Recharge, decompression, and collapse : dynamics of volcanic processes
text Non-linear volcanic and magmatic processes control the occurrence and behavior of volcanic eruptions. Consequently, understanding the responses of volcanic systems to processes of different length scales, timescales, and magnitudes is critical to interpreting ancient deposits, understanding cur...
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ftunivtexas:oai:repositories.lib.utexas.edu:2152/7824 2023-05-15T16:59:13+02:00 Recharge, decompression, and collapse : dynamics of volcanic processes Andrews, Benjamin James Gardner, James Edward, 1963- 2009-05 electronic application/pdf http://hdl.handle.net/2152/7824 eng eng http://hdl.handle.net/2152/7824 Copyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works. Chichon Mexico volcanic eruptions El Chichón Volcano eruptions Ksudach Volcano eruptions Mount Saint Helens eruptions Magmatism Calderas Kamchatka Peninsula Russia 2009 ftunivtexas 2020-12-23T22:22:06Z text Non-linear volcanic and magmatic processes control the occurrence and behavior of volcanic eruptions. Consequently, understanding the responses of volcanic systems to processes of different length scales, timescales, and magnitudes is critical to interpreting ancient deposits, understanding current eruption dynamics, and predicting future activity. Here I present the results of three studies wherein analytical geochemistry, experimental petrology, and turbulent flow analysis describe otherwise obscured volcanic processes. Injections of new magma are common events in magma chambers. Recharging magma can change the chamber composition and temperature and may facilitate assimilation of country rock. Plagioclase phenocrysts provide an opportunity to examine recharge and assimilation processes, because their compositions are sensitive to temperature and their Sr isotopic ratios can record compositional variations in the chamber. Chemical and isotopic microanalyses of crystals from 7 eruptions of El Chichón Volcano, Mexico, reveal that recharge and assimilation events are very common and mixing is efficient, but individual events seldom affect the entire chamber. During every eruption, magma decompresses and ascends through a conduit from a chamber at depth to a vent at the surface. Changes in pumice textures during the 1800 ¹⁴C yr BP eruption of Ksudach Volcano, Kamchatka, suggest that conduit structure changed following caldera collapse. Decompression experiments show that the post-collapse pumice decompressed at ~0.0025 MPa/s, compared to pre-collapse decompression rates of >0.01 MPa/s. By balancing those results with eruptive mass fluxes I quantify the effects of caldera collapse on a conduit, and show that collapse resulted in a conduit with a very broad base and narrow vent. Turbulent air entrainment controls whether an eruption column rises buoyantly or collapses to generate pyroclastic flows. Through extensive re-evaluation of video and photographs of the 18 May 1980 eruption of Mount St. Helens, I report the first measurements of the turbulent velocity field of a volcanic column and show that changes in its turbulence reflect changes in eruption behavior. Those results indicate collapse was caused by a reduction in eddy size and turbulent air entrainment initiated by an increased vent size and the development of a buoyant annulus surrounding a dense, collapsing core. Geological Sciences Other/Unknown Material Kamchatka Kamchatka Peninsula The University of Texas at Austin: Texas ScholarWorks Kamchatka Peninsula ENVELOPE(160.000,160.000,56.000,56.000) |
institution |
Open Polar |
collection |
The University of Texas at Austin: Texas ScholarWorks |
op_collection_id |
ftunivtexas |
language |
English |
topic |
Chichon Mexico volcanic eruptions El Chichón Volcano eruptions Ksudach Volcano eruptions Mount Saint Helens eruptions Magmatism Calderas Kamchatka Peninsula Russia |
spellingShingle |
Chichon Mexico volcanic eruptions El Chichón Volcano eruptions Ksudach Volcano eruptions Mount Saint Helens eruptions Magmatism Calderas Kamchatka Peninsula Russia Andrews, Benjamin James Recharge, decompression, and collapse : dynamics of volcanic processes |
topic_facet |
Chichon Mexico volcanic eruptions El Chichón Volcano eruptions Ksudach Volcano eruptions Mount Saint Helens eruptions Magmatism Calderas Kamchatka Peninsula Russia |
description |
text Non-linear volcanic and magmatic processes control the occurrence and behavior of volcanic eruptions. Consequently, understanding the responses of volcanic systems to processes of different length scales, timescales, and magnitudes is critical to interpreting ancient deposits, understanding current eruption dynamics, and predicting future activity. Here I present the results of three studies wherein analytical geochemistry, experimental petrology, and turbulent flow analysis describe otherwise obscured volcanic processes. Injections of new magma are common events in magma chambers. Recharging magma can change the chamber composition and temperature and may facilitate assimilation of country rock. Plagioclase phenocrysts provide an opportunity to examine recharge and assimilation processes, because their compositions are sensitive to temperature and their Sr isotopic ratios can record compositional variations in the chamber. Chemical and isotopic microanalyses of crystals from 7 eruptions of El Chichón Volcano, Mexico, reveal that recharge and assimilation events are very common and mixing is efficient, but individual events seldom affect the entire chamber. During every eruption, magma decompresses and ascends through a conduit from a chamber at depth to a vent at the surface. Changes in pumice textures during the 1800 ¹⁴C yr BP eruption of Ksudach Volcano, Kamchatka, suggest that conduit structure changed following caldera collapse. Decompression experiments show that the post-collapse pumice decompressed at ~0.0025 MPa/s, compared to pre-collapse decompression rates of >0.01 MPa/s. By balancing those results with eruptive mass fluxes I quantify the effects of caldera collapse on a conduit, and show that collapse resulted in a conduit with a very broad base and narrow vent. Turbulent air entrainment controls whether an eruption column rises buoyantly or collapses to generate pyroclastic flows. Through extensive re-evaluation of video and photographs of the 18 May 1980 eruption of Mount St. Helens, I report the first measurements of the turbulent velocity field of a volcanic column and show that changes in its turbulence reflect changes in eruption behavior. Those results indicate collapse was caused by a reduction in eddy size and turbulent air entrainment initiated by an increased vent size and the development of a buoyant annulus surrounding a dense, collapsing core. Geological Sciences |
author2 |
Gardner, James Edward, 1963- |
author |
Andrews, Benjamin James |
author_facet |
Andrews, Benjamin James |
author_sort |
Andrews, Benjamin James |
title |
Recharge, decompression, and collapse : dynamics of volcanic processes |
title_short |
Recharge, decompression, and collapse : dynamics of volcanic processes |
title_full |
Recharge, decompression, and collapse : dynamics of volcanic processes |
title_fullStr |
Recharge, decompression, and collapse : dynamics of volcanic processes |
title_full_unstemmed |
Recharge, decompression, and collapse : dynamics of volcanic processes |
title_sort |
recharge, decompression, and collapse : dynamics of volcanic processes |
publishDate |
2009 |
url |
http://hdl.handle.net/2152/7824 |
long_lat |
ENVELOPE(160.000,160.000,56.000,56.000) |
geographic |
Kamchatka Peninsula |
geographic_facet |
Kamchatka Peninsula |
genre |
Kamchatka Kamchatka Peninsula |
genre_facet |
Kamchatka Kamchatka Peninsula |
op_relation |
http://hdl.handle.net/2152/7824 |
op_rights |
Copyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works. |
_version_ |
1766051432142733312 |