Glaciers, Wind, and Water: Shaping the Earth’s Surface
Glaciers: Shaping the Landscape
Glaciers currently cover 10% of the Earth’s continental surface. A glacier is a thick mass of ice that moves over land, distinct from an ice floe. There are two main types:
Types of Glaciers
Alpine Glaciers
Found in high-elevation mountain ranges, these glaciers are confined by the surrounding mountain valleys.
Continental Glaciers
Also known as polar ice sheets, these glaciers cover vast areas in polar regions and are not restricted by topography.
Parts of an Alpine Glacier
- The Cirque: The uppermost section, rounded in shape, where snow accumulates and transforms into ice.
- The Glacial Valley (Ice Tongue): The channel where the ice descends.
- The Terminal Zone: The lowest section where ice melts and deposits carried material.
Glacial Erosion, Transport, and Deposition
Erosion
Despite their slow movement, glaciers cause significant erosion through:
- Plucking: The glacier pulls loose material and fragmented rock from the valley walls and bed, incorporating them into the ice.
- Abrasion: Rock fragments embedded in the ice carve and polish the valley walls and floor, creating striations (scratches) and grooves (indentations).
Transport
Glaciers carry eroded material from the cirque and valley, ranging in size from small particles to large boulders.
Deposition
As glacial ice melts, it deposits the transported material, forming landforms called moraines.
Depositional Landforms: Moraines
Moraines refer to both the material carried by a glacier and the sediment it deposits.
Wind as a Geological Force
Deflation and Abrasion
Deflation occurs when wind removes loose particles from the Earth’s surface. Smaller particles are transported by suspension, while larger particles (over 2mm) are dragged in a process called creep. The remaining surface is known as desert pavement.
Aeolian abrasion happens when wind-borne particles impact rocks, causing polishing and wearing away.
Erosional Landforms Caused by Wind
- Mushroom Rocks: Formed by more intense wind abrasion near the ground, shaping isolated boulders.
- Honeycombs: Created when low-density or heterogeneous rock is exposed to wind-blown sand, forming small hollows.
- Desert Pavement: The result of deflation, leaving behind only larger particles on the desert surface.
Where Does Wind Erosion Occur?
Wind erosion requires:
- Presence of Loose Material: Wind cannot erode solid rock or large fragments.
- Absence of Vegetation: Plant roots bind soil, while stems and leaves reduce wind speed, hindering erosion.
Common locations include deserts and coastal areas.
Depositional Landforms
- Dunes: Mounds of wind-transported sand, constantly changing shape due to wind forces.
- Loess: Extensive deposits of fine-grained particles like silt, often transported far from their origin, enriching soil quality.
Water Movement and Coastal Erosion
Waves and Tides
Waves are generated by wind action on the water’s surface, moving towards land in wave trains.
Tides are oscillations in sea level caused by the gravitational pull of the moon and sun on water.
Coastal Erosion
Wave impact erodes the base of cliffs, forming a notch. The overhanging rock eventually collapses, causing the cliff face to retreat.
Landforms Caused by Coastal Erosion
- Headlands and Bays: Formed on coastlines with alternating resistant and less resistant rock.
- Natural Bridges: Created from eroded cracks or weaker zones in the rock.
- Wave-Cut Platforms: Horizontal rock areas formed near the base of cliffs.
- Cliffs: Nearly vertical rock masses separating land and sea.
- Sea Stacks: Remnants of former headlands, detached from the mainland.
The Origin of Beach Sand
Most beach sand originates from continental erosion, transported by rivers, glaciers, or wind. Coastal transport occurs through:
- Wave Action: Waves drag material onto the beach and back out, rounding and reducing particle size.
- Longshore Drift: Wind and waves transport material along the coastline.
Landforms Caused by Deposition
- Lagoons: Coastal bodies of water partially or completely separated from the sea by sandbars.
- Spits: Sandbars connected to the mainland at one end.
- Deltas: Deposits formed at river mouths.
- Tombolos: Deposits connecting a sea stack to the mainland.
- Marshes: Shallow wetlands where salt and freshwater mix.
- Beaches: Sand or gravel deposits along the coastline.
- Sandbars: Elongated sand deposits forming islands near the coast in shallow water.
Living Organisms as a Geological Force
Living organisms contribute to:
Formation and Protection of Relief
- Physical Weathering: Plant roots widen cracks in rocks, and animals break rocks through digging.
- Chemical Weathering: Acids from lichens, microorganisms, and animal waste weaken rocks.
- Erosion: Vegetation can accelerate or prevent erosion by influencing soil stability.
Deposition and Rock Formation
- Coquina Formation: Accumulation of shells and other remains.
- Rock Formation from Microorganism Carapaces: Deposition of microorganism shells.
- Direct Rock Construction: Some organisms directly build rock structures.
- Coal and Petroleum Formation: Accumulation and modification of plant matter.