy fragments Lapilli or cinders - 2-64 mm diameter Blocks - ejected as hardened lava Bombs - ejected as hot lava 4-10  Materials Extruded During an Eruption Pyroclastic materials Types of pyroclastic debris by composition and texture Scoria - vesicular ejecta from mafic magma Pumice - vesicular ejecta from silica-rich magma (lighter colour and less dense than scoria) 4-11 4-12  Materials Extruded During an Eruption Nueé ardente: A deadly pyroclastic flow Also called “glowing avalanches” Fiery pyroclastic flows made of hot gases infused with ash and other debris. Race down the slopes of a volcano at speeds of over 100 km per hour! Trapped air provides buoyancy to debris can can carry large boulders great distances. 4-13 Materials Extruded During an Eruption 4-14  Materials Extruded During an Eruption Lahars: Mudflows on Active and Inactive Volcanoes Lahar - mudflow off steep sided volcanoes Triggers: Large volume of ice and snow melt during an eruption Can occur when heavy rainfall saturates weathered volcanic deposits 4-15  Chapter 5: Weathering and Soil Biao Li, Concordia 5-1  Earth’s External Processes Weathering and soil External processes – weathering, mass wasting and erosion. Internal processes –plate tectonics, mountain building & volcanic activity. All of these contribute to the gradual elevation of parts of Earth’s surface. 5-2  Earth’s External Processes Weathering and soil Weathering - the physical breakdown (disintegration) and chemical alteration (decomposition) of rock at or near Earth’s surface. Mass wasting – the transfer of rock and soil downslope by gravity. Erosion – the physical removal of material by water, wind, or ice. 5-3  Weathering Weathering and soil Two types of weathering: Mechanical weathering - breaking of rocks into smaller pieces by physical forces. Does not change chemical composition of rock Chemical weathering – involves chemical transformation of rock into one or more new compounds 5-4  Mechanical Weathering Mechanical weathering increases the surface area exposing more surfaces to chemical weathering Smart video 1 Surface Area 5-5  Mechanical Weathering Frost wedging Water works its way into cracks in rock, freezes, expands, and enlarges the openings, thus breaking rock. Most pronounced in mountainous regions, where there are daily freeze-thaw cycles. Creates large piles of broken rock called talus slopes. Smart video 2 wedging 5-6  Mechanical Weathering Sheeting The process by which large masses of igneous rock such as granite are exposed by erosion, and concentric slabs begin to break loose. Likely occurs by a reduction in pressure when overlying rock is eroded away. Continued weathering causes slabs to separate and spall (flake) off, creating exfoliation domes. Smart video 3 Sheeting 5-7 Mechanical Weathering Smart video 3 Sheeting 5-8  Mechanical Weathering Biologic activity Weathering may result from plants (roots), burrowing animals, and humans. As they grow into, and expand, fractures, it forms a pathway for water and chemical infiltration. Lichens and mosses also enhance the breakdown of rock surfaces. 5-9  Chemical Weathering Weathering and soil Breaks down rock components and internal structures of minerals. Converts original constituents to new minerals or releases them to the surrounding environment. Most important agent involved in chemical weathering is water. 5-10  Chemical Weathering Dissolution Easiest type of decomposition. One of the most water-soluble minerals is halite. The addition of even small amounts of acid to water aids significantly in breaking down minerals. Example: carbonic acid created when CO2 dissolves in raindrops. 5-11  Chemical Weathering Oxidation Any chemical reaction in which an element loses electrons. Important in decomposing ferromagnesian minerals. Presence of water speeds the process. Example: O2 combines with Fe in olivine, pyroxene or amphibole to form hematite or goethite. 5-12  Chemical Weathering Hydrolysis Silicates primarily decompose this way. The reaction of any substance with water. Hydrogen ion attacks and replaces other positive ions in the mineral causing the crystal structure to collapse. Example: K-feldspar in granite generates clay minerals, soluble salt and some silica. 5-13 Chemical Weathering 5-14  Chemical Weathering Alterations caused by chemical weathering Decomposition of unstable minerals. Generation or retention of materials that are stable. Spheroidal weathering - Physical changes such as the rounding of corners or edges caused by water flowing through joints. 5-15  Rates of Weathering Rock characteristics Rocks containing silicate minerals (granite) are relatively resistant Rocks containing calcite (marble and limestone) readily dissolve in weakly acidic solutions Silicate minerals weather in the same order as their order of crystallization (see Bowen’s Reaction Series) 5-16  Rates of Weathering Climate Temperature and moisture are crucial factors affecting chemical weathering rate. The optimum environment for chemical weathering is warm temperatures and abundant moisture. Chemical weathering is ineffective in polar regions and arid regions. 5-17  Rates of Weathering Differential weathering The uneven weathering of rock. Results in many unusual rock formations and landforms: Example: Hoodoos of Drumheller, Alberta Important influencing factors: Number and spacing of joints Composition Size of particles 5-18  Rates of Weathering Soil Soil is called “The bridge between life and the inanimate world”. Soil is an interface; a common boundary where different parts of Earth’s system interact. Soil is sensitive to environmental changes. 5-19  Rates of Weathering What is Soil? Regolith - the layer of rock and mineral fragments produced by weathering which covers Earth’s surface Soil - combination of mineral and organic matter, water, and air and supports plant growth Humus - the organic component of soil 5-20 Controls of Soil Formation 1. Parent Material 2. Time 3. Climate 4. Plants and animals 5. Topography 5-21  Controls of Soil Formation Parent Material The source of weathered mineral matter. Residual soils - parent material is underlying bedrock. Transported soils - soil forms on unconsolidated sediment transported from elsewhere. Example: Glacial deposits that cover much of Canada 5-22  Controls of Soil Formation Time In general, the longer a soil has been forming, the thicker it becomes, and the less it resembles the parent material. Climate Most influential control on soil formation. Key factors are temperature and precipitation. 5-23  Controls of Soil Formation Plants and animals Organisms influence the soil’s physical and chemical properties. Plants and animals supply organic matter to the soil. Microorganisms like fungi and bacteria play an active role in the decay of plant and animal remains. Burrowing animals mix the soil. 5-24  Controls of Soil Formation Topography Steep slopes often have poorly developed soils. Lowland, poorly drained soil is typically thick, dark, and contains only partially-decayed organics. Optimum terrain is a flat-to-undulating upland surface, well drained with minimum erosion. 5-25  Chapter 6: Biao Li, Concordia 6-1 What is a Sedimentary Rock? Sedimentary rocks are products of mechanical and chemical weathering. They account for about 5% (by volume) of Earth’s outer 16 km. Contain evidence of past environments Provide information about sediment transport Commonly contain fossils 6-2 What is a Sedimentary Rock? Sedimentary rocks are important economically because they may contain: Coal Petroleum and natural gas Sources of iron, aluminum, manganese, fertilizer, and raw materials for the construction industry 6-3 Turning Sediment Into Sedimentary Rock: Diagenesis and Lithification Diagenesis All the chemical, physical, and biologic changes that occur after sediments are deposited, but prior to metamorphism. Occurs in upper few kilometers of Earth’s crust at temperatures generally less than 200˚C. 6-4 Turning Sediment Into Sedimentary Rock: Diagenesis and Lithification Diagenesis includes: Re-crystallization – development of more stable minerals from less stable ones. Lithification – unconsolidated sediments are transformed into solid sedimentary rock by basic processes of compaction and cementation. Natural cements include calcite, silica, and iron oxide. 6-5  Sedimentary Environments An environment of deposition is a geographic setting where sediment is accumulating. Geographic setting and environmental conditions determine the nature of the sediment that accumulates (grain size, grain shape, colour, etc.). Uniformitarianism – applied here when we study present environments and observe the same features in ancient rocks. 6-6 Sedimentary Environments Types of sedimentary environments 1. Continental 2. Transitional 3. Marine 6-7  Sedimentary Environments Types of sedimentary environments 1. Continental Dominated by erosion and deposition associated with streams. In frigid environments, glaciers can move large volumes and sizes of sediment. Streams are a dominant factor in moving sediment. Aeolian (wind) deposits are well-sorted. 6-8  Sedimentary Environments Types of sedimentary environments 2. Transitional (shoreline) Quiet water conditions may form tidal flats. Higher energy water conditions tend to form beaches, spits, bars, and barrier islands. Sheltered, brackish water conditions can form lagoons. Deltas are common, and form when river velocity slows at river/sea interface, and sediment is deposited. 6-9  Sedimentary Environments Types of sedimentary environments 3. Marine Divided according to depth. Shallow (up to 200 m); may include land- derived sediment, skeletal debris, and coral reef accumulation. Deep (deeper than 200 m); tiny skeletons of organisms rain down on sea floor. Strong turbidity currents may move material from Smart video continental shelf to deeper environments. 6-10 Sedimentary Environments Sedimentary facies Lateral unit of sedimentary rock reflect changes in past environments. Characteristics of each unit (facies) reflect the environment in which it formed. Different sediments often accumulate adjacent to one another at the same time. The merging of adjacent facies tends to be a gradual transition. 6-11 Sedimentary Environments Gradual transition of sedimentary facies Smart video 6-12 Types of Sedimentary Rocks Sediment has three principal sources: 1. Mechanical/chemical weathering of existing rock. These are called detrital sedimentary rocks. 2. Soluble material produced by chemical weathering. These are called chemical sedimentary rocks. 3. Organic matter from once-living organisms. These are rich in carbon. Example: plant remains accumulating in a swamp. 6-13 Detrital Sedimentary Rocks The chief constituents of detrital sedimentary rocks include: Clay minerals, quartz, feldspars, micas Referred to as siliciclastic sediment Particle size is the primary basis to distinguish among the various types of detrital rocks, and tells us about depositional environment. The stronger the current, the larger the particle size carried. 6-14 Detrital Sedimentary Rocks Shale and other mudrocks Consists of clay to silt-sized particles that deposit in by gradual settling in quiet water. As silt and clay accumulate, they form thin layers called laminae. Shale exhibits fissility (splits into thin layers); but siltstone does not. Mudstone breaks into chunks. Most common type of detrital sedimentary rock. 6-15 Detrital Sedimentary Rocks Sandstone Sand-size particles; account for 20% of sedimentary rocks. Forms in a variety of environments - transported by wind and water. Sorting – degree of similarity in particle size Smart (well-sorted, poorly sorted). video Roundness- the degree to which corners and edges of grains have been smoothed down. Types: quartz sandstone (most dominant), arkose, wacke. 6-16 Detrital Sedimentary Rocks Conglomerate and breccia Conglomerate is generally rounded pebbles and cobbles that vary greatly in size. Coarse particles in a conglomerate indicate strong wave activity or stream action. If the large particles are angular rather than rounded, the rock is called breccia. The angular rocks in breccia indicate the gravel did not travel far. 6-17 Chemical Sedimentary Rocks Rocks formed from chemical sediments that were carried in solution to lakes or seas. Examples: limestone, rock salt potash Precipitation of material occurs in two ways 1. Inorganic processes e.g., Evaporation or chemical activity 2. Organic processes Aquatic organisms form chemical sediments 6-18 Chemical Sedimentary Rocks Limestone Most abundant chemical sedimentary rock. Composed mainly of the mineral calcite. Organic limestones - coral reefs, coquina (broken shells), fossiliferous limestone and chalk (microscopic organisms). Inorganic limestones - include travertine (caves) and oolitic limestone (with spherical grains). 6-19 Chemical Sedimentary Rocks Dolostone Composed of calcium-magnesium carbonate mineral dolomite (Mg replaces some Ca). Chert Microcrystalline silica (SiO2). Varieties include flint and jasper (banded form is called agate). Occurs as nodules in limestone and as tabular layers. Also found in banded iron formations. 6-20 Chemical Sedimentary Rocks Evaporites Evaporation triggers deposition of chemical precipitates. Examples include rock salt (NaCl), rock gypsum (CaSO4-2H2O), and sylvite (KCl; potash, used as a fertilizer). Salt flats – dissolved material precipitated as white crust on ground. 6-21  Coal: An Organic Sedimentary Rock Composed of organic matter Types of coal in order of increasing formational temperatures and pressures: 1. Peat - partial decomposition of plant remains in O2-poor environment. 2. Lignite - soft brown coal. 3. Bituminous coal - fixed carbon increases, coal is harder, blacker. 4. Anthracite - very hard, shiny black metamorphosed coal. 6-22 Coal – Stages of Formation 6-23  Classification of Sedimentary Rocks Divided into two groups: detrital and chemical. Two major texture subdivisions: Clastic - “broken” mainly for detrital rocks with discrete sized fragments and particles Bioclastic - rocks with skeletal remains Non-clastic - (AKA crystalline texture) mainly for chemical rocks with interlocking crystals; may resemble an igneous rock 6-24  Classification of Sedimentary Rocks 6-25  Sedimentary Structures Provide information useful in the interpretation of Earth’s history. Types of sedimentary structures: Bedding – layers of sedimentary rock. The most common characteristic. Separated by bedding planes. Cross-bedding - inclined layers. Graded bedding - rapid deposition from water; coarse material settles first. Mud cracks – shrinkage on exposure to air. 6-26  Sedimentary Structures Types of sedimentary structures (continued): Ripple marks – small waves of sand formed by moving water Current ripple marks - stream currents (asymmetric) Oscillation ripple marks - waves Hummocky cross stratification (HCS) – low angle laminations with undulations (up to 1 m long), formed by storms. 6-27 Chapter 7: Metamorphism and Metamorphic Rocks 7-1  Metamorphism Metamorphism Changes that take place when a rock is subjected to temperatures or pressures very different from where they formed. Parent rock can be any type metamorphic, igneous or sedimentary. During metamorphism the rock remains solid. The degree to which a parent rock is changed depends on the degree of the processes involved. 7-2  Controlling Factors in Metamorphism Composition of parent rock Heat Pressure Chemically active fluids 7-3  Controlling Factors in Metamorphism Composition of parent rock Clay minerals can re-crystallize to form micas, and the calcite in marble is derived from a limestone parent. Only in extreme cases of fluid migration do metamorphic rocks change in composition from their parent rocks. 7-4  Controlling Factors in Metamorphism Heat as a metamorphic agent The most important agent of metamorphism. Influences the mobility and reactivity of chemically active fluids. Heating can occur: 1. From intrusive igneous bodies 2. From Earth’s internal heat Different minerals are stable at different temperatures, so change occurs at different times. When T is beyond 200°C, clay minerals become unstable and start change to micas. 7-5  Controlling Factors in Metamorphism Pressure (stress) as a metamorphic agent Changes the physical characteristics of rocks. Confining pressure (uniform stress) Applies forces equally in all directions; harder and denser metamorphic rocks. Directed pressure (differential stress) Unequal pressure in different directions; results in distortion of a body. 7-6 Controlling Factors in Metamorphism 7-7  Controlling Factors in Metamorphism Pressure (stress) as a metamorphic agent Three basic types of directed pressure: 1. Compressional 2. Tensional 3. Shear Rocks are brittle at the surface and fracture when subjected to directed pressure. Rocks are ductile at depth, and can flatten and elongate, depending on conditions. 7-8  Controlling Factors in Metamorphism Pressure (stress) as a metamorphic agent Directed pressure forms a layered or banded texture called foliation. Foliation is the preferred orientation of platy and elongate minerals in a metamorphic rock; it is oriented parallel to the direction of minimum stress. 7-9  Controlling Factors in Metamorphism Pressure (stress) as a metamorphic agent Three factors influence foliation: 1. Rotation of platy and/or elongate mineral grains into a new orientation. 2. Changing the shape of equi-dimensional grains into elongate shapes aligned in the preferred orientation. 3. Re-crystallization of minerals to form new grains growing in direction of preferred orientation. 7-10 7-11  Controlling Factors in Metamorphism Chemically active fluids At depth, higher temperatures and pressures cause minerals to dehydrate. Ions are expelled with the water and can travel from to other sites in crystal structure, causing recrystallization. Fluids with different chemical makeup may change the composition of surrounding host rock. This is called metasomatism. [,mɛtə'somə,tɪzm] 7-12 Metamorphic Grade and Index Minerals Metamorphic grade is the intensity/degree of metamorphism that rocks have experienced. Indicated by the sequential appearance of minerals that are stable at progressively higher temperatures (index minerals), and by textures. Index minerals are stable under specific ranges of pressure-temperature (P-T). 7-13 Metamorphic Grade and Index Minerals Index minerals and metamorphic grade Changes in index minerals occur from regions of low-grade metamorphism to regions of high- grade metamorphism. Low grade = chlorite (around 200ºC). High grade = sillimanite (around 600ºC). Metamorphic rocks will be foliated or non- foliated depending on pressure conditions. 7-14 Metamorphic Grade and Index Minerals 7-15  Example questions 1. What are the controlling factors that determine the type of metamorphism and the texture of the rocks that are formed? Answer: The type of metamorphic rock that is formed depends on the pressure, temperature, fluids, and original parent rock composition. 2. What are two ways that pressure (stress) drives metamorphism? Answer: 1) forms new, generally denser minerals stable at higher pressure conditions. 2) reorients mineral grains to accommodate the stress or increased pressure. 3. What three factors or processes govern the development of foliation? Answer: 1) rotation of platy or elongate grains, 2) changing the shape of equidimensional grains, 3) re-crystallization to grow new grains in preferred orientations that reflect the new stress field 7-16 Chapter 8: Geologic Time 8-1  Geologic Time James Hutton recognized the immensity of Earth history in the late 1700s. In the 1800s, Sir Charles Lyell demonstrated Earth had been through many mountain building episodes. Although these early scientists knew Earth was very old, they had no way of knowing exactly how old. 8-2 Geology Needs a Time Scale Rocks record geologic events and changing life forms of the past. Interpreting Earth’s history is a prime goal of geology, based on clues found in rocks. The geologic time scale was developed and Earth’s history was discovered to be exceedingly long. 8-3 Relative Dating: Key Principles Geologic time Scientists tried to determine a numeric date for Earth. Relative dating means that rocks are placed in their proper sequence of formation. Doesn’t give us the age of rocks, only their order. 8-4 Relative Dating: Key Principles Law of Superposition In an undeformed sequence of sedimentary rocks, each bed is older than the one above it, and younger than the one below it. Developed by priest/geologist Nicolaus Steno in the 17th century. Applies to all surface-deposited materials such as lava flows, ash beds. 8-5 Relative Dating: Key Principles 8-6 Relative Dating: Key Principles Principle of original horizontality Layers of sediment are generally deposited in a horizontal position. Rock layers that are flat have not been disturbed. Principle of cross-cutting relations Younger features (dykes, faults) cut across older features (pre-existing rocks). 8-7 Relative Dating: Key Principles 8-8 Relative Dating: Key Principles Inclusions Fragments of one rock unit that have been enclosed within another. The rock containing the inclusion is younger than the inclusion itself. 8-9 Relative Dating: Key Principles Unconformities An unconformity is a break or gap in the rock record caused by erosion and/or non-deposition of rock units. When there is no break in the rock record, the rocks are considered conformable. Unconformities represent significant geologic events in Earth’s history. 8-10 Relative Dating: Key Principles Types of Unconformities Angular unconformity – Tilted rocks are overlain by younger, flat-lying rocks. Disconformity – Strata on either side of the unconformity are parallel. Nonconformity – Separates older metamorphic or igneous rocks from younger sedimentary strata. 8-11 Relative Dating: Key Principles 8-12 On the blank provided beside each geologic cross section below, write the name of the specific type of unconformity that is labeled with an arrow. The v-pattern indicates igneous rocks. All other patterns are different types of sedimentary rocks. a) ______________________________ b) ______________________________ c) ______________________________ Answer: a) nonconformity b) disconformity c) angular unconformity Chapter 9: Crustal Deformation 9-1 Structural Geology: A Study of Earth’s Architecture Earth is a dynamic planet: some rocks that contain marine fossils are now high above sea level. Structural geologists study the shape and forces responsible for the deformation of Earth’s crust. Rock structure interpretation has economic significance. 9-2  Deformation Deformation is a general term that refers to all changes in the original form and/or size of a rock body. Can also produce changes in the location and orientation of a rock. Most crustal deformation occurs along or near plate margins. 9-3  Deformation Force, stress, and strain Force – Tends to put stationary objects in motion, or changes the motions of moving bodies. Stress – Forces that deform rock. Strain – Visible response to stress; changes in the shape or size of a rock body caused by stress. 9-4  Deformation Types of stress Differential stress is applied unequally from different directions. Compressional stress shortens a rock body. Tensional stress elongates a rock body. Shear stress is similar to slippage between individual playing cards when the top of the deck is moved relative to the bottom. 9-5 Deformation Deformation of Earth’s crust caused by tectonic forces and associated stresses 9-6  Deformation How rocks deform: two stages Solid rocks first respond by deforming elastically. Changes that result from elastic deformation are recoverable. Rocks subjected to stresses greater than their own strength (exceed the elastic limit ) begin to deform usually by folding, flowing, or fracturing (plastic deformation). 9-7  Deformation Factors affecting rock deformation 1) Temperature and confining pressure: Brittle failure (brittle deformation) – Low temperatures and pressures near the surface (like glass breaking). Ductile deformation – Where temperatures and pressures are high, rocks exhibit ductile behaviour, a type of solid state flow. Smart video 9-8  Deformation Factors affecting rock deformation 2) Rock Type: Mineral composition and textures of rock influence deformation style. Example: Rocks with minerals with strong molecular bonds tend to fail by brittle fracture. 3) Time: Small amounts of stress over geologic time cause large changes. 9-9 Mapping Geologic Structures When studying a region, a geologist identifies and describes the dominant rock structures. Usually a structure is so large that only a portion of it is visible from a vantage point. Work is aided by advances in aerial photography, satellite and GIS imagery, Global Positioning Systems (GPS), seismic reflection data, and drill holes. 9-10 Mapping Geologic Structures Strike and dip Strike (bearing) The compass direction of the line produced by the intersection of an inclined rock layer or fault with a horizontal plane. Generally expressed in azimuth form, as an angle clockwise from north. 9-11 Mapping Geologic Structures Strike and dip Dip (inclination) Angle of inclination of surface of a rock unit or fault measured from a horizontal plane. Includes both the inclination and the direction toward which the rock is inclined (direction that water will run down the rock surface). Dip will always be at 90˚ to the strike. 9-12 Mapping Geologic Structures 9-13 Mapping Geologic Structures 9-14  Folds During crustal deformation, rocks are often bent into a series of wave-like undulations called folds. Folds in sedimentary strata form as if you were holding both ends of a piece of paper, and then pushed them together. Most folds result from compressional stresses which shorten and thicken the crust. 9-15  Folds Parts of a fold Limbs – Refers to the two sides of a fold. Axis – A line drawn down crest of the fold. Plunge – A fold axis inclined at an angle (complex folding). Axial plane – An imaginary surface that divides a fold as symmetrically as possible. 9-16  Folds Types of folds Anticline – Up-warped or arched rock layers. Syncline – Down-warped or troughs of rock layers. Depending on orientation these folds can be: Symmetrical Asymmetrical Recumbent (a fold lying on its side) Plunging 9-17 Folds Horizontal (A) and plunging (B) anticlines 9-18  Folds Types of folds Monoclines – Large, step-like folds in otherwise horizontal sedimentary strata. Domes and basins Dome Up-warped displacement of rocks. Circular or slightly elongated structure. Oldest rocks in centre, younger rocks on the flanks. Smart video 9-19  Folds Domes and basins Basin Down-warped displacement of rocks. Circular or slightly elongated structure. Youngest rocks are found near the centre, oldest rocks on the flanks. 9-20  Folds Circular outcrop patterns are typical for both domes and basins 9-21  Joints Joints are fractures that result from brittle deformation. There is typically no displacement. One of the most common rock structures. Most occur in roughly parallel groups. Causes of Joint types: Columnar joints (igneous) Gently curved due to sheeting Brittle fracture due to crustal deformation 9-22  Joints Significance of joints Chemical weathering tends to be concentrated along joints. Many important mineral deposits are emplaced along joint systems. Highly-jointed rocks often represent a risk to construction projects. 9-23  Faults Faults are fractures in rocks along which appreciable displacement has taken place. Sudden movements on faults cause most earthquakes. Active faults often pulverize rocks into fault gouge or polish and striate surfaces as slickensides. Faults are classified by their relative movement which can be horizontal, vertical, or oblique. 9-24  Faults Dip-slip faults Movement is mainly parallel to the dip of the fault surface. Fault scarps are long low cliffs produced by up and down displacement. Hanging wall - Rock above the fault surface. Footwall - Rock below the fault surface. Two major types of dip-slip: Normal faults Reverse faults (thrust when low angle) 9-25 Faults Hanging wall and footwall 9-26  Faults Dip-slip faults Normal Faults Hanging wall block moves down relative to the footwall block. Most have steep dips that flatten with depth. Accommodate lengthening (extension) and thinning of the crust. 9-27  Faults Dip-slip faults Normal Faults Normal faulting is also prevalent at spreading centres where plate divergence occurs. Graben – Central block bounded by normal faults; drops as plates separate. Horst – Raised blocks between grabens, also bounded by normal faults. 9-28 Faults 9-29  Faults Dip-slip faults Reverse and thrust faults Hanging wall block moves up relative to the footwall block. Reverse faults have dips greater than 45o and thrust faults have dips less then 45o. Accommodate shortening of the crust due to compression. 9-30  Faults Dip-slip faults Reverse and thrust faults Blocks move toward each other. Strong compressional forces. Common in mountain belts like the Alps and Rockies. The isolated remnant of a thrust sheet is called a klippe. 9-31 Faults 9-32  Faults Strike-slip faults Dominant displacement is horizontal and parallel to the strike of the fault. Types of strike-slip faults Right-lateral – Facing the fault, the block on the opposite side of fault is displaced to the right. Left-lateral – Facing the fault, the block on the opposite side of fault is displaced to the left. 9-33 Faults 9-34  Faults Strike-slip faults Transform Fault Special type of large strike-slip fault that cuts through the lithosphere. Accommodates motion between two large lithospheric plates. Links spreading oceanic ridges. Example: The San Andreas fault, California Smart video 9-35  Example questions 1. What are the three types of differential stress in the Earth's lithosphere? A) compression, shear, and tension B) confined, unconfined, and directed C) hydrostatic, lithostatic, and vibratory D) upwards, downwards, and sideways 2. How does elastic deformation of rocks differ from brittle or plastic deformation? A) It only occurs are very fast or high strain rates. B) It is reversible or recoverable and when the stress is removed, the rocks snap back to their original shape or position. C) It only happens to rocks that can bounce. D) It can only occur once and never happens in cycles. 3. When measuring the orientation of a planar structure in rocks the dip direction is measured ________ to the strike. A) at 90 degrees B) parallel C) backwards D) sideways  Example questions 4. How rocks deform, describe the two stages? 5. Also describe about the major factors affecting rock deformation 1) Temperature and confining pressure: Rocks in low temperatures and pressures region near the surface tend to have brittle deformation. By contrast, in high temperatures and pressures region, rock tend to have ductile deformation. 2) Rock Type: Mineral composition and textures of rock influence deformation style. For example, rocks with minerals with strong molecular bonds tend to fail by brittle fracture. 3) Time: Small amounts of stress over geologic time cause large changes.  Example questions 3) On the blanks provided below, fill in the name of the specific type of geologic feature that have been labelled. Answer: (a) graben (b) horst (c) normal faults Chapter 10: Earthquakes and Earth’s Interior 10-1 Earthquake on Engineering OR Better design 10-2  What is an Earthquake? An earthquake is the vibration of Earth produced by the rapid release of energy. The hypocentre is point of energy release, and radiates in all directions from its source. The epicentre is the location on the surface, directly above the hypocentre. Earthquakes generate seismic waves that radiate throughout the earth. 10-3 What is an Earthquake? 10-4  What is an Earthquake? Earthquakes and faults Movements that produce earthquakes are usually associated with large faults in Earth’s crust. Most of the motion along faults can be explained by plate tectonics theory. Most earthquakes occur along faults associated with plate boundaries. 10-5  What is an Earthquake? Elastic rebound Mechanism for earthquakes was first explained by H.F. Reid (early 1900s). Rocks on both sides of an existing fault are deformed by tectonic forces. Rocks bend and store elastic energy. The springing back of the rock after stress is overcome is called elastic rebound. Video earthquakes-fault-movement 10-6  What is an Earthquake? Foreshocks and aftershocks Aftershocks - Adjustments that follow a major earthquake often generate smaller earthquakes. Foreshocks - Small earthquakes often precede a major earthquake by days or even by as much as several years. 10-7  Seismology Seismology, the study of earthquake waves, dates back almost 2000 years to the Chinese. Seismographs are instruments that record seismic waves. Today’s instruments record the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape. 10-8  Seismology Seismographs Work when inertia of an object keeps the mass in place while Earth and supports under the mass move. The movement of Earth in relation the stationary mass is recorded on a rotating drum, magnetic tape, or digital device. The records that reveal the behaviour of seismic waves are called seismograms. 10-9  Seismology Left seismograph records horizontal ground motion, right one records vertical motion 10-10  Seismology Types of seismic waves Waves that are generated by the slippage of rock mass are divided into two categories: 1. Body waves – Waves that travel through Earth’s interior (P and S Waves). 2. Surface waves – Waves that travel along the outer part of the Earth (L waves). 10-11  Seismology Body waves Primary (P) waves Push-pull (compress and expand) motion, changing the volume of material. Travel through solids, liquids, and gases. Secondary (S) waves Shear motion at right angles to their direction of travel. Slightly greater amplitude than P waves. Travel only through solids. Vedio: S-and-p-body-waves 10-12  Seismology Surface (L or long) waves Travel along outer part of Earth. Complex motion, cause greatest destruction. Exhibit greatest amplitude, slowest velocity. Have the longest periods (time interval between wave crests). 10-13 Seismology Basic types of seismic waves and their characteristic motion 10-14  Seismology Typical seismogram showing arrival of P, S, and surface waves 10-15  Locating the Source of an Earthquake Difference in velocities of P and S waves help to locate the epicentre. Three seismic station recordings are needed to locate an epicentre. The time interval between the arrival of the first P wave and the first S wave at a station location is calculated. A travel-time graph is used to determine each station’s distance to the epicentre. 10-16  Locating the Source of an Earthquake Earthquake belts About 95 percent of the energy released by earthquakes comes from relatively narrow zones around the globe. Major earthquake zones include the Circum- Pacific belt, Mediterranean Sea region to the Himalayan complex, and the oceanic ridge system. 10-17 Locating the Source of an Earthquake 10-18  Measuring the Size of Earthquakes Two measurements that describe the size of an earthquake are: 1. Intensity – a measure of the degree of earthquake shaking at a given locale based on the amount of damage. 2. Magnitude – estimates the amount of energy released at the source of the earthquake. 10-19  Measuring the Size of Earthquakes Intensity scales The Modified Mercalli Intensity Scale was developed using California buildings as its standard and individual descriptions. Uses Roman numerals I-XII. The drawback of intensity scales is that destruction may not be a true measure of the earthquakes’ actual severity. 10-20  Measuring the Size of Earthquakes Magnitude scales Richter magnitude introduced by Charles Richter in 1935. Richter scale is based on the amplitude of the largest seismic wave recorded on seismogram. Accounts for the decrease in wave amplitude with increased distance. 10-21  Measuring the Size of Earthquakes Magnitude scales Richter scale (ML) Largest magnitude recorded on a Wood- Anderson seismograph was 8.9. Magnitudes less than 2.0 are not felt by humans. Each unit of Richter magnitude increase corresponds to a tenfold increase in wave amplitude and a 32-fold energy increase. Video: Intensity-vs-magnitude 10-22 Measuring the Size of Earthquakes 10-23  Measuring the Size of Earthquakes Magnitude scales Other magnitude scales Moment magnitude (MW) - Derived from the amount of displacement that occurs along a fault zone. Takes amount of displacement, area of rupture surface and shear strength of rock into account. Roughly equivalent to Richter scale but better for large earthquakes. 10-24  Earthquake Destruction Destruction from seismic vibrations Depends on: Intensity of the vibrations. Duration of the vibrations. Nature of the material upon which the structure rests. Design of the structure. 10-25  Earthquake Destruction Destruction from seismic vibrations Amplification of seismic waves Region near the epicentre will experience about the same intensity of ground shaking. Destruction varies considerably, mainly due to the nature of the ground on which the structures are built. 10-26  Earthquake Destruction Destruction from seismic vibrations Liquefaction In areas where unconsolidated materials are saturated with water, earthquake vibrations can generate liquefaction. Not capable of supporting buildings. Underground structures like sewers and storage tanks can float to the surface. Video: Liquefaction-hazards 10-27  Earthquake Destruction Tsunami Destructive seismic sea waves, incorrectly called “tidal waves”. Causes: Vertical displacement along a shallow fault located on the ocean floor. Large earthquake-triggered submarine landslide. Travel at speeds of about 800 km/hr. As waves near shore, they increase in height. 10-28 Earthquake Destruction Formation of a tsunami Video: Tsunamis-sunda-megathrust 10-29  Earthquake Destruction Landslides and ground subsidence Landslides may cause considerable damage triggered by seismic waves. The cause of most damage in the 1964 Alaskan earthquake. Fire Likely when ground shaking breaks gas lines and sparks ignite gas. 10-30 Can Earthquakes be Predicted? Short-range predictions No absolutely reliable method for making predictions. Goal is to provide warning for location and magnitude within hours or days. Current research concentrates on precursor studies (measuring uplift, subsidence, and strain in the rocks). 10-31 Can Earthquakes be Predicted? Long-range forecasts Gives the probability of a certain magnitude earthquake occurring on a time scale of 30 to 100 years, or more. Based on the premise that earthquakes are repetitive or cyclic. Using historic records, some faults had not had movement in more than a century. These areas are seismic gaps. 10-32 Can Earthquakes be Predicted? Long-range forecasts Paleoseismology studies layered deposits that were offset by prehistoric seismic activity. These studies are important because they provide information used to: Develop earthquake building standards. Assist in land-use planning. Strengthen dams, structures. 10-33 Can Earthquakes be Predicted? Seismic gap just west of Haida Swaii denotes the most likely location for the next large earthquakes along the Queen Charlotte Fault. 10-34  Probing Earth’s Interior Knowledge of Earth’s interior comes from the study of seismic waves. When waves travel through Earth, they carry information about the material they passed through. Travel times of P and S waves through Earth vary depending on the properties of the materials. The variations correspond to changes in the materials encountered. 10-35  Probing Earth’s Interior The nature of seismic waves To understand Earth’s composition we must study wave transmission (propagation). Seismic energy radiates from source in waves. The pathway of the waves are called rays. 10-36  Probing Earth’s Interior The nature of seismic waves Velocity of waves depends on the density and elasticity of earth material. Wave speed generally increases with depth due to pressure forming a more compact elastic material. Compressional waves (P waves) are able to propagate through liquids and solids. 10-37  Probing Earth’s Interior The nature of seismic waves S waves cannot travel through liquids. In all materials, P waves travel faster than S waves. When seismic waves pass from one material to another, the path of the wave is refracted (bent). The boundary between two layers where waves are refracted and reflected is called a discontinuity. 10-38  Probing Earth’s Interior Seismic waves and Earth’s structure Earth is not homogeneous. The abrupt changes in seismic-wave velocities that occur at particular depths helped seismologists conclude that Earth must be composed of distinct shells. Vedio: Velocity-structure 10-39 1) The ________ is the point of origination for an earthquake. A) fault plane B) hypocentre C) seismic belly button D) epizone 2) ________ is the widely accepted explanation for the mechanism that generates earthquakes. A) Dow's recovery theory B) Dupont's plastic-slip theory C) Richter's wave-snap theory D) Reid's elastic rebound theory 3) What are the two fundamentally different types of seismic waves? A) body waves and surface waves B) P waves and S waves C) seismic earth waves and seismic sea waves (tsunamis) D) tidal waves and breaking waves a) Which of these two identical homes would suffer the most damage if an earthquake occurred along the active fault? ______________________________ b) Explain your answer. ______________________________________ _____________________________________ Chapter 11: The Ocean Floor 11-1  Mapping the Ocean Floor The depth of the ocean floor was originally measured by lowering weighted lines overboard. Echo sounder (also known as sonar): Invented in the 1920s. Primary instrument for measuring depth. Reflects sound waves from ocean floor. By knowing the velocity of sound waves in water and the time required for the wave to hit the floor, depth can be established. 11-2  Mapping the Ocean Floor Multi-beam sonar Employs an array of sound sources and listening devices. Obtains a detailed profile of a narrow strip of seafloor. Satellites Use radar altimeters to record seafloor topography by bouncing microwaves off the sea surface. 11-3 Mapping the Ocean Floor Echo sounders (A) and multibeam sonar (B) 11-4  Mapping the Ocean Floor Oceanographers have identified 3 major topographic units of the ocean floor: 1. Continental margins 2. Deep-ocean basins 3. Mid-ocean ridges 11-5 Mapping the Ocean Floor Exploring-ocean-floor 11-6  Continental Margins Two main types of continental margins - active and passive. Passive continental margins Found along coastal areas that surround the Atlantic ocean. Not associated with plate boundaries. Experience little volcanism and few earthquakes. 11-7  Continental Margins Passive continental margins Continental shelf Flooded extension of the continent. Varies greatly in width (Average is 80 km). Gently sloping submerged surface. Contains important mineral deposits. Some areas are mantled by extensive glacial deposits. 11-8  Continental Margins Passive continental margins Continental slope Marks the seaward edge of the continental shelf. Relatively steep feature (5˚ to 25˚ slope). Boundary between continental crust and oceanic crust. Represents original rift after a continent like Pangaea split apart; true edge of a continent. 11-9  Continental Margins Passive continental margins Continental rise Continental slope merges into a more gradual incline – the continental rise. May extend for hundreds of kilometres. Thick accumulation of sediment. At the base of the continental slope turbidity currents