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Laacher See - The bubbling volcanic Lake |
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 Situated 40 km south of Bonn, LaacherSee is the largest lake and the most famous volcanic formation in the Eifel massif. Its is 2.5 km in diameter and 270 m deep, and lies in the midst of a swarm of tephritic and basanitic cinder cones that rise from a plateau blanketed with thick layers of white pumice (Schmincke& Mertens 1979). Laacher See seems to be a complex ash flow caldera formed by tectonic foundering. There is no doubt about the explosions. About 11 000 years ago, in the space of perhaps little more than a week, and almost certainly less than a year, Laacher See was the site of a Plonian eruptions of over 16 km of fragments and flows of phonolitic ash and pumice that are still over 50 m thick near the vent. The debris covers many adjacent cinder cones and forms a clear indicator bed in deposits far beyond the confines of the region (Bogaard & Schmincke1984, 1985). The eruptions were generated by a phonolitic magma in a reservoir situated between 3 km and 6 km below the surface, which had probably evolved from an original basanitic magma that had already erupted the surrounding swarm of cinder cones about 270 000 years ago.
 The
most differentiated, highly alkaline and gas- rich phonolites from the
uppermost parts of the reservoir were ejected first, followed by less
differentiated crystal- rich phonlites, at temperatures between 800°C,
as the eruptions concluded. The eruption may have been precipitated a
few hours after fresh basanitic magma invaded the reservoir, although
it is possible, on the other hand, that the new magma arose only when
the old had been ejected from the reservoir (Wörner & Wright 1984).
The eruptions proceeded at a very rapid pace and most of them had
marked hydro volcanic components. The Plinian columns of pnonlitic
fragments soon superseded the breccias expelled during the initial vent
clearing. The wind winnowed pumice from the columns and spread it
widely, and nuées ardentes surged outwards whenever the columns
collapsed (Fisher et al. 1983, Schumacher & Schmincke 1990). The
nuées ardentes rushed between the cinder cones and swamped the valleys
with as much as 10 m of pumice for up to 3 km better- sorted pumice
that reached as far a field as Stockholm, Berlin and Turin (Bogard
& Schmincke 1984, 1985). This eruption brought the activity of the
East Eifel area to a spectacular, but perhaps temporary, invaded the
magma reservoir about 11 000 years ago, and fumaroles are still present
a Alte Burg, the Laacher See volcano should not be considered extinct.
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