school energy&environment

Caves remember the past

Caves are formed progressively in relatively long geological periods and evolve continuously: their history depends on many factors, among which the amount of water (depending mainly on climate), the way in which the latter enters the system, the variations of the base level and of the surface topography. Modifications in the topography can change the hydraulic supply of a cave causing, for example, the transfer of phreatic conduits to vadose zones, or bring about variations in position and functioning of springs, and much more: every modification in the cave surroundings, such as tectonic movements, climatic variations or topographical changes result in modifications within the karst system which tend towards a new equilibrium in the new situation. Hence, caves are not stable and unchanging in time and space and one must always keep in mind that they were formed in topographi and climatic conditions very different from the present ones (for example, caves in the Lombard Prealps started forming a little less than 30 million years ago when the valley presently occupied by Lake Como did not exist and there was a tropical climate with a dense rain forest covering the entire area). Any variation is promptly registered within a cave both as karst features that originated in conditions different from the present ones and as deposits of minerals and sediments that vary depending on the amount of water or on the climate (for example, in many caves in Northern Italy it is possible to find sediments related to the advance of the great glaciers that, during the last 2 million years, have repeatedly scoured the valleys from the Alps). Since on the surface erosion often results in the disappearance of all traces of the geological history of a region, caves, being on the contrary a very conservative environment, are often an important archive of precious geological data. Cavers, who are the only visitors in this environment, are often asked to unearth these data. Hence it is important that cavers should have some geological knowledge to be able to recognise the main karst features and collaborate effectively with speleologists who are engaged in researches in this field.