Preliminaries to Erosion: Weathering and Mass Wasting Chapter 15.
GEOG 100--Weathering and Mass Wasting (F'13)
Transcript of GEOG 100--Weathering and Mass Wasting (F'13)
![Page 1: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/1.jpg)
Weathering and Mass Weathering and Mass WastingWasting
Chapter 10
![Page 2: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/2.jpg)
22
External vs. Internal ProcessesExternal vs. Internal Processes(the dynamic equilibrium model)(the dynamic equilibrium model)
![Page 3: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/3.jpg)
33
Dynamic EquilibriumDynamic Equilibrium
• Equilibrium stability (fluctuating around some average)
[Geomorphic threshold is reached]
• Destabilizing event• Adjustment• New condition of equilibrium stability
33
![Page 4: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/4.jpg)
4
The Grand CanyonThe Grand Canyon
![Page 5: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/5.jpg)
5
DenudationDenudation—Large-scale removal of —Large-scale removal of material that lowers the overall profile of material that lowers the overall profile of the topographythe topography
![Page 6: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/6.jpg)
66
Denudation ProcessesDenudation Processes
• Weathering—The combined action of all atmospheric and biologic processes that cause rock to disintegrate physically and decompose chemically because of exposure near Earth’s surface (from bedrock to regolith)
• Mass wasting—spontaneous downslope movement of soil and eroded rock fragments under the influence of gravity, but without the action of moving air, water or ice
• Erosion—extensive removal of rock material, generally transported long distances
![Page 7: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/7.jpg)
7
Weathering of BedrockWeathering of Bedrock
► Wherever bedrock is Wherever bedrock is exposed to the exposed to the natural elements, it natural elements, it weathersweathers
► Any crack, joint, or Any crack, joint, or cavity in the rock cavity in the rock will allow will allow weathering agents weathering agents to penetrate and to penetrate and break it apartbreak it apart
![Page 8: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/8.jpg)
Jointing in Bryce Canyon, UT
![Page 9: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/9.jpg)
As rocks weather, surface area increases, offering more surfaces to be weathered…
![Page 10: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/10.jpg)
…producing this result.
![Page 11: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/11.jpg)
1133
Mechanical WeatheringMechanical Weathering
• Physical disintegration of rock as a result of natural phenomena, without a change in its chemical composition– Pounding, pushing, cracking, breaking,
wedging apart
![Page 12: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/12.jpg)
Mechanical WeatheringProcesses
• Frost wedging• Salt wedging• Unloading/pressure-release jointing• Thermal expansion and contraction• Biologic weathering
![Page 13: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/13.jpg)
Frost Wedging
• Repeated growth and melting of ice crystals in pore spaces of rock fractures or joints
• Expanding ice exerts pressure, breaking rocks apart
• Most effective where there is repeated freeze and thaw (as in arctic or tundra environments)
![Page 14: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/14.jpg)
Frost Wedging
![Page 15: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/15.jpg)
Salt Wedging
• Similar to frost wedging• Growth of salt crystals breaks rocks apart• Most effective in coastal environments
and semi-arid environmentsHoneycomb (tafoni), Salt Point, Sonoma Coast
![Page 16: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/16.jpg)
18
Unloading or Pressure-release jointing• Rock brought near the surface as the rocks above (or
even glaciers) erode away relieves confining pressure and allows the rock to expand slightly, forming cracks– Sheeting—The breaking away of layers of rock in sheets,
caused by expansion, usually from unloading processes
• Exfoliation dome—Sheeting on a massive scale, over the face of a large segment of rock (Half Dome in Yosemite, Sierra Nevada Mtns.)
![Page 17: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/17.jpg)
Thermal Expansion and Contraction
• When rock is heated, it expands slightly, and when cooled, it contracts
• Rapid expansion and contraction of the surface of the rock causes cracks to form and propagate
• Most effective in regions with large differences in temperature between daily highs and nightly lows
![Page 18: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/18.jpg)
Thermal Expansion and Contraction
![Page 19: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/19.jpg)
Biologic Weathering• Growth of plant roots,
burrowing animals
• Pressure is exerted by the growth of tiny rootlets in joint fractures, which causes the loosening of small rock particles and mineral grains
• Burrowing animals such as squirrels and oysters may also erode rocks
![Page 20: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/20.jpg)
Chemical Weathering
• Decomposition of rock through chemical alteration of its minerals
• Exposed to water or other solutions, minerals in rocks undergo a chemical change, weakening internal structures– Air, soil water solutions, and groundwater
solutions contain dissolved oxygen, carbon dioxide, or other reactive elements
– Water is the greatest agent of chemical weathering
![Page 21: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/21.jpg)
Chemical Weathering:The Influence of Temperature and
Precipitation
Chemical weathering is most effective in warm, moist climates
![Page 22: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/22.jpg)
Oxidation
• Oxygen dissolved in soil water or ground water can bond with the chemical elements of the minerals to form new minerals
• Causes expansion and exerts pressure that breaks the rocks apart
• Example: iron (Fe) turning to rust (Fe2O3) in the presence of oxygen and water
![Page 23: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/23.jpg)
Hydrolysis and Hydration
• Hydrolysis--minerals reacting with water split into other compounds (may also split the water molecules)– granite: feldspar turns to clays + quartz sand– contributes to spheroidal weathering
![Page 24: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/24.jpg)
Hydrolysis and Hydration
• Hydration--The whole water molecule forms chemical bonds to become part of the chemical composition of the rock, causing expansion and grain-by-grain destruction of rocks
Formation of gypsum from anhydrous calcium sulfate (the mineral anhydrite) which has absorbed water into its chemical structure
![Page 25: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/25.jpg)
Carbonic Acid
Limestone and marble are most susceptible to this type of weathering
Carbon dioxide dissolved in water creates a weak acid called carbonic acid which can dissolve some minerals, especially calcium carbonate
![Page 26: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/26.jpg)
Acid Precipitation
• Urban pollution from sulfur and nitrogen oxide gases mixes with atmospheric water, forming acid precipitation
• Dissolves limestone and marble (often used for public statues and tombstones) and other types of building stones; destroys vegetation, affects human health
![Page 27: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/27.jpg)
Organic Acids• Decaying vegetation mixes w/ water to form
soil water w/ complex organic acids that can react to dissolve or chemically alter minerals
![Page 28: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/28.jpg)
Mass Wasting
• Material is moved a short distance down a slope under the influence of gravity
• Angle of repose—the steepest angle that loose fragments can lie without movement if undisturbed
![Page 29: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/29.jpg)
31
![Page 30: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/30.jpg)
Mass Wasting
• The type of mass wasting event that occurs will depend upon speed and the degree of saturation
![Page 31: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/31.jpg)
Mass Wasting(another view)
![Page 32: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/32.jpg)
Types of Mass Wasting
• Rock fall• Rock slide and
Topple
• Debris flow• Earth flow• Mudflow
• Slump• Solifluction• Creep
• Induced mass wasting
![Page 33: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/33.jpg)
Rock Fall
Talus slopes—Regolith which has fallen down steep slopes, funneled into “blankets” of rock called talus cones
Fresh slopes are very unstable
![Page 34: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/34.jpg)
Rock Fall
![Page 35: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/35.jpg)
Rock Slide
![Page 36: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/36.jpg)
Mudflow and Debris Flow
• Mudflow—Rainwater mixed with soil flowing very quickly downslope as a river of mud– Usually in canyons of
mountainous regions– Can carry large objects,
destroying property and taking lives
– Flows until mud thickens, slows, and eventually stops
• Debris flow—More rock fragment than mudflow, but similar in other characteristics
![Page 37: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/37.jpg)
Earthflow
• Water-saturated soil or rock material
• Moves a limited distance down slope as one large mass
• Generally slower in motion (over the course of hours)
• Common form of earth movement causing road closures and property destruction during heavy rains
![Page 38: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/38.jpg)
Near La Conchita Slide, alongHwy. 101 in Ventura County
![Page 39: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/39.jpg)
La Conchita Slide (Earthflow)Hwy. 101, Ventura County
![Page 40: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/40.jpg)
La Conchita Slide (Earthflow)Hwy. 101, Ventura County
![Page 41: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/41.jpg)
Slump—Slow, concave sliding
![Page 42: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/42.jpg)
Slump
![Page 43: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/43.jpg)
Slump
![Page 44: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/44.jpg)
Solifluction
• Continuous freeze and thaw cycles slowly move weathered particles downslope
• Over time, the entire slope moves downhill
![Page 45: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/45.jpg)
Solifluction
![Page 46: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/46.jpg)
Solifluction
![Page 47: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/47.jpg)
Soil Creep
![Page 48: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/48.jpg)
Induced Mass Wasting
Mass wasting caused by human activity
• Moving weathered rock material downslope during construction on steep hillsides – Carried away as debris flows or mudflows during heavy rains
• Removal of material supporting the base of a slope
• The wetting of weathered rock material and soil from pipe breakage, lawn watering, etc. causing slippage
• Debris removal by heavy rains after fire may also remove stabilizing vegetation
![Page 49: GEOG 100--Weathering and Mass Wasting (F'13)](https://reader035.fdocuments.in/reader035/viewer/2022062405/55575a00d8b42a63448b514b/html5/thumbnails/49.jpg)
Induced Mass Wasting:Construction of the Panama Canal