Badlands (géomorphologie)

Badlands are a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded. They are characterized by steep slopes, minimal vegetation, lack of a substantial regolith, and high drainage density. Ravines, gullies, buttes, hoodoos and other such geologic forms are common in badlands. Badlands are found on every continent except Antarctica, being most common where there are unconsolidated sediments. They are often difficult to navigate by foot, and are unsuitable for agriculture. Most are a result of natural processes, but destruction of vegetation by overgrazing or pollution can produce anthropogenic badlands. Badlands are characterized by a distinctive badlands topography. This is terrain in which water erosion has cut a very large number of deep drainage channels, separated by short, steep ridges (interfluves). Such a drainage system is said to have a very fine drainage texture, as measured by its drainage density. Drainage density is defined as the total length of drainage channels per unit area of land surface. Badlands have a very high drainage density of 77 to 747 miles per square mile (48 to 464 kilometers per square kilometer). The numerous deep drainage channels and high interfluves creates a stark landscape of hills, gullies, and ravines. In addition to a dense system of drainages and interfluves, badlands often contain buttes and hoodoos ("mushroom rocks"). These are formed by resistant beds of sandstone, which form the caprock of the buttes and hoodoos. Badlands arise from a combination of an impermeable but easily eroded ground surface, sparse vegetation, and infrequent but heavy rainfall. The surface bedrock is typically mudrock, sometimes with evaporites, with only occasional beds of more resistant sandstone. Infrequent heavy rains lead to heavy erosional dissection. Where sudden precipitation cannot penetrate impermeable clays, it is channeled into a very dense system of streamlets that erode a dense system of ever-enlarging, coalescing gulleys and ravines.