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