Papers by Thomas E Christopher
Sulphur dioxide (SO 2) diffusion tube monitoring has been undertaken on Montserrat since 1995, pr... more Sulphur dioxide (SO 2) diffusion tube monitoring has been undertaken on Montserrat since 1995, providing a unique and insightful long-term dataset of ground-level SO 2 concentrations during the eruption of the Soufrière Hills Volcano (SHV). The monitoring of ground-level SO 2 is important to assess the potential of human exposure to high levels of SO 2 that may impact on health. Air-quality objectives for SO 2 are present in some countries to prevent potential health impacts. Here we summarise diffusion tube monitoring in Montserrat and analyse concentrations with respect to the potential for exposure to levels above recommended levels. We explore relationships that may exist with SO 2 flux measurements and volcanic events. Concentrations have been higher during pauses in lava extrusion. Diffusion tube concentrations are highest within 5 km of the volcano and at locations downwind of the plume. Areas where concentrations have exceeded relevant limits have been uninhabited since 1996. The potential for human exposure above recommended limits is, therefore, currently considered low, as the population would not have been exposed to high concentrations for extended periods of time. Full-time occupation and/or long-term exposure in the areas where concentrations exceed the relevant limits would not be advised.
Soufrière Hills Volcano produced prodigious quantities of sulphur dioxide (SO2) gas throughout 19... more Soufrière Hills Volcano produced prodigious quantities of sulphur dioxide (SO2) gas throughout 1995– 2013. An unprecedented, detailed record of SO2 flux shows that high SO2 fluxes were sustained through eruptive pauses and for two years after the end of lava extrusion and are decoupled from lava extrusion rates. Lava extrusion rates have exhibited strong 1-to 2-year cyclicity. Wavelet analysis demonstrates periodicities of c. 5 months and c. 2 years within the SO2 time series, as well as the shorter cycles identified previously. The latter period is similar to the wavelength of cycles in lava extrusion, albeit non-systematically offset. The periodicities are consistent with pressure changes accompanying deformation in a coupled magma reservoir system whereby double periodic behaviour may arise from limited connectivity between two reservoirs. During periods of lava extrusion SO2 is released together with the lava (yielding the c. 2 year period), albeit with some offset. In contrast, when magma cannot flow because of its yield strength, SO2 is released independently from lava (yielding the c. 5 month period). Our results have implications for eruption forecasting. It seems likely that, when deep supply of magma ceases, gas fluxes will cease to be periodic.
The 20th May 2006 lava dome collapse of the Soufrière Hills Volcano, Montserrat, had a total non-... more The 20th May 2006 lava dome collapse of the Soufrière Hills Volcano, Montserrat, had a total non-dense rock equivalent (non-DRE) collapse volume of approximately 115×10 6 m 3. The majority of this volume was deposited into the ocean. The collapse was rapid, 85% of the mobilized volume being removed in just 35 min, giving peak pyroclastic flow flux of 66×10 3 m 3 s −1. Channel and levee facies on the submarine flanks of the volcano and formation of a thick, steep-sided ridge, suggest that the largest and most dense blocks were transported proximally as a high concentration granular flow. Of the submerged volume, 30% was deposited from the base of this granular flow, forming a linear, high-relief ridge that extends 7 km from shore. The remaining 70% of the submerged volume comprises the finer grain sizes, which were transported at least 40 km by turbidity currents on gradients of <2°. At several localities, the May 2006 distal turbidity currents ran up 200 m of topography and eroded up to 20 cm of underlying substrate. Multiple turbidites are preserved, representing current reflection from the graben margins and deflection around topography. The high energy of the May 2006 collapse resulted in longer submarine run out than the larger (210×10 6 m 3) Soufrière Hills dome collapse in July 2003.
The andesite lava erupted at the Soufrie`re Hills Volcano (SHV) is crystal-rich with 33–63% pheno... more The andesite lava erupted at the Soufrie`re Hills Volcano (SHV) is crystal-rich with 33–63% phenocrysts of plagioclase (65%), amphibole (28%), orthopyroxene (7%), and minor Fe–Ti oxide and clinopyroxene microphenocrysts. The andesite hosts mafic enclaves that have similar mineral phases to the andesite. The enclaves are generally crystal-poor but can have up to 27% of inherited phenocrysts from the andesite, the majority of which are plagioclase. The eruption is defined by discrete periods of extrusion called phases, separated by pauses. The enclaves exhibit bulk geochemical trends that are consistent with fractionation. We infer that the intruded mafic liquids of Phases I and II interacted and assimilated plutonic residue remaining from the multiple prior mafic intrusions, while the basaltic liquids from Phases III and V assimilated relatively little material. We also infer a change in the basaltic composition coming from depth. The bulk Fe contents of both magma types are coupled and they both show a systematic interphase variation in Fe content. We interpret the coupled Fe variation to be due to contamination of the andesite from the intruding basalt via diffusion and
advection processes, resulting in the erupted andesite products bearing the geochemical imprint of the syn-eruptive enclaves.
Geophysical Research Letters, 2010
Arc volcanoes commonly show evidence of mixing between mafic and silicic magma. 19
Geophysical Research Letters, 2010
Volcanic gas emissions illustrate a complex volatile
budget for Soufrie`re Hills Volcano, Montse... more Volcanic gas emissions illustrate a complex volatile
budget for Soufrie`re Hills Volcano, Montserrat. Fluxes of
sulphur dioxide, carbon dioxide, hydrogen sulphide and
hydrogen chloride (and probably water) are substantial
from this arc volcano. Additional sources of volatiles in
addition to the erupting andesite are required to satisfy the
mass balance defined by gas emissions and petrological
constraints. Mafic magma is intruded at depths of >10 km,
supplying volatiles by quenching, crystallising and
vesiculating at the andesite-mafic magma interface.
Sulphur, carbon dioxide and other volatiles supplied to the
system migrate to the surface and their fluxes remain high
while mafic recharge at depth is sustained. Decompression
degassing of porphyritic andesite supplies chlorine and
water to the gas plume. Chlorine partitions into vapour
from the melt during periods of active extrusion, making
the HCl/SO2 ratio of volcanic gases a reliable indicator
of the onset of eruptive activity. Studies of this volatile
budget highlight the role of deep degassing and vapour
production at arc volcanoes, which are important
mechanisms for driving the eruption due to its effects on
magma buoyancy and the advection of heat through the
system.
Uploads
Papers by Thomas E Christopher
advection processes, resulting in the erupted andesite products bearing the geochemical imprint of the syn-eruptive enclaves.
budget for Soufrie`re Hills Volcano, Montserrat. Fluxes of
sulphur dioxide, carbon dioxide, hydrogen sulphide and
hydrogen chloride (and probably water) are substantial
from this arc volcano. Additional sources of volatiles in
addition to the erupting andesite are required to satisfy the
mass balance defined by gas emissions and petrological
constraints. Mafic magma is intruded at depths of >10 km,
supplying volatiles by quenching, crystallising and
vesiculating at the andesite-mafic magma interface.
Sulphur, carbon dioxide and other volatiles supplied to the
system migrate to the surface and their fluxes remain high
while mafic recharge at depth is sustained. Decompression
degassing of porphyritic andesite supplies chlorine and
water to the gas plume. Chlorine partitions into vapour
from the melt during periods of active extrusion, making
the HCl/SO2 ratio of volcanic gases a reliable indicator
of the onset of eruptive activity. Studies of this volatile
budget highlight the role of deep degassing and vapour
production at arc volcanoes, which are important
mechanisms for driving the eruption due to its effects on
magma buoyancy and the advection of heat through the
system.
advection processes, resulting in the erupted andesite products bearing the geochemical imprint of the syn-eruptive enclaves.
budget for Soufrie`re Hills Volcano, Montserrat. Fluxes of
sulphur dioxide, carbon dioxide, hydrogen sulphide and
hydrogen chloride (and probably water) are substantial
from this arc volcano. Additional sources of volatiles in
addition to the erupting andesite are required to satisfy the
mass balance defined by gas emissions and petrological
constraints. Mafic magma is intruded at depths of >10 km,
supplying volatiles by quenching, crystallising and
vesiculating at the andesite-mafic magma interface.
Sulphur, carbon dioxide and other volatiles supplied to the
system migrate to the surface and their fluxes remain high
while mafic recharge at depth is sustained. Decompression
degassing of porphyritic andesite supplies chlorine and
water to the gas plume. Chlorine partitions into vapour
from the melt during periods of active extrusion, making
the HCl/SO2 ratio of volcanic gases a reliable indicator
of the onset of eruptive activity. Studies of this volatile
budget highlight the role of deep degassing and vapour
production at arc volcanoes, which are important
mechanisms for driving the eruption due to its effects on
magma buoyancy and the advection of heat through the
system.