Earth's Surface Changes: Geological Agents and Processes

The geological cycle describes the changes Earth's surface undergoes over time. These changes are driven by two main agents: internal forces (related to Earth's heat and relief) and external geological forces (processing relief through solar energy and gravity).

External Geological Agents

Atmosphere

The atmosphere directly acts on rocks through chemical weathering and mechanical processes.

Water

Water plays a crucial role in several ways: as surface water, underground water, ice, and seawater.

Wind

Wind, powered by wind energy, is a significant agent in areas with little to no vegetation.

Factors Determining External Geological Agents' Impact

Several factors influence how external geological agents wear down the Earth's surface:

• Climate: The presence and dominance of specific external geological agents in a zone depend on the climate. Climate is determined by latitude, elevation, topography, and proximity to sea currents, influencing temperature and rainfall.
• Rock Type: The type of rocks, whether loose (like clay and sand) or compact (like limestone and granite), affects their susceptibility to weathering and erosion.
• Vegetation: Vegetation cover influences erosion rates. More vegetation generally leads to less erosion.
• Relief: Steeper slopes experience greater erosion.

Glacial Geological Agents

Glacial agents operate in low-temperature environments where snow compacts into ice. Glacial ice forms large masses called glaciers, which are categorized into two types:

• Continental Glaciers (Ice Caps): These are vast ice sheets that cover large portions of the land relief.
• Mountain Glaciers: Found above the perpetual snow line, these glaciers have distinct zones:
  • Circus: A circular depression where snow accumulates.
  • Tongue: The mass of glacial ice flowing through a valley.
  • Front: The zone where ice melts and deposits sediment.

Glacial Processes, Structures, and Features

Glacial processes include erosion, transport, and sedimentation, creating distinct landforms:

• Circus: A vertical, circular depression carved by glacial erosion.
• Horn: A sharp, pyramidal peak formed by glacial erosion on multiple sides.
• Arête: An sharp-edged ridge separating glacial valleys.
• U-shaped Valley: Valleys carved by the erosive power of glaciers.
• Striae: Scratches or lines on rocks caused by glacial abrasion.
• Roches Moutonnées: Rounded, polished rock formations shaped by glacial erosion.
• Moraines: Deposits of glacial till (sediment) transported and deposited by glaciers. Types include bottom, lateral, medial, and terminal moraines.

Desert and Sub-Desert Geological Agents

In desert and sub-desert environments, physical weathering (like thermoclasty) and wind are the primary geological agents.

Wind Processes in Deserts

Wind erosion and transport are significant, especially in areas with loose particles, large temperature fluctuations, minimal vegetation, and sparse rainfall. Key processes include erosion, transport, and sedimentation.

Desert Deposition and Erosion Structures

• Loess: Fine materials transported by wind, forming fertile soils.
• Undercutting (Socavaduras): Wind eroding rock against its base, leading to overhangs and collapse, with more intense erosion at lower altitudes.
• Reg (Desert Pavement): Areas where wind deflation removes fine materials, leaving behind only stones.
• Erg (Sandy Deserts): Zones characterized by sand dunes. Dunes form as wind encounters obstacles, creating a gentle windward slope and a steep leeward slope (slip face).