Rock Weathering and Geological Agents Modeling

Weathering of Rocks by Atmospheric Agents

Clasts are fragments of rock torn from a larger rock mass. The fragmentation of rocks is caused by atmospheric agents such as rain and snow. These agents wet the rock, dissolving minerals and reacting with them. Temperature changes also contribute: the expansion of rocks as the sun heats them contrasts with the contraction caused by freezing. Water seeps into cracks in rocks, subjecting them to pressure during freezing (gelifraction).

Weathering is the set of processes due to atmospheric agents that produce the alteration and disintegration of rocks.

• Mechanical Weathering: The rock is fragmented due to expansion and contraction, the freezing of water, or the impact of falling rocks.
• Chemical Weathering: Disintegration is due to chemical reactions that alter the constituent minerals.
• Biological Weathering: Weathering is due to the action of living beings.

Factors Influencing Weathering

• Temperature: Variable temperatures favor chemical weathering.
• Humidity: High humidity favors chemical weathering; very wet and hot climates favor mechanical and biological weathering.

Modeling by Geological Agents

Geological agents perform erosion, transport, and sedimentation.

• Erosion: The removal of materials from their place of origin. It is determined by the energy of the geological agent and the rock's resistance.
• Transport: The carrying of materials. This can occur by rolling, suspension (without touching the ground), or saltation.
• Sedimentation: The deposition of materials.

Classification of Geologic Agents

Wind

Wind has a greatly reduced transport capacity. Its erosive action forms clumps called dunes. The windward side of a dune faces the wind, while the leeward side is opposite. Wind-blown dust (loess) can lead to fertile ground through deflation (the removal of clay and sand). Accumulation of sand forms desert dunes (ergs) and crescent-shaped dunes (barchans). Wind abrasion is the sanding of rock by wind-blown sand. Stone fields (regs) are also a result of wind action.

Glaciers

Glaciers are moving masses of ice. They form where snow accumulates, such as at the poles (ice caps) or in mountains (alpine glaciers). Alpine glaciers feature tongues of ice extending from a cirque. Glacial moraines (lateral, central, and frontal) are accumulations of rock debris. Glaciers carve U-shaped valleys.

Wild Waters

Wild waters, also known as runoff, have great erosive capacity and shape the landscape, especially in areas with dry climates and heavy rainfall. Water erosion creates gullies in areas with maximum slope. Creeks form gully catchments, spillways, and dejection cones. When a dejection cone is large, it is called an alluvial fan.

Rivers

Rivers are permanent watercourses that converge into each other. A river and its tributaries form a drainage basin. Rivers carve V-shaped valleys when they have high energy. When they lose power, they originate meanders and floodplains (flat valleys occupied during overflows). Peneplains are almost flat plains formed by the accumulation of clasts at the end of a river's course. Deltas are also formed by sediment accumulation.

Groundwater

Groundwater accumulates in aquifers, which can be exploited through wells. Karst topography is characterized by underground and surface features produced by the dissolution of rocks. Stalactites form on the ceiling of caves, while stalagmites form on the floor. Sinkholes are depressions caused by the collapse of underground cavities. Potholes are vertical ducts connected to the surface.

Sea

Waves are produced by wind. Currents are caused by temperature differences. Tides are caused by the gravitational pull of the sun and moon. Waves erode coastlines, creating cliffs and abrasion platforms. Drift currents transport sediment carried by the wind, forming sand beaches, sandbars, and spits (parallel to the coast). Tombolos connect the mainland to an island. Cliffs are formed by wave action, which also creates abrasion platforms. The accumulation of sand from beaches forms as waves erode the cliff, and when the wind is oblique, currents can form isolated lagoons.