Geography Lectures 22 26 Introduction to Geomorphology Definition The science of landforms their origin evolution form and spatial distribution The development and changes on the earth s surface over time Basic Terms Landform individual element of a landscape EX a mountain a river a hill etc Topography Earth s ridges valley s other surface features the change in elevation over the Earth s surface Uniformitarianism The theory that geologic events and others are caused by natural processes many of which are operating at the present time and that the processes we see today operate in the same way today as they did in the past EX the way a volcano operates today is the same as it did 1000 yrs ago or 1million years ago or 1 billion years ago Types of Landforms Tectonic developed by the rearrangement of the Earth s crust driven by internal energy Fluvial those developed by moving liquid water Glacial those developed by glacial ice solid water Coastal those developed by waves Eolian those developed by wind Landforms and systems change but tend to be in some form of an equilibrium state when viewed over geologic time Steady state little change with inputs and outputs equal Dynamic Equilibrium fluctuates around an average value but demonstrates a trend over time Geomorphic Processes relationship between external and internal processes and forces Internal Processes those processes which occur or originate within Earth s crust volcanism diastrophism mountain building plate tectonics massive crustal rearrangements External Processes those processes which occur on the Earth s surface weathering erosion by fluvial glacial eolian coastal EARTH S INTERNAL STRUCTURE Characteristics arranged in concentric layers heavier elements towards the center each layer distinct in chemical composition or temperature Result of cooling since formation of the earth some 4 6 billion years before present BYBP How do we know only by indirect evidence Seismic waves By analyzing the behavior of seismic waves their speed and direction waves change with changes in the T and density of material Cooler higher velocity hotter slower velocity density may reflect or refract the waves 3 types of seismic waves P waves push or compressional waves S waves shear or shake waves L waves surface waves the ones we feel The Earth s Layers Inner Core solid rigid consists of iron Fe nickel Ni 3200 mi below sea level bsl 760 mi thick Outer Core liquid molten more plastic Consists of Fe Ni but at lower pressure so its melting T is lower liquid 1800 mi bsl 1400 mi thick Generates 90 of the Earth s magnetic field Gutenberg discontinuity an uneven broad transition zone between the Outer Core and the Lower Mantle discontinuity a physical difference or change esp density between two layers Lower Mantle solid partially molten Consists of oxides of Fe magnesium Mg silicon Si 415 mi bsl 1385 mi thick Upper Mantle partially molten Consists of silicate minerals 25 mi bsl about 380 mi thick Upper Lower Mantle comprise about 80 of Earth s volume Asthenosphere molten Between 43 155 mi bsl Source of magma which pushes up into the crust onto the surface Lithosphere Uppermost solid portion of mantle plus the crust Varies between 25 50 miles thick Zone of contact between the uppermost mantle and the crust is the Mohorovicic discontinuity or Moho Moho is closer to the surface under oceanic crust vs continental crust Crust is about 5 mi thick under oceans about 25 mi thick under continents Continental crust vs Usually lower density Sialic rock or sial Si Aluminum EX granite shale marble Oceanic crust higher density simatic rocks or sima Si Magnesium EX basalt lava The Crustal Surface Topography or topographic relief the vertical difference between highest elevation and lowest elevation High relief mountains vs low relief costal plain Each continent has a core or nucleus of crystalline rock a craton Usually low elevation Very old 570 MYBP Precambrian An exposed craton is called a continental shield Earth s relief Highest point above sea level Mt Everest 29 035 ft Lowest point below sea level Mariana Trench 36 198 ft Total relief 65 226 ft about 12 5 mi Geologic Time Scale Figure 11 1 page 299 A method of indicating the age of the Earth A sequence based on relative positions of rock strata layers Is a relative time scale Assumes superposition that younger rocks sediments are near the top of a formation older material is near the bottom Is governed by uniformitarianism Absolute ages are determined by methods such as radioactive isotope dating The oldest rocks 4 billion years ago know eras beginning and ending Paleozoic begins 540 250 billion Mesozoic 250 65 million Cenozoic 65 million to present Tertiary 65 million 1 8 million years ago Quaternary 1 8 million present GEOLOGIC CYCLE The vast cycling of material that occurs in and on the lithosphere encompassing the hydrologic tectonic rock cycles The building and wearing down of landforms 3 components Hydrologic cycle movement of water Tectonic cycle movement of crustal material and magma Rock cycle formation of the three basic types of rock ROCK CYCLE What are rocks Mineral an element or combination of elements that forms an inorganic natural compound which has specific qualities such as a unique crystalline structure hardness etc Ex Silicates based on silicon Si Carbonates based on carbon C These together make up 90 of all minerals 3000 minerals only about 10 20 make up 90 of the crust Rock an assemblage of minerals bound together usually 2 to 5 different materials Sometimes as a mass of a single mineral Thousands of rock types but all the result of 3 rock forming processes igneous sedimentary metamorphic The interactions interrelationships between these 3 processes is the Rock Cycle Igneous Process Rocks Formed by crystallization of magma the solidifying of magma lava either below or above the surface May cool fast creating a fine grained structure extrusive or slow creating a coarsegrained structure intrusive Intrusive types form below the surface within the crust EX plutons batholiths laccoliths Made of granitic type material granite rhyolite Many mountains and ranges are exposed plutons Sierra Nevada CA NV Black Hills SD Stone Mt GA Extrusive types form on the surface of the crust EX lava or basalt volcanic ash obsidian pumice the ocean floor is primarily composed of basaltic igneous rock Sedimentary Process Rocks Formed from existing material by weathering erosion transport and deposition