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3. Field Report

"Rough Ice" taken from a height of about 5000 ft. It is an example of a rather horrible rubble field. The round pans are old "polar" ice - perhaps 20 ft thick. However, this picture was chosen to show the ice at its worst; most of the route is not nearly this bad, and in general there are lots of places that helicopter could land. Photo: Ron Verral.
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Alert, 3 April, 2006
Received from Ron Verral and Trine Dahl-Jensen
Edited by Henrik Højmark Thomsen, GEUS

First test shots on the ice

During the Twin Otter flight to the ice camp on 2 April we had a good look at the ice all the way out. Most of it was 'annual' ice formed this year. The amount of old polar ice was probably less than 10%. This means that we won't have any trouble finding thin ice (less that 6-ft. thick). As you know, we will be wanting to lower explosives into the water below the ice, and we need to find relatively thin ice so that we won't waste hours drilling. On the other hand, the annual ice this year is badly broken up. The previous days strong offshore winds have pushed the ice around until much of it is rubble. The rubble can be so bad that a helicopter would be hard pressed to land in it. However most of the route is not nearly this bad, and in general there are lots of places that helicopter could land. It is the Twin Otter landing sites that we are worried about.

We will use both Twin Otter and helicopters during the work on the seismic lines. One of the main functions of the Twin Otter is to act as a "resupply" for the helicopters. The helicopters have to carry a lot of explosives to each blast site, but they are relatively slow, and they can't carry the loads that an Otter can. Thus, it makes more sense for the Otter to make a number of caches of fuel and explosives and for the helicopters to work out of these caches. If the ice were so smooth that we could land a Twin Otter anywhere, we wouldn't bother with the helicopters. But nature is not that accommodating, and so we need to use both fixed-wing and helicopters.

The explosives are special made, so that the charges fit into a borehole with a diameter of 25 cm. Here the explosives are laid out in-line with a rope running through the centre hole and primacord (an explosive) running through the two off-centre holes. The chain of explosives is lowered down the hole by the rope and is suspended at a depth of 100 m. A length of a primacord connects the explosives with the surface. An electrical detonator cap is attached to the primacord above the water, and a long extension wire is taken off a safe distance to a "blasting box". This box puts out a fairly large current at an exactly known time. The current sets off the detonator cap, and the cap ignites the primacord. The detonation runs along the primacord at a rate of 6 km per second, so it takes only a few milliseconds for the detonation to get down to the main explosives and set them off. Photo: John Boserup.
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3 April, 2006
Weather in Alert: -26, slight overcast, no wind

This morning the Twin Otter took a group of blasters out to the ice camp to conduct a test shot. It is a requirement from Natural Resources Canada, Department of Fisheries and Oceans that we conduct a test shot and make required measurements of the sound pressure from the large blasts (350 kg). A report will be made and included in the final fieldwork report. The most convenient place to do this right now is the ice camp. As well as satisfying the legal requirement, the blasters will get to test out their equipment and their technique. They will also get to study the ice and inspect the ice camp. Jopee Kiguktak who is the official wild life observer from Nunavut was also there. He is part of the process that ensures that the marine environment is properly protected.

The test was successful including both a small charge of 17,5 kg of explosives and a full charge of 350 kg explosives. The pictures show the different phases of the test, and they also show the hard and cold condition on the ice for the blasters. We had 10 recording instruments on site as well as two in Alert. All recorded normally and the large shot was clearly visible. The small charge of 17.5 kg was seen but very faintly.

The three helicopters made it to Resolute Bay today and the intention is to continue to Alert tomorrow.

Tim Cartwright hauling the explosives toward the ice hole and Dave Forsyth guiding them from the other end. Photo: John Boserup.
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Small trench made in the snow and ice, when the primacord exploded. There is no trace of the main explosion, because it is set off 100 m under the water. Photo: John Boserup.
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Christian Marcussen
Christian Marcussen
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Peer Jørgensen
Peer Jørgensen
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Søren Bredvig
Søren Bredvig
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Last modified : December 6, 2009
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