An example of enhanced tephra deposition driven by topographically-induced atmospheric turbulence

Watt, Sebastian F. L. and Gilbert, Jennifer Susan and Folch, Arnau and Phillips, Jeremy C. and Cai, Xiaoming M. (2015) An example of enhanced tephra deposition driven by topographically-induced atmospheric turbulence. Bulletin of Volcanology, 77: 35. ISSN 0258-8900

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Spatial variations in the thickness and grain-size characteristics of tephra fall deposits imply that tephra depositional processes cannot be fully captured by models of single-particle sedimentation from the base of the eruption plume. Here, we document a secondary thickness maximum in a ∼9.75 ka tephra fall deposit from Chaitén volcano, Chile (Cha1 eruption). This secondary thickness maximum is notably coarser-grained than documented historical examples, being dominated by medium-grained ash, and an origin via particle aggregation is therefore unlikely. In the region of secondary thickening, we propose that high levels of atmospheric turbulence accelerated particles held within the mid- to lower-troposphere (0 to ∼6 km) towards the ground surface. We suggest that this enhancement in vertical atmospheric mixing was driven by the breaking of lee waves, generated by winds passing over elevated topography beneath the eruption plume. Lower atmospheric circulation patterns may exert a significant control on the dispersal and deposition of tephra from eruption plumes across all spatial scales, particularly in areas of complex topography.

Item Type:
Journal Article
Journal or Publication Title:
Bulletin of Volcanology
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Copyright The Author(s) 2015. This article is published with open access at
Uncontrolled Keywords:
?? tephra fall volcanic ash aggregationlee wavemountain wavetopographychaiténgeochemistry and petrology ??
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Deposited On:
07 Mar 2016 10:26
Last Modified:
22 Jul 2024 00:05