Seyed Mohsen Mortazavi
Abstract
Damavand is a stratovolcano and has power full explosive eruptions during its activity. Pyroclastic products in Damavand volcano has been mostly deposited as pyroclastic fall and flow deposits. Pyroclastic fall deposits in some locality extending up to 20 km from the summit. Damavand pyroclastic deposits ...
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Damavand is a stratovolcano and has power full explosive eruptions during its activity. Pyroclastic products in Damavand volcano has been mostly deposited as pyroclastic fall and flow deposits. Pyroclastic fall deposits in some locality extending up to 20 km from the summit. Damavand pyroclastic deposits cover much of the eastern and southern flanks of the volcano suggested that during the eruption, tephra dispersal axes was toward to the east. There are a major young pumice deposits, named as Karam Poshteh pumices, are identified and consists of a coarse-grained pumice fall deposit with proximal welded facies dispersed to the west, but lacks pyroclastic flow deposits with provisional ages in the interval >7.3 ka and < 25 ka.This young pumice fall deposit is distributed over much of the western and south-western flanks and is located at the foot of the steep Damavand cone at the mouth of a ravine where the proximal welded facies is well exposed on the ravine walls. The deposit can be divided into thin more distal unconsolidated pumice fall deposits and think proximal welded pumice fall deposits. Karam poshteh deposits also consist of welded beds of pale pink pumice with minor cross-layered ash beds. Atmospheric information, in particular wind data, is crucial in order to perform tephra dispersal simulations. Tephra transport and sedimentation is controlled by wind in the atmosphere and is a function of wind velocity and provenance for tropospheric and stratospheric levels. Mehrabad meteorological station is supplied wind data at different altitudes. We apply and intemperate wind data between 1995 to 2010 at Damavand volcano to understand regional distribution of tephra fall. Westerly winds are persistent during winter and summer time at troposphere. The most prominent features in the stratospheric circulation are a westerly jet in the winter hemisphere and low velocity easterly jet in the summer hemisphere. Easterly jet in the summer implies that Westward transport of tephra in Karam poshteh.
