Unit 1: Landforms September 2014 What is Geography? Geography is the study of how the earth works and how people interact with it. We are first concerned about understanding the forces that shaped the earths surface What shaped the Earths Surface? Earths Structure A look Inside Inner Core and Outer Core Inner core Outer core Mantle Mohorovicic Discontinuity Asthenosphere Lithosphere Earths Structure (contd) Review video:erkerk Landforms Plates:The earths crust is made up of different tectonic plates How Compressional and Tensional Forces are Created Plate Tectonics: The movement of the earths plates. Includes both compressional and stretching (tensional) forces Compression Stretching/Tensional Compressional Processes Compressional Force: Parts of the earths crust pushing toward each other, causing colliding parts to rise, fall and buckle underneath. Subduction zone:Place where two tectonic plates collide. The more dense plate goes under, or subducts, to the other A Subduction Zone Tensional Force: A stretching force in the earths surface which may cause faulting. Plates break apart and move away, or past, each other. This will often cause a trench as one plate moves downward. Ridges sometimes form as the magma rises between the plates Relating Tectonic Plates to Compressional and Tensional Forces Compressional Forces: Plates (arrows) colliding Tensional Forces: Plates (arrows) moving away from each other Wegeners Theory of Continental Drift: Explains the movements of tectonic plates Plates carried by hot magma (Proven by Tuzo Wilson) All continents were once joined together called Panagaea. They broke into two sections about 200 million years ago. These two sections broke pieces. They drifted to their present locations. Based upon fossils and rock formations we know today Panagaea Wegeners Critics Argued how did the plates move? Wegener could not prove it Wilson to the Rescue! In the 1960s Canadian Tuzo Wilson revisited Wegeners work Volcanoes beneath the ocean erupted magma. Magma carried the plates further away from each other Sea floor spreading moved continents. Sea Floor Speading Landforms Read pp. 6-10 Compressional Forces Creating Fold Mountains Fold Mountains: Caused by compressional forces moving the earths crust together to collide Different forces and pressures create simple or complex forms Fold Mountains Differentiate Anti-cline and Syncline Anti-Cline: It is the peak (top) of a folded mountain An arch-like upfold Top of the A Syncline: It is the bottom or the valley A downfold of rock layers Bottom or the S Fold Mountains: What is Faulting? Faulting: The breaking apart or fracturing of rock Caused when rocks are compressed together under intense pressure On earths surface or deep into the earths crust Result of earths crust pushed up or dropped down Plates move over, away, or past each other Faulting Tensional Forces creating Normal Fault Normal Fault: Caused by tensional forces (crust moving away) One plate drops down lower (hanging wall) than the upper plate (footwall). Tensional Forces creating Rift Valley Rift Valley: When two parts of the earths crust move away from each other The plate in between drops down, leaving a valley Compressional Forces creating Reverse Fault Reverse Fault: There are compressional forces pushing one block up over the other When the two pieces push against each other. Compressional Forces creating Overthrust Fault Overthrust Fault: Compressional forces (crust pushing together) Crust has already undergone folding Its folded layers are pushed up and thrust over layers on the faults other side Volcanoes What causes a Volcano to Erupt? 1. Heat is generated because of friction, pressure and decay of materials 2. Magma is produced when heat melts rock and materials beneath the crust 3. Heat and pressure causes magma to rise. It reaches the surface through fractures, vents or craters 4. Lava is liquid rock. It is magma that reaches the earths surface Volcanoes Remember! The trigger for a volcano to erupt is heat. Magma is produced when crusts meet. Magma is melted rock Volcano Terms Ash: Small dust like fragments of rock, minerals and glass emitted from volcanoes Vent: Small opening where magma erupts Crater: Large opening where magma erupts Cinder: Low density igneous rock, characterized by bubbles, emitted from volcanoes. Larger than ash. Volcanic Ash Cinder Volcanoes Three kinds: 1.Ash and Cinder Cones: Shape is symmetrical Steep sides Large crater Eruptions consist of mainly ash and cinder Thick, slow flowing, rapidly solidifying lava. Creates violent eruptions Ash and Cinder Cones Shield Cone 2.Shield Cone: Usually milder eruption Little or no ash or cinders Very thin, liquid lava Broad, flat cones Volcanoes 3. Composite Cones: Undergoes periods of explosive and quiet activity Ash and cinder mixed with lava Weak spots may develop on sides with smaller lava flows forming smaller craters Composite Volcanoes Volcanoes Related to Plates Meeting Usually found along plate boundaries Plate Boundariesand Volcanoes Plate Boundariesand Volcanoes. Why are Most Volcanos found where Plates Meet? Because thats where plates collide or converge Denser plate melts at the subduction zone Rocks melt to form magma Pressure increases, magma rises and erupts Volcanoes form What about Volcanos found where Plates do Not Meet? Intra-Plate Volcanoes Why? Plates move over magma hot spots in the lithosphere Magma bursts through the crust Forms linear chain of volcanic mountains i.e. Hawaiian Islands Global Patterns in the Location of Landforms What landform patterns can be seen from the diagram? How did this Land Distribution Come About? Remember! The earths landforms are constantly in a state of change This is due to forces that build up the land and those that wear it down In Conclusion First, we looked at forces that build up and shape landforms.next we will look at forces which wear down the land