Sunday, October 26, 2008

Blasted dive holes

We make dive holes two ways: blasting and melting. Blasting involves drilling a small hole through the ice using a "Jiffy Drill" and a carefully sharpened drill bit. Explosive experts ("blasters") then measure the ice thickness based on the length of the drill stem, and insert the appropriate amount of dynamite. They are meticulous in their work, and always ensure that everyone is a safe distance from the blast site. Some ejected ice chunks are the size of refrigerators -- you don't want one of those landing on your head! The countdown is given, and then the blaster shouts "fire in the hole, fire in the hole, fire in the hole!" Cameras click and the explosion is heard, followed by echoes and whoops of excitement from long-shadowed onlookers.

The holes are then cleared of slush and chunks of ice, a process called "mucking a hole." Mucking is hard work that is made a little more tolerable by singing songs, telling stories, or wearing silly clothing. The last step is for a diver to drop into the hole to figure out if it's wide enough for safety. We insist that holes are wide enough for at least two divers to fit through 14-18 ft (~5 meter) shafts. After all, that's how divers must ascend through the hole in case of an emergency.

Blasting dive holes sounds destructive, but one must remember some simple laws of physics. The vast majority of the blast energy is dissipated by fracturing ice and ejecting it into the atmosphere. (Water is an essentially non-compressible fluid, so most of that energy goes upwards.) The underwater shock wave that is created does not damage marine life in the vicinity -- in fact, we collect our specimens right under the holes.

Still, there is concern that the ears of nearby seals may be damaged by blasting, so one of the first things we do is to confirm that none are in the area (e.g., hauled out on the ice through tide cracks). If there are, we do not blast. A simple rule to minimize our impact on the environment as we conduct our studies.

1 comment:

  1. Love the vest, Sam: practical, but with a sense of style.