During the late night, there was a large phreatic explosion near the northern shore of Lake Dellen in Sweden, long thought to be the result of an ancient meteor strike. Fortunately it was in an unpopulated area and no casualties have been reported. The eruption cloud rose to more than 12 km in height and it has forced a major rethink about the origin and immediate future of the Lake Dellen formation, says Professor Einar Pall Sigurdurson and Professor Bödvar Reynirson of the Institution of Geosciences at Uppsala University.
Because lamellar quartz similar to shocked quartz has been found in the area, it was assumed a meteorite strike was responsible for the formation of the 12 by 17 km structure. This ignored the substantial amounts of obsidian found on and near the resurgent dome dividing Lake Dellen into North and South Dellen.
Further indications that the structure is volcanic come from geothermal and gravity field surveys. It was found that the area had a very high temperature potential for geothermal exploitation. According to Professor Sigurdurson, the gravity data, which was originally thought to be proof of an impact structure, is really the signature of a very large body of magma. Unfortunately, there is no monitoring of the area and the quakes reported by locals since last autumn were too small to register at the Uppsala Institution. It would seem we have had a significant magmatic intrusion going on right under our nose, Professor Sigurdurson continues.
Yesterday’s phreatic explosion proves beyond the shadow of a doubt that the feature is volcanic and Professor Sigurdurson says it is most likely a caldera system, a supervolcano, that may be in the last stages before an eruption. The size of the body of magma is many times larger than that which caused the original caldera. The reason we have not known about it, Professor Sigurdurson continues, is that the many periods of glaciation and deglaciations over the past half a million years have effectively removed all the usual telltales of volcanic activity and basically left only granitic structures and even those heavily distorted by glacial erosion. Also, we had thought volcanism extinct (in Scandinavia) for at least 90 million years. But there are many factors that now make sense such as that the point of highest land rise known, 800 metres since deglaciation and currently 8 cm per year lies on the coast, not far from Lake Dellen according to Professor Sigurdurson.
In a press release, Professor Bödvar Reynirson, head of the Institution of Geosciences, says they will begin to monitor the area starting tomorrow. We will of course bring you any further news as soon as we can.
CARL & HENRIK
Source: Sture Erkell et al. “Lake Dellen, meteoritic origin in doubt.”, 2013 in Baltic Journal of Geology