Fragmentation of basaltic melt in the course of explosive volcanism

Abstract

Abstract. With the aim to enhance interpretation of fragmentation mechanisms during explosive volcanism from size and shape characteristics of pyrodasts experimental studies have been conducted using remelted volcanic rock (olivine-melilitite). The melt was fragmented and ejected from a crucible by the controlled release of pressurized air volumes (method 1) or by controlled generation of phreatomagmatic explosions (Molten Fuel Coolant Interaction (MFCI); method 2). Both methods were adjusted so that the ejection history of the melt was identical in both cases. The experiments demonstrate that exclusively during MFCI, angular particles in the grain size interval 32 to 130 ptm are generated that show surface textures dominated by cracks and pitting. The physical process of their generation is described as a brittle process acting at cooling rates of > 106 K/s, at stress rates well above 3 GPa/m 2, and during ~700 pts. In this time period the emission of intense shock waves in the megahertz range was detected, releasing kinetic energy of > 1000 J. By both experimental methods, three more types of particles were produced in addition, which could be identified and related to the acceleration and ejection history of the melt: spherical particles, elongated particles, and Pele's hair. Abundance and grain size distribution of these particles were found to be proportional to the rate of acceleration and the speed of ejection but were not influenced by the experimental method used. Pele's hair occurred at ejection speeds of >75 m/s.

Rapid injection of particles and gas into non-fluidized granular material, and some volcanological implications

“…The values of the experimental parameters that most influence the flow velocities (initial gas pressures and host thicknesses) are chosen as to qualitatively reproduce the range of phenomena thought possible in debris-filled volcanic vents above explosion sites; we do not impose a control on flow velocities. The gas pressures were also chosen using insights gained from phreatomagmatic and "magma blowout" experiments at the same laboratory (e.g., Zimanowski et al 1991Zimanowski et al , 1997. More specifically, during blowout experiments, magma was expelled from a crucible (of the same type as the one used here) using compressed air.…”

Neogene-Quaternary Volcanic forms in the Carpathian-Pannonian Region: a review

“…The formation of a maar volcano is directly related with some sort of subsidence generated by mass-deficit beneath the surface [49][50][51] as a consequence of explosive interaction between hot magma and water and/or water saturated sediments [52,53]. Maar volcanoes, gradually subside long after their formation as a result of resettling of the water-soaked debris accumulated in the volcanic conduit beneath the crater that is commonly referred to as a diatreme [54,55].…”

CARIBIC aircraft measurements of Eyjafjallajökull volcanic clouds in April/May 2010

“…The explosive part of the recent eruption began on 14 April 2010 and lasted with interruptions until 22 May 2010 (Sigmundsson et al, 2010). The contact of meltwater from the overlying glacier with the hot magma increased the strength and explosivity of the eruption during the first days (phreatomagmatic explosion, Zimanowski et al, 1997Zimanowski et al, , 2003. The high explosive force was accompanied by the production of unusually fine ash particles with samples from the first two days showing 50 %-70 % of them being smaller than 100 µm (Sanderson, 2010;Taddeucci et al, 2011), 20 % being smaller than 10 µm and 7 % being smaller than 2.6 µm in diameter in ash samples collected close to the volcano (Gíslason and Alfredsson, 2010).…”