Geomorphic Processes:II. Exogenic

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

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

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

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

A Conceptual Model

of

Gradation(Erosion + Deposition)

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

Relationship:WeatheringMass WastingErosionand Transportation

Together, these processes areresponsible for

Denudationof Earth’s surface

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

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

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

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

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

Classification of Mass WastingBased on• Speed of Movement• Kind of Earth Material Involved• Kind of Motion Involved

Soil Creep

Classification of Mass Wasting

Based on

Moisture ContentandSpeed of Movement

La Conchita Debris Flow/Earthflow, January 10, 2005

Monterey Park Debris Flow, 1980

Landslide/Earthflow on PCH near Pacific Palisades

November 1956

Slump in Coastal California near San Clemente January 7, 2011

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

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

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

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.

• 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.

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