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Victoria University Antarctic Research Expedition Science and Logistics Reports 1990-91: VUWAE 35

Abstract of Scientific Work Achieved

Abstract of Scientific Work Achieved

During the field season, 25 days of seismic telemetry and TV video recording were made of the eruptive and seismic activity of Erebus volcano. The lava lake was in the form of two main pools, which were convecting and fuming without strong explosive activity. No eruptions were witnessed while we Here on the mountain, although members of the party were at or above the upper hut on 7 days.

A seismic refraction survey was made on the summit plateau over a 1.4km distance between shot points in the Side Crater and near Truncated Cones. Three contiguous 330m spreads of the Nimbus seismograph were shot from each end of the line, using shots up to 10kg in one meter deep holes. The arrivals were weak but readable. They have been interpreted by ray–tracing as showing a 1.3km/s sub–permafrost layer up to 100m thick overlying a refractor with lateral velocity variations between 1.6 and 3.7 km/s. The maximum delay time relative to a homogeneous 4 km/s model is only 0.21s, and shows that the delays of 1.5s previously found in the waves from explosions in the lava lake do not originate under the summit plateau. The elimination of this possibility makes it more certain that the delay originates in the lava lake due to reduction of the velocity in lava due to vesiculatian.

Prior to removing the Victoria University television station, infrasonic microphones, and preamplifiers, and the NIPR long period seismometer from the mountain, the 3 MSF telemetry stations in the summit area were serviced. The El station seismometer has shorter period and lower sensitivity than standard, but the only spare was itself faulty. NSF equipment abandoned between the main and side craters after destruction by the 1984 eruptions was removed and the mountain left tidy. The magnetic induction loop was also pulled out of the ground were possible, and all equipment and non–burnable rubbish was returned to Mew Zealand, with much appreciated help from Scott Base staff.