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Internal Forces and Climate Chapter 2 Lago Atitlán, Guatemala Lachniet, 2009
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Figure 2-1 The Endogenic Effect The Earth has relief Two main levels: land surface and sea floor Without endogenic processes, exogenic processes would weather the earth to a state of minimum relief.
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Tectonism Driven by endogenic processes Orogenic –Structural mountain formation –Rocky Mountains Epeirogenic –Uplift, warping, disruption –But not folding or thrust processes –Colorado Plateau
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Rates Uplift and tectonism –Most rapid –Episodic Denudation (erosion) –Slower but steadier –Rate governed by climate
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Uplift rates Change over time as masses approach equilibrium Shorelines on the coast of Greenland had rapid uplift following deglaciation Slowing to the present Figure 2-3
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Neotectonics Recent or active tectonism Black Hills fault, Boulder City (Eric Fosset, UNLV M.S.) Eric Fosset, photo
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Geomorphic Expression of Normal Faulting Tilted fault-block mountains Basins and Ranges (Horsts and Grabens) Large offsets: –Sierra Nevada: 3300 m –Grand Tetons: 7500 m –Red Rock Canyon (ss bluff): 1100 m
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Fault-bounded mountain Age of faulting inferred from sinuosity of mountain front Sinuosity (J) = ratio of real (L j ) versus straight-line (L s ) distance across front Highly active faulting J = 1.0- 1.5 Inactive faulting J = 3-10 Figure 2-4
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From AGI, 2003. Laboratory Manual in Physical Geology, (Ed. Busch), sixth edition. Basin and Range landforms
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Las Vegas Valley Las Vegas Valley. Foto: Lachniet (2003)
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Geomorphic evidence of faulting Offsetting of land surface –Laterally: strike-slip –Vertically: Normal, thrust faulting Fault scarps Differential Erosion Triangular Facets Drag Folding
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Fault Scarps Steep linear bluffs along fault Vertical motion Often record multiple offsets (~1-10 m) Fault Scarp Evolution Steepness of scarp related to age and activity Fresh scarps are steep Old scarps are less steep
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Fault scarp on alluvial fan Death Valley National Park, CA. Photo by Stephen Hlowjski, 2004 Displacement
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Fault Scarp Evolution Denudation Follows Orogeny Episodic mountain building from endogenic processes (episodic and rapid), followed by gradual but steady erosion. Figure 2-5 Triangular Facets
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Triangular Facets along the Wasatch Fault, Utah (W.K. Hamblin) Characteristic of Normal faulted blocks Represent the scarp face Incised by stream erosion
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Drag folds – many fault types http://www.gly.uga.edu/railsback/1121DragFolds.jpeg Las Vegas Valley shearzone
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Landforms associated with strike-slip Faulting
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Shutter Ridges http://www.opentopography.org/index.php/resources/lidarlandforms
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Carrizo Plain Photo: Garret Speeter, 2005
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San Andreas Fault photo by Robert E. Wallace Stream Offset, San Andreas Fault, Carrizo Plain, CA
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Shelton Linear Ridges Linear Valley or trough San Andreas fault. California
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Shelton Sag pond on trace of 1906 break along San Andreas fault. California
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Springs/trees associated with fault
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Thrust faulting landforms Low angle Stratigraphic Inversion possible Klippes –Erosional remnants of overthrust rock Scarps Ragged outlines of thrust sheet extent
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Keystone thrust, Las Vegas
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Keystone Thrust Photo Lachniet 2007
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Klippe
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Deformed surfaces and uplift Examples include –Stream terraces –Beach terraces Surface slopes don’t follow the ‘typical’ slope –Upwarping along center of deformation axis Figure 2-11
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Climatic Geomorphology Landforms characteristic of certain climates –Temperature, precipitation amount, precipitation type, winds Also driven indirectly by changes in sea level –From both isostatic adjustment of continents, and ice volume on land Relict landforms indicate past climates –Example: glacial deposits in Missouri Table 2-3 Figure 2-15
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Quaternary Climate Change Paleoclimatology (GEOL 437/637) Glacial to interglacial climates –5 to 10 o C annual temperature change –100,000-year Ice-Age cycle –Last full glacial period only 21,000 yr ago –Sea level falls when glaciers grow –This drives incision and base level lowering Great Basin was wetter than today
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Late Quaternary Climate Change
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North America 21,000 years ago Modern winter jet stream Last Ice Age Winter jet stream Laurentide Ice Sheet Cordilleran Ice Sheet
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Climate Influence on Rivers The effects of climate are manifested through geological and vegetation ‘filters’ Figure 2-19
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Extra Slides
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The V f ratio Ratio of the width (W vf ) of the valley floor divided by the relief of the valley walls –Incision from active tectonics results in very low values (0.5 to 0.05). –Larger values = less tectonism Relief – distance between local high (A ld, A rd ) and low spot (A sc ) Vf = W vf ÷ ((A ld,- A sc ) + (A rd,- A sc )/2) Figure 2-7
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Tilted fault block mountain Spring Mountains, S. Nevada. Foto: Lachniet (2004)
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Black Mountains fault scarp
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San Andreas Fault
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Ground offset
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Shelton Trees mark where San Andreas fault crosses stream bed Offset River channel San Andreas Fault
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Carrizo Plain Photo: Garret Speeter, 2005
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Carrizo Plain Photo: Garret Speeter, 2005
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Keystone Thrust Photo Lachniet 2007
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Keystone Thrust
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River responses to climate Cold climates need less rainfall than warm climate to produce a similar quantity of sediment I.e., cold climates are more erosive Figure 2-17, for basins in the western United States
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