Scientific Endeavours and Achievements

No new equipment was introduced this year. Rather we reluctantly relinquished the Windless Bight Infrasonic Array, in order to return the radio thermoelectric generator (RTG) to NSF. The ever deepening snow covering the microphones was reducing the sensitivity to Erebus eruption signals.

Thanks to the dedication of Howard Nicholson and Bruce McGregor, the Scott Base recording equipment required little servicing on our belated arrival in Antarctica on 28 November (a record 4 turnarounds) and we immediately prepared for put in on Erebus.

We flew to Fang Glacier in 3 lifts (one for the Grizzly) starting mid afternoon on 2 December, as the weather improved. S- 081 had flown up a few hours before us. The advance party of S- 081 came down and drove them up next day, while we waited out our planned 2 day acclimitisation, and drove up to the tower hut with S-081 help on 4 December.

Work on the summit comprised changing the infrasonic microphone battery at Truncated Cones (CONI) and E1 (E1S1), and readjusting the long period horizontal seismometer at E1 (E1LH). We tested and checked the receiver and antenna at MACZ station, newly installed by S-081, to find why it was not receiving and relaying the signal from BOMB, and checked that it was in the best possible site.

We moved up to the upper hut for 2 days, and using the space heater to keep the Nimbus stacking refraction seismograph warm, recorded 2 seismic lines 180 and 330 m long from the hut to Nausea knob for shallow velocity data. The surface velocity was 3000+/− 300 m/s on the undisturbed volcanic cone, and 2100+/−300 m/s on the old slump under the hut. The seismic source was sledge hammer blows for the 180 m line, and 1.5 m lengths of detonating cord laid on the surface for the 330 m line. Electric dets and the Nimbus shot box were used without incident by taking care to earth ourselves before handling detonators, and holding the bare ends of wires in each hand before connecting them, so that static voltages were discharged through the body. The start circuit for the Nimbus was wrapped around the det cord so it was opened by the shot, thus overcoming a fault in the start signal provided by the Nimbus shot box. A minimum of 5 shots had to be stacked to record at 330 m distance, and unluckily the Nimbus double-triggered on the 5th one, and ruined the record. It is estimated that 10 times more charge per shot win be required for the main survey next season.

While Dibble and O'Brien did the seismic survey, Shimizu and Kennedy began infrared temperature measurements at the crater rim, and continued after we all shifted back to the lower hut. To begin with, fume obscured the view inside the crater, and on subsequent attempts the thermometer malfunctioned in that the spot which was being measured could not be seen through the viewfinder. Inspite of the hand warmers strapped around it, the instrument got too cold sitting on its tripod, and became unreliable.

Upon return to Scott Base, Shimizu immediately began playback of analog magnetic tapes containing seismic data. Significant earthquakes since August 1989 were played back to charts from these tapes. He also collected amplitude data from E1SPZ events recorded on the SAN-EI long term chart recorder for that period. O'Brien began continuous video recording of the TV signal from the Erebus summit and took over archiving well recorded earthquakes on the digital seismograph from McGregor. During his stay 270 three hour videotapes were recorded, on which the lava lakes were visible 60% of the time. 16 explosive-type eruptions of the eastern lava lake were recorded on VCR and by the six seismograph stations and two microphones on the volcano. After Dibble and Shimizu's departure for New Zealand, O'Brien continued the magnetic tape playback, printing two sets of charts for study in Japan and New Zealand. 1782 events triggered the digital seismograph during O'Brien's laboratory work, but only 247 were volcanic earthquakes recorded well enough for focal determination.