Planet Earth Course (GEOL 110) BLT Form - Chapter 3 PDF

Planet Earth Course (GEOL 110)- BLT form Chapter 3: Earth Shaping processes Delivery method: mainly online Dr. Dalal Alshamsi Geology Department, College of Science United Arab Emirates University Session 1 Earth surface shaping factors are: 1. Climate: a) Weathering b) Erosion...

Planet Earth Course (GEOL 110)- BLT form Chapter 3: Earth Shaping processes Delivery method: mainly online Dr. Dalal Alshamsi Geology Department, College of Science United Arab Emirates University Session 1 Earth surface shaping factors are: 1. Climate: a) Weathering b) Erosion 2. Plate Tectonics Climate Unlike the weather which changes over short time, the climate is the average weather conditions over a long period of time. Climate has changed throughout geological time (millions of years). What is climate change, and how do geologists know about it? The Earth’s temperature change naturally over time scales ranging from decades, to hundreds of thousands, to millions of years. Proof of climate change is preserved in an extensive range of geological settings, including marine and lake sediments, ice sheets and fossils (Geological Society of London, 2010). https://www.britishecologicalsociety.org/climate-change-emmisions-reduction-targets-scotland-bill-call-evidence/  Climate What are the driving forces of climate change? Many factors interact on different time scales and cause the climate change: Over millions of years the continents move, oceans open and close, mountains rise and fall, volcanoes erupt and emit gases. All of these changes affect the atmosphere and oceans and in turn the overall climate on earth. Scientists think that climate change is driven by changes in the Earth’s orbit axial tilting which result in releasing CO2 from oceans. Effects of climate change on earth shape During ice ages, the sea level drops. For example in the most recent ice age 12000 years ago, the Arabian Gulf was dry with only a river channel. In contrast, the ice sheets melt and the sea level rises in the green house ages. The earth in the most recent ice age 12000 years ago Weathering Weathering in general refers to a group of processes that are grouped into: A. Mechanical weathering: rock disintegrates (breaks out) into smaller particles without changing their chemical and mineralogical composition. B. Chemical weathering: rock dissolves into water and this process will change the chemical and mineralogical composition of the rock. The weathering processes often are slow (hundred to thousands of years). Mechanical weathering examples: Frost wedging Water penetrates cracks, then freezes. The expanding ice wedges the crack apart Thermal cracking Hot conditions followed quickly by cold conditions produce thermal stresses that can crack the rocks Root wedging Plant roots invade a crack in the rock. As the plant grows the root gradually opens the crack in the rock. Root wedging Mechanical weathering Boulder split by thermal stresses Tree roots wedging apart a rock along a crack Mechanical weathering in Jais Mountain, RAK  Chemical weathering examples: Oxidation Fe2+ in minerals oxidizes to form Fe oxides like hematite (Fe2O3) Dissolution Carbonate minerals (like calcite which occurs mainly in limestone) dissolve in slightly acid rainwater Chemical weathering- dissolution in Hafit Mountain resulted in cavities  Erosion Erosion is the removal (transportation) of weathered and unweather materials from their original place to a lower elevation drainage systems. Erosion in Hafit Mountain produced by running water or wind Weathering and erosion shaping effect differs according to climate Jebel Hafit Mountain was shaped in Hot arid climate Alps Mountains were shaped in cold glacial climate Session 2 Plate tectonics The rocky outer skin of the Earth is a thin shell called the crust. We live on the crust so we know more about it than the rest of the Earth. The crust is very thin and consists of two types of material: 1- Continental crust 2- Oceanic crust Usually 10 – 70 km thick and relatively Only 3– 15km thick and denser low in density. It has an average than continental crust. It has composition like granite an average basalt composition The crust is divided into a mosaic of “plates” that are variable in size and are usually composed of both oceanic and continental crust. North American plate has continental crust and oceanic crust Each plate is outlined by plate boundaries Pacific plate is entirely oceanic crust Tectonics The cause of plate movement is probably due to the effect of giant thermally driven The plates are not static – they are convection cells in the mantle. These transfer moving, each in its own direction. heat from the core towards the surface. The plates are moving in different directions: 1. Plates moving away from each other = Divergent plate boundaries 2. Plates moving toward from each other = Convergent plate boundaries 3. Plates moving parallel to each other = Transform plate boundaries  1- Divergent plates Divergent (splitting) starts in a weak part of As we learnt in chapter 1, basalt is the crust, where the lava can rise up in a line. dominant rock type in the oceanic This separation line is called Spreading crust! So the formed basalts around ridge. the spreading ridge will be new oceanic crust which means a new sea will form in the area of divergent plate Along the spreading ridge, a line of small boundaries. volcanoes are erupting lavas. The new sea opens more and more When these lava cool and solidify, igneous with time forming am ocean. rocks -particularly basalt- are formed. Most of the Earth’s seas and oceans were formed due to the divergent plate boundaries movement. Examples: African Rift Valley, Red sea, Atlantic Ocean.  1- Divergent plates Modified after: https://www.zmescience.com/science/what-is-wilson-cycle/ Divergent plates are considered constructive because a new oceanic crust is created 1- Divergent plates Most of the volcanism along the spreading ridges is under the sea. In some cases the ridge reaches the surface of the ocean and the volcanism can produce islands. For example: Iceland 2- Convergent plates When two plates move toward each other, they meet. These meetings (collision) will result in different phenomenon depending on the crust type in each side! Convergent plates might occur as: 1. Continental crust colliding continental crust 2. Continental crust colliding oceanic crust 3. Oceanic crust colliding oceanic crust 2- Convergent plates 1. Continental crust colliding continental crust Results in: 1. Mountains building 2. Crust thickening = constructive effect 3. Earthquakes Example: When Indian plate collide the Eurasian plate, the Himalaya Mountains were built up! www.Wikipedia.org  About 225 million years ago, India was a large island near the Australian coast! When Pangaea broke apart about 200 million years ago, India began to move northward, until it collided Asia around 50 million years ago! The result of collision was the Himalaya Mountains! https://pubs.usgs.gov/gip/dynamic/himalaya.html The Himalayan Mountains marks the line of collision https://www.tes.com/lessons/OFrLtMf3T56kPQ/science-changing-earth  2- Convergent Plates 2. Continental crust colliding oceanic crust Results in: 1. The denser oceanic crust is subducted (going beneath) under the continental crust 2. Destroying part of the oceanic crust, which is dipped partially in the mantle and melt= destructive effect 3. The melted part will rise up as volcanic arc on the continent 4. Forming Trench at the area of subduction. 5. Earthquakes and may be Tsunami * Trench is: deep zone and lies along the line where the two plates meet. * Subduction is zone where two plates meet. Example: The pacific plate collide the South American plate forming the Andes Mountains (Andes volcanic arc). Continental crust colliding oceanic crust https://www.tes.com/lessons/OFrLtMf3T56kPQ/science-changing-earth 2- Convergent Plates 3. Oceanic crust colliding oceanic crust Results in: 1. Both oceanic crust are dense, but the older denser one is subducted under the another. 2. Destroying part of the oceanic crust, which is dipped partially in the mantle and melt = destructive effect 3. The melted part will rise up as large areas of lava. These lavas cool and solidify forming volcanic islands in the sea (like Japan Islands, Mariana Islands). 4. Forming Trench at the area of subduction. 5. Earthquakes and may be Tsunami Oceanic crust colliding oceanic crust Mariana Islands Mariana Trench https://slideplayer.com/slide/5913252/ www.geology.com  3. Transform Plates The plates simply slide past each other, with no divergence and no convergence The friction from this movement might result in earth quakes This type of boundary is conservative, because neither crust is destroyed nor is created. Examples: 1. Dibba fault zone in the UAE 2. San Andreas fault in California, USA https://www.researchgate.net/figure/Epicenter-map-PDE-data-for-the-UAE-and-southern-Iran- Solid-stars-mark-epicenters-of_fig1_226345564 End of Chapter 3