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

S. F. L. Watt, Jennie S. Gilbert, Arnau Folch, Jeremy C Phillips, Xiaoming M. Cai

Research output: Contribution to journalArticle (Academic Journal)peer-review

24 Citations (Scopus)
265 Downloads (Pure)

Abstract

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.

Original languageEnglish
Article number35
Number of pages14
JournalBulletin of Volcanology
Volume77
Issue number5
Early online date12 Apr 2015
DOIs
Publication statusPublished - May 2015

Keywords

  • Chaitén
  • Lee wave
  • Mountain wave
  • Tephra fall
  • Topography
  • Volcanic ash aggregation

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