During the Quaternary there were four main glaciations in Europe. The glacial periods are characterized by the presence of enormous glacial masses that covered most of the lands. The Valtellina was also affected by this phenomenon and its current forms result mainly from the intense work of the glacial movements.
The most important glaciations, called Günz, Riss, Mindel and Würm, were interspersed with interglacial periods in which the climate was milder and the global average temperature was warmer.
During the last glacial expansion, which had its peak about 20,000 years ago, the main glacier in the Valtellina stretched for 200 km from the upper valley down to the todays area of Brianza. The last glaciation ended around 12,500 to 10,000 years ago.
The graph is representing the sequence of glacial and interglacial phases.
The movements of the glacier has shaped the valley in a characteristic U-shaped profile, that retains in the upper part of the Val Grosina. After the ice had retreated, in addition the Roasco River has carved the rocks, especially in the lower section of the valley.
The Rupe Magna is an example of a Rôche Moutonnée (or Sheepback). The shape was formed by the intensive movements of the ice. By slow and continuous sliding of the ice on the Rupe and by carrying sand and boulders the Rupe Magna got smoothened.
On the Rupe Magna signs of glacial striation are clearly to recognize, in fact they were done by two different glacier movements. These linear scratches with a width of 1 to 2 cm and a length of a few meters were carved into the bedrock, the Rupe Magna, by the main glacier of Valtellina on the one hand and by the glacier coming out of the Val Grosina on the other hand.