Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/11819
Authors: Scollo, Simona* 
Bonadonna, Costanza* 
Manzella, Irene* 
Title: Settling-driven gravitational instabilities associated with volcanic clouds: new insights from experimental investigations
Issue Date: 22-Apr-2017
Series/Report no.: /79 (2017)
DOI: 10.1007/s00445-017-1124-x
URI: http://hdl.handle.net/2122/11819
Abstract: Downward propagating instabilities are often observed at the bottom of volcanic plumes and clouds. These instabilities generate fingers that enhance the sedimentation of fine ash. Despite their potential influence on tephra dispersal and deposition, their dynamics is not entirely understood, undermining the accuracy of volcanic ash transport and dispersal models. Here, we present new laboratory experiments that investigate the effects of particle size, composition and concentration on finger generation and dynamics. The experimental set-up consists of a Plexiglas tank equipped with a removable plastic sheet that separates two different layers. The lower layer is a solution of water and sugar, initially denser than the upper layer, which consists of water and particles. Particles in the experiments include glass beads as well as andesitic, rhyolitic and basaltic volcanic ash. During the experiments, we removed the horizontal plastic sheet separating the two fluids. Particles were illuminated with a laser and filmed with a HD camera; particle image velocimetry (PIV) is used to analyse finger dynamics. Results show that both the number and the downward advance speed of fingers increase with particle concentration in the upper layer, while finger speed increases with particle size but is independent of particle composition. An increase in particle concentration and turbulence is estimated to take place inside the fingers, which could promote aggregation in subaerial fallout events. Finally, finger number, finger speed and particle concentration were observed to decrease with time after the formation of fingers. A similar pattern could occur in volcanic clouds when the mass supply from the eruptive vent is reduced. Observed evolution of the experiments through time also indicates that there must be a threshold of fine ash concentration and mass eruption rate below which fingers do not form; this is also confirmed by field observations.
Appears in Collections:Papers Published / Papers in press

Files in This Item:
File Description SizeFormat 
Scollo_et_al_2017.pdf11.05 MBAdobe PDFView/Open
Show full item record

Page view(s)

4
Last Week
0
Last month
0
checked on Jan 18, 2019

Download(s)

4
checked on Jan 18, 2019

Google ScholarTM

Check

Altmetric