Earth

Surface karst landscape

Karst landscapes have two peculiar characteristics which make them immediately identifiable even where rocks are covered by soil and vegetation: particular forms of dissolution on the surface and the practically total absence of watercourses on the surface, as all the water or most of it, rapidly is swallowed into the depths. This characteristic makes the work of speleologists particularly important, because karst zones are generally characterized by water supply problems: the identification of underground water reserves, their localization and the study of the possibility of exploiting them are a very important contribution to the wellbeing of local populations, specially in the arid zones of developing countries. Among the most particular karst forms, besides the afore mentioned karren or lapiez, which are forms on a small scale, dolines are surely the most well known and striking. These can be of different origins, but for cavers the most interesting ones are surely those formed by collapse, which often allow access to cave systems. Dolines formed by collapse, often are shafts and their cross-section is often sub-circular. At times they are very deep (like the famous sòtanos in Mexico, of which the Sotano de las Golondrinas, 370 m deep, is the most well-known representative) . At times forms of this type allow direct access to flooded systems: as in the case of the cenotes (those in Yucatan are the most famous, but there are many in most coast areas in tropical zones). More complex and larger forms are polja (singular: polje), large flat bottom depressions characterised by caves, the ponores, that act alternatively as sinkholes during dry season or as springs during rainy season, when the water flowing within the karst system exceeds the drainage capacity of the system. Water rises up the sinkoles from which it flows out, often forming temporary lakes (for example the polja in the karst area of Postojna, in Slovenia). Tropical zones are characterized by particular karst landscapes, such as cone karst and tower karst (famous tower karst can be found in Southern China or Thailand). The formation of underground drainage systems often brings about the swallowing of surface water through sinkholes, leaving valleys “dry”. Thus dry valleys are formed with water courses in which water no longer flows; in blind valleys, water courses disappear underground, often sinking into large entrances. Pocket valleys are on the contrary valleys suddently closed upstream, where waters comes out a spring, often at the base of a wall, or beginning at big karst springs (for example the famous Fontaine de Vaucluse, in France).