Water

The Quaternary period

The Quaternary period is divided into two periods. Pleistocene, characterized by numerous glaciations, ended 10,000 years ago with the end of the last glaciation. Each glaciation is separated from the previous and subsequent ones by warm periods known as interglacial periods, with climates similar to the present day climate, and even hotter. In the subsequent period, the Holocene, even though  there was an alternation of warmer and colder periods, there were no real glaciations at a global scale  but only small episodes of glacier advance and retreat in the higher latitudes and higher altitudes. In the past 4 Quaternary glaciations were classified and named: starting with the most ancient, these are named Gunz, Mindel, Riss and Würm from the names of the locations in which they were recognized and studied for the first time. However today we know  that there were many more glacial episodes, with great differences in the number of stages and the surface area occupied in the different parts of the Earth. For example, in the Alps, in the Lake Como-Lake Maggiore amphitheatre, at least 13 advance and retreat episodes have been noted instead of the 4 traditional ones. The last glaciation began approximately 75,000 years ago after a long hot interglacial period, and reached its maximum expansion  during the period 30,000 to 18,000 years ago, covering approximately 30% of the land above sea level. The Laurentian Ice Sheet covered most of North America and a vast ice-sheet also covered North Europe, while the Alpine glaciers moved Southward occupying part of the plain of the Po river. In the Alps, the retreat began 14,000-15,000 years ago; a study of the moraine ridges  enables the reconstruction of the stages of the retreat and shows that it was not a regular and progressive retreat, but there were many small advances and subsequent retreats, the so-called tardiglacial pulsations.
At the beginning of the Holocene there was a period of climatic oscillations that was followed, around 8,000 years ago, by a hot period called Climatic Optimum, with much smaller glaciers than the present ones.  It was the period, for example, of the mummified Similaun man, an evidence of the fact that in those times many mountain passes in the Alps could be crossed and were used. Various studies enabled the reconstruction, for the Italian Alps, of a series of events, with local advances between 1300 and 1400 B.C and 900-300 B.C., followed by a warm period between 400 and 750 A.D., that coincides with the expansion of the Roman Empire, which is then followed by a short medieval advance, between 1150 and  1350 A.D. and what is called the Little Ice Age between 1150 and 1860, the maximum ice advance after the end of the Pleistocene glaciations. Many of the large moraines that are visible near the glaciers today date back to the Little Ice Age (as for example the Engadine Morteratsch Glacier in Switzerland, over 40 m high).
Evidence of the expansion of the Little Ice Age is also to be found in many reproductions, paintings and, more recently, photographs of great historical value,. Evidence of the great retreat at the end of the LIA can be seen in numerous man-made structures, initially these were build near the fronts and now are very far from them, such as the Albergo dei Forni hotel, that is now over 2 km from the front near to which it was built.  The retreat was also accompanied by a great decrease in the ice thickness, as the trenches of World War I and the Alpine shelters testify,  at times these now can be seen hanging various dozens of metres above the  surface of the glaciers, as for example the Konkordia Hostel on the Aletsch glacier, in the Jungfrau Group of mountains, that can now be reached  climbing 100 m up a rocky cliff.  Also the Aletsch Glacier retreated approximately 3 km since 1860, the year in which the LIA ended. Small pulsations were recorded in the subsequent years, between 1880 and 1890 , in 1920 and more recently, between 1960 and 1980, following a period of lower temperatures, in the Fifties and Seventies. Presently all the Alpine glaciers  show a retreat and a negative mass balance. In the past years, the only year with a positive balance was  2000-2001, with plentiful snowfall in winter and spring, but this has not led , at present, to any positive oscillation. The study of the climatic oscillations and the advance and retreat of the glaciers of the past enables us to better understand the mechanisms regulating the existence and “state of health” of the present glaciers, and we realize that glaciers are sensitive indicators of variations in the climate, and in particular of the temperature and  precipitation.