Laboratory Experiments on Volcano Ice Interaction (original) (raw)
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Heat transfer in volcanic settings: Application to lava-ice interaction and geothermal areas
2016
The theme of this thesis is the study of heat transfer from lava or hot rocks where water, including ice melt, is the main medium transferring heat to the surroundings. This is done through (1) laboratory studies of lava-ice and rock-water interaction, (2) observations and analysis of the progression of lava under ice, and (3) measurements of heat loss from a high temperature geothermal area in its natural state. (1) The laboratory experiments were done on benmoreite samples from Eyjafjallajökull 2010, and involved both direct contact between ice and molten lava and settings where a small space existed between ice and melt. The direct contact experiments provided initial ice-melt contact temperature of 1100°C and heat flux of up to 900 kWm−2, declining to <100 kWm−2 and melt-ice contact temperature of 200-300°C in 2-3 minutes. The same heat flux values for the no contact experiments were 100-180 kWm−2, and 50-80 kWm−2. Experiments with cooling of initially hot rock cubes provided...
experiments ice/snow interactions from large-scale basaltic melt − Insights on lava
2013
Quantitative measurements of interactions between lava and ice/snow are critical for improving our knowledge of glaciovolcanic hazards and our ability to use glaciovolcanic deposits for paleoclimate reconstructions. However, such measurements are rare because the eruptions tend to be dangerous and not easily accessible. To address these diffi culties, we conducted a series of pilot experiments designed to allow close observation, measurements, and textural documentation of interactions between basaltic melt and ice. Here we report the results of the fi rst experiments, which comprised controlled pours of as much as 300 kg of basaltic melt on top of ice. Our experiments provide new insights on (1) estimates for rates of heat transfer through boundary layers and for ice melting; (2) controls on rates of lava advance over ice/ snow; (3) formation of lava bubbles (i.e., Limu o Pele) by steam from vaporization of underlying ice or water; and (4) the role of within-ice discontinuities to ...
Journal of Geophysical Research: Solid Earth, 2017
Subglacial explosive volcanism generates hazards that result from magma-ice interaction, including large flowrate meltwater flooding and fine-grained volcanic ash. We consider eruptions where subglacial cavities produced by ice-melt during eruption establish a connection to the atmosphere along the base of the ice sheet that allows accumulated meltwater to drain. The resulting reduction of pressure initiates or enhances explosive phreatomagmatic volcanism within a steam-filled cavity with pyroclast impingement on the cavity roof. Heat transfer rates to melt ice in such a system have not, to our knowledge, been assessed previously. To study this system, we take an experimental approach to gain insight into the heat transfer processes and to quantify ice-melt rates. We present the results of a series of analogue laboratory experiments in which a jet of steam, air and sand at approximately 300 °C impinged on the underside of an ice block. A key finding was that, as the steam to sand ratio was increased, behavior ranged from predominantly horizontal ice melting to predominantly vertical melting by a mobile slurry of sand and water. For the steam to sand ratio that matches typical steam to pyroclast ratios during subglacial phreatomagmatic eruptions at c. 300 °C we observed predominantly vertical melting with upward ice-melt rates of 1.5 mm s-1 , which we argue is similar to that within the volcanic system. This makes pyroclast-ice heat transfer an important contributing ice-2 melt mechanism under drained, low pressure conditions that may precede subaerial explosive volcanism on sloping flanks of glaciated volcanoes.
Ice Melt Rates in Liquid-Filled Cavities During Subglacial Explosive Eruptions
2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014), 2014
Subglacial eruptions are often associated with rapid penetration of overlying ice and release of large flow rates of water as jökulhlaups. Observations of recent subglacial eruptions indicate rapid syn-eruptive ice melting within liquid-filled subglacial cavities, but quantitative descriptions of possible heat transfer processes need to be developed. Calculations of heat flux from the ice cavity fluid to the melting ice surface indicate that up to 0.6 MW m À2 may be obtained for fluids undergoing single-phase free convection, similar to minimum estimates of heat flux inferred from observations of recent eruptions. Our model of boiling two-phase free convection in subglacial cavities indicates that much greater heat fluxes, in the range 3-5 MW m À2 , can be obtained in the vent region of the cavity and may be increased further by momentum transfer from the eruption jet. Rapid magma-water heat transfer from fragmented magma is needed to sustain these heat fluxes. Similar heat fluxes are anticipated for forced convection of subcooled cavity water induced by momentum transfer from an eruption jet. These heat fluxes approach those required to explain jökulhlaup flow rates and rapid ice penetration rates by melting in some, but not all recent eruptions. 1.1. Ice Melting Rates and Heat Fluxes in Subglacial Eruptions Gudmundsson et al. [2004] studied the Gjálp 1996 eruption beneath Vatnajökull, Iceland. Monitoring of the development of ice cauldrons and other depressions in the ice, together with the rise in water level in Grimsvötn, gave two independent measures of meltwater production rate. Around 3 km 3 of ice was melted during the eruption, with a melting rate of 0.5 km 3 per day during the first 3 days of the eruption. The heat flux during the first 3 days may be estimated by dividing the power input of 1.8 TW by the heat transfer area. Gudmundsson et al. [2004] used the area of the volcanic edifice as an estimate of the heat transfer area: this was 3 km 2 for the first 1.5 days, increasing to 5-6 km 2. The resulting heat flux estimate was 0.5-0.6 MW m À2 and is likely to be a minimum estimate for the heat flux in the vent region [Gudmundsson et al., 2004]. WOODCOCK ET AL.
Insights on lava-ice/snow interactions from large-scale basaltic melt experiments
Geology, 2013
Quantitative measurements of interactions between lava and ice/snow are critical for improving our knowledge of glaciovolcanic hazards and our ability to use glaciovolcanic deposits for paleoclimate reconstructions. However, such measurements are rare because the eruptions tend to be dangerous and not easily accessible. To address these diffi culties, we conducted a series of pilot experiments designed to allow close observation, measurements, and textural documentation of interactions between basaltic melt and ice. Here we report the results of the fi rst experiments, which comprised controlled pours of as much as 300 kg of basaltic melt on top of ice. Our experiments provide new insights on (1) estimates for rates of heat transfer through boundary layers and for ice melting; (2) controls on rates of lava advance over ice/ snow; (3) formation of lava bubbles (i.e., Limu o Pele) by steam from vaporization of underlying ice or water; and (4) the role of within-ice discontinuities to facilitate lava migration beneath and within ice. The results of our experiments confi rm fi eld observations about the rates at which lava can melt snow/ice, the effi cacy with which a boundary layer can slow melting rates, and morphologies and textures indicative of direct lava-ice interaction. They also demonstrate that ingestion of external water by lava can create surface bubbles (i.e., Limu) and large gas cavities. We propose that boundary layer steam can slow heat transfer from lava to ice, and present evidence for rapid isotopic exchange between water vapor and melt. We also suggest new criteria for identifying ice-contact features in terrestrial and martian lava fl ows.
Interactions between lava and snow/ice during the 2010 Fimmvörðuháls eruption, south-central Iceland
Journal of Geophysical …, 2012
basaltic effusive eruption at Fimmvörðuháls, southern Iceland, was an important opportunity to directly observe interactions between lava and snow/ice. The eruption site has local perennial snowfields and snow covered ice, and at the time of eruption it was covered with an additional $1-3 m of seasonal snow. Syn-eruption observations of interactions between lava and snow/ice are grouped into four categories: (1) lava advancing directly on top of snow, (2) lava advancing on top of tephra-covered snow, (3) snow/ice melting at lava flow margins, and (4) lava flowing beneath snow. Based on syn-and post-eruption observations in 2010/11, we conclude that the features seen in the lava flow field show only limited and localized evidence for the influence of snow/ice presence during the eruption. Estimated melting rates from radiant and conductive heating at the flow fronts are too slow (on the order of 5 m/hr) to allow for complete melting of snow/ice ahead of the advancing lava flows, at least during periods of observed rapid lava advance rates (15-55 m/hr). Thus we conclude that during those periods, which largely established the aerial extent of the lava flow field, lava advanced on top of snow; that this likely was the predominant mode of lava emplacement for much of the eruption is supported by many syn-eruption field observations. Examination of the lava flows subsequent to the eruption has so far only found subtle evidence for interactions between lava and snow/ice; for example, locally lava flows have fractured and are collapsing, or have developed marginal rubble aprons from melting of snow banks that were partly covered by lava flow margins.
Bulletin of Volcanology, 2004
The 13-day-long Gjµlp eruption within the Vatnajökull ice cap in October 1996 provided important data on ice-volcano interaction in a thick temperate glacier. The eruption produced 0.8 km 3 of mainly volcanic glass with a basaltic icelandite composition (equivalent to 0.45 km 3 of magma). Ice thickness above the 6-km-long volcanic fissure was initially 550-750 m. The eruption was mainly subglacial forming a 150-500 m high ridge; only 2-4% of the volcanic material was erupted subaerially. Monitoring of the formation of ice cauldrons above the vents provided data on ice melting, heat flux and indirectly on eruption rate. The heat flux was 5-610 5 W m -2 in the first 4 days. This high heat flux can only be explained by fragmentation of magma into volcanic glass. The pattern of ice melting during and after the eruption indicates that the efficiency of instantaneous heat exchange between magma and ice at the eruption site was 50-60%. If this is characteristic for magma fragmentation in subglacial eruptions, volcanic material and meltwater will in most cases take up more space than the ice melted in the eruption. Water accumulation would therefore cause buildup of basal water pressure and lead to rapid release of the meltwater. Continuous drainage of meltwater is therefore the most likely scenario in subglacial eruptions under temperate glaciers. Deformation and fracturing of ice played a significant role in the eruption and modified the subglacial water pressure. It is found that water pressure at a vent under a subsiding cauldron is substantially less than it would be during static loading by the overlying ice, since the load is partly compensated for by shear forces in the rapidly deforming ice. In addition to intensive crevassing due to subsidence at Gjµlp, a long and straight crevasse formed over the southernmost part of the volcanic fissure on the first day of the eruption. It is suggested that the feeder dyke may have overshot the bedrock-ice interface, caused high deformation rates and fractured the ice up to the surface. The crevasse later modified the flow of meltwater, explaining surface flow of water past the highest part of the edifice. The dominance of magma fragmentation in the Gjµlp eruption suggests that initial ice thickness greater than 600-700 m is required if effusive eruption of pillow lava is to be the main style of activity, at least in similar eruptions of high initial magma discharge.
Bulletin of Volcanology, 2004
The 13-day-long Gjµlp eruption within the Vatnajökull ice cap in October 1996 provided important data on ice-volcano interaction in a thick temperate glacier. The eruption produced 0.8 km 3 of mainly volcanic glass with a basaltic icelandite composition (equivalent to 0.45 km 3 of magma). Ice thickness above the 6-km-long volcanic fissure was initially 550-750 m. The eruption was mainly subglacial forming a 150-500 m high ridge; only 2-4% of the volcanic material was erupted subaerially. Monitoring of the formation of ice cauldrons above the vents provided data on ice melting, heat flux and indirectly on eruption rate. The heat flux was 5-610 5 W m-2 in the first 4 days. This high heat flux can only be explained by fragmentation of magma into volcanic glass. The pattern of ice melting during and after the eruption indicates that the efficiency of instantaneous heat exchange between magma and ice at the eruption site was 50-60%. If this is characteristic for magma fragmentation in subglacial eruptions, volcanic material and meltwater will in most cases take up more space than the ice melted in the eruption. Water accumulation would therefore cause buildup of basal water pressure and lead to rapid release of the meltwater. Continuous drainage of meltwater is therefore the most likely scenario in subglacial eruptions under temperate glaciers. Deformation and fracturing of ice played a significant role in the eruption and modified the subglacial water pressure. It is found that water pressure at a vent under a subsiding cauldron is substantially less than it would be during static loading by the overlying ice, since the load is partly compensated for by shear forces in the rapidly deforming ice. In addition to intensive crevassing due to subsidence at Gjµlp, a long and straight crevasse formed over the southernmost part of the volcanic fissure on the first day of the eruption. It is suggested that the feeder dyke may have overshot the bedrock-ice interface, caused high deformation rates and fractured the ice up to the surface. The crevasse later modified the flow of meltwater, explaining surface flow of water past the highest part of the edifice. The dominance of magma fragmentation in the Gjµlp eruption suggests that initial ice thickness greater than 600-700 m is required if effusive eruption of pillow lava is to be the main style of activity, at least in similar eruptions of high initial magma discharge.
Bulletin of Volcanology, 2016
During the 2010 Eyjafjallajökull eruption in South Iceland, a 3.2-km-long benmoreite lava flow was emplaced subglacially during a 17-day effusive-explosive phase from April 18 to May 4. The lava flowed to the north out of the ice-filled summit caldera down the outlet glacier Gígjökull. The flow has a vertical drop of about 700 m, an area of ca. 0.55 km 2 , the total lava volume is ca. 2.5•10 7 m 3 and it is estimated to have melted 10-13•10 7 m 3 of ice. During the first 8 days, the lava advanced slowly (<100 m day −1), building up to a thickness of 80-100 m under ice that was initially 150-200 m thick. Faster advance (up to 500 m day −1) formed a thinner (10-20 m) lava flow on the slopes outside the caldera where the ice was 60-100 m thick. This subglacial lava flow was emplaced along meltwater tunnels under ice for the entire 3.2 km of the flow field length and constitutes 90 % of the total lava volume. The remaining 10 % belong to subaerial lava that was emplaced on top of the subglacial lava flow in an ice-free environment at the end of effusive activity, forming a 2.7 km long a'a lava field. About 45 % of the thermal energy of the subglacial lava was used for ice melting; 4 % was lost with hot water; about 1 % was released to the atmosphere as steam. Heat was mostly released by forced convection of fastflowing meltwater with heat fluxes of 125-310 kWm −2 .