Fire avalanche
A glowing avalanche is a variant of the pyroclastic flow that rushes down the volcanic slopes at 300–1000 km / h and temperatures of 350 to 1000 ° C and can spread for kilometers. It is caused by a phreatomagmatic eruption in which large amounts of cap rock and magma / lava are ejected, often at the expense of the entire summit ( St. Helens , Tambora ).
The eruption column heats the surrounding air and rises with it as a turbulent gas mixture and convection current for kilometers into the atmosphere. This column is also known as the Plinian column after Pliny the Elder. J. named who was the first (during the eruption of Vesuvius in August 79) to share this phenomenon with those about Herculaneum and Pompeiidescribed falling glowing avalanches. After the convection has broken off as a result of cooling and thus the lack of the necessary energy for further heating of the ambient air, the column collapses (collapse) and falls at high speed onto the volcanic flanks. The resulting glowing avalanches from overheated particle-gas aerosol now rush down the volcanic slopes for kilometers (depending on temperature) into the surroundings of the volcano (also over hills). It is assumed that they glide with extremely low friction on the cool air of the ground, like on an air cushion . What remains is a burned lane and, depending on the particle content , a meter-high, loose and fertile layer of sediment . Any life within the avalanche path rarely has a chance of survival.
Similar are the glowing clouds ( Montagne Pelée , Mount St. Helens ) caused by lateral volcanic flank eruptions , which also speed down to the valley as an avalanche. Despite the u. Depending on the composition of ground lava rock, ashes and gases, both phenomena with the classic lava dome collapse are often referred to as variants or scenarios of the pyroclastic flow .
literature
- Jacques-Marie Bardintzeff: Vulcanology . Enke-Verlag, Stuttgart, 1999; Elzevier, Munich, 2007; ISBN 3-8274-1221-8
- Barbara & Robert Decker: Volcanoes - Image of the Earth's Dynamics. Spektrum Akademischer Verlag, Heidelberg, 1992, 1998; ISBN 3-8602-5020-5
- Hans-Ulrich Schmincke: Vulcanism . Scientific Book Society, Darmstadt 1986, 2000; ISBN 3-534-14102-4
