Rock Weathering, Erosion, and Geological Agents: Shaping Earth’s Surface
Rock Weathering: Atmospheric Agents
Fragments of rock of any size, composition, or origin are called clasts.
The Role of Rain and Snow
Water dissolves rocks and produces some of the minerals that compose them.
Temperature Changes and Weathering
Dilation occurs when the sun heats the rocks, and contraction happens at night as they cool.
The Freezing of Water
Water infiltrates cracks in rocks, exerts strong pressure, and breaks them apart.
Weathering is the set of processes caused by atmospheric agents that lead to the breakdown and disintegration of rocks.
Weathering Processes
Mechanical Weathering
Rock fragments due to expansion and contraction, and the pressure exerted by freezing water.
Chemical Weathering
Disintegration occurs in rocks due to chemical reactions altering minerals.
Biological Weathering
Originates from the actions of living beings that break down rocks.
Factors Influencing Weathering
Temperature
High temperatures facilitate chemical reactions. Low temperatures hinder them. Changing temperatures cause mechanical weathering. Heavy frosts in winter and warm summers contribute to mechanical weathering.
Humidity
High humidity promotes chemical weathering, such as in jungles, whereas in dry environments, these reactions cannot occur.
Geological Agents and Their Actions
Geological agents are forces shaping the landscape, transporting materials, and accumulating them naturally.
Erosion
Erosion is the removal of materials from their place of origin.
The modeling of relief corresponds to changes produced by geological agents causing erosion of the landscape.
- Each geological agent creates a different modeling effect.
- Not all agents erode at the same rate.
The Energy of Geological Agents
The Resistance of Rocks
Transportation
Bottom Transport
The movement of clasts produced by the current dragging them along the bottom.
Suspension Transport
Clasts are transported without touching the bottom (saltation).
Sedimentation
Sedimentation occurs when a geological agent deposits clasts permanently in one place.
- Wind: Its action is carried out throughout the earth’s surface.
- Glaciers: Have a very large capacity for erosion and transport.
- Ephemeral Streams: Pass through an area after heavy rainfall.
- Rivers: Are permanent water courses.
- Groundwater: Its action consists of dissolving rocks.
- The Sea: Its action on the coasts creates cliffs.
The Wind
The wind has a very reduced erosive capacity. The wind transports dust, called loess.
Glaciers
Ice masses move from areas of snow accumulation until the ice melts.
- Cirque: Where snow and ice accumulate.
- Ice Tongue: Drags large quantities of stones.
- Lateral Moraine: Accumulates on the side of the ice tongue.
Ephemeral Streams
Have a large geological erosive capacity.
Rivers
Are permanent courses of water that converge to form a mainstream.
- Upper Course: Steep slopes, much erosion, little transport. Waterfalls and rapids are common.
- Middle Course: Less steep, less erosion, more transport, and low sedimentation.
- Lower Course: Gentle slopes, little erosion, more transport, and much sedimentation.
Aquifers
Groundwater accumulations that can be exploited using wells.
Karst Modeling
Karst is the set of surface and underground features caused by the dissolution of rocks.
The Sea
- Waves: Produced by wind. Perform erosion, transportation, crushing, and sedimentation in sheltered areas.
- Currents: Formed by differences in temperature and salinity of water, causing transportation.
- Tides: Sea movements due to gravitational influence.
Sedimentary Rocks
Examples: limestone, clay, sandstone.