The High Coast was chosen as a World Heritage area because of the geologically rapid uplifting of the land since the last ice age. When the most recent ice sheet covered the area, it was approximately 3 kilometres thick and the High Coast was its centre. The ice was incredibly thick and pushed down earth's crust. When the ice began melting about 20 000 years ago, the land began to rebound. The rebound has been the greatest where the crust was pushed down the most. Nowhere else in the world has the total land uplift been as great as the High Coast. At most, the crust was 800 metres lower than it is today. Since the ice melted and the sea began forming the coast, the land has risen 286 metres above the sea and continues to rise today. Currently, the land is rising at 8 millimetres a year.
Till-capped hilltops, shingle fields, caves and former bays that have now been cut off from the sea are the clearest evidence of the rising land. The capped tops are made up of moraines that the sea did not wash away because they were above the highest shoreline. One of the unique features of the High Coast is that the highest shoreline is so close to the current shoreline. Sometimes just a few kilometres separate them.
As the land rose, the layers of soil and rock along the beaches were exposed to the relentless force of the sea. In steep areas, the bedrock is washed bare as the fine-grained material was washed out to sea. The coarse and heavy material was carried only short distances or remained unmoved. The rocks rolled against each other, polishing away rough edges and leaving what we see today as shingle fields. The area has many types of rocks since glaciers carried many rocks long distances from far inland. The range of rocks along with the green of the lichen makes the shingle fields a kaleidoscopic of colours. You'll find the world's highest shingle fields on Högklinten and at Norrfällsviken where the process of forming rubble continues. Locals refer to the shingle fields as the Devil's fields.
The ongoing land uplift means that new land is constantly being exposed to erosion by the sea's waves. In particularly exposed areas, the water has carved out caves in more brittle rock along slopes. Caves are found along the entire High Coast. Several excellent examples are found on northern Ulvön, Högbonden and on Mjältön at an elevation of 105 metres. These caves were formed quickly; some caves were formed in as little time as 500 years.
Throughout the period after the ice age sheet melted, the sea has become shallower. Often the entrances to bays have been closed as the land rose to form lakes. These in turn have sometimes evolved into wetlands. Many lakes still have small prawns that would normally be found in the sea.