Esempi di rimodellamento di apparati morenici nell'arco alpino italiano

Exemples of paraglacial adjustment of moraines in the Italian Alps

Abstract

Recent rainstorms did involve moraines, mostly of the Little Ice Age, inducing modifications sometimes sensible of their shape. These events gave to the authors a chance to investigate the most important natural processes concurring to remodel moraines after their deposition. The study, extended to the whole Italian Alpine arc, has been conducted through analysis of aerial photos taken in different years, literature examination and direct observations. Water played a decisive role in initiating high-magnitude debris flows (tens or hundreds of thousands of cubic meters) encompassing glacial sediments, on the occasion of severe rainfall events or sudden emptying of englacial or proglacial lakes. One of the most striking effects is moraine downcutting up to tens of meters in the course of a single event. Landslides proved to be further causes of moraines reshaping: they can properly start in the glacial sediments (sometimes resulting in important dislocation of portions of the moraine as unified blocks) or overlap them, obliterating the moraine. Very frequently the internal side of the most recent moraines appears to be gullied as a consequence of rill erosion, which can proceed up until completely dismantling the glacial deposit. Much more rare, but significant also for the paleoclimatic implications, are cases of rock glaciers overflowing moraine crests lying crossways. Exogenous processes, although being far the most active, are not the only agents of moraines remodeling: tectonics and human interventions can cause sporadic but sometimes heavy changes of moraine shape. The examined case histories point out that the original structure of a moraine can be modified by processes developing at very diversified rates: they can proceed for hundreds of years but, more frequently, they can be almost instantaneous. The large number of examined case histories can also provide a new key to the genetic interpretation of similar morphologic features which have been produced by unknown processes.