NARRATIVE

We were ready to start up Erebus on 4 December, but the weather was unsympathetic to us right from the start.

Between 9 and 19 December, Kienle, Estes and Kaminuma installed the telemetry receiver and recorder at Scott Base, and the geophones and transmitter at Abbotts Peak and Hoopers Shoulder on the flanks of Erebus. The main party of 10 including the writer, flew to the acclimatisation camp at the Fang on 10 December, and 8 of us reached the summit by helo on 17 December.

The second party flew to the Fang on 19 December. Continuous cloud developed there (although the summit remained clear) and they walked up a few at a time, the last arriving at the Summit Hut on 24 December.

In all, 105 man days were spent acclimatising instead of the planned 30.

By 19 December I had installed a low frequency microphone (8 inch Philips Hi Z speaker in 2 cubic foot sealed enclosure) and pre-amplifier in position on the rim between the main and side craters. It was connected by cable to an amplifier and monitor speaker in the Hut. The frequencies below 50 Hz were also recorded on channel 3 of tape seismograph A. Channels 1 and 2 were connected to a Willmore seismometer (Mk 1, Z, T₀ = 1s) installed 220m towards the crater from the Hut.

By 20 December, Terai and Osada were recording a 4 geophone array (of 2km diameter surrounding the Hut) on their 2 tape seismographs.

By 23 December a figure of 8 induction loop, consisting of 3.6km of single conductor 1.5mm² PVC appliance wire, had been laid around the main crater rim and the Hut area by Prosser, Parish, Summerville, Terai and myself.

The crater rim loop (3) was recording on channels 1 (high gain) and 2 (low gain) of tape seismograph B, and the Hut loop (4) on channel 3 (separate high gain amplifier) as shown in Figure 8.

By 26 December the loops were completely buried c. 50mm deep, eliminating noise due to the wire moving in the wind, but static discharge spikes limited the usable gain until bypassed by 1000 microfarad capacitors across the loops on New Year's Day.

Although Kienle had begun to telemeter signals from his summit geophone to Scott Base on sub-carrier 2380 Hz before Christmas, using a small Gel-cell battery, the main Carbonaire battery, and my three voltage controlled oscillators (VCO) for the telemetry link were not installed until 2 January (when we stopped waiting for the Helo "close support" and carried them). The batteries, the VCO and transmitter were in protective boxes buried in warm ground. In a change of plan, the wide-band frequency signals from the micro page 32

Figure 8: Schematic diagrams of the author's equipment on Erebus.

page 33 phone were rectified and modulated on a 1700 Hz sub-carrier, instead of directly modulating the main carrier.

Scott Base were asked to tune the spare discriminator to 1700 Hz and to monitor the rectifie microphone signal. Subsequently they reported an extremely high level of signal.

On 4 January signals from the microphone were reduced by connecting a 10 ohm resistor across the microphone cable at the VCO box. The modulation of the 1020 Hz sub-carrier (and presumably the 1700 Hz one also) was then peaking at 10% in a 15 knot wind. This was determined at the Summit Hut by means of the Alaska Test Receiver and a 1020 Hz discriminator, and of course an anemometer.

On 5 January the loops were disconnected from tape seismograph B and connected in figure of 8 configuration to the 1360 Hz VCO and transmitter. All signals were then being telemetered, as in Appendix 2C, but our communication radios had failed and Scott Base could not be asked to monitor the signals and report the background level and number and size of events back to us, so that we could optimise the adjustments, and calibrate the system.

The entire party returned to Scott Base on 9 January. The Abbott Peak, Hooper's Shoulder, and Summit geophones were recording correctly, but of my three channels only the 1700 Hz microphone channel was connected, and it was tuned to 3700 Hz instead of 1700 Hz. Generous help from Tom Earle and Stan Whitfield enabled us to get the 1020, 1360 and 1700 Hz discriminators installed and the channels recording as in Appendix 2C (although the 1700 Hz discriminator was noisy due to a faulty component we could not find), and also my cargon packed before returning to New Zealand on 10 January (the last flight in time for my daughter's wedding).

Regrettably, there was insufficient time in which to confirm that good data from the microphone and the loop were being recorded. As expected, the signal levels on a quiet volcano during a calm day were very low - perhaps too low! The weather which trapped the entire party at the summit, and the lack of communications with Scott Base denied us the opportunity to get it right with certainty. Plate VIA, B and C show equipment at the transmitter, the Summit Hut and Scott Base.