Earth’s Surface: Shaping Forces and Landforms
Basins and Sedimentary Environments
Sedimentary basins are large areas of land surface subsidence. A present sedimentary environment is the exact spot where an agent collects geological materials. There are three types:
- Continental: River, torrential, glaciers, wind, karst.
- Marine: Coastal, reef, continental shelves, turbidite.
- Transitional: Beaches, deltas, estuaries.
River Modeling
River modeling includes:
- V-Shaped Valleys: These occur when a river has great erosive capacity and is deeply embedded in the ground, producing a cut with walls softened by the wild waters and streams.
- Flat-Bottomed Valleys: As a river cuts the ground, it becomes less able to be fitted, and forms curves (meanders).
- Peneplains: The final result of fluvial erosion.
Torrents and Wild Waters
Torrents and wild waters are ephemeral streams that carry water only after rainfall. Wild waters are channeled waters that run through the field after heavy rain. Characteristic forms include:
- Gully-Grooves: Deep in the terrain.
- Canyoning-Vee: Deep valleys that form in areas of high slopes.
- Ramblas: Large channels that can remain dry for years.
Wind Modeling
Erosive processes include:
- Deflation: The wind blows away the smaller materials and leaves larger ones, creating a desert pavement.
- Abrasion: The sand-laden wind produces sanding on the surface of the rocks.
Dunes: They are accumulations of sand that can be crescent-shaped.
Coastal Modeling
The stronger the waves, the stronger the abrasion. Erosive processes include:
- Cliff Retreat: The waves erode the bottom of the cliffs, causing the collapse of blocks.
- Crushing and Washing Materials: The blocks and fragments of rocks and waves are broken down. Sea currents carry the finest materials, leaving sand and gravel on the coast.
- Accumulation of Sand Beaches: In areas of low slope.
- Bars and Arrows: Sandy cords perpendicular or parallel to the coast, which tend to isolate small coastal lagoons and marshes.
Glacier Modeling
The geological agent is a glacier, formed by large masses of ice. Sedimentation in the middle of glaciers produces tillite, which are accumulations of clasts produced by glaciers. Moraines are frequently associated with the movement of the glacier tongues.
Karst Modeling
The geological agent is composed of karst, surface water, and groundwater with the ability to dissolve the rocks, causing eroded shapes both on the surface and underground. Surface features include:
- Dissolution: The rainwater running over rocks produces soluble grooves, sometimes called lapiaces. In landscapes, it also forms ruiniformes.
- Collapse: When the roof of an underground cavity collapses, depressions appear on the surface called sinkholes.
Underground features include:
- Galleries: Horizontal tunnels.
- Simas: Vertical or less vertical ducts that sometimes reach the surface.
- Salas: Large, irregularly shaped cavities.
Factors that Condition Modeling
- Climate: In arid areas, there are no glaciers or rivers. In temperate and rainy areas with plenty of vegetation, wild waters and the wind exert an important action. In polar regions or high mountains, water remains as ice, determining the action of the glacial agent.
- Geological-Tectonic and Structural: Rivers tend to be encased along faults. Glacier tongues tend to fit into areas where there are more fractures. The lifting of the ground makes the rivers recover potential energy and thus erosive capacity.
- Lithologic: Soft materials erode more easily, while the hardest materials originate protrusions in the relief. On the coasts, where the waves have a constant erosion on rocks, soft materials produce the strongest incoming and outgoing. Limestone rocks determine the development of karst modeling.
- Anthropic: Slopes and embankments attempt to prevent or slow the erosion of wild waters. Streams and rivers are often channeled to prevent flooding. Ports and coastal recreation areas are protected from wave erosion by seawalls, etc.