Erratic block

An erratic (or erratic block) is a rock that has been transported more or less far by a glacier and has remained in ice-free terrain after the melting of the glacier.

During the last ice age, for example, boulders were transported from the Rhone Glacier to the Swiss Mittelland. Because of the hard rock and because they prevented efficient agriculture, many of the boulders were used for the construction of buildings or blown up. Later, numerous boulders were placed under protection and can still be admired today.

The type of rock of which a boulder consists provides information about the origin of the erratic blocks. This made it possible to reconstruct the extent and flow direction of the glaciers during the Ice Age.

Various erratic blocks show traces of their use as sacrificial stones.