Tunnelgrottor

Useful Information

Location:	()
Open:	no restrictions. [2022]
Fee:	free. [2022]
Classification:	sea cave
Light:	bring torch
Dimension:
Guided tours:
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History

Description

Tunnelgrottor is located on the eastern coast of an island, which is connected with mainland Sweden by a city. The town Härnösand is built on both sides of the canal between the island and the mainland. The cave named Smitingen is only a few kilometers from the city, and a popular place. The rocks around the caves were developed by two marked trails the Grottstigen (cave trail) and the Geologistigarna (geologic trail).

The caves are located from sea-level up to some tenth of meters asl. They are important signs for the isostatic uplift of Scandinavia. During the last Ice Age the weight of 3.5 kilometre thick glaciers pressed the crust deep into the molten lava of the upper mantle, like a heavily loaded ship. When the ice melted some 10,000 years ago the now empty ship started to uplift.

The caves shows this development, as sea caves are always formed at sea level. So each cave was formed while it was at sea level, and its formation ended when it was lifted out of the reach of the waves. The uppermost caves are the oldest becoming younger towards sea level. The movement of the isostatic uplift is very fast, in geologic terms, and it is still going on. The whole series of caves was formed during the last 3,000 years.