Geography Lectures 22-26Introduction to GeomorphologyDefinition: 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 surfaceUniformitarianism: 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 pastEX: 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 energyFluvial: those developed by moving liquid waterGlacial: those developed by glacial ice (solid water)Coastal: those developed by wavesEolian: 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 timeGeomorphic 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 STRUCTURECharacteristics:*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 Tº 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 feelThe Earth's Layers: Inner Core: * solid & rigid * consists of iron (Fe) & nickel (Ni)- 3200 mi below sea level (bsl), 760 mi thickOuter 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 layersLower Mantle: *solid, partially molten *Consists of oxides of Fe, magnesium (Mg) &silicon (Si) * 415 mi bsl; 1385 mi thickUpper 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 surfaceLithosphere: 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. Oceanic crust *Usually lower density * higher density*Sialic rock or sial *simatic rocks or sima(Si & Aluminum) (Si & Magnesium)*EX: granite, shale, marble *EX: basalt, lavaThe 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 datingThe oldest rocks: 4 billion years ago, know eras (beginning and ending)Paleozoic begins 540-250 billion, Mesozoic 250-65 million, Cenozoic 65 million to presentTertiary 65 million-1.8 million years ago, Quaternary- 1.8 million- presentGEOLOGIC 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 waterTectonic cycle: movement of crustal material and magmaRock cycle: formation of the three basic types of rockROCK CYCLEWhat 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 orabove the surface *May cool fast