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.
- ArĂȘtes: 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.