ENV 241 Lithosphere Notes PDF

ENV 241 LITHOSPHERE NOTES Earth Structure and Composition The layers of the Earth’s interior include the crust, mantle, liquid outer core, and solid inner core Layers of the Earth Crust: o Outermost / outercovering layer, thinnest and solid o Composed of continental and...

ENV 241 LITHOSPHERE NOTES Earth Structure and Composition The layers of the Earth’s interior include the crust, mantle, liquid outer core, and solid inner core Layers of the Earth Crust: o Outermost / outercovering layer, thinnest and solid o Composed of continental and oceanic crust (granite and basalt) o Oceanic crust is denser / thicker (that’s why its moving down) than continental crust Mantle: o Thick layer beneath the crust (just below the crust) o Semi-solid rock that flows slowly o Involved in tectonic activity (all tectonic activitys happen there) (both are composed of nickel and iron) / both have high temprature but inner have high pressure becsause it has all layers pressure on it Outer Core: o Liquid layer beneath the mantle o Composed mainly of iron and nickel o Generates the Earth's magnetic field Inner Core: o Innermost layer, solid sphere – because of high pressure o Primarily iron and nickel o Extremely hot and under immense pressure (lithosphere flows over asthnesphore) Lithosphere  Definition: Rigid outer layer of Earth (crust + upper mantle). – solid form Composition: Solid rock (continental and oceanic crust). – main copostition is solid rocks Characteristics: Divided into tectonic plates; involved in earthquakes and volcanic activity. Asthenosphere Definition: Semi-fluid layer of the upper mantle beneath the lithosphere. Composition: Partially molten rock. – main composition Characteristics: Allows tectonic plate movement; drives convection currents. Lithosphere can move because of asneosphere because its in a semi liquid state (convection current) Rocks Rock is an aggregate (collection) of mineral particles. Types of rocks  Igneous Rocks: Formed from the solidification of molten magma or lava (it will solidify then become a rock). They can be divided into: Intrusive (Plutonic) – two names: Crystallize slowly beneath the Earth's surface (e.g., granite). (magma) Extrusive (Volcanic) – two names: Erupt and cool quickly on the surface (e.g., basalt). (lava) Sedimentary Rocks: Formed from the accumulation and compaction of sediments, which can include fragments of other rocks, minerals, and organic materials. (forming layers) Metamorphic Rocks: Created when existing rocks are transformed by heat, pressure, or chemically active fluids. This process, known as metamorphism, changes the mineral composition and structure (e.g., schist from shale, marble from limestone). Composition of earth A total of 91 elements occur naturally in the Earth’s crust. However, eight elements make up more than 98 percent of the earth’s crust. A mineral (main component of rocks) is a naturally occurring, inorganic solid with a characteristic chemical composition and a crystalline structure - Felsic rocks (comprising the crust) are high in silica content: “acid / acidic rocks”. We can see it in the crust - Ultramafic rocks (comprising the mantle) are high in magnesium and iron content: “basic rocks”. We can see it in the mantle Plate tectonics Alfred Wegner (in 1912) – continental drift is the theory proposed the theory that the crustal plates are moving over the mantle. He argued that today’s continents once formed a single landmass, called Pangaea (Greek for "all land"). Later on they came up with plate tectonics model, the uppermost mantle and the overlying crust behave as a strong, rigid layer, known as the lithosphere, which is broken into segments commonly referred to as plates The earth’s lithospheric shell is divided into six great lithospheric plates and at least nine lesser plates Ø Divergent boundaries (Constructive) occur where two plates slide apart from each other. (A) Ø Convergent boundaries (Destructive) occur where two plates slide towards each other commonly forming either a subduction zone (if one plate moves underneath the other) or a continental collision (if the two plates contain continental crust). (B) Ø Transform boundaries (Conservative) occur where plates slide past each other along transform faults. (C) Divergent- rift valley and tilted block mountains Convergent – Trenches, mountain ranges, island arcs, volcanic arcs (key features : what will be formed after it happens) Relief features refer to the physical and topographical variations in the Earth's surface. They include the different elevations, depressions, and formations that shape landscapes. About 29 percent of the earth’s surface is land and 71 percent oceans (adding the 6 percent of shelf area to the continents increases the area of the continents to 35 percent and decreases the ocean basin area to 65 percent) Oceanic relief features  A mid-oceanic ridge with a central rift where crust is being pulled apart Continental shelves that accumulate thick deposits of continental sediments Continental slopes that are the edge of the continental crust Oceanic trenches where oceanic crust is sliding beneath continental crust Continents divided into two types of region: active mountain-making belts and inactive regions of old, stable rock. There are two types of stable structures—continental shields and mountain roots. Mountain Roots are the deep, stable portions of the Earth's crust that support mountain ranges Time scale All time older than 570 million years (MY) Before the present is Precambrian time Three eras of time follow: Paleozoic, Mesozoic, and Cenozoic The geologic eras are subdivided into periods We live in the Holocene period (the last 12,000 years) Earthquakes The shaking and trembling (huge amount of energy will be released then converted into waves) those results from movement of rock beneath Earth’s surface Most severe earthquakes occur near plate collision boundaries Earthquakes is the sudden release of stored energy It is a result of fast movement between two blocks of rock. The released energy radiated away from the earthquake. Main cause of earthquake is faults on the crust of earth. A fault is a (crack) break between Two blocks of rocks in response to stress Know those two terms Origin of the earthquake (where fault begins) is the focus or hypocenter The point on the Earth’s surface, directly above the focus (top of the break) , is the epicenter Elastic rebound theory of earthquakes (earthquakes happen because of this theory) Geophysical model that explains how energy is stored in deformed rocks along fault lines (near fault zones) and released during an earthquake. Seismic waves are vibrations that travel through Earth carrying energy released during an earthquake Two types of waves are produced during an Earthquake 1. Body waves : body / core of the earth a. P wave (primary) P wave (also called a compressional wave) is an elastic wave that causes alternate compression and expansion of the rock b. S wave (secondary) A second type of body wave, called an S wave, is a shear wave. S waves are slower than P waves 2. Surface waves : then reaching to the surface a. R wave Rayleigh wave moves with an up-and down rolling motion like an ocean wave. b. L wave Love waves produce a side-to-side vibration. Most destructive : surface wave is more destroying than the body waves Less destructive: body wave Richter Scale- rating (measuring) of an earthquake’s magnitude (which is giving us number) based on the size of the earthquake’s seismic waves  Mercalli Scale = Rate earthquakes on the level of damage or intensity at a certain place - The Plate Tectonics Theory explains the movement of Earth's lithospheric plates (oceanic and continental) and is fundamental in understanding earthquakes, volcanic activity, and the formation of various geological features. Secondary perils (after math) refer to the risks and damages that arise because of the initial seismic event – shaking of earth, immediate effect Landslides: Ground shaking can trigger landslides, especially in hilly or mountainous areas. Liquefaction: In saturated soils, shaking can cause the ground to behave like a liquid, leading to significant structural damage. Tsunamis: Underwater earthquakes can generate tsunamis, which can cause widespread flooding and destruction in coastal areas. Fires: Damaged gas lines and electrical systems can lead to fires, which may be difficult to control in the chaos following an earthquake. Aftershocks: These smaller earthquakes that follow the main event can cause additional damage to already weakened structures. Infrastructure failure: Damage to roads, bridges, and utilities can complicate rescue and recovery efforts Volcanoes A volcano is an opening in the earth's crust through which lava, volcanic ash, and gases escape. Volcanic eruptions are partly driven by pressure from dissolved gas (know the structure) The narrow opening of volcano is called vent The upper part of vent is a cup shaped depression called crater. Secondary cone Volcanoes are formed when magma from within the Earth's upper mantle works its way to the surface. At the surface, it erupts to form lava flows and ash deposits. Magma is liquid rock inside a volcano. Lava is liquid rock (magma) that flows out of a volcano; outside. – the flow Layers of ash and lava can be seen – alternating layer Lava, gas, rock materials and ash Types of volcano  Volcanoes are located at boundaries of tectonic plates and at hotspots The Pacific Ring of Fire is an area of frequent earthquakes and volcanic eruptions encircling the basin of the Pacific Ocean. The Ring of Fire has 452 volcanoes. 90% of the world's earthquakes and 81% of the world's largest earthquakes occur along the Ring of Fire. - The Ring of Fire is a horseshoe-shaped zone around the edges of the Pacific Ocean, known for its high volcanic and earthquake activity due to tectonic plate movements. - Hotspots are locations in the Earth's mantle where plumes of hot material rise, creating volcanic activity independent of tectonic plate boundaries. Volcanic Explosivity Index (VEI) is a numeric scale that measures the relative explosivity of historic eruptions. Volume of products, eruption cloud height, and qualitative observations are used to determine the explosivity value. A caldera is a large, basin-like depression that forms after a volcanic eruption. (the dip after the top is erupted) Types of volcanic eruptions a. Effusive eruptions-characterized by the relatively quiet outpouring of lava b. Explosive eruptions-characterized by energetic ejection of pyroclastic material (all are exllopsive eruptions ) 1. Strombolian eruption (Stromboly, Italy) fountaining of lava, forms cinder cones 2. Vulcanian eruption (Vulcano, Italy) moderate to violent blasts of viscous blocks, can produce thick lava 3. Pelean eruption (large scale violent eruptions, development of domes & pyroclastic flows, 4. Plinian eruption (Mt. Vesuvio, Italy,79 AD) large explosive events, enormous dark columns of tephra 5. Hydroexplosive eruption - violent steam explosions, fragments the magma into fine- grained ash  Composite Volcanoes: -Steeper slopes -explosive eruptions, -formed from alternating layers of lava and volcanic material. Shield Volcanoes: -Gentle slopes, -effusive eruptions -built from fluid lava flows (lava is sticky and slop is steep in composite volcanos – lava is fluidy in sheild) Effects of volcanic eruption Primary effects Immediate and come from eruption itself Volcanic gases – magma contains dissolved gases Lava flows –streams of molten rock Pyroclastic flows – hot ash, rock fragments and gas Tephra refers to the fragments of volcanic rock and ash that are ejected into the air during a volcanic eruption Secondary effects Lahars - These are mixtures of water, rock, ash, sand and mud that originate from the slopes of a volcano (from the slope and coming down) Land slides Flooding Damage to human life and property Denudation Denudation refers to the long-term processes that cause the wearing away of the earth's surface (weathering away, three process) Processes Weathering Erosion Mass wasting/ mass movement I. Weathering (three types) 1. Physical / mechanical Weathering Breaking down of rocks by the physical or mechanical stress (4 types) a. Freeze thaw b. Salt crystallization c. Thermal expansion and contraction / onion peal the rock will expand, then the cold weather causes it to contract.  d. Wetting and drying – hostil regions / near water Addition of water to mineral causes expansion 2. Chemical weathering (five types) Decomposition of rocks due to external forces like air, rain,𝑪𝑶𝟐 , and organic acids a. Oxidation (oxygen) Oxidation weathering is a chemical process where minerals in rocks react with oxygen. Iron-rich minerals in rocks react with oxygen from the air or water and form rust, making the rock weaker and more prone to breaking down b. Carbonation (carbonic acid after carbon dioxide react with water) carbonation is a process where carbon dioxide (CO₂) reacts with water to form carbonic acid. This acid reacts with carbonate minerals. The reaction dissolves the rock c. Hydration (water) d. Hydrolysis Hydration involves adding water to a mineral’s crystal structure, forming a new mineral called a hydrate. Hydrolysis is when water reacts chemically with silicate minerals, breaking them down. The process alters the rock's composition and can weaken it. e. Solution a type of chemical weathering where minerals dissolve in water. 3. Biological weathering – activity of living things (plants, animals , roots , microorganisms) is the breakdown of rocks through the actions of living organisms: Plant Roots: Roots grow into cracks, exerting pressure and breaking rocks apart. Lichen and Moss: These organisms produce acids that chemically weather rock surfaces. Animal Activity: Burrowing animals disturb soil and rock, exposing them to weathering. Microbial Action: Bacteria and fungi release organic acids that help break down minerals.  Regolith is the layer of loose material on the Earth's surface made up of rock fragments, soil, and organic matter. It forms from weathering and covers bedrock, supporting plant life and playing a key role in soil development II Erosion – movement / transpostation due to three reasons Movement of weathered materials to another location Causes Water: Rainfall, rivers, and ocean waves can wash away soil and rock. Wind: Strong winds can lift and transport loose particles, especially in dry areas. Ice: Glaciers scrape and move debris as they advance III. Mass movement (mainly in slopes becauase of gravity) Continual downslope movement of eroded rock and soil due to the gravity