Eychenne Rowan Julia, Rust A. C., Cashman K. V., Wobrock W. (2017). Distal enhanced sedimentation from volcanic plumes : insights from the secondary mass maxima in the 1992 Mount Spurr fallout deposits. Journal of Geophysical Research : Solid Earth, 122 (10), p. 7679-7697. ISSN 2169-9313.
Titre du document
Distal enhanced sedimentation from volcanic plumes : insights from the secondary mass maxima in the 1992 Mount Spurr fallout deposits
Eychenne Rowan Julia, Rust A. C., Cashman K. V., Wobrock W.
Source
Journal of Geophysical Research : Solid Earth, 2017,
122 (10), p. 7679-7697 ISSN 2169-9313
Some tephra fallout deposits show an increase of mass and thickness at distances from the source >100km (areas of secondary mass maximum, ASMM) which demonstrates distal enhanced sedimentation from volcanic plumes. We explore development of the ASMMs during the 1992 August and September Mount Spurr eruptions, USA, by combining field data on the spatial distribution of mass and grain size with (1) simulations of individual particle settling through a homogeneous and horizontally stratified atmosphere and (2) mesoscale models of the three-dimensional wind field that include the effect of the underlying topography. The crosswind and downwind variations of deposit characteristics indicate that the increase of sedimentation at the ASMMs is not formed solely because of preferential settling of small ash particles (<125m), as commonly assumed in aggregation models. Instead, ASMM grain sizes correspond to the fine modes of the bimodal total grain size distributions. There also appears to be a link between the ASMM and the topography: the mass local minima occur across the windward flank of 2km high mountain ranges, while the ASMMs spread on the leeward flank. Mesoscale models of the three-dimensional wind field show vertical oscillations in the wind over mountainous regions which may enhance mechanisms of en masse sedimentation (aggregation, hydrometeor formation, and particle boundary layers), as well as strong spatial variations of the horizontal wind field in the lower troposphere. Our study demonstrates the importance of using grain size, as well as mass, data to constrain the complex processes responsible for particle sedimentation from volcanic plumes.
Plan de classement
Géologie et formations superficielles [064]
;
Géophysique interne [066]
