1/14/11 Geoid • Equipotenal surface – surface with the same potenal energy – Geoid – The gravitaonal equipotenal surface corresponding to mean sea level, including the level at which the sea would stand in a connental area if it were able to do so. – Spheroid – mathemacal representaon of sea‐level with all irregular influences removed – Gravity anomalies – The gravitaonal acceleraon remaining aer allowing for other factors 0.875 km – average elevaon of connents Isostasy 3.729 km – average depth of the ocean floor • 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 • Endogenic: “from the inside” geomorphic processes – 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 Exogenic – surfacial geomorphic processes? • Weathering and erosion • Structural and • Glaciation stratigraphic arrangement • Eolian (wind driven) of rock layers and • Biological masses • Hydrologic cycle • Previous tectonic • Anthropogenic/animal displacement • Present state of deformation 2 1/14/11 Climate Soils • Establishes the temperature and moisture • Humid regions – Materials (soil, rocks, etc) conditions at and near the earthʼs surface are in contact with moisture – Most important long-term control of for long periods of time • Increased chemical and weathering processes physical weathering – Intense leaching and – Driven by solar radiation deep weathering • Worldwide pattern of soil types reflects • Tropics – High humidity and high climate zonation temperatures – Arid regions – very little rainfall • Intense weathering – Produces red soils • Limited contact time between soil and water – High amounts of iron – Limits chemical weathering and aluminum oxides • Mid-latitude deserts – Temperatures are high, Vegetation and climate precip is low chemical weathering slow • Thin, carbonate rich soils • Vegetation affects the amount of water • Humid, high latitude that permeates into the ground versus the – Low temps, moderate precip amount that runs off the surface • Intermediate soils • Polar regions • Heavy vegetation less runoff, more – Low temp and low precip water enters soil • poor soil development – 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 • Climate affects – Water retention promotes chemical environmental factors weathering which in turn affect processes – Root action promotes mechanical weathering • Ex. Sea-Level – Organic acids chemically attack rocks Fluctuation – Organic material from decaying plants added – Base-level to soils – Eustatic change – water level rise or fall 24,000 year History of Sea Level Rise 4 1/14/11 5 .