Salpausselkä

It is a large terminal moraine formation that formed in front of the Baltic ice lake during the Younger Dryas period about 12,250–10,400 years ago.

It traps the extensive river and lake systems of Central Finland known as Finnish Lakeland (Finnish: Järvi-Suomi, "Lake Finland") and forces the water to flow through few breaches in the ridge.

From there the water subsequently flows through river Neva into the Gulf of Finland, bypassing the Salpausselkä.

The Kymi River flows from Päijänne into the Gulf of Finland.

Salpausselkä has been used for transportation because of the easy terrain for centuries; later on both railways and highways have been built to follow it.