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Transcript
1/14/11 Geoid • Equipoten0al surface – surface with the same poten0al energy – Geoid – The gravita0onal equipoten0al surface corresponding to mean sea level, including the level at which the sea would stand in a con0nental area if it were able to do so. – Spheroid – mathema0cal representa0on of sea‐level with all irregular influences removed – Gravity anomalies – The gravita0onal accelera0on remaining aEer allowing for other factors 0.875 km – average eleva0on of con0nents 3.729 km – average depth of the ocean floor Isostasy • The Earthʼs crust adjusts to changes in mass that occur in the earth surface • Equilibrium within the Earthʼs crust – Forces acting to elevate landmasses are balanced by forces acting to depress them – e.g. Ice sheets, mountain building • Lithospheric plates “float” at a given elevation depending on their thickness 1 1/14/11 Endogenic vs Edogenic geomorphic processes Exogenic – surfacial • • • • • • Weathering and erosion Glaciation Eolian (wind driven) Biological Hydrologic cycle Anthropogenic/animal • Endogenic: “from the inside” – formed beneath the surface of the Earth • Volcanism: hotspot activity, sea-floor spreading, volcanic arcs • Seismicity/Plate Tectonics • Regional uplift and subsidence What do we mean by structural control on geomorphic processes? • Structural and stratigraphic arrangement of rock layers and masses • Previous tectonic displacement • Present state of deformation 2 1/14/11 Soils Climate • Establishes the temperature and moisture conditions at and near the earthʼs surface – Most important long-term control of weathering processes – Driven by solar radiation • Worldwide pattern of soil types reflects climate zonation – Arid regions – very little rainfall • Limited contact time between soil and water – Limits chemical weathering • Mid-latitude deserts – Temperatures are high, precip is low chemical weathering slow • Thin, carbonate rich soils • Humid, high latitude – Low temps, moderate precip • Intermediate soils • Polar regions – Low temp and low precip • poor soil development • Humid regions – Materials (soil, rocks, etc) are in contact with moisture for long periods of time • Increased chemical and physical weathering – Intense leaching and deep weathering • Tropics – High humidity and high temperatures • Intense weathering – Produces red soils – High amounts of iron and aluminum oxides Vegetation and climate • Vegetation affects the amount of water that permeates into the ground versus the amount that runs off the surface • Heavy vegetation less runoff, more water enters soil – Chemical weathering more effective • Sparse vegetation high runoff, less water enters soil – Chemical weathering less effective 3 1/14/11 Vegetation and soil • Humid regions – Water retention promotes chemical weathering – Root action promotes mechanical weathering – Organic acids chemically attack rocks – Organic material from decaying plants added to soils • Climate affects environmental factors which in turn affect processes • Ex. Sea-Level Fluctuation – Base-level – Eustatic change – water level rise or fall 24,000 year History of Sea Level Rise 4 1/14/11 5