Internal Forces and Climate
Lago Atitlán, Guatemala
Lachniet, 2009
Chapter 2
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.
Figure 2-1
Tectonism
• Driven by endogenic processes
• Orogenic
– Structural mountain formation
– Rocky Mountains
• Epeirogenic
– Uplift, warping, disruption
– But not folding or thrust processes
– Colorado Plateau
Rates
• Uplift and tectonism
– Most rapid
– Episodic
• Denudation (erosion)
– Slower but steadier
– Rate governed by climate
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
Neotectonics
• Recent or active tectonism
• Black Hills fault, Boulder City (Eric Fosset, UNLV M.S.)
Eric Fosset, photo
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
Fault-bounded mountain
• Age of faulting inferred from
sinuosity of mountain front
• Sinuosity (J) = ratio of real (Lj)
versus straight-line (Ls)
distance across front
• Highly active faulting J = 1.01.5
• Inactive faulting J = 3-10
Figure 2-4
Basin and Range landforms
From AGI, 2003. Laboratory Manual in Physical Geology, (Ed. Busch), sixth edition.
Las Vegas Valley
Las Vegas Valley. Foto: Lachniet (2003)
Geomorphic evidence of faulting
• Offsetting of land surface
– Laterally: strike-slip
– Vertically: Normal, thrust faulting
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Fault scarps
Differential Erosion
Triangular Facets
Drag Folding
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
Fault scarp on alluvial fan
Displacement
Death Valley National Park, CA. Photo by Stephen Hlowjski, 2004
Fault Scarp Evolution
• Denudation Follows Orogeny
• Episodic mountain building from endogenic
processes (episodic and rapid), followed by
gradual but steady erosion.
Triangular Facets
Figure 2-5
Triangular Facets
• Characteristic of Normal faulted blocks
• Represent the scarp face
• Incised by stream erosion
Triangular Facets along the Wasatch Fault, Utah (W.K. Hamblin)
Drag folds – many fault types
http://www.gly.uga.edu/railsback/1121DragFolds.jpeg
Landforms associated with strike-slip Faulting
Shutter Ridges
http://www.opentopography.org/index.php/resources/lidarlandforms
Carrizo Plain
Photo: Garret Speeter, 2005
San Andreas Fault
Stream Offset, San Andreas Fault, Carrizo Plain, CA
photo by Robert E. Wallace
Shelton
San Andreas fault. California
Shelton
Sag pond on trace of 1906 break along San Andreas fault. California
Springs/trees associated with fault
Thrust faulting landforms
• Low angle
• Stratigraphic Inversion possible
• Klippes
– Erosional remnants of overthrust rock
• Scarps
• Ragged outlines of thrust sheet extent
Keystone thrust, Las Vegas
Keystone Thrust
Photo Lachniet 2007
Klippe
Deformed surfaces and uplift
Figure 2-11
• Examples include
– Stream terraces
– Beach terraces
• Surface slopes don’t follow the
‘typical’ slope
– Upwarping along center of
deformation axis
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
Figure 2-15
Table 2-3
Quaternary Climate Change
• Paleoclimatology (GEOL 437/637)
• Glacial to interglacial climates
– 5 to 10oC 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
Late Quaternary Climate Change
North America 21,000 years ago
Laurentide Ice Sheet
Modern winter jet stream
Last Ice Age
Winter jet stream
Climate Influence on Rivers
• The effects of climate are manifested through geological and
vegetation ‘filters’
Figure 2-19
Extra Slides
The Vf ratio
• Ratio of the width (Wvf) 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 (Ald, Ard) and
low spot (Asc)
• Vf = Wvf ÷ ((Ald,- Asc) + (Ard,- Asc)/2)
Figure 2-7
Tilted fault block mountain
Spring Mountains, S. Nevada. Foto: Lachniet (2004)
Normal Fault and Alluvial Fans
Black Mountains fault scarp, Death Valley National Park
San Andreas Fault
Ground offset
• San Andreas Fault
Offset River channel
Shelton
Trees mark where San Andreas fault crosses stream bed
Carrizo Plain
Photo: Garret Speeter, 2005
Carrizo Plain
Photo: Garret Speeter, 2005
Keystone Thrust
Photo Lachniet 2007
Keystone Thrust
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