A journey through time in the tracks of the land uplift
The High Coast and the Kvarken Archipelago are the best places on earth to make a journey through time in the tracks of the post-glacial rebound.
The land has been depressed by ice several times but it rebounds after every ice age. The clearest evidence of land uplift can be seen right here at the World Heritage site – and it’s still in progress.
A world under ice
It was during this period that the extent of the inland ice was at its peak. The ice sheet was at its thickest right over the High Coast – a massive 3 km thick! The heavy, thick ice depressed the earth’s crust by 1,000 meters.
Eventually the climate became warmer and the inland ice began to melt. It then began receding towards the north and northwest. As the ice melted, it relieved the pressure on the land, which began to rise rapidly at first, up to 10 cm a year. Nowadays the rate of land uplift is 8 mm a year.
10,000 years ago
10,000 years ago, the inland ice had receded so far that the High Coast was completely free of ice and much of what is now land was just sea and a few islands back then.
The ice melts
The ice was at its highest and thickest 20,000 years ago. 10,000 years ago, the High Coast
had emerged from the ice sheet. But almost everything was under water.
The Highest Coastline
About 10,000 years ago, the highest mountain tops stuck out of the sea as small islands and skerries. The waves scoured the mountain sides bare. The boundary between these bare, flat rocks and the forest-covered tops is what we now call the Highest Coastline.
Large hills with tops that were never submerged under the sea after the inland ice had receded are known as “calot hills” in Swedish. This is because when these hills were islands, the moraine on the top of the hills was not washed away by the sea and formed a cap, or calot. Because this was material in which trees could grow, the moraine caps are now covered in forest.
Shingle is small boulders and stones that have been washed out of the soil by the waves and deposited in one spot. The movement of the waves has caused them to grind together, which gives them their round shape. The shingle fields comprise a wide variety of rock types because many of the stones were carried a long way by the ice. Shingle fields are sometimes referred to as prehistoric beaches because they were previously located at sea level, but the land uplift has moved them a long way from the current waterline.
The highest concentration of tunnel caves in Sweden can be found along the High Coast The tunnel-shaped caves were originally cracks in the rock and normally take about 1,000 years to develop. When the land uplift lifted the cracks to shoreline level, they began to be eroded by the sea and the waves. Stones and boulders were carried back and forth into the crack by the force of the waves and eventually a cave was formed. They are sometimes known as onion caves due to their characteristic onion-like shape.
As land slowly rises out of the sea, bays become cut off and gradually develop into lakes. Today you can find evidence that a lake used to be a bay because the lake can contain species that are left over from the time when it was connected to the Gulf of Bothnia. For example, marine crustaceans can still be found in some larger lakes in the High Coast such as Skulesjön and Vågsfjärden.
Shells from dead gastropods, mussels and barnacles can be found in every sea, mixed with sand and gravel on the seabed. They are carried with the currents to calm bays, where banks of shell gravel form. Due to the dramatic land uplift on the High Coast, the shell gravel banks have been moved a long way inland, far from the existing seashore. Because the shells contain a large proportion of lime, some plants such as kidneywort (Anemone hepatica) and orchids flourish in the shell gravel banks. Look carefully on the ground and you’ll spot the seashells!
Ever since the Stone Age, people have left their mark along the High Coast. The land that has emerged from the sea has gradually been colonised, which is why there are traces of human activity such as settlements, fishing villages and routes from different ages at different elevations in the landscape. This is what distinguishes the High Coast from most other areas, where remains and traces are preserved on top of one another.
The first inhabitants along the High Coast subsisted by seal hunting and fishing. Seal hunting continued up until the 19th century and fishing was the most important industry until the 1950s.
Fishing sheds and fishing villages are traces of this important source of nutrition. There are cultural remains of a slightly different kind below sea level: wrecked ships have been preserved on the sea bottom due to the lack of shipworms.