Geological Actions of Groundwater, Ice, Wind, and Sea
Geological Actions of Groundwater
Rainwater and snowmelt seep into the ground if the rocks are permeable or fractured. This water, known as groundwater, percolates downward until it encounters impermeable layers like clay. These layers trap the water, forming aquifers.
Aquifers
Aquifers consist of two main zones:
- Zone of Saturation: The layer completely filled with water.
- Zone of Aeration: The area between the ground surface and the zone of saturation.
The top of the saturated zone is called the groundwater level. When this level coincides with the ground surface, springs and rivers can emerge. There are two types of wells that tap into aquifers:
- Artesian Wells: Water in a confined aquifer is under pressure, causing it to rise in the well without pumping.
- Free Wells: Water in an unconfined aquifer requires pumping to reach the surface.
Aquifers face two main threats: over-exploitation and pollution.
Modeling Karst
Rainwater, combined with carbon dioxide, forms carbonic acid. This acid reacts with calcium carbonate rocks, primarily limestone. This process creates distinctive karst formations:
- Simas: Vertical shafts that may connect to the surface.
- Galleries: Horizontal passages that can enlarge into caves or caverns.
- Caves or Caverns: Large underground chambers connected to the surface, often adorned with formations like stalactites and stalagmites.
- Stalactites: Icicle-shaped formations that hang from cave ceilings, formed by dripping water depositing calcium carbonate.
- Stalagmites: Upward-growing formations on cave floors, formed by dripping water depositing calcium carbonate.
- Columns: When a stalactite and stalagmite join together.
- Lapies: Grooves or furrows in the rock surface.
- Sinkholes: Circular depressions that may or may not hold water.
Geological Action of Ice
Glaciers, massive bodies of ice, cover about 10% of the Earth’s surface. They form in polar regions and high mountains where temperatures remain below freezing. Snow accumulates, compacts, and recrystallizes to form these icy giants. There are two main types of glaciers: ice caps and alpine glaciers.
Ice Caps
Ice caps cover vast areas, primarily in polar regions. They hold approximately 85% of the Earth’s freshwater and can reach thicknesses of up to 4 kilometers. Ice caps appear white or blue depending on the amount of air trapped within the ice. When an ice cap reaches the sea, it can break apart into icebergs.
Alpine Glaciers
Alpine glaciers form in high mountain valleys. They consist of:
- Cirque: A bowl-shaped depression where snow accumulates.
- Glacier Tongue: The flowing mass of ice that carves out U-shaped valleys.
- Glacier Front: The leading edge of the glacier where ice melts and deposits sediment.
Geological Action of Glaciers
Glaciers move slowly downhill, eroding the sides and bottom of valleys. They carry rock fragments, polish bedrock surfaces, and carve grooves into the landscape. The material transported by a glacier is called moraine. Moraines are classified by their location: lateral, medial, or terminal.
Geological Action of the Wind
Wind affects all land surfaces, but its erosive power is most pronounced in arid and semi-arid regions. Wind erosion occurs through two main processes:
- Deflation: The wind lifts and removes loose particles, such as sand and dust.
- Abrasion: Windblown particles strike rock surfaces, causing erosion. This process is most effective near the ground where heavier particles are concentrated.
Wind erosion creates distinctive landforms like grooves, natural arches, mushroom rocks, and honeycomb weathering. Wind also plays a significant role in sediment transport and deposition, creating features like:
- Rocky Deserts (Regs): Vast plains covered with rocks, remnants of wind erosion.
- Sandy Deserts (Ergs): Accumulations of sand, often forming dunes.
- Dunes: Mounds or ridges of sand sculpted by the wind. Common types include barchan dunes (crescent-shaped) and transverse dunes (linear).
Movement of Dunes
Dunes migrate as wind pushes sand grains up the windward slope and over the crest. The steeper, leeward side is sheltered from the wind, causing sand to accumulate.
Geological Action of the Sea
The sea is a powerful force that shapes coastlines through erosion, transportation, and deposition. Waves, tides, and currents all contribute to these processes.
Waves
Waves are generated by wind and can be amplified by earthquakes or underwater landslides, creating tsunamis.
Tides
Tides are the periodic rise and fall of sea level caused by the gravitational pull of the moon and, to a lesser extent, the sun.
Currents
Surface currents are driven by wind, while deep ocean currents are driven by differences in water temperature and density.
Erosion
Coastal erosion is most intense in areas with high wave energy and weak or unconsolidated rocks. Physical weathering (wave impact) and chemical weathering (saltwater dissolving rock) both contribute to erosion. Common coastal erosion features include:
- Cliffs: Steep rock faces eroded by waves. Undercutting can create wave-cut notches and eventually lead to cliff collapse.
- Platforms: Flat or gently sloping surfaces left behind as cliffs erode.
- Bays and Inlets: Indentations in the coastline formed by erosion of softer rocks.
- Headlands: Projections of harder rock that resist erosion.
- Sea Caves: Cavities carved into cliffs by wave action. These can eventually erode through to form arches and stacks.
Sedimentation
Coastal sedimentation creates a variety of landforms, including:
- Beaches: Deposits of sand, gravel, and shells along the shoreline.
- Tombolos: Sandbars that connect an island to the mainland.
- Barrier Islands: Long, narrow islands that run parallel to the coast.
- Spits: Sandbars that extend from the shore into a bay or estuary.
- Lagoons: Bodies of water separated from the open sea by a barrier island or spit.
- Marshes: Low-lying areas that flood at high tide, often found behind barrier islands.