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Immediate report of Victoria University of Wellington Antarctic Expedition 1989-90: VUWAE 34

MOUNT EREBUS ERUPTION MECHANISM STUDY (K044)

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MOUNT EREBUS ERUPTION MECHANISM STUDY (K044)

Aims

The aim of the IMEEMS project is to understand the mechanism of the strombolian eruptions, and the velocity structure of Erebus Volcano. The present methods are telemetry recordings at Scott Base of seismic, infrasonic, and video data from the volcano, over as great a part of the year as possible.

This season a pilot seismic refraction survey was made on the summit cone, and infrared temperatures of the crater wails and lava lake were measured, paralleled by short term measurements of volcanic gas output, and petrology of the lava being erupted, made by international groups of cooperating scientists from USA. NZ. Italy, Japan, and France. The Windless Bight Infrasonic Array ceased operation on 3/1/90, and RTG was returned to NSF.

Seismic Refraction Survey at Upper Erebus Hut

As a pilot study of the shallow velocity structure of Erebus, needed to complete a study of the velocity structure of the erupting magma column, two refraction lines were run between the upper hut and Nausea Knob, using the Nimbus 12 channel stacking seismograph. The seismograph was kept at operating temperature (0-30 degrees C) by the space heater in the hut, and the line was run over the near horizontal snow free ground between the hut and Nausea Knob. The first 100 m of the line was on Camp Plow, which is actually a slump, separated from the undisturbed cone by a line of ice towers (fumaroles) extending from the main crater rim to the Tramways.

Line 1 was 180 m long, with geophones at 30 m spacing on Camp Flow, and 10 m spacing over the 80 m length on the undisturbed cone. Stacked sledgehammer blows were used at each end and in the middle on the cone side of the fumarole line. On the cone, velocity was 3000 +/−300 m/s, and on the slump it was 2100 +/− 300 m/s. Onsets were much better on the cone than on the slump.

Line 2 was 330 m long, and extended further towards Nausea Knob, because all geophone spacings were 30 m. Sledgehammer blows proved inadequate, and up to 5 shots of 1.5m of red detonating cord, laid in a circle on the ground were stacked per record. The Nimbus blaster in its recently overhauled state was unable to trigger the Nimbus through 330 m of cable. Triggering was by tying the shot instant cable around the det. cord so that it open circuited during the shot Fair records were obtained on the Nimbus screen using 100 Hz bandpass littering, but printer noise marred the printout. Also the only stacked record of 5 shots was ruined by the shot instant cable re-shorting momentarily after the 5th shot, retriggering the Nimbus during maximum amplitudes. We had no spare det. cord to repeat it.

One direct comparison between stacked hammer blows and a single shot of det. cord was made on line 1, and showed that det. cord and lowpass filtering gave the best result. However to get good arrivals over 330m distance the effective charge weights will have to be increased to about 30 stacks of 1.5m lengths of red det. cord per record. This would best be done by using a heavier grade det. cord, because appreciable trigger-induced: system noise appears when too many shots are stacked. For the 1990/91 survey, when spreads up to 1 km long are planned, the shots will have to be even larger in effect by up to 10 times and 1.5 kg charges of Gelignite in 1 m deep shot holes are planned.

Planning

This has been carried out at four levels: Event proposals to RDRC; discussions within the VUW Antarctic Research Centre; communications between foreign scientists; and with other NZ events on Erebus.

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The International communications are distributed through the year, and concern the expeditions, distribution of data, presentation of results at conferences, joint publications, direction of future work, and the willingness and ability of each National group to do it.

The VUWAE discussions are concerned with finance and grant applications, selection of student research assistants, and the preparation of yearly reports. The discussions with event K 092 concerned the resources and facilities on the mountain, and how to share them without conflict.

The RDRC proposals are the earliest formal plans, but on a continuing project such as IMEEMS are strongly guided by the thinking of the International group on Erebus.

Cargo

Cargo movements were as follows:
Oct 89 Cargon of NZ/Japan equipment, Wgtn-Scott Base 200 kg
Nov 89 Handcarry computer seismograph, Wgtn-S.B. 20 kg
Dec 89 Tapes, paper, infrared thermometer, Tokyo-S.B 30 kg
21 Jan 90 Handcarry recordings, computer, SB-Wgtn 35 kg
21 Jan 90 Ship equip and records, S.B. to Wgtn 200 kg
14 Feb 90 Airfreight record to date, SB-Wgtn 20 kg
31 Mar 90 Airfreight record to date, Wgtn-Tokyo 10 kg

Field Preparations

For IMEEMS, field preparations begin with servicing the recording equipment at S.B., because the field telemetry equipment cannot be serviced reliably if signals cannot be recorded. In view of our delayed arrival in Antarctica, it was fortunate that Dr Bill McIntosh of S-081 was already on the mountain, and had serviced our TV camera, and shifted the telemetry station from Terror to a new site (MACZ) on the ESE rim of the Erebus plateau before our put-in. Also technicians Nicholson and McGregor had left little undone in the Science Lab. With remaining problems on Erebus identified, and only a high false trigger problem at Scott Base, we succeeded in doing the survival course (Ray only one day) and preparing for put-in within 4 days of arriving. Gerry had already checked Grizzly G5 on steep slopes near the ski field.

Relations with Base Staff

This was very good, and the willing help and cooperation from everyone was much appreciated.

Field Transport

The put-in at Fang Glacier was by 3 helicopter loads, totalling 3000 lb, including the Grizzly which was underslung as the last load. We arrived at Fang a few hours after S-081. Transport up from Fang, and on the plateau was by Grizzly toboggan and one of the Yamahas garaged at the lower hut. S-081 lent us a Skiddoo, and carried skiddoo loads for us on several occasions. Our fuel requirements proved to be underestimated, but we could not have taken appreciably more on only 3 lifts. Our return to Scott Base was in one flight by Kiwi helo from the lower hut. The Grizzly, Fang camp, generator, cooking box, and some spare food were left for K 092 to use at their request. Three helicopter flights to repair BOMB seismic station were attempted. The first with K 092 was aborted when the Kiwi helo was found to have cracks in the tail (grateful thanks to the crew), and the second with K 092 took us twice around Erebus to reduce weight for the landing on the small cone at BOMB. Unfortunately low cloud encroached on McMurdo, and we had insufficient time on the ground to effect repairs. The third flight was with Dr. Ray Chuan of S-081, and our one hour on the ground was just sufficient. Ken Sims of S-081 made a further flight to remove batteries from the old TERROR site, and add recharged and tested batteries to BOMB. VXE-6 could not have been more helpful, and the flights were excellent.

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Field Conditions

No unusual conditions were encountered. The snow was firm, giving good traction for the toboggans, especially on the routes up from Fang, and up Rays Gully to the summit, and to CONE and MACZ seismic stations. Some ice was encountered on the gentle lower slopes of the plateau below the upper hut, but enough gravel was present for good traction, visibility was generally excellent except in the crater, and there was little wind. The 2 huts provided excellent shelter, and working space.

Weather

Although our arrival was delayed by chronic bad weather, it improved rapidly on the day of our put-in, and remained good thereafter. Only one day of our time on Erebus was unworkable, although Dr Shimizu often found the crater to be obscured by fume and cloud. After descending from the summit, the view into the crater on TV was clearer than I had seen before. The two flights I made with telecom technicians to repair BOMB seismic station were both in perfect calm weather, although increasing low cloud around McMurdo during the first one saw us snatched from BOMB before we had opened the cases.

We were very lucky compared with the S-081 advance party on Erebus, who had problems de-icing and starting their skiddoos almost every time they used them.

Event Diary

19 Nov Dibble, O'Brien, and Shimizu fly to Chch.
24 Nov Fly South S hours; turn-around due to weather.
25 Nov Fly South 5 hours; turn-around due to weather.
27 NOV Fly South 5 hours; turn-around due to weather.
28 Nov Fly South 0.5 hours; turn-around due to oxygen leak.
28 Nov Fly to McMurdo after replacing oxygen pipeline.
30 Nov O'Brien and Shimizu begin Survival School.
1 Dec Dibble, O'Brien, Shimizu complete Survival School
2 Nov Dibble, 0;Brien, Shimizu and Kennedy fly to Fang.
4 Nov All toboggan up to lower hut, helped by S-081.
6 Nov Check why new station MACZ does not relay BOMB signal; remove receiver and antenna for test.
7 Nov Service CONE microphone, and all move to upper hut with help from S-081, Begin refraction survey.
8 Nov Shimizu/Kennedy take infrared thermometer to rim. Dibble/O'Brien make refraction survey between upper hut and Nausea Knob.
9 Nov Service E1 microphone, and all move back to lower hut.
10 Nov Dibble/O'Brien search for signal from BOMB with portable receiver. Shimizu/Kennedy take infrared thermometer to rim via Ray's Gully.page 44
11 Nov Dibble/O'Brien find BOMB not transmitting; confirm MACZ is best site, and reinstall receiver/antenna. Shimizu/Kennedy continue thermometry.
12 Nov All K044 fly down together, leaving gear for K092.
13 Nov O'Brien begins video recording 24 hours/day; Shimizu begins tape playback and earthquake count.
15 Nov Dibble/Robertson fly to BOMB with K-092, but no time to repair it due to cloud at McMurdo.
18 Nov Dibble completes antennae overhaul. Stops 5400 skeds from triggering the digital seismograph.
20 Nov Dibble/Fairhall fly to BOMB with S-081. Replace failed batteries with new Ant Div one. Then OK.
23 Nov Dibble and Shimizu return to Christchurch.
24 Nov O'Brien copies videotapes of the lava lake fuming at the times S-081 were analysing plume gases.
26 NOV S-081 fly to TERROR and remove batteries, and to add more batteries at BOMB.
28 Nov 1990 O'Brien starts playback of recent magnetic tapes.
6 Jan Decipher time-codes on chart recordings.
3 Jan Windless Bight Recordings cease. RTG to NSF.
24 Jan Complete video-file of all recorded eruptions, and make several copies in PAL and NTSC.
25 Jan McGregor is handed over the reins.
26 Jan O'Brien returns to Christchurch.

Field Equipment

The use of Polar tents at Fang, and Dome tents at the lower Erebus hut again proved ideal. This year the entire Fang camp was left intact for K-092 to use for acclimatising, and the Grizzly and generator were left at lower and upper huts respectively. Grizzly G5 which had been so successful in 1987/88, was again fully equal to the tasks on Erebus. All the equipment was good.

Radio Communications

The Tait VHF radio provided good comms everywhere except at Fang Glacier. The Compac radio was also barely adequate there. The solar panels were again excellent. The radio skeds were very good, and the operators very helpful.

Lab Facilities

The Science Lab is more excellent than before, and I am very grateful for the generous space provided to IMEEMS. Brent O'Brien set up the analysis computer beside the TV/VCR, and Hiroshi Shimizu set up the tape playback equipment in the visitors room. I greatly appreciated Howard Nicholson maintaining and operating my new computer-based equipment in 1989, and warmly welcome Bruce McGregor's expertise and interest this year. The only major maintenance task for me at the lab was to dissemble and clean all the Yagi receiving antennae. Corrosion was page 45 causing some rectification, which caused many false triggerings of the digital seismograph during 5400 transmissions. A spare antenna and lead- in were added to avoid the problem last winter, when one signal from Erebus was lost by an antenna fault.

Huts

Both huts on Erebus are in good order, and equipped with adequate heating, cooking, and eating equipment, fuel, food, table and chairs. There are no tents or sleeping bags, except in the survival boxes outside. The lower hut (Jamesway) was extended last year by S-081 to provide an instrumental observing room with a large window, facing the crater.

Waste Disposal

No disposal areas are available on Erebus, and all waste is returned to Scott Base/McMurdo by helicopter.

Place Names

The 1984 eruption obliterated the Lava Lake, and the Active Vent, and new lava pools called (from NE to SW) the Main Vent, the Potato, and the Penny have formed. The Black Hole occupies the approximate site of Werner's Fumarole, which also disappeared in 1984. S-081 and K 044 refer to the toboggan trail to the ENE rim of the main crater as "Ray's Gully", although Dr Bill McIntosh was the first person to drive up by skiddoo.

General

I wish to record my appreciation of Dr Bill McIntosh and Dr Nelia Dunbar for servicing my TV camera, and for recovering the telemetry station from Mt Terror, and reinstalling it on Erebus, so as to greatly improve the TV picture quality, and the effectiveness of the seismic net.