The Aletsch Glacier flows down the valley from its beginning high in a pass between two massive mountains, the Jungfrau and the Monch. Located in south-central Switzerland, it measures some 15 miles (25 kilometers) in length and encompasses about 50 square miles (130 square kilometers), making it both the longest and the largest glacier in the Alps.
Glaciers are often thought of as rivers of ice—rivers that are made of snow that has compacted under pressure. Like ordinary rivers, they have their sources, tributaries, and outlets. In the case of the Aletsch, three ice streams—the Great Aletsch Firn (fern is the name used for compacted snow), the Jungfrau Firn, and the Ewigschneefeld (“Eternal Snow Field”) —come together in the region called the Concordia Platz. From this point the great glacier moves south toward the Rhone Valley, flowing at an average rate of 500 to 650 feet (150 to 200 meters) per year.
Along the way small tributary glaciers feed into the main glacier. However, most of the tributary glaciers are melting back and have become disconnected from the main glacier, so that ice from them no longer reaches the Aletsch.
On its left bank the Aletsch Glacier forms a wall, damming up the waters of a small tributary valley and creating a lake called the Marjelensee. In the past the lake sometimes drained unexpectedly into channels beneath the ice, but now the drainage has been controlled to avoid flooding.
The last big ice advance occurred in the 17th century, but today there is not enough snow to compensate for loss by melting. Since 1892 the terminal snout of the Aletsch has receded more than 3,300 feet (1,000 meters), and the glacier now occupies only about half of its former basin. Traces of irrigation canals, which were dug into the old valley floor and then buried by the ice during the late Middle Ages, have now become visible again. Along the sides of the glacier a line of boulders and rocky debris (lateral moraines) shows the former extent of the ice.
But even at its present size, the Aletsch Glacier stores a tremendous amount of water. In fact the Massa River, which is a tributary of the Rhone, consists entirely of meltwater from the Aletsch. Though in winter the stream almost runs dry, its torrential summer flow supplies a seasonally operated hydroelectric station.
At one time difficult to reach, the Aletsch region now attracts many visitors, who can take a tram up the side of the Jungfrau to the highest point in Europe that is reachable by rail. Also, several cable cars run up from the Rhone Valley to vantage points above the glacier itself.
The glacier provides exceptional terrain for skiers, even in spring, and the Aletschhom (the highest peak in its basin) offers a challenge to the most experienced mountain climbers. In addition, there is a nature reserve (the Aletschwald), as well as two resorts at Belalp and Riederalp, which provide accommodations for visitors interested in glacier excursions. The beautiful scenery and the pure air are clearly reasons enough for visiting Switzerland’s Aletsch Glacier for an adventure.