Understanding Earth’s Dynamic Landscapes: From Debris Flows to Karst Formations
Understanding Earth’s Dynamic Landscapes
Debris Flows and Soil Creep
Debris flows are movements that involve large flows of regolith, with so much water that they could be categorized as quasi-river flows. If these flows transport abundant fine material, they are called earthflows. Soil creep, or simply creep, is a slow process that is sometimes the dominant evolutionary force in a field. Its driving force is gravity and is favored by seasonal changes in temperature, such as freeze-thaw cycles. Its effects can be observed in trees. When it reaches the colluvium zone, it creates very fertile plains. Gelifluction or solifluction are characteristic of freeze-thaw environments.
The Influence of Climate History and Glaciation
The climate history is essential to understanding the current landscape. There were cold glacial and interglacial periods. The current relief dates back to the Miocene. The snowy layer is important, as evidenced by oxygen isotopes. The last glaciation in Europe was the Würm glaciation. Glaciers formed characteristic fleecy rocks. Associated with mountain systems are features such as older cirques (excavated cells), edges (sharp peaks formed after the erosion of a cirque), horns (angular peaks), drumlins (glacial deposits in the shape of a whale), “U”-shaped valleys, and basins of over-excavation. On a medium scale, there are rocks with a striated and smooth edge and a fragmented one. On a smaller scale, there are grooves and channels. Permafrost, or permanently frozen ground, is divided into the active layer (mollisol), the first 1.5 meters, and the permafrost itself, which can extend to depths of 400 or 1000 meters. The active layer is affected by the sun, while the permafrost is affected by internal heat.
Karst Landscapes and Processes
Karst refers to landscapes formed by the dissolution of carbonate rocks, such as limestone. This term originates from the Croatian region of Kras. In principle, karst landscapes are associated with limestone, halides, and sulfates. Karstification is the set of processes that model karst landscapes, and in some cases, it can be reversible.
Processes Involved in Karstification
- Physico-chemical: Pressure favors the solubility of CO2. When CO2 precipitates, it helps dissolve the rock. Hydrostatic pressure, temperature, water turbulence, and ion exchange also play a role. The presence of substances dissolved in water, such as halite, carnallite, or sylvite, can enhance the solubility of CaCO3, while dolomite or gypsum can reduce it.
- Lithologic: Plaster and halides are soluble, so karstification is very active in these materials. Limestone, dolomite, quartzite, and sandstone can also favor karst landscapes under certain external conditions. In limestone, a higher concentration of CaCO3 leads to greater solubility and karstification.
- Structural: Faults, stratified areas, and clasts foster dissolution in clumps.
- Biological: Organisms produce CO2, which encourages dissolution, in addition to the mechanical action of roots and the production of organic acids.
- Climate: Climate is vital because it controls all other factors.
Karst Landforms
Karst landforms can be classified as endokarstic (underground) or exokarstic (subaerial), destructive or constructive (depending on whether they are formed by dissolution or precipitation), and older or younger.
- Dolinas: These are conical or circular depressions, also known as sinkholes.
- Uvala: These are oval depressions resulting from the fusion of multiple dolinas.
- Polje: These are large depressions that can be 2 km wide, often with springs, sinks, and a water table near the surface.
- Karst pavement: These are areas often weathered along stratification planes, with karstification advancing along joints.
- Karst valleys: These include areas with underground pipes, canyons, and gorges, formed by both fluvial and karst erosion through the dissolution of carbonates.
- Mogotes, towers, and pinnacles: These are pyramidal, conical, or cylindrical formations found in tropical regions.
- Lapiaz: These are smaller-scale features that develop on the surface, superimposed on larger landforms.
- Tufa and travertine: These are constructive landforms formed by the precipitation of calcium carbonate outdoors.
- Decalcification trays: These are found inside massive caves.
- Caves and galleries: These are underground ducts formed by the erosion and dissolution of filtered water.
- Potholes and drains: These are vertical features where precipitation can deposit speleothems.