Land uplift phenomenon
Our World Heritage rises still from the sea because of the latest Ice Age. When the three kilometres thick inland ice of the Ice Age covered the World Heritage Site, it pressed the Earth’s crust down about one kilometre. When the ice melted slowly away, it released the pressure, and the land started rising towards its original position. This phenomenon is called postglacial land uplift, and it occurs everywhere in the area, also beneath the water surface. The land uplift was extremely fast at first and the Earth’s crust had already risen 500 metres in the High Coast when the inland ice had melted.
Speed of the land uplift
The land continues to rise nowadays with a speed of about 8-9 millimetres per year in the World Heritage area. The speed is fast enough to see the changes in the landscape in a few decades. The elderly locals remember where the popular swimming spot used to be, but water is not deep enough anymore, and vegetation has started to cover the shore.
Can land sink too?
The land can also be sinking in the areas that were outside the ice edge during the Ice Age, like in the Netherlands and northern Atlantic. There the land is now sinking, because during the Ice Age the land rose up instead of being pressed down by the inland ice. When the enormously heavy inland ice pressed down the Earth’s crust, large quantities of magma retreated and lifted the crust up outside the ice edge. Because of this, the Netherlands sinks by one millimetre each year, while the seabed in the northern Atlantic off the Norwegian coast sinks by five millimetres a year.
The world’s highest coastline
When the inland ice melted 10,500 years ago, there were only small islands emerging above sea level in the High Coast. The first shoreline of these islands is nowadays the World’s highest coastline, which the land uplift raised as much as 286 metres above sea level. The islands are now also the tops of the highest hills in the High Coast.
The tops of the hills have a cap of forest that grows in the till transported by the inland ice, and that is why the hills are called till-capped hills. Only a few pines and shrubs can grow on the steep hillsides because there is not enough suitable soil to grow on. Waves washed away the finer materials when the hillsides were under the sea. The finer soil ended up lower down on the seabed, which nowadays is the green valleys between the hills.
The border between the forest at the top and bare hillsides is still easy to see in nature today, 10 500 years later. This border on Skuleberget mountain marks the highest coastline of the world.
The highest measured land uplift in the world
The world’s highest coastline is also a great indicator for the World Heritage Site’s land uplift record, which is the highest measured land uplift above sea level. The record differentiates the site from other parts of the world where the land rises.
The low-lying Kvarken archipelago
The Kvarken archipelago is also affected by the land uplift phenomenon, although the landscape does not meet the heights of the High Coast. The land has been rising in the Kvarken Archipelago as much as in the High Coast since the melting of the inland ice. Still, the highest points of the low-lying Kvarken Archipelago are only 20 metres above sea level. Read here more about why the Kvarken Archipelago is so low and the High Coast so high.
Since the Kvarken Archipelago is so low-lying and shallow, new land becomes apparent just in a matter of decades. Researchers have calculated that the World Heritage area in the Kvarken archipelago gets about one square kilometre more land each year to its shorelines. Boaters need to be careful, because the land uplift and countless stones make the boat passages shallower and more treacherous over time.
Cobble fields in the World Heritage Area
The inland ice, waves and sea ice have created cobble fields, which are rough-looking beaches covered with rocks. Cobble fields are made of the unsorted soil material called till, which the inland ice ground and transported over the area. As the land uplift elevated the till to sea surface, waves washed away finer materials. Remaining stones ended up on shallow shores. Storms and sea ice rolled the stones against each other, which made them rounder. Finally, there was a cobble field with round and almost same sized stones.
Due to land uplift, you can find cobble fields also on dry land. New cobble fields can form to exposed beaches. The World’s highest cobble field is in the High Coast, and it is about 260 metres above sea level. In In Finland these cobble fields are called ‘devil’s fields’, since they were unsuitable for cultivation and obviously made by an evil spirit.
Sometimes the stones can look a bit like massive stairs, which climb up the beach. The stair-like formations are called beach ridges, and you can find them on rocky, sand or gravel beaches. Beach ridges start to form when storms and sea ice compress soil material into ridges. Then the land uplift lifts the ridges up the beach, above the reach of the waves. Over time, several beach ridges form, each telling the location of the shoreline back in time.
Due to land uplift, you can find cobble fields also on dry land. New cobble fields can form to exposed beaches. In Finland these cobble fields are called ‘devil’s fields’, since they were unsuitable for cultivation and obviously made by an evil spirit.
Onion-shaped tunnel caves
Tunnel caves are a special feature in the High Coast scenery, and they are shaped by the forces of the sea. Tunnel caves start as a crack in a steep cliff which is below water surface. Waves erode the crack so that it becomes wider. Then the land uplift gradually raises the cliff so that new parts of the crack are eroded. Waves move stones and boulders back and forth in the crack, and eventually carve out a cave with smooth walls. Tunnel caves are narrowest at the top and widest at the bottom, just like onions. That is why tunnel caves are also called onion caves. There are only about 60 tunnel caves in the World, and half of them are in the High Coast.
Where did the water go?
Researchers have not always known why the land rises. From the 17th century almost to the 19th, the prevailing theory on both sides of the Bothnian Sea was the disappearance of the water, wattuminskningen. There were many explanations for the disappearance of the water, for example a hole in the bottom of the sea or the erosion of the straits in the Baltic sea. The land uplift was suggested already in the 18th century, but that explanation became more popular in the 19th century when the researchers discovered the connection to the Ice Age.
Next chapter: ever-changing nature
The rising land and the geology of this site affect the nature and offer both opportunities and challenges for the flora and fauna.
What is the nature like here?