Post on 01-Jan-2016
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Geomorphic Processes:II. Exogenous
II. Gradation Processes – Weathering, Mass
Wasting, Erosion, Transportation
and Deposition
Geomorphic Processes:
Physical processes which create and modify landforms on the surface of the earth
Endogenous (Endogenic) vs.Exogenous (Exogenic) Processes
Rock Cycle
A. Endogenous ProcessesA. Endogenous Processes Endogenous 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
B. Exogenous ProcessesB. Exogenous ProcessesAlso called Gradational Processes, they comprise degradation and aggradation – they modify relief
a continuum of processes – Weathering Mass Wasting Erosion Transportation Deposition
these processes are carried through by Geomorphic Agents: gravity, flowing water (rivers), moving ice (glaciers), waves and tides (oceans and lakes), wind,plants, organisms, animals and humans
1. Degradation Processes Also called Denudation Processes
a. Weathering , b. Mass Wasting and c. Erosion and Transportation
2. Aggradation Processesa. Deposition – fluvial, eolian, glacial, coastal
Relationship:WeatheringMass WastingErosionand Transportation
Together, these processes areresponsible for
Denudationof Earth’s surface
WEATHERINGWEATHERING
Weathering is disintegration and decomposition of rocks in situ – no transportation involved produces regolith
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
Types of Weathering: 1) Physical or Mechanical Weathering, 2) Chemical Weathering, and 3) Biological Weathering
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
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)
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
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
La Conchita Landslide, January 10, 2005
Monterey Park Debris Flow, 1980
PCH near Pacific Palisades, November 1956
EROSION and TRANSPORTATIONEROSION and 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.
• 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
glacial troughs (U-shaped valleys), hanging valleys, glacial lakes,.
DEPOSITIONDEPOSITION– 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