Periglaciate
In geomorphology, the term periglacial refers to geomorphic processes created by the freezing of water into ice and the areas where these processes operate. The original, now obsolete meaning of the word Periglacial was restricted to areas and processes that occurred in the areas surrounding glaciers. Currently the term periglacial is used to associate certain landforms with the freezing of water or a cold climate regime, although many landforms ascribed to periglacialism have been shown to exist in places where water does not freeze, and the role of ice in producing certain forms in cold places it has also been questioned. It is estimated that approximately a quarter of the Earth's surface above sea level presents periglacial conditions.
The periglacial system
The periglacial morphoclimatic system appears in areas close to the glaciers, whether they are valley glaciers or continental glaciers The zones where the periglacial processes take place surround those that correspond to the glacial morphoclimatic system. Periglacialism also appears in some mountain ranges where there are insufficient conditions for the development of glaciers.
The climates that determine this domain are subarctic continental, tundra polar and high mountain. The processes and agents involved in periglacial modeling are ice, the formation of moraines and other glacial deposits (esker, kame, etc.), fluviotorrential processes and slope phenomena.
Processes and agents
Although not as exclusively as in glacial systems, ice is still the most important modeling agent in the periglacial system. This agent is responsible for gelifraction, the most relevant phenomenon of this system.
This type of periglacial modeling arises as a consequence of the ice that forms inside the rocky cracks on the slopes of the mountains, which produce the increase in volume, the desquamation and the subsequent disintegration of the rock. The generated fragments fall and accumulate at the edge of the mountains in accumulations called quarries or gravel, which are usually called scree if they are angular fragments.
The fluviotorrential processes produced by the stream water, coming from the melting of the ice and from the precipitations, model the slopes. The slope phenomena are a set of mechanisms that occur on the slopes of the mountains as a result of the weathering process and the effect of the force of gravity, which cause the movement of materials to lower areas.
Three slope phenomena are important in the periglacial system: mudflows, which consist of the displacement of clayey material that occurs when the soil is soaked; creeping, slow movement of soil materials down the slope; and the solifluction, small soil flows that occur when it pools in the thaw season.
Periglacial landforms
The following landforms are typical in this domain:
In sloping areas, terraces (systems of steps), scree, rocky glaciers (accumulation of debris with mud or ice), etc. can be formed. In horizontal areas, stone wedges are formed (cracks initially covered with ice that, when thawing, are occupied by fragments of rock and clay), polygonal soils (cracked surfaces with rock fragments that acquire polygonal shapes) and cushion grass (structures shaped like mounds covered with grass or moss). Due to the low temperatures, an upper part can be distinguished in the soil, called mollisoil, which freezes and thaws depending on the temperature, and a lower part, called permafrost, which remains frozen all year round.