Geomorphology: Landscapes Shaped by Earth’s Processes

Posted on Oct 27, 2024 in Geology

1. Fluvial Landscapes (Rivers and Streams)

Erosional Processes

  • Downcutting: Vertical erosion of a river channel, leading to the formation of V-shaped valleys.
  • Lateral Erosion: Widening of the river channel, creating features like floodplains.
  • Headward Erosion: Extension of the river channel at its source, contributing to the lengthening of the river.

Depositional Landforms

  • Floodplains: Flat areas next to the river, formed by periodic flooding and deposition of sediments.
  • Alluvial Fans: Cone-shaped deposits formed when rivers lose energy, typically at the base of mountains.
  • Deltas: Triangular or fan-shaped landforms created where rivers meet a standing body of water, depositing sediments.
  • Point Bars: Accumulations of sediment on the inside bends of rivers, formed due to slower flow velocity.

Other Fluvial Features

  • Drainage Basins: Areas drained by a river and its tributaries, separated by topographic divides called drainage divides.
  • Stream Flow Types:
    • Laminar Flow: Smooth, orderly flow of water, typical of slow-moving streams.
    • Turbulent Flow: Irregular, swirling flow, common in fast-flowing streams and responsible for increased erosion.
  • Types of Channels:
    • Meandering Channels: Curved river channels that form large loops and bends due to lateral erosion.
    • Braided Channels: Networks of interwoven channels separated by sediment bars, often found in areas with high sediment supply and variable flow.
  • Fluvial Systems: Dominated by rivers and streams that transfer sediment from upland to lowland areas, contributing to landscape evolution. Key components include sediment production, sediment transport, and sediment deposition.
  • Floods and Flood Control: Floods are natural events where rivers overflow their banks, depositing nutrient-rich sediments. Flood control measures include levees, dams, and floodways to manage water levels.

2. Aeolian Landscapes (Wind Erosion and Deposition)

Processes

Erosion

  • Deflation: Removal of loose particles, creating depressions called blowouts.
  • Abrasion: Wind-driven particles wear down rock surfaces, resulting in features like ventifacts (wind-polished rocks).

Transportation

  • Saltation: Short-distance hopping of sand grains, the primary method of sand movement.
  • Suspension: Fine particles like silt and clay carried long distances by wind.
  • Creep: Larger particles roll or slide along the ground surface.

Deposition

  • Formation of dunes (e.g., barchan, transverse, star dunes) and loess (wind-blown silt deposits).

Landforms

Erosional

  • Yardangs: Streamlined ridges formed by wind erosion, typically oriented parallel to prevailing winds.
  • Ventifacts: Rocks shaped by wind-driven sand, often displaying facets.

Depositional

  • Sand Dunes: Mounds or ridges of sand shaped by wind direction and speed.
  • Loess Plains: Thick deposits of wind-blown silt, often forming fertile soils.

Other Aeolian Features

  • Desert Environments: Aeolian processes are most effective in arid and semi-arid environments with sparse vegetation. Deserts like the Sahara and Gobi exhibit extensive wind erosion and deposition features.
  • Climatic Impact: The effectiveness of aeolian processes depends on factors such as wind speed, sediment availability, and vegetation presence.

3. Glacial Landscapes (Ice and Glacial Processes)

Types of Glaciers

  • Alpine Glaciers: Found in mountainous regions, flowing through valleys initially carved by rivers.
  • Continental Ice Sheets: Massive ice masses covering large areas, such as Greenland and Antarctica.

Glacial Movement

  • Basal Slip: Movement of a glacier over bedrock, facilitated by meltwater.
  • Plastic Flow: Internal deformation where ice crystals slide past each other under pressure.

Erosional Features

  • Cirques: Bowl-shaped depressions carved by the head of a glacier.
  • Arêtes: Sharp ridges formed between two cirques or glacial valleys.
  • U-shaped Valleys: Valleys with steep sides and flat bottoms, formed by glacial erosion.
  • Fjords: Deep, glacially carved valleys flooded by seawater.

Depositional Features

  • Moraines: Accumulations of debris deposited by a glacier (lateral, medial, or terminal).
  • Drumlins: Smooth, elongated hills formed by glacial till, often in clusters.
  • Eskers: Long, winding ridges of sand and gravel deposited by meltwater streams beneath glaciers.

Other Glacial Features

  • Glacial Mass Balance: The difference between accumulation and ablation. Positive mass balance leads to glacier advance, while negative mass balance causes retreat.
  • Ice Ages: Periods of extensive glaciation shaping many landscapes, leaving features like the Great Lakes and moraines.

4. Coastal Landscapes (Wave Action and Coastal Dynamics)

Wave Dynamics

  • Wave Erosion: Waves erode coastlines through hydraulic action, abrasion, and corrosion, creating features like wave-cut cliffs and sea stacks.
  • Longshore Transport: Sediment movement along the coast, driven by wave action and currents.
  • Wave Refraction: The bending of waves as they approach the shore, focusing energy on headlands and reducing it in bays.

Coastal Features

Erosional Landforms

  • Wave-cut Platforms: Flat, bench-like surfaces left behind as cliffs retreat.
  • Sea Arches: Natural arches formed by wave erosion on both sides of a headland.
  • Sea Stacks: Isolated rock columns left standing after a sea arch collapses.

Depositional Landforms

  • Beaches: Accumulations of sand or pebbles along the shoreline.
  • Spits: Narrow sand ridges extending from the coast into open water, formed by longshore drift.
  • Baymouth Bars: Sandbars completely crossing a bay, formed by deposition.
  • Tombolos: Sand ridges connecting an island to the mainland or another island.
  • Barrier Islands: Long, narrow islands parallel to the coast, formed by wave action and sediment deposition.

Other Coastal Features

  • Tidal Influences: Tides affect coastal environments, creating tidal flats, estuaries, and influencing sediment movement.
  • Mangroves: Coastal wetlands with salt-tolerant trees and shrubs, important for coastal protection and biodiversity.
  • Coral Reefs: Underwater structures formed by coral polyps (fringing reefs, barrier reefs, and atolls).
  • Sea Level Changes: Rising or falling sea levels impact coastal landscapes, creating emergent or submergent coastlines.
  • Coastal Classification: Coastlines are classified as rocky, sandy, gravelly, or muddy based on their dominant sediment type.
  • Human Impact: Coastal erosion is often exacerbated by human activities like construction and sea wall development.

5. Karst Landscapes (Solutional Weathering of Limestone)

Processes

  • Dissolution: Carbonic acid in rainwater dissolves carbonate rocks (limestone and dolostone), creating voids and conduits.
  • Precipitation: Formation of speleothems (stalactites, stalagmites) from mineral-rich water in caves.

Surface Features

  • Dolines (Sinkholes): Depressions formed by the collapse of underground voids or surface rock dissolution.
  • Cone Karst: Conical hills formed in tropical karst regions due to intense dissolution.
  • Tower Karst: Steep, isolated hills with sharp edges, often in areas with significant underground drainage.

Subterranean Features

  • Caves: Natural underground spaces formed by soluble rock dissolution.
  • Stalactites: Icicle-shaped formations hanging from cave ceilings, formed by mineral precipitation.
  • Stalagmites: Upward-growing formations on cave floors from dripping mineral-rich water.
  • Underground Rivers: Rivers flowing through cave systems, often re-emerging at the surface.

Human Impact

  • Karst landscapes are vulnerable to groundwater contamination due to high permeability, making them important for water resource management.

6. Fundamental Geomorphological Processes

Weathering

  • Mechanical Weathering: Physical breakdown of rocks into smaller pieces without chemical alteration.
  • Chemical Weathering: Decomposition of rocks through chemical reactions, often involving water and gases.

Other Processes

  • Erosion: Removal and transportation of weathered material by agents like water, wind, ice, or gravity.
  • Mass Wasting: Downslope movement of soil and rock under gravity (landslides and rockfalls).
  • Transportation: Movement of eroded material by natural agents (rivers, glaciers, and wind).
  • Deposition: Laying down of transported sediment, forming various landforms.

7. Earth Systems Interactions

  • Atmosphere, Hydrosphere, Geosphere, and Biosphere: These four spheres interact continuously, shaping Earth’s surface. Fluvial processes, for example, involve the hydrosphere eroding the geosphere, influenced by atmospheric conditions.
  • Climate Influence: Climate plays a crucial role in geomorphological processes. Glacial landscapes form in cold climates, while aeolian landscapes dominate arid regions.

8. Examples of Geoheritage Sites

  • Fluvial: Grand Canyon (USA) – Carved by the Colorado River, showcasing fluvial erosion.
  • Glacial: Swiss Alps Jungfrau-Aletsch (Switzerland) – Glacial landscape with extensive ice fields and glacial erosion.
  • Karst: Guilin Karst (China) – Notable for tower karst formations created by dissolution in a humid climate.
  • Coastal: Great Barrier Reef (Australia) – World’s largest coral reef system, shaped by biological and coastal processes.