Evolution and environmental impacts of the eruption of Laacher See Volcano(Germany) 12,900 a BP

Laacher See Volcano (LSV), 40 km south of Bonn, explosively erupted ca. 6.3 km(3) of chemically strongly zoned phonolite magma probably during spring, 12,900 years ago, the resulting eruption column having reached at least 20 km in height. The bulk of the Laacher See Tephra (LST) was deposited east of the volcano within the Neuwied Basin. LST ashes form the most important stratigraphic marker in Lateglacial deposits over much of Central Europe. A minimum of 2 Mt total S was calculated to have been released during the er uption by comparing pre- and posteruptive volatile concentrations in glass inclusions and pumice matrix glasses. Because a separate S-bearing vapor ph ase was probably present in the magma prior to eruption as indicated by the high melt-H2O contents close to saturation level, the actual amount of S r eleased during the eruption, could have significantly exceeded 2 Mt. The su lfuric acid aerosol layer resulting from the massive stratospheric S-input probably resided in the stratosphere for years and most likely had a signif icant impact on climate and thus the environment. Increased precipitation i n central Europe and/or impairment of the vegetation cover for several year s is suggested by several. proxies, especially increased sediment supply in to lakes. Proximal to the eruptive center, major environmental impacts incl ude an initial blast that felled trees up to 4 km away from vent. Fast depo sition of huge tephra volumes led to the complete disruption of Rhine River within the lower Neuwied Basin and the damming up of a lake ca. 140 km(2) in areal extent. Sudden collapse of the temporary tephra dam caused a catas trophic flood wave downstream whose deposits are recognized as far north as Bonn. Reworking of unconsolidated tephra deposits over several 100 km(2) w as widespread and extensive, generating abundant lahars and flood plain dep osits. A braided-river system, established in Neuwied Basin, probably persi sted up to several years. Recent reports for a second eruption of LSV are n ot confirmed. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.