KARST (Ital. Carso), in the limited sense the name given to the limestone mountain belt which extends from the River Isonzo towards the Gulf of Quarnero, north-east of the peninsula of Istria. By extension the term is also applied by physical geographers to the type of scenery characteristic of areas in which massive, well-jointed limestone rocks predominate. Such karst lands occur not only throughout a large part of the Dinaric Alps and other chains of the Balkan peninsula, but in the Causses of France, in the Jura, on a small scale in the Pennine region of England and in many other parts of the earth's surface. Karstic phenomena have been studied in most detail in the Balkan region both because of their wide prevalence there, and because of their marked effects on human life.
The essential feature is that owing to the solubility of lime stone in rain water, and the percolation of water along joints en larged by solution, land-f orms are determined mainly by sub terranean drainage. Over large areas, even where the rainfall is considerable, surface streams may be totally absent. When they occur they tend to run in deep, steep-sided, canyon-like gorges, often ending blindly at either end. At the upper end the river may originate from powerful springs rising at the base of lime stone cliffs, and at the lower may sink into a deep chasm. Equally characteristic are the closed depressions, often rounded or ellipti cal with a sink or swallow-hole down which surface water flows (dolines), or much larger (reaching a length of 6-12 m.), flat
bottomed and elongated (poljen). Dolines and poljen alike have usually a covering of soil (terra rossa) representing the insolu ble residue of limestone rocks. Thus within them cultivation is usually possible, while the intervening plateau areas may be com posed of bare limestones, with at best a scanty plant cover where soil accumulates in fissures and cracks. Some of the poljen of the Dinaric Alps are traversed by streams which emerge from one bounding wall and disappear again at another. During the winter rainy season the supply of water maybe too great to be carried off by the underground channel and the polje becomes a tempo rary lake. Cases of seasonal reversal of drainage are also frequent, a chasm at one period absorbing water and at another functioning as a spring. Whether or not the floor of the polje is periodically flooded the water table is usually near the surface, so that poljen are well suited for the growth of maize and other water-demand ing plants. As a corollary to these surface features there is in Karst lands a great development of underground channels and caves, which often results in the collapse, partial or complete, of the overlying rocks, producing chaotic surface relief.
See de Martonne, Traite de Geographic Physique, iv. ed., t. (1926, bibl.).