Neotectonic Caves

Neotectonic Caves are formed by the forces of post-glacial rebound, a result of the melting of the ice shields after the last ice age and the isostatic uplift caused by the vanished weight.

Post-glacial rebound (isostatic rebound, crustal rebound) is typical for Scandinavia, or more general, for areas which were lately covered by a thick layer of ice. This area was covered by a glacier which was up to 3.5 km thick during the last cold phase of the ice ages. The plates are swimming in the molten rocks of the upper mantle, which are not liquid in the common sense, but molten and able to flow very, very slowly. The heavy weight pushed the whole plate down, like a boat, swimming in water, which is entered by a passenger. 100,000 years, while the ice shield existed, the whole package moved slowly downwards. This mechanism is called isostacy, the theory of the balance between gravity lowering the crust and buoyancy raising the crust.

10,000 years ago the end of the last ice age came. In a short time of several hundred years the ice melted and thus lowered the weight of the plate. The passenger left the boat and it stared to lift to the height where it was before. In scientific terms: it started to move up driven by its buoyancy, in order to reach the isostatic state. This movement is still going on lifting the whole scandinavian plate several centimeters every year. Today it is possible to measure the amount using satellites.

This is an enormous force, producing stress inside the rocks. These tensions are at some places released in relatively small and local earthquakes which break up the solid rock into boulders. This is why those caves are called neotectonic caves, neo means new, and the caves were formed during the last 8,000 years, which is very new for cave. And while the name actually includes any tectonic cave, which was formed by this young process, the great majority of the caves are Speleologytalus caves.

The finest example of a neotectonic cave is Torkulla Kyrka in the province of Östergötland. That this cave was formed after the last cold age is proven by small scratches from the ice (isräfflor) on top of the hill. So the whole hill was scraped by the rocks at the bottom of the glacier, the pattern is quite unique, like a fingerprint. It is possible to match this pattern from different rocks and so we know the relative location of the boulders during the cold age. As a result we know that the blocks were moved to form the cave after the ice was molten. Other fine examples in Sweden are Gillberga Gryte and Bodagrottorna.