HR: 1400h
AN: V33B-03    [Abstracts]
TI: Unusual Ice-Rich Lahars From the 23 September 1995 Eruption of Mt. Ruapehu, New Zealand
AU: * Fagents, S A
EM: fagents@hawaii.edu
AF: University of Hawaii, 1680 East-West Road, Honolulu, HI 96822, United States
AU: Houghton, B F
EM: bhought@soest.hawaii.edu
AF: University of Hawaii, 1680 East-West Road, Honolulu, HI 96822, United States
AB: Interactions between explosive eruptions and summit ice or snowpack are among the most hazardous lahar- forming events at snow-capped volcanoes, as demonstrated by the 1985 disaster at Nevado del Ruiz, Colombia. A case of contrasting impact is the 23 September 1995 eruption at Mt. Ruapehu, New Zealand, in which an ice- rich lahar traveled <3 km before coming to rest on relatively steep slopes (10-16°). Addressing the diverse thermal and fluid dynamic consequences of such events is therefore critical to understanding the threat to surrounding areas. In the 1995 Ruapehu eruption, a series of explosions through the Crater Lake ejected jets of hot tephra and warm lake water upon the snow cover, generating two bifurcating lahars that took paths directly down a ski-field. The late hour and limited runout precluded any loss of life or property. Fieldwork immediately after the event acquired samples and multiple thickness profiles across the deposit. Componentry and geochemical analyses showed that the deposit consisted of 10-30 wt% tephra and lake sediments, 1-4 wt% frozen lake water, and 65-85 wt% snow and ice. We infer that the evolving thermal balance within the lahar induced it to come to rest as the liquid component (lake water and melted snow/ice) progressively froze with distance from the source. We will present progress in development of a treatment of the heat transfer and fluid dynamics tephra-water-ice mixtures to constrain conditions leading to the widely varying runout distances and associated hazards of such events.
DE: 1810 Debris flow and landslides
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8428 Explosive volcanism
DE: 8486 Field relationships (1090, 3690)
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly