Earth

An example close by

Even caves close to the big prealpine lakes (Maggiore, Como and Garda) have experienced a similar evolution: Lake Como, for example, is set in a deep canyon whose formation dates back more than 5 million years and hence is not of glacial origin (like its fellow-lakes, Lake Maggiore, Lake Iseo and Lake Garda). At present, Lake Como is over 400 m deep, which means that its bed is 200 m below sea level, but the bottom of the canyon, filled with sediments, is 700 m deeper. Considering that it is surrounded by highly karstifiable rocks, it is most probable that complex, highly developed karst systems are present in the depths, in equilibrium with the old base level at the bottom of the canyon. Successively, a little over 2 million years ago, the sea flooded the border of the Lombard Prealps, as ancient valleys filled by clays containing fossils of marine organisms testify. Hence, even deep caves at the bottom of the canyon were flooded, filled with sediments and colonized by marine organisms. The sea then withdrew, emptying the caves once again, and the canyon filled up with alluvial sediments, first of marine and then of glacial and fluvio-glacial origin, when the big Adda Glacier advanced repeatedly down the valley now occupied by the lake. Along the steep submerged walls of the lake, big flooded galleries must therefore exist. The proof of this is given by the springs of the most important karst systems of Pian del Tivano and of the Grigna Settentrionale. The springs that are visible on the surface are only overflow springs, whose discharge is very poor with respect to the great amounts of water that enter the system in the catchmente zone. The main springs must therefore be below lake level, but they have not been found yet. All this simply means that the origin of caves is usually very ancient and that their evolution is often complex and closely controlled by geographical events in the area. Speleologists and cave-divers have on hand the keys to open the important archives of geological data contained in the darkness of the caves. And these data can, in turn, give important suggestions for new explorations!