Geology
Pangea and the danse of continents, from two billion year ago...
The Pangea is the name of a super continent that appeared around 335 million years ago from the coalescence of all continental units that existed long before it. In fact there were at least two other supercontinents before Pangea, Columbia (2 billion years ago) and Rodinia (1.1 billion years), which subsisted until 750 million years ago. But little is known of these supercontinents as compared to Pangea, except the fact that there were gigantic volcanoes that resulted in the high concedntration of metals that is found in northern and central (Bergslagen) Sweden including iron, zinc, copper, lead, silver and gold .
This period is therefore characterised by the "danse" of contnental units that alternated converging in supercontinents and diverging in separate continental units.
Baltica was one of these continental unit that existed before Pangea. It appeared after Rodinia broke-up in three pieces, 750 million years ago, Proto-Laurasia, the supercontinent of Proto-Gondwana, and the smaller Congo craton. Proto-Laurasia itself split apart to form the continents of Laurentia, Siberia and Baltica. But they all merged again for a short period in the Pannotia supercontinent around 540 million years ago and broke again in 3 continents, Laurentia, Baltica, and the southern supercontinent of Gondwana around 500 million years ago.
Origin of scandinavian mountains, from 400 million years
And the danse of continents continued, as they collided with each other for million of additional years. The formation of the Caledonian chain resulted in one of these collision, 400 million years ago, between Laurentia, which will become North America, and Baltica, which will become Scandinavia. The resulting Caledonian chain was probably much higher than the current Scandinavian mountains. Over the next millions of years, the Caledonaian chain got almost completely eroded, becoming a "peneplain" (a flat land resulting from erosion) explaining why the top of the Scandinavian mountains in Norway today tend to be flat and not rocky.
Pangea started to drift and break around 175 million years ago. The drifting of continents created rifts and new ocean, such as the Atlantic Ocean. Around 150 million years ago, Gondwana boke-up in many pieces, at the origin of Africa, South America, India, Antarctica, and Australia. Around 60 million years ago, Laurasia in turn split when North America/Greenland (also called Laurentia) broke free from Eurasia, opening the Norwegian Sea.
The last volcano eruption in Sweden took place 100 million year ago in Skåne.
Over the next million years, the continents will take gradually the place they have today on the surface of earth.
The Scandinavian mountains are the longest in Europe, spreading over 1700 km, from the south of Norway, through the north of Sweden and finland. Scientists are convinced that the current mountains in Noway date only 20 millions years ago, from an uplift of the flat and low "peneplain". At this stage, the tectonic plates started drifting away, therefore not generating any uplift as the one that resulted from their collision in the past. In the absence of collision, the theories are diverging quite a lot about what could have created the uplift at the origin of the Scandinavian alps as we know them:
- Some are thinking that the thining of the earth crust related to the drifting of plates resulted in the molten magma underneath pushing up the crust on the edge of the tectonic plates.
- Others are considering that the erosion of the top of the mountains resulted in the mountain moving-up in a way similar to an iceberg that would move up in water when the ice at his top melts. This is called isostasy, and it means that every time one kilometre of mountain is eroded, 800 meters will 'pop up' again from the "mountain root".
- Yet others are thinking that the mountains resulted from a folding of the earth crust related to the motion of continents.
Weichselian glaciation, 115,000-11,600 BP
Two and a half million years ago starts the quaternary period and the glaciation, resulting in the Fenno-Scandian ice sheet (inlandis) covering most Scandinavia. The thick glaciers above the uplifted"peneplain" will create the dramatic relief that is seen today in Norway, with relatively flat tops and very abrupt and deep fjords created by erosion. Seventeen periods of glaciation will occur, lasting 50,000 to 100,000 years each, separated by periods of 10,000 to 20,000 years. The alternance of these periods will result in important variations in the ocean water level. During the last glaciation, 18,000 years ago, the sea level was 120 metre lower than today.
Doggerland, 16,000-6,000 BP
With such low level of waters in the sea, the british islands, france, belgium, the Netherland, up to Denmark of today were all connected as a big land, Doggerland. The North sea was a glacier lake as was the Baltic sea! The Seine, Thames, Meuse, Scheldt and Rhine rivers were all merging and flowing together towards the west through what will become the Channel once the overflow of the North sea lake will open the way beween the north sea and the Atlantic.
Baltic Ice lake, 12,600-10,300 BP
The climate became warmer around 12,000 BC, the inlandis started to melt gradually, rising the level of the water in the lakes and oceans, while the land started to uplift as a result of the ice melting. The southern limit of the inlandis retracted to southern Sweden. The lake was higher than the sea level by 40 metres, and the sea level was significantly lower than it is today.
Yoldia sea, 10,300-9,500 BP
https://en.wikipedia.org/wiki/Yoldia_Sea
The resulting uplifting closed the drainage channel of the lake through Øresund. As a result the level of the lake continued to rise until around 11,200 when the overflow of the lake opened a passage around Billingen, pretty much along what is today the Göta Kanal. The resuting rapid decrease in lake water level was called the Billingen catastrophe, when the lake lost 25 metres of water in two years. Over the next 400 years, the lake will loose 55 metres in total!
Ancylus lake, 9,500-8,000 BP
https://en.wikipedia.org/wiki/Ancylus_Lake
At this point, a new glaciation took place with the glaciers spreading again southward and blocking again the Billingen overflow route. The Yoldia sea became a lake again, the Ancylus lake! After rising by another 25 metres, the overflow opened a new passage through the Øresund. But not long after the climate became warmer, opening again the Billigen overflow route, resulting in a 25 metre decrease in lake water level.
Mastogloia Sea, 8,000–7,500 BP
https://en.wikipedia.org/wiki/Mastogloia_Sea
At this stage, the water level in the lake had decreased at a time where the ocean water level had increased drammatically because of the ice melting, resulting for the first time in some reverse flow of salted water from the sea into the lake that would become the Mastogloia sea. The continuing rise of the sea level opened more widely the connexion between the lake and the sea. This stage is a transition between the Ancylus lake and the Littorina sea.
Littorina Sea, 7,500–4,000 BP
https://en.wikipedia.org/wiki/Littorina_Sea
The littorina sea is the phase when the Baltic sea will take pretty much the shape it has currently. I was more extended than nowadays, but this is in relation with the uplift of the land that started to take place significantly at this time when most of the inlandis had melted.
Storegga tsunami, 6,000 BC
https://en.wikipedia.org/wiki/Storegga_Slide
This is the time as weel when an earthquake probably related to the land uplift generated a mega tsunami trigerred by a underwater huge landslide off the coast of Norway, resulting in very high waves that ravaged the coast of Island, Feroe islands, Scotland, Great Britain and Denmark, and giving its final shape to the Channel. It probably resulted in lot of damages and human loss along the shores of what has once been the Doggerland.
References
- Baltic Ice Lake (12,600–10,300 BP)
- Yoldia Sea (10,300–9,500 BP)
- Ancylus Lake (9,500–8,000 BP)
- Mastogloia Sea (8,000–7,500 BP)
- Littorina Sea (7,500–4,000 BP)
- Modern Baltic Sea (4,000 BP–present)