Vättern is a lake in southern Sweden that is long, narrow and deep. It lies between the counties of Västergötland and Östergötland. It borders Närke to the north and Småland to the south. Vättern is Sweden’s second largest lake, both in area (1 893 km²) and volume (77.6 km³), and is the sixth largest inland lake in Europe. The water level is 88.5 m above sea level and drains through the Motala stream into the Baltic Sea. Vättern is connected to Lake Vänern and the Baltic Sea by the Göta Canal. Geologically, the lake is located in a wrinkle area that was formed 650 million years ago.
Geology
The geological history of Lake Vättern begins with the geological processes that caused the break-up of the supercontinent Rodinia about a billion years ago. At that time, all the continents clustered mainly in the southern hemisphere. The Baltic Sea (Sweden, Finland, western Russia) collided with the Amazon crater (Venezuela) to form high mountain ranges in southwestern Sweden and southern Norway and northern Venezuela. The Taberg south of Vättern was formed at this time. Erosion of the surrounding mountain ranges produced the sediments known as the Visingsogroup, a group of sedimentary rocks formed by the products of weathering caused by erosion. A series of continental sandstones over 1 000 metres thick formed first, followed by marine sediments (argillaceous and limestones with stromatolites). These sediments are found in both Sweden and Venezuela.
The formation of the lake
650 million years ago, the Baltic Crater broke away from Rodinia and formed the Vättern Graben. During this event, the sediments of the Visingsögroup were submerged and preserved by this fault. The spread between the bottom of Lake Vättern and the surrounding fault uplands is now up to 330 metres. From the bottom to the mountain bedrock there are another 300 metres of thick sediment layers. The difference in height between the highest and lowest bedrock in the Vättern basin is therefore more than 600 metres, despite 650 million years of erosion. Similar differences in bedrock are otherwise only found in high mountain areas.
After a land-based period in southern Sweden (Vendium), when erosion created flat surfaces (Västgöta, Östgöta and Närkeslättern), the sea intruded at the beginning of the Cambrian 550 million years ago, now with all animal groups present (the so-called Cambrian explosion), including vertebrate ancestors. Then, over the course of 150 million years, approximately 200 m thick layers of Cambrosilurian-rich fossils, including trilobites, were deposited.
Today, these layers are preserved, for example at Motala. Scandinavia then collided again about 400 million years ago. This time with Greenland and the result was the Scandinavian mountain chain (the Caledonides). In connection with this, the rest of Sweden was once again raised above sea level. For the next 350 million years up to the present day, the Baltic Sea has always been above sea level, except for southern Sweden. Which has occasionally been underwater. Before and during the Mesozoic Era. Large rivers flowed through the Vättern Drift into the extensive delta areas in Skåne and southern Småland.
