Laacher See

Laacher See (), also known as Lake Laach or Laach Lake, is a volcanic caldera lake with a diameter of in Rhineland-Palatinate, Germany, about northwest of Koblenz and south of Bonn, and is closest to the town of Andernach situated to the east on the river Rhine. It is in the Eifel mountain range, and is part of the East Eifel volcanic field within the larger Volcanic Eifel. The lake was formed by a Plinian eruption approximately 12,900 years BP with a Volcanic Explosivity Index (VEI) of 6, on the same scale as the Pinatubo eruption of 1991.
Description.
The lake is oval in shape and surrounded by high banks. The lava was quarried for millstones from the Roman period until the introduction of iron rollers for grinding grain.
On the western side lies the Benedictine Maria Laach Abbey (""), founded in 1093 by Henry II of Laach of the House of Luxembourg, first Count Palatine of the Rhine, who had his castle opposite to the monastery above the eastern lakeside.
The lake has no natural outlet but is drained by a tunnel dug before 1170 and rebuilt several times since. It is named for Fulbert, abbot of the monastery from 1152–1177, who is believed to have built it.
The eruption.
Volcanism in Germany can be traced back for millions of years, due to the collision between the African and Eurasian plates, but it has been concentrated in bursts associated with the loading and unloading of ice during glacial advances and retreats. 
The initial blasts of Laacher See, which took place in late spring or early summer, flattened trees up to four kilometres away. The magma opened a route to the surface that erupted for about ten hours, with the plume probably reaching a height of 35 kilometres. Activity continued for several weeks or months, producing pyroclastic currents that covered valleys up to ten kilometres away with sticky tephra. Near the crater deposits reach over fifty metres in thickness, and even five kilometres away they are still ten metres thick. All plants and animals for a distance of about sixty kilometres to the northeast and forty kilometres to the southeast must have been exterminated. 
An estimated of magma erupted, producing around of tephra. This 'huge' Plinian eruption thus had a Volcanic Explosivity Index (VEI) of 6.
Tephra deposits from the eruption dammed the Rhine, creating a lake. When the dam broke, an outburst flood swept downstream, leaving deposits as far away as Bonn. The fallout has been identified in an area of more than 300,000 square kilometres, stretching from central France to northern Italy and from southern Sweden to Poland, making it an invaluable tool for chronological correlation of archaeological and palaeoenvironmental layers across the area.
Aftermath of the eruption.
The wider effects of the eruption were limited, amounting to several years of cold summers and up to two decades of environmental disruption in Germany. However, the lives of the local population, known as the Federmesser culture, were disrupted. Before the eruption, they were a sparsely distributed people who subsisted by foraging and hunting, using both spears and bows and arrows. According to archaeologist Felix Riede, after the eruption the area most affected by the fallout, the Thuringian Basin occupied by the Federmesser, appears to have been largely depopulated, whereas populations in southwest Germany and France increased. Two new cultures, the Bromme of southern Scandinavia and the Perstunian of northeast Europe emerged. These cultures had a lower level of toolmaking skills than the Federmesser, particularly the Bromme who appear to have lost the bow and arrow technology. In Riede's view the decline was a result from the disruption caused by the Laacher See volcano.