Internal Forces and Climate Chapter 2 Lago Atitlán, Guatemala Lachniet, 2009

Internal Forces and Climate

Chapter 2

Lago Atitlán, GuatemalaLachniet, 2009

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.

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– Red Rock Canyon (ss bluff): 1100 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 = 1.0-1.5

• Inactive faulting J = 3-10

Figure 2-4

From AGI, 2003. Laboratory Manual in Physical Geology, (Ed. Busch), sixth edition.

Basin and Range landforms

Las Vegas Valley

Las Vegas Valley. Foto: Lachniet (2003)

Geomorphic evidence of faulting

• Offsetting of land surface – Laterally: strike-slip– Vertically: Normal, thrust faulting

• 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

Death Valley National Park, CA. Photo by Stephen Hlowjski, 2004

Displacement

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

Triangular Facets

Triangular Facets along the Wasatch Fault, Utah (W.K. Hamblin)

• Characteristic of Normal faulted blocks• Represent the scarp face• Incised by stream erosion

Drag folds – many fault types

http://www.gly.uga.edu/railsback/1121DragFolds.jpeg

Las Vegas Valley shearzone

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

photo by Robert E. Wallace

Stream Offset, San Andreas Fault, Carrizo Plain, CA

Shelton

Linear RidgesLinear Valley or trough

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

• Examples include– Stream terraces– Beach terraces

• Surface slopes don’t follow the ‘typical’ slope– Upwarping along center of

deformation axis

Figure 2-11

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 2-3Figure 2-15

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

Modern winter jet stream

Last Ice AgeWinter jet stream

Laurentide Ice SheetCordilleran Ice Sheet

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)

Black Mountains fault scarp

San Andreas Fault

Ground offset

Shelton

Trees mark where San Andreas fault crosses stream bed

Offset River channel

• San Andreas Fault

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