The development of the landscape
A brief description of the development of the landscape in Ragunda
The formation of the 1 900 million year-old bedrock
Some 2 billion years ago a sea covered most of what we now call Northern Sweden. For many hundred millions of years, large quantities of sediment were deposited on the bottom of the sea. The material was abraded into gravel, sand and mud which were carried by rivers and the wind into the sea.
On the bottom of the sea thick layers of sediment were formed. As the layers of sediment grew thicker, they were compressed through their sheer weight, and eventually the sediments transformed into rock. The remains of the old sea and its sediment have formed the bedrock nowadays covering most of mid-Sweden. For example, you can see it at Döda fallet.
Melted rock mass formed the 1 500 million years old magma chambers
1 500 million years ago a weak zone appeared, reaching from the present southern Finland in the east, westwards through Ragunda and onwards towards the mountain range of today. In this region, the outmost layer of Earth, the crust was stretched and thinning.
The pressure on the underlying rock and melted rock mass, magma, was reduced. The reduced pressure enabled two kinds of magmas, formed in the innermost Earth, to push upwards through the older bedrock aiming for the surface of earth, rather like bubbles when you open a bottle of sparkling water.
When the magmas failed to rise any higher towards the surface they remained at a depth of about three kilometres. There they formed several magma chambers, a bit like enormous balloons. The magma chambers raised the crust of the earth to form rounded shapes.
When in due course the magmas cooled and became solid they formed rocks. One of the magmas was dark, almost black and became gabbro, while the other one was red and became granite.
Younger rocks pushed upwards in cracks and rifts after the rock had cooled
The youngest rocks in Ragunda pushed upwards in cracks and rifts in the cool crust at a later stage. In order to date these, more thorough investigations must be carried out.
One of the younger kinds of rock is porphyry. The porphyry stems from the same magma chamber as the other kinds of rock in Ragunda but was formed at a later stage, when the crust had cooled and cracked. Magma of porphyry could then push upwards through the cracks in the rock and solidify relatively quickly.
The wind, water and ice eroded the rock surface
Following these processes came a period of some 600-700 million years without any significant changes in the area. During the period the rock was abraded, i. e. worn down by erosion. The loose material was carried off by the wind, water and ice and eventually a more or less flat rock surface had been formed, a peneplain.
Crevices crumbled away and became deep valleys
Some 200-100 million years ago, Sweden was part of the supercontinent Pangea. Our country was positioned in more southerly latitude and was covered by desert. The dry and warm climate enabled crevices to crumble away, affecting the flat rock surface.
The crumbling hollowed out the cracks and crevices and through erosion the material was carried off. The most easily carved out parts of the peneplain became valleys while the more resilient parts were preserved as hills.
In our days, the peneplain constitutes the tops of the hills. You can see it from Kullstabergets utsiktsplats and Böle-Hoo utsiktsplats.
Water from the melting ice carried off lighter material
The landscape we look at nowadays was mainly formed by and in the ice ages over the past 2.6 million years, and especially during the most recent called the Weichselian, and the second most recent, Saalian, that have impacted the landscape.
20 000 years ago, during the Weichselian, a sheet of ice several kilometres thick – the Inland Ice - covered all of Sweden. From then on the ice started to melt and diminish in size. To start with, the melting was slow but gradually the process quickened. Geologists are not entirely certain but Ragunda was probably free from ice some 10 000 years ago.
At the time when the ice was melting the most, enormous quantities of water rushed through the landscape. The melting water carried away lighter material such as sand and gravel and wore down the rocks. What remained was clean-washed, rounded large slabs and boulders that the water was unable to carry off.
At Nornan you can see giant boulders left by the masses of water and at Getgrottan you can see other boulders probably carried there by ice during one of the ice ages.
Melting water formed new land
When the rushing water slowed down and no longer was able to carry that much material the sand and gravel sank and was deposited on the bottom to form ridges and large areas of sand. Some examples of these land areas are found at Getryggen and Döviken – Zorbcenter.
Blocks of ice formed kettle holes and kettle lakes
In the area around Getryggen can also demonstrate kettle holes and kettle lakes. Kettle lakes are water-filled kettle holes; they were formed when ice blocks came loose and were embedded in the material that the melting ice had left behind. When the ice blocks melted, holes - kettles - were formed of the same size as the ice blocks had been. A kettle hole can also be studied at Fors skogskyrkogård.
The land uplift uncovers land areas
As the most recent inland ice disappeared from Ragunda the melting water carried along large quantities of fine material. The material was deposited in the valley of the River Indalsälven, at that time a bay in the Baltic Sea.
The heavy ice pressed down the earth’s crust as much as 1 000 metres. As the climate grew milder and the ice melted the pressure on the crust was lessened and the land started rising anew. In our days the land uplift is almost one centimetre per year.
Because of the land uplift it is nowadays possible to find the material deposited in the valleys as well as far up on the hills, like at Ammerån Våle.
Flowing water continues to alter the landscape
Ever since the ice melted the flowing water has continued to alter the landscape in the process of bringing, wearing down and transporting materials such as sand, gravel and mud. New land has been formed and continues to be formed with the material deposited. An example of this are the sandbanks found in the River Ammerån .
Whirling water with sand, gravel and stones formed giant caves
In the dry riverbed in Döda fallet are giant holes in the bedrock, some of them quite deep and others shallow. The giant caves were formed when water flowing for thousands of years undermined the bedrock. Small stones, gravel and sand whirled with the water for a long time and carved out the holes in the rock. At the same time the surface of the giant cave was polished smooth. In some of the caves lies a smooth, oval stone, called a runner stone.
Natural disaster caused by man
The emptying of Lake Ragundasjön is one of the worst natural disasters in Swedish history caused by a man. On 6 June 1796 Magnus Huss, “Vildhussen”, was attempting to redirect the water past the 30-metre high waterfall Storforsen. Things did not go according to his plans and Lake Ragundasjön upstream from the waterfall was emptied in only a few hours. What remained was a dead waterfall, Döda fallet, together with the nearly 800 metres long dry riverbed, a canyon.
