geomorphic processes: ii. exogenic ii. gradation processes – weathering, mass wasting, erosion,...
TRANSCRIPT
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Geomorphic Processes:II. Exogenic
II. Gradation Processes – Weathering, Mass
Wasting, Erosion, Transportation
and Deposition
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Geomorphic Processes:
Physical processes which create and modify landforms on the surface of the earth
A. Endogenic (Endogenous) vs. B. Exogenic (Exogenous) Processes
These processes operate in episodic manner – with earthquakes and volcanic eruptions causing a
punctuated equilibrium
These processes relate closely to the Rock Cycle
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A. Endogenic Processes Endogenic Processes are large-scale landform
building and transforming processes – they create relief.
1. Igneous Processes
a. Volcanism: Volcanic eruptions Volcanoesb. Plutonism: Igneous intrusions
2. Tectonic Processes (Also called Diastrophism)
a. Folding: anticlines, synclines, mountainsb. Faulting: rift valleys, graben, escarpmentsc. Lateral Faulting: strike-slip faults
Earthquakes evidence of present-day tectonic activity
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B. Exogenic Processes Also called Gradational Processes
-- comprise degradation and aggradation -- they modify relief
A continuum of processes – Weathering Mass Wasting Erosion Transportation Deposition
Operates through Geomorphic Agents: gravity, flowing water (rivers), moving ice (glaciers), waves and
tides (oceans and lakes), wind, chemicals, plants, organisms, animals and humans
1. Degradation Processes Also called Denudation Processes
a. Weathering , b. Mass Wasting and c. Erosion (+ Transportation)
2. Aggradation Processesa. Deposition – fluvial, eolian, glacial, coastal
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A Conceptual Model
of
Gradation(Erosion + Deposition)
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Degradation Processes:Weathering, Mass Wasting,Erosion (+ Transportation)
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Relationship:WeatheringMass WastingErosionand Transportation
Together, these processes areresponsible for
Denudationof Earth’s surface
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WEATHERING Weathering is disintegration and decomposition of rocks in situ – no transportation involved produces regolith → eventually soil and sediments
More precisely, it involves the mechanical or physical disintegration and/or chemical decomposition that fragments rock masses into smaller components that amass on-site, before being moved by gravity or transported by other agents
The processes begin in microscopic spaces, cracks, joints, faults, fractures, lava
vesicles and other rock cavities
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Factors affecting Weathering: (1) Strength and resistance of rocks, (2) Climate, especially temperature
and humidity regimes, (3) Slope and relief of the land, and (4) Type and density of vegetative cover
Types of Weathering: 1) Physical or Mechanical Weathering, 2) Chemical Weathering, and 3) Biological Weathering
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Physical or Mechanical Weathering® Disintegration and decay of rocks via weather elements: high
temperatures, extreme cold and freeze-thaw cycles® No change in chemical composition of rocks
• Exfoliation – due to thermal expansion/contraction and/or release of pressure when buried rocks are uplifted and exposed
e.g., Exfoliation Dome (Stone Mountain, GA) and Exfoliation Sheets (Sierra Nevada)
• Frost Wedging
• Salt Wedging
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Chemical Weathering decomposes rocks through a chemical change in its minerals
Oxidation – important in iron-rich rocks – reddish coloration like rust
Hydrolysis – igneous rocks have much silica which readily combines with water
Carbonation and Solution – carbon dioxide dissolved in water reacts with carbonate rocks to create a soluble product (calcium bicarbonate)
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Biological Weathering– plants and animals contribute to weathering.
Roots physically break or wedge rock
Lichens (algae and fungi living as single unit), remove minerals and weaken rock by releasing acids
Burrowing animals can increase weathering.
Lichens
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MASS WASTINGProcess whereby weathered material is moved downslope under the immediate influence of gravity.
However, gravity being a passive force needs a triggering factor to create instability and initiate mass wasting – groundwater, meltwater, rain water and vibrations produced by earthquakes, explosions, heavy trucks and trains, and amount and type of vegetation cover are all potential triggers
Slope Angle and Angle of Repose (the steepest angle that can be assumed by
loose fragments on a slope without downslope movement) are strongly related to rates of mass wasting
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Talus Conesin the Canadian Rockies
Talus – pieces of rock at bottom of a rock fall
LandslidesCan cause much destruction
A msssive 300-ton boulder blocks a road in Southern California
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Classification of Mass WastingBased on• Speed of Movement• Kind of Earth Material Involved• Kind of Motion Involved
Soil Creep
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Classification of Mass Wasting
Based on
Moisture ContentandSpeed of Movement
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La Conchita Debris Flow/Earthflow, January 10, 2005
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Monterey Park Debris Flow, 1980
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Landslide/Earthflow on PCH near Pacific Palisades
November 1956
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Slump in Coastal California near San Clemente January 7, 2011
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Massive Slump, PCH, San Pedro, CA, November 20, 2011
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Massive Slump, PCH, San Pedro, CA, November 20, 2011
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Massive Slump, PCH, San Pedro, CA, November 20, 2011
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EROSION ( + TRANSPORTATION )
– Various Geomorphic Agents, associated Processes, and resulting Erosional Features
• Flowing Water – Fluvial Morphology
Humid regions: Perennial streams and entrenched channels, rapids, waterfalls, plunge pools, potholes, meandering streams, bank erosion, oxbow lakes, etc.
Arid regions: Intermittent streams (washes, arroyos, wadis), badlands topography, plateaus, mesas, buttes, inselbergs, etc.
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• Wind – Eolian Landscapes deflation hollows, ventifacts, yardang, etc
• Tides and Waves – Coastal Morphology
Sea cliffs, sea caves, sea arches, sea stacks, wave-cut beaches, etc..
• Moving Ice – Glacial Morphology
Alpine: arête, horn (e.g., Matterhorn), col, glacial
troughs (U-shaped valleys), hanging valleys, paternoster lakes, fjords;
Continental: ice-scoured plains, glacial lakes, kettles and kettle lakes.
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DEPOSITION– Various geomorphic agents, associated processes and
resulting Depositional Features
• Fluvial – Humid regions: Braided streams, sand bars, floodplains (alluvium deposits), natural levees, distributaries, deltas
Arid regions: Alluvial fans, bajadas, piedmont alluvial plains, playas, playa lakes, Salinas (salt flats)
• Eolian – Sand dunes (Barchans, Parabolic, Transverse,
Longitudinal, Star), and sand sheets
• Coastal – Sea beaches and coral reefs
• Glacial – Alpine: Glacial drifts, tills, moraines (lateral, medial, end, terminal, recessional, and ground)
Continental: Till plains, outwash plains, drumlins, eskers, kames, erratic