1972 Montebello Islands Survey, Western Australia
by Andrew Turk, December 2014
In 1972 there was a need to provide additional ground control for the NATMAP 1:100,000 scale topographic map sheet series covering the coast and adjacent islands in Western Australia’s Pilbara region. Publication of the map sheets in that region was a priority because of the iron ore mining boom. Hence, the Melbourne Office-based Tellurometer traversing party (led by Surveyor Class 1, Andrew Turk) was sent to the area in mid-September and a network of Tellurometer measurements and horizontal angles between coastal trigonometrical points and all the main islands was measured from North West Cape to Barrow Island.
The intention was to establish ground control from the coast all the way to the Montebello Islands. However, because of the British atomic tests in that island group in the 1950s, entry into the area was restricted due to the radiation risk. This restriction thus generated a request from Natmap to the Atomic Energy Safety Committee for permission to visit the Montebello Islands. That committee had previously commissioned radiation surveys in the area, carried out by military personnel. They urgently wanted another survey, reportedly because the then Federal Government was keen to announce permission for oil search drilling in the Montebello Islands prior to the Federal Election planned for that November.
Figure 1 : Map showing the location of the islands mentioned in the text.
The radiation risk was due to a bay of Trimouille Island being used on 3 October 1952, as the site of Operation Hurricane, the first ever atomic weapon’s test by the United Kingdom. The weapon had a yield of 25 kilotons. This was followed by Operation Mosaic on 16 May 1956 with the detonation of a bomb on a tower at Trimouille Island, with a yield equalling 15 kilotons; and on 19 June 1956 another detonation of a bomb on a tower at Alpha Island, with a yield equalling 98 kilotons. This was the highest yield atomic test ever conducted in Australia. Since the test yield broke an assurance made personally by Prime Minister Anthony Eden of the United Kingdom to Prime Minister Robert Menzies of Australia that the yield would not exceed 2.5 times that of Hurricane (thus about 62 kilotons), the true yield was concealed until 1984. Further information can be found here and here.
Before leaving Melbourne, Turk attended a confidential meeting with Natmap Assistant Director John Dunstan (Joe) Lines and the Chairman of the Atomic Energy Safety Committee. Natmap received approval to visit the islands but was asked to undertake the radiation survey (and other activities) because the army had estimated the job as requiring 150 man-days, which the committee could not afford. Natmap agreed to undertake the work on the basis that there was not a significant health risk to staff. Because of the political connection, Turk was sworn to secrecy about this mission; not even being able to tell the field party members prior to arrival on the islands.
Figure 2 : Warning sign on Alpha Island.
The field party departed Dampier on the Northern Venture on 24 October, dropped Jim Steed and Dave Abreu at Barrow Island and then Bob Goldsworthy and Ken Brown at Lowendal Island. A Tellurometer connection was then observed between the two islands. The next morning the remaining six field party members (Andrew Turk, Ed Burke, Noel Goldsworthy, Mick Lloyd, Ross Stapleton and Ted Rollo) proceeded to Alpha Island in the Montebello’s, where Turk was able to reveal the true purpose of the trip and what was in the large wooden box picked up from Karratha Airport and loaded onto the boat.
Figure 3 : Ted Rollo on Trimouille Island reading the radiation level at ship debris.
Natmap Assistant Director Lines was very keen to open up the opportunity for his field parties to undertake other sorts of scientific work beyond their primary mapping mission and had instructed Turk to give the radiation measurements top priority, hence, extending the traverse into the Montebello Islands was deferred until the next year. The work required at Alpha and Trimouille islands, where atomic bombs had been detonated in the 1950s involved:
· survey measurements between old British mapping control stations, ground zero (where the towers holding the bombs had been located) on each of the two islands and subsequently constructed exclusion fences;
· Geiger counter radiation readings at points on radial grids surrounding both ground zero locations, at points on a large rectangular grid and at points on mapped locations covering significant areas beyond the grids;
· soil samples for radiation testing at each of the radial and rectangular grid points;
· laying down and securing white plastic crosses at key locations for subsequent aerial photography; and
· a photographic record of the condition of the exclusion fences.
The British armed services had completed detailed mapping of the islands prior to the atomic tests but these maps were not connected to the Australian survey network and did not include the locations of the exclusion fences subsequently built. Radial grids (about 100 metres radius) had to be laid out surrounding the two ground zero locations and a large rectangular grid (about 100 metres by 300 metres) laid out on Trimouille Island, adjacent to where a device was detonated aboard an anchored British Naval vessel HMS Plym in October 1952.
Figure 4 : Andrew Turk digging soil samples at Alpha Island.
As well as briefing field party members about the work to be done, Turk discussed the safety aspects. No protective clothing had been provided and no specialised equipment, apart from the two Geiger counters. Turk had been assured that there was not a significant health risk from the limited exposure to background radiation during the few days on the islands, provided that nobody touched any metal objects. The previous radiation survey party were supposed to have removed all the metal (which was a major task given a large naval ship had been exploded next to one of the islands), however, some very radioactive metal objects were encountered and there was a considerable amount of old equipment and structures still on Trimouille Island. Refer Figure 3.
Figure 5 : Ed Burke and Ted Rollo taking radiation readings at Alpha Island.
The main health danger was from breathing in contaminated soil while digging up samples, so Turk decided he would carry out this task. The samples had to be taken from discrete levels below the surface. The detailed report of this work is not available, however, from memory, the depth specification was probably samples from each 3 cm to the depth of 15 cm. The special equipment for this task was not available, so Turk improvised with an old jam tin and a length of stake with notches carved at appropriate distances apart (which had the advantage of allowing work by feel late in the day when light was fading). Small plastic bags were filled with soil (mostly sand) from each discrete depth at each location on the grids (for sending to Melbourne for analysis of radiation levels, etc.).
Figure 6 : Camp at Alpha Island.
On arriving at Alpha Island on 25 October, the party set up camp. Refer Figure 6. After laying out the radial grid centred on ground zero, the taking of radiation readings and the digging of soil samples at each grid point commenced. Refer Figure 4. Next day a traverse was undertaken to the exclusion fences, radiation readings were taken at mapped positions between the exclusion fences and ground zero, soil sampling was continued, and photographs were taken to illustrate written descriptions of the condition of the exclusion fences and the plastic cross laid out at ground zero to indicate this point on the subsequent aerial photography. Refer Figures 5 and 7.
Figure 7 : Ed Burke and Ted Rollo laying out plastic cross at ground zero on Alpha Island.
Early on 27 October the terrestrial photography was completed and the camp at Alpha Island packed-up before the party left for Trimouille Island. Refer Figure 8. Arriving an hour later, the party quickly set up camp then carried out surveys in the ground zero area, including laying out the radial grid, and proceeded to take radiation readings and soil samples. With time rapidly running out, the next day involved continuous work from dawn to after sunset: setting out the rectangular grid; taking radiation readings and digging soil samples and photo-marking, with a plastic cross, ground zero and the Goat Hill survey mark. On this calm day, the temperature between the bare sand hills exceeded 50°C. Returning to camp at dark, most of these seasoned field staff went straight to bed, some so exhausted they didn’t even eat first. The final morning on Trimouille Island was spent on a traverse to the fence, photography and collecting the remaining radiation readings and soil samples.
Figure 8 : Departing Alpha Island; Ross Stapleton left and Andrew Turk right.
The time on the islands was limited as Turk was only permitted by the then Finance Regulations to spend a maximum of $1,000 on boat hire at any port. As it was, the seven-day boat hire included one day for free, for the good of the Nation, agreed to by the captain of the Northern Venture.
During the afternoon of 29 October the field party was taken back to Barrow Island for an overnight anchorage. Next day the Barrow Island party came on board and the boat returned to Dampier. The entire trip had lasted seven days, with a total of only 24 man-days to complete all the tasks at the atomic sites, except the connection to the national survey network, which was achieved during an Aerodist and Tellurometer survey in September 1973.
Some weeks later in Melbourne, Turk was advised that the soil samples had been assessed and demonstrated a very high level of differentiation between the samples from different depths. In response to an enquiry as to how this was achieved without the special machine for this purpose, Turk sent to the Atomic Energy Safety Committee a lengthy scientific description of the method used, accompanied by the well-worn notched length of wooden stake!
Figure 9 : At Potshot Hotel, Exmouth, sorting survey and camping equipment (L-R) Andrew Turk, Bob and Noel Goldsworthy.