Press release: Magmatic system may still be active

Nr. 165/2010 - 23.08.2010

Göttingen geochemists investigate young volcanic rock – magmatic system may still be active

Indications of imminent volcanic eruptions can usually be picked up over a period of weeks, or sometimes months, prior to the event. But up to now the question of how long molten rock, known as magma, accumulates in the earth’s interior before an eruption takes place has been subject to little research. Together with scientists from the University of California in Los Angeles, geochemists working at the University of Göttingen have now examined the pre-eruption crystallisation history of the magma at the Laacher See (Lake Laach) volcano in the Eifel region. Isotope-geochemical analysis demonstrates that the eruption 13,000 years ago had a long prehistory: the first signs of a magma accumulation date back 17,000 years prior to the outbreak, and 4,000 years before the eruption the subterranean magma chamber again expanded in size. The team of scientists suspects that the very long-lasting magmatic system is still active today. Results of the investigations have been published in the international journals Journal of Petrology and American Mineralogist.

The Eifel is one of the most recently active volcanic areas in central Europe; it is also considered by volcanic experts to be one of the world’s most fully researched. The key data concerning origin of the magma, sequence of events during the eruption and volume of magma ejected are well known. “In order to be able to warn of volcanic eruptions and assess the effectiveness of geophysical methods for magma depth sounding, it is important to know how long the magma was present in the volcanic subsurface. But up to now, little information has been available on the history of the partial solidification of molten rock through crystallisation prior to the eruption”, explains Professor Dr. Gerhard Wörner of Göttingen University’s Centre of Geosciences in the Department of Geochemistry.

In a project funded by the German Research Foundation, the team of German and American scientists has now pieced together the prehistory of the magma at Laacher See. Adopting a novel approach to dating crystals that formed before the eruption took place, they looked for the minerals zircon and pyrochlore in certain types of fragments from the border of the Lake Laach magma chamber. Due to their high uranium and thorium content, the crystallisation age of these minerals can be determined with particular precision.

This enables the scientists to trace the long prehistory of the Laacher See magma chamber. “As many as 30,000 years ago, molten rock collected at a shallow depth. An especially large proportion of the minerals analysed display an age of 17,000 years”, Professor Wörner points out. He sees this as indicating that the first signs of the magma chamber are already 30,000 years old and that it increased substantially in size some 4,000 years in advance of the volcanic eruption.

Currently, one can only speculate why, after thousands of years of crystallisation at shallow depth, the magma erupted 12,900 years ago. Tectonic tensions in the earth’s crust, excess pressure in the chamber as a result of an accumulation of volcanic gases, or a further magma thrust from the earth’s mantle are possible explanations. “Our analyses have shown that the development of the Laacher See magma chamber continued over a period at least twice as long as that which has elapsed since the first eruption. This proves the longevity of the magma system under scrutiny and suggests that the system remains active. Renewed activity of the Laacher See volcano in the course of the coming thousand years is certainly not to be ruled out; in fact it is highly likely”, says Professor Wörner.