Drill & Probes

Transportable Cable Drill and Sub-Glacial Sediment Probes

Alaska's glaciers are commonly refered to as "warm base" glaciers, meaning that they have a large liquid water component and that their movements are related to the deformation of ice at its pressure melting point. It is thought that the sediments upon which many glacier ride, are high in water content and deform like toothpaste. (In contrast, a "cold base" glacier, having little or no liquid component, deform more as a solid, rigid body commonly refered to as plastic deformation.)

Some glaciers rapidly advance over a short period of time. These surges are not well understood. In an effort to understand more about the behavior of surging glaciers, Geophysical Institute glaciologists have enlisted the expertise within the Institute's Machine Shop to construct a tilt-meter probe package and a method of placing these packages under nearly two thousand feet (600 m.) of ice into the sediments underneath Black Rapids Glacier in the Alaska Range during the spring of 2002.

 

While a portable, steam-powered drill will complete the holes down to the sediment layer sandwiched between the glacier and the bedrock, the radio transmitting tilt-meter probes (developed by the Geophysical Institute's Electronics Shop) will be driven into the watery muck and gravel beneath the glacier with a transportable cable drill designed and built by the GI Machine Shop. Unlike the familiar rotary drill used in the oil industry which turns-round a drill bit attached to a "string" of drill pipe through which a lubricant circulates, a cable drill uses a weighted bit which is raised and dropped, driving the pointed bit into the substrate by pulverizing the rocks in its path.

The up and down motion of the cable drill is similar to pile-driving witnessed at many construction sites. The radio transmitting probes will be pounded like piles into the substrate beneath the glacier. The unique design of the probe package features a drill point on one side and a hydraulic activated, spring release mechanism to detach the probe package from the drill cable and weights. Each probe contains sensors for pressure, temperature, and x,y,z axis orientation. Data from the probes is relayed via ELF radio waves to receivers frozen in the glacial ice a few hundred feet above the probe positions. These receivers transmit their collected data via cable to a surface receiver where it is logged and stored.

 

Epilogue:??   Accompanied by an assortment of unexpected problems, researchers and engineers successfully deployed four probes underneath Black Rapids Glacier during the spring of 2002. Images and text by Jeff Pederson