Geological Action of Rivers, Groundwater, Ice, and Wind

Characteristics of River Formations

Rivers originate in different mountain areas. In the upper reaches, the waters run at high speed and tend to deepen the channel, causing a cross-section in the form of a V. In the middle stretch of the river, the erosive action is shared between the substance and the margins, expanding the valley so a floodplain (plain of inundation) originates. In its lower course, the river can erode its own floodplain, deepening the channel on sedimented materials. Thus, before emerging on both sides, stepped surfaces of the channel called fluvial terraces are formed.

Geological Action of Groundwater

Groundwater acts by dissolving limestone, giving rise to karst landscapes. Water infiltrates through rock crevices, which progressively expand by solution, forming vertical channels or potholes and cavities of different sizes (caves, galleries) through which the water circulates. In caves, calcium carbonate deposits are generated, forming stalactites when they grow from the ceiling and stalagmites when they grow from the floor.

Aquifers and Groundwater Reserves

Aquifers are reservoirs in the subsurface formed when water from precipitation infiltrates into the soil and fills existing gaps or pores in rocky materials. In an aquifer, two zones can be differentiated:

• Zone of Aeration: In the area traversed by infiltration water, part of the pores are occupied by air.
• Zone of Saturation: The water soaks into the field totally; all the holes are occupied by water. The upper limit of the saturation area is called the water table.

Groundwater Exploitation

Groundwater is an essential resource usable through wells. The amount of water extracted from the aquifer should always be less than the quantity of precipitation water that infiltrates and refills it. If this balance is not maintained, we over-exploit the resource, eventually exhausting it. Overexploitation causes the water table to drop, which can lead to the disappearance of springs and moisture, along with the living species that inhabit them.

Geological Action of Ice

As ice flows, it erodes rocks and pulls fragments from the bottom. Some of these fragments are transported. A typical aspect of glacier morphology is the cross-section in U-shaped glacial valleys.

Geological Action of the Wind

The wind is an active modeler of relief, especially when it reaches a certain speed across the surface with variable intensities. Some areas are more prone than others depending on the prevailing wind directions.

• Transport: The wind transports small-sized materials.
• Sedimentation: With decreasing velocity, the wind loses its transport capacity and deposits materials. The larger materials deposit first, followed by the smaller ones.

Aeolian Landforms

• Rocky Desert (Reg): An area marked by the accumulation of rocks where finer materials have been transferred to other zones.
• Dunes: Accumulations of sand moved by the wind from one place to another.