Not even 13,000 years have passed since the last volcano spewed lava in Germany's mountainous Eifel region, devastating large parts of the landscape in the process. In the space of only a few days, enormous quantities of volcanic ash and pumice were hurled out, covering an area that extends as far as the Rhine valley with a layer up to seven metres thick. The finer deposits of the explosion can also be found in Sweden and Northern Italy as a thin tephra horizon.
The most visible remnant of this volcanic eruption is the Laacher See ("Laach Lake") near the city of Koblenz. Although, with its average diameter of 1600 metres, the lake is widely regarded as the largest maar (or tuff cone) in the Volcanic Eifel area, it is strictly speaking not a maar and not even a real crater lake, but rather a water-filled caldera - a crater type that arises through the collapse of the volcanic structure after the magma chamber below the volcanic cone has been emptied.
From the geological standpoint, the Eifel is still volcanically active, a fact which is noticeable through the multitude of microquakes in this region. Reputed volcanologists believe there is a high probability of eruptions occurring here again. But when? In a few years? Or only after many centuries? With a view to clarifying this question, scientists have repeatedly called for the installation of a system for monitoring the geological processes, but such a project has not yet been implemented, for reasons of cost.
To investigate the usefulness of autonomous underwater vehicles for geological examinations, a two-day exploration of the Laacher See was conducted at the end of April in cooperation with the University of Duisburg-Essen. The goal of the mission was to find zones in the lake from which carbon dioxide is bubbling up from the bottom. Owing to the great depth of the water - as much as 56 metres - the gas bubbles do not reach the surface of the lake, because they are go into solution during the ascent. As a result, the extent of volcanic activity below the sea is not known with any accuracy.
The underwater vehicle of the type "SeaWolf" used for this purpose is a diving robot, about two metres in length, that is able to carry out its mission fully automatically, i.e. without needing a connection to the outside world. The vehicle moves at a distance of about five metres above the bottom of the lake, using sonar equipment to map the bottom surfaces laterally to the left and right.
This task was completed in only a few hours, yielding data recordings that impressed the experts. In addition to charting the gas discharge points, the sonar images revealed crater-shaped structures that had been entirely unknown thus far. On the strength of these initial recordings, a more intensive examination of the caldera's topology is planned for next year.