In the footsteps of the fiery past of the Vogelsberg

Core drilling is to provide new information about the volcanic area

Core drilling in the High Vogelsberg southeast of the Hoherodskopfs. © HLUG
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To investigate the inner structure of the largest closed volcanic area in Central Europe, the Hessian State Office for the Environment and Geology (HLUG) is currently drilling a core hole in the High Vogelsberg southeast of the Hoherodskopf.

"Extensive investigations in the borehole, at the borehole cores and in the vicinity of the borehole in cooperation with various university institutes as well as the Institute for Geoscientific Joint Tasks in Hanover will substantially advance the knowledge about the volcanic area of ​​the Hohen Vogelsberg", emphasized the President of the HLUG. Thomas Schmid at the presentation of the project. The volcanic area was active 14 to 17 million years ago.

Among other things, the drilling serves to support the geological mapping of Bl. 5521 Gedern, which belongs to the HLG Geological Map of Hesse. The Gedern leaf is one of the last so-called "white leaves", that is an area that has never been geologically mapped on a scale of 1: 25, 000.

Remains of high-explosive volcanic eruptions

According to HLUG, the drilling begins in a volcanic sequence of rocks previously unknown in Vogelsberg. "These so-called trachytic tuff deposits are the product of high-explosive volcanic eruptions, which resulted in devastating glut avalanches (block and ash flows), " says the regional geologist for the Vogelsberg, HLUG. Dieter Nesbor the situation on site. Comparable processes have taken place in historical times up to the present worldwide again and again, for example on various Caribbean islands or in Japan.

Before the eruption at that time, a molten rock above the Vogelsberg rose from a magma chamber above the 700 ° Celsius to the earth's surface. This trachyte magma was extremely viscous due to its high silica content and formed a lava dome in the volcanic crater. By inflowing molten rock, this slowly filled up the crater and pushed over the edge of the crater until the overhanging parts broke off. display

Dangerous ember avalanches

Ember avalanches of hot ash and up to several cubic meters of glowing rocks flowed down the slopes of the volcano at speeds of over 100 kilometers per hour. They preferred to follow the course of valleys and fill them up - as here south of today's Hoherodskopfs.

Under the then subtropical climate, the ash content of the tuff deposits weathered to a light gray tone. Because of its impermeability, it acts as a water stagnant and is therefore of particular interest for the assessment of the hydrogeological conditions in this area - especially since the groundwater of the Vogelsberg makes an important contribution to both the regional and the supraregional water supply guaranteed.

(idw - Hessian State Office for Environment and Geology, 24.07.2007 - DLO)