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BELLWORK • Name the 3 types of plate boundaries and an example of each. Deforming the Earth’s Crust Moving Continents • http://www.suu.edu/faculty/colberg/hazards/platetectonics/18_Pangaea.html Tracking Tectonic Plates Scientists use GPS to track plate movement. Radio waves are beamed from satellites to GPS ground stations which record their position. 3 Possible Driving Forces • Convection Currents • Ridge Push and Slab Pull – Ridge Push – At mid-ocean ridges, the oceanic lithosphere is higher than it is where it sinks into the asthenosphere. Because of ridge push, the oceanic lithosphere slides downhill under the force of gravity. – Slab Pull – Because oceanic lithosphere is denser than the asthenosphere, the edge of the tectonic plate that contains oceanic lithosphere sinks and pulls the rest of the tectonic plate with it in a process called slab pull. • Plate movement causes geological events such as mountain formation, volcanic eruptions, and earthquakes. Deformation • The process by which the shape of a rock changes because of stress. – Stress is the amount of force per unit area on a given material. • Different things happen to rock when different types of stress are applied. – Rock layers bend when stress is placed on them. – When enough stress is placed on rocks, they can reach their elastic limit and break. Compression • The type of stress that occurs when an object is squeezed, such as when two tectonic plates collide. • When compression occurs at a convergent boundary, large mountain ranges can form. Tension • Stress that occurs when forces act to stretch an object • Tension occurs at divergent plate boundaries, such as mid-ocean ridges, when two tectonic plates pull away from each other. Folding • The bending of rock layers because of stress in the Earth’s crust. • Types of Folds – depends on how the rock layers deform: – Anticlines – Synclines – Monoclines Anticline • Upwardarching folds. • Caused by horizontal stress. Syncline • Downward, troughlike folds. • Caused by horizontal stress. Monocline • Fold where both ends are horizontal. • Cause by vertical stress. Faulting • The surface along which rocks break and slide past each other. – Some rock layers break when stress is applied – The blocks of crust on each side of the fault are called fault blocks. Footwall & Hanging Wall • When a fault is not vertical, its two sides are either a hanging wall or a footwall. Normal Fault • When a normal fault moves, it causes the hanging wall to move down relative to the footwall. • Caused by rocks being pulled apart (tension). Normal Fault Reverse Fault • When a reverse fault moves, it causes the hanging wall to move up relative to the footwall. • Caused when rocks are pushed together (compression). Reverse Fault Strike-Slip Fault • When opposing forces cause rock to break and move horizontally. Mountain Building • When tectonic plates undergo compression or tension, they can form mountain ranges in several ways. Folded Mountains • The highest mountains in the world are formed when rock layers are squeezed together and pushed upwards to form folds. – This occurs at convergent boundaries where plates collide. – The plates buckle and thicken. – The continental crust is pushed upward, forming mountains. Examples of Folded Mountains • Himalayas • Alps In central Europe • Ural Mountains in Russia • Great Smoky Mountains Fault-Block Mountains • Form when large blocks of the Earth’s crust drop down relative to other blocks. • Tension produces mountains that have sharp, jagged peaks. Examples of Fault-Block Mountains • Teton Range in Wyoming. • Sierra Nevada mountain range in California • Harz Mountains in Germany Volcanic Mountains • Form when magma rises to the Earth’s surface and erupts. Examples of Volcanic Mountains • Mount St. Helens in Washington • Mount Pinatubo in the Phillipines Uplift and Subsidence • Uplift is the rising of regions of the Earth’s crust to higher elevations. – Rebound – When the crust slowing springs back to its previous elevation, as when a glacier melts. • Subsidence is the sinking of regions of the Earth’s crust to lower elevations. – Rocks that are hot take up more space than cooler rocks. Tectonic Letdown • Subsidence can also occur when the lithosphere becomes stretched in rift zones. Quiz 1. Name the 3 types of faults. 2. Name the 3 types of folds. 3. What is compression? 4. What is tension? 5. Would you find a folded mountain at a mid-ocean ridge? Why or why not?