Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Explosive subglacial rhyolitic eruptions in Iceland are fuelled by high magmatic H2O and closed system degassing.
AU - Owen, Jacqueline
AU - Tuffen, Hugh
AU - McGarvie, David W.
PY - 2013/2
Y1 - 2013/2
N2 - Rhyolitic eruptions beneath Icelandic glaciers can be highly explosive, as demonstrated by Quaternary tephra layers dispersed throughout northern Europe. However, they can also be small and effusive. A subglacial rhyolitic eruption has never been observed, so behavioral controls remain poorly understood and the influence of pre-eruptive volatile contents is unknown. We have therefore used secondary ion mass spectrometry to characterize pre-eruptive volatile contents and degassing paths for five subglacial rhyolitic edifices within the Torfajökull central volcano, formed in contrasting styles of eruption under ice ∼400 m thick. This includes the products of the largest known eruption of Icelandic subglacial rhyolite of ∼16 km3 at ca. 70 ka. We find pre-eruptive water contents in melt inclusions (H2OMI) of up to 4.8 wt%, which indicates that Icelandic rhyolite can be significantly more volatile-rich than previously thought. Our results indicate that explosive subglacial rhyolite eruptions correspond with high H2OMI, closed-system degassing, and rapid magma ascent, whereas their effusive equivalents have lower H2OMI and show open-system degassing and more sluggish ascent rates. Volatile controls on eruption style thus appear similar to those for subaerial eruptions, suggesting that ice plays a subsidiary role in influencing the behavior of subglacial rhyolitic eruptions.
AB - Rhyolitic eruptions beneath Icelandic glaciers can be highly explosive, as demonstrated by Quaternary tephra layers dispersed throughout northern Europe. However, they can also be small and effusive. A subglacial rhyolitic eruption has never been observed, so behavioral controls remain poorly understood and the influence of pre-eruptive volatile contents is unknown. We have therefore used secondary ion mass spectrometry to characterize pre-eruptive volatile contents and degassing paths for five subglacial rhyolitic edifices within the Torfajökull central volcano, formed in contrasting styles of eruption under ice ∼400 m thick. This includes the products of the largest known eruption of Icelandic subglacial rhyolite of ∼16 km3 at ca. 70 ka. We find pre-eruptive water contents in melt inclusions (H2OMI) of up to 4.8 wt%, which indicates that Icelandic rhyolite can be significantly more volatile-rich than previously thought. Our results indicate that explosive subglacial rhyolite eruptions correspond with high H2OMI, closed-system degassing, and rapid magma ascent, whereas their effusive equivalents have lower H2OMI and show open-system degassing and more sluggish ascent rates. Volatile controls on eruption style thus appear similar to those for subaerial eruptions, suggesting that ice plays a subsidiary role in influencing the behavior of subglacial rhyolitic eruptions.
KW - Rhyolite - Volatiles - Vent - Eruption transitions - Shear - Permeable - Tuffisite
KW - obsidian
KW - iceland
KW - Torfajokull rhyolite obsidian subglacial eruption Pleistocene glaciovolcanism Iceland
KW - eyjafjallajokull
KW - explosive eruption
KW - ash plume
U2 - 10.1130/G33647.1
DO - 10.1130/G33647.1
M3 - Journal article
VL - 41
SP - 251
EP - 254
JO - Geology
JF - Geology
SN - 0091-7613
IS - 2
ER -