Geomorphic Processes and Erosion Overview

Geomorphic Processes

• Geomorphic processes are physical processes that create and modify landforms on Earth's surface
• They can be categorized as endogenous (internal) or exogenous (external) processes
• Exogenous processes (gradational) modify Earth's surface relief through degradation and aggradation
• Degradation involves processes like weathering, mass wasting, erosion, and transportation
• Aggradation involves processes like deposition (by rivers, streams, glaciers, and coasts)

Degradation Processes

• Denudation: The process of wearing down landforms
• Weathering: The breakdown of rocks and minerals in situ (without being moved)
• Mass wasting: The downslope movement of rock and soil due to gravity
• Erosion: The wearing away of rocks and soil by natural forces
• Transportation: The movement of eroded material (sediment)

Erosion

• Earth materials are worn away by natural forces
• A type of mass wasting, involving normal movement

Transportation

• The process of moving eroded sediment

Deposition

• Eroded rocks and sediments settle somewhere new

Aggradation Processes

• Deposition by rivers and streams
• Sedimentation occurs in fluvial, glacial, and coastal environments

Weathering

• The disintegration and decomposition of rocks in situ (without being moved)
• Creates regolith (loose materials from rocks)
• Involves mechanical (physical) or chemical disintegration and decomposition
• Fragments rock into smaller components which stay in place
• Happens in microscopic spaces, cracks, joints, faults, fractures, lava vesicles, and other rock cavities

Types of Weathering

• Physical (Mechanical) Weathering: Disintegration of rocks due to elements such as high temperatures, extreme cold (freeze-thaw cycles)
• Chemical Weathering: Decomposition of rocks by chemical mechanisms
  • Oxidation: Important in iron-rich rocks (rust)
  • Hydrolysis: Igneous rocks react with water
  • Carbonation/Solution: Carbon dioxide in water reacts with carbonate rocks, creating soluble products

Biological Weathering

• Weakening and disintegration of rock by plants, animals, and microbes

Mass Wasting

• Downslope movement of rock, soil, and other debris due to gravity
• Affected by factors like the speed of movement, the type of material, nature of movement, water, soil cover, and geologic features

Factors Affecting Mass Wasting

• Angle of Repose: The highest angle that a slope of unconsolidated sediment can achieve without sliding

Water

• Moist sand can have a steeper angle of repose as water fills spaces and increases cohesion
• Too much water, the grains slide past each other, leading to a lower angle of repose

Soil Cover

• Expansion and contraction of soil containing clay minerals affects the stability
• Increases the susceptibility to mass wasting

Geologic Features

• Structures (beddings, joints, and faults) affecting stability, and potentially increase potential for slides
• Bedding planes weaken the rock structures
• Potential for slides affected by the presence of joints and faults in the rock

Triggering Events

• Earthquakes and excessive rainfall
• Volcanic eruptions increase the potential for slides

Endogenous Processes

• Geomorphic processes beneath the Earth's surface
• Create large-scale landforms; include tectonic and igneous processes
• Tectonic Processes: (Diastrophism)
  • Folding (anticlines, synclines, mountains)
  • Faulting (rift valleys, strike-slip faults)
• Igneous Processes:
  • Volcanism (volcanic eruptions)
  • Plutonism (igneous intrusions)
  • Earthquakes

Magma

• Molten or semi-molten rock mixture found under the Earth's surface
• Usually comprised of a hot liquid base, crystallized minerals, incorporated solid rocks, and dissolved gases

Decompression Melting

• Upward movement of Earth's mostly-solid mantle causes decompression
• Pressure reduction enables mantle rock to melt and form magma (often at divergent boundaries, like rift valleys, which create spaces for rising magma)
• Can also occur at mantle plumes (hot spots) that rise from Earth's high pressure core to its lower-pressure crust

Flux Melting

• Adding water or carbon dioxide to rock lowers melting temperatures, creating magma. Common at subduction zones.

Plutonism

• Intrusive igneous rock formation beneath the Earth's surface

Volcanism

• Molten rock discharge or discharge of pyroclastic fragments or hot water/steam

Metamorphism

• Change in rock composition and structure, caused by extreme heat or pressure
• Types include:
  • Contact, cataclastic, hydrothermal, regional, and burial metamorphisms.
  • Shock/Impact Metamorphism due to external stresses (e.g., impacts by meteorite or other large bodies, large volcanic eruptions)