How was the Salpausselka and the Lake Region in Finland Formed?
Rows of rampartlike ridges span the south of Finland and overlook a rolling heartland that is filled with a labyrinth of crystal-clear lakes. Among the most striking and distinctive landscape features of southern Finland is a long double line of rampartlike ridges that span the entire country. Rising as much as 260 feet (80 meters) above their flat surroundings, the more or less parallel lines of hills extend some 300 miles (500 kilometers) from northeast to southwest. The tops of the ridges, which in places are up to 21/2 miles (4 kilometers) wide, form a sort of natural causeway; for long distances they are used as the roadbed for a major highway and a railroad line. One part is even flat and wide enough to serve as an airfield.
The ridges, known as the Salpausselka, also provide superb vantage points for viewing Finland’s Lake Region, which stretches off to the north. From horizon to horizon the flat terrain is a mosaic of blue and green—lakes by the thousands, of every size and shape imaginable, are dotted with islands and encircled by dense, dark evergreen forests. Lake Saimaa, considered the largest, is actually an interconnected network of more than 100 smaller lakes. Most of the lakes, in fact, are linked by rivers and canals, forming a vast and beautiful inland waterway system. The Lake Region, an increasingly popular vacation area, is at its best in the haunting twilight of long summer evenings, when the fringing forests are reflected in the tranquil waters. But even in winter, when the lakes are locked beneath a cover of ice and snow, the region has a stark and somber beauty all its own.
At one time it was thought that the Salpausselka ridges act as a natural dam and so account for the profusion of lakes that dot the region. In fact the origins of the lakes and ridges are quite different, though both are products of the Ice Age. The lake basins for the most part were created as the glaciers advanced; the ridges, as they retreated.
During the Ice Age, continental ice caps advanced several times across the ancient gneiss and granite bedrock of Scandinavia. With each advance the crushing mass of ice, laden with debris and boulders, scoured the surface of the land and gouged shallow depressions in the bedrock. The hollows in time became the basins of the region’s many lakes.
Some of the lakes and marshes are different, however; they are contained by natural dams of glacial debris: long, narrow mounds of gravel, sand, and pebbles that snake across the country side. Generally about 100 feet (30 meters) high and often many miles long, these natural levees, known as eskers, sometimes form the margins of lakes and marshes. The winding belts of debris mark the courses of streams that flowed through or under the ice. Long thought to be streambed deposits, eskers are now believed by some scientists to be chains of deltas deposited at the mouths of tunnels where streams emerged from the receding front of the glacier.
The Salpausselka ridges are also products of glacial retreat. Basically they are a pair of so-called terminal moraines, deposited when the Ice Age drew to a close about 10,000 years ago. Each of the two lines of ridges marks a pause in the glacial retreat: a period when the ice was melting along the glacial front at about the same rate that new ice was advancing from the north. As the ice melted, all the rock debris trapped in it accumulated in a great mound along the front of the glacier. After the southern line of ridges had been deposited, the climate warmed up and the glacier retreated about 15 miles (25 kilometers) toward the north. The glacier then “stalled” again, and the second line of terminal moraines was formed before the ice cap went into its final retreat. Leslie writes the Prague guide and loves travel.