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Geomorphic Processes: II. Exogenic

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Presentation on theme: "Geomorphic Processes: II. Exogenic"— Presentation transcript:

1 Geomorphic Processes: II. Exogenic
II. Gradation Processes – Weathering, Mass Wasting, Erosion, Transportation and Deposition

2 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 

3 A. Endogenic Processes Endogenic Processes are large-scale landform building and transforming processes – they create relief. 1. Igneous Processes Volcanism: Volcanic eruptions  Volcanoes Plutonism: Igneous intrusions Tectonic Processes (Also called Diastrophism) Folding: anticlines, synclines, mountains Faulting: rift valleys, graben, escarpments Lateral Faulting: strike-slip faults Earthquakes  evidence of present-day tectonic activity

4 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) Aggradation Processes a. Deposition – fluvial, eolian, glacial, coastal

5 A Conceptual Model of Gradation (Erosion + Deposition)

6 Degradation Processes: Weathering, Mass Wasting, Erosion (+ Transportation)

7 Relationship: Weathering Mass Wasting Erosion Denudation and
Transportation Together, these processes are responsible for Denudation of Earth’s surface

8 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

9 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

10 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

11 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)

12 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

13 MASS WASTING Process 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

14 in the Canadian Rockies
Talus Cones in the Canadian Rockies Talus – pieces of rock at bottom of a rock fall Landslides Can cause much destruction A msssive 300-ton boulder blocks a road in Southern California

15 Classification of Mass Wasting
Based on Speed of Movement Kind of Earth Material Involved Kind of Motion Involved Soil Creep 

16 Classification of Mass Wasting
Based on Moisture Content and Speed of Movement

17 La Conchita Debris Flow/Earthflow, January 10, 2005

18 Monterey Park Debris Flow, 1980

19 Landslide/Earthflow on PCH near Pacific Palisades
November 1956

20 Slump in Coastal California near San Clemente January 7, 2011

21 Massive Slump, PCH, San Pedro, CA, November 20, 2011

22 Massive Slump, PCH, San Pedro, CA, November 20, 2011


24 Massive Slump, PCH, San Pedro, CA, November 20, 2011

– 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.

26 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.

27 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

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