Hail formation triggers rapid ash aggregation in volcanic plumes.

• Main Authors: Van Eaton, Alexa R, Mastin, Larry G, Herzog, Michael, Schwaiger, Hans F, Schneider, David J, Wallace, Kristi L, Clarke, Amanda B
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Science and Business Media LLC 2015
• Subjects: 0403 Geology; Anchorage; New Zealand; glacier; Alaska
• Online Access: https://www.repository.cam.ac.uk/handle/1810/248708

During explosive eruptions, airborne particles collide and stick together, accelerating the fallout of volcanic ash and climate-forcing aerosols. This aggregation process remains a major source of uncertainty both in ash dispersal forecasting and interpretation of eruptions from the geological record. Here we illuminate the mechanisms and timescales of particle aggregation from a well-characterized 'wet' eruption. The 2009 eruption of Redoubt Volcano, Alaska, incorporated water from the surface (in this case, a glacier), which is a common occurrence during explosive volcanism worldwide. Observations from C-band weather radar, fall deposits and numerical modelling demonstrate that hail-forming processes in the eruption plume triggered aggregation of ∼95% of the fine ash and stripped much of the erupted mass out of the atmosphere within 30 min. Based on these findings, we propose a mechanism of hail-like ash aggregation that contributes to the anomalously rapid fallout of fine ash and occurrence of concentrically layered aggregates in volcanic deposits. AVE acknowledges NSF Postdoctoral Fellowship EAR1250029 and a seed grant from NASA Ames Supercomputing Center. Integrated Data Viewer (IDV) software from UCAR/Unidata was used in the analysis and visualization of the large-eddy simulation. ASTER GDEM is a product of NASA and METI. NCAR Reanalysis data provided by the NOAA/OAR/ESRL Physical Sciences Division, Boulder, Colorado, USA. We acknowledge Victoria University of Wellington, New Zealand, for access to the laser particle size analyzer, and Matt Rogers at University of Alaska, Anchorage for use of the freeze dryer. Rick Hoblitt is thanked for discussions and comments on the manuscript. This is the final version of the article. It first appeared from NPG via http://dx.doi.org/10.1038/ncomms8860