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SUMMARY:Walking on broken glass: investigating magmatic processes in explo
 sive and effusive rhyolitic eruptions - Hugh Tuffen\, Lancaster Environmen
 t Centre\, Lancaster University
DTSTART:20130205T163000Z
DTEND:20130205T173000Z
UID:TALK39317@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:Eruptions of rhyolite magma occur fairly infrequently\, but th
 eir hazardous nature is clear from the abundant and widely dispersed depos
 its they produce. Examples such as Novarupta 1912 are among the largest hi
 storic eruptions and Earth's largest supervolcanoes such as Toba\, Yellows
 tone and Taupo are invariably rhyolite producers. There is even rhyolitic 
 ash scattered over much of northern Britain from Holocene Icelandic erupti
 ons. Rhyolitic melt is initially volatile-rich and the highly viscous melt
  hinders gas escape\, yet initially-explosive eruptions somehow produce la
 rge volumes of degassed lava. The mysterious explosive-effusive transition
  is one of many aspects of rhyolitic volcanism that have long remained poo
 rly constrained\, partly due to a lack of observed eruptions. However\, tw
 o recent rhyolitic events in Chile - Chaitén (2008) and Cordon Caulle (20
 11-2012) - have provided unprecedented insights into eruption dynamics. \n
 \nIn this seminar I will describe ongoing research into the degassing\, cr
 ystallisation and deformation of rhyolitic magma\, using experimental\, ge
 ochemical and field approaches. I will also report some of the latest find
 ings from Chile\, including observations of synchronous explosive and effu
 sive eruptions that call the notion of an explosive-effusive transition in
 to question\, and the first measurements of how active obsidian flows adva
 nce. \n\n\nEichelberger\, J.C.\, Carrigan\, C.R.\,Westrich\, H.R.\,Price\,
  R.H.\, 1986. Non-explosive silicic volcanism. Nature 323\, 598-602.\n\nCa
 stro\, J.M.\, Cordonnier\, B.\, Tuffen\, H.\, Tobin\, M.\, Puskar\, L.\, M
 artin\, M.C.\, Bechtel\, B.\, (2012) Defusing explosive rhyolite eruptions
  by melt-fracture degassing. Earth and Planetary Science Letters\, 333-334
 \, 63-69.\n\nGonnermann\, H.M.\, Manga\, M.\, 2003. Explosive volcanism ma
 y not be an inevitable consequence of magma fragmentation. Nature 426\, 43
 2-435.
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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