20 July, 1999
This morning, grad student Don Lindsay, PI Andrew Fountain and I loaded up the borehole video camera equipment onto a pack board and hiked out to the drill site. We were going to view the inside of the borehole, this time without water. We were going to look for a mechanism from which the drainage of water from the hole had occurred. When we arrived at the hole, its diameter was smaller. Why?
The borehole video camera epitomizes the elegance of modern technology. It is small, compact, and easy to use. The lens/camera is the size of a golf ball. It is ringed with bright red LEDs, (light-emitting diodes) which provide light. Two hundred meters (about 600 feet) of triaxial video cable separates this lens from the video recorder and power supply. Triaxial means that there are three wires within the cable. All of them are nested. The central wire is a single, heavy gauge copper wire which transmits images into the video recorder, which in this case is a hand-held digital camcorder. The camcorder has a 3x5-inch LCD display from which images can be viewed. The central wire is surrounded by insulation, which is wrapped with a braided, fine-gauged copper wire. This "layer" is also wrapped in insulation, around which is another braided, fine-gauged copper wire. These outer layers of fine-gauged wire are connected to a 12-volt power source. Once the 12-volt power supply is engaged, the borehole camera begins returning a signal to the camcorder.
These data from the borehole camera do not help in quantifying the dynamics of glacier response to the outburst flood. However, the images enhance a picture of what is occurring within the borehole. We observed numerous fractures running across the borehole. This was expected. From a structural mechanics perspective, the borehole represents a weakness in the ice. Local stress within the ice will be concentrated at this location, from which new fractures will emanate. It is similar to ripping a piece of paper which has a notch along one of its edges. A new tear in the paper will originate at the notch, which represents a weakness in the structural properties of the paper.
In addition to fresh fractures, we observed what was inferred to be an englacial conduit, which is a channel within the glacier which drains water. It appeared as a cavity in the sidewall of the borehole. In this instance, there was no water flowing into or out of the conduit. Pebbles and sand were resting on a ledge at the mouth of the cavity. It was interesting to be viewing the interior plumbing of a glacier.
At the beginning of this journal entry I asked a question. Why would the diameter of the borehole be getting smaller? The answer is that no one really knows. But there has been lively discussion about various hypotheses. One idea was that the movement of the glacier is squeezing the hole shut. This happens to most openings in glaciers. However, the hole was closing faster than expected, and the hole was retaining its round shape. If being squeezed shut, one would expect the shape of the hole to become elliptical. The other idea was that melt water was running down the sides of the glacier and freezing to the walls. The problem with this hypothesis is that temperate glaciers are typically at the melting/freezing point of water (0 degrees celsius) during the summer. With an air temperature above zero celsius, they are usually melting out water, and not freezing water. However, it was suggested that since the lake had drained, this portion of the glacier was under tension - it was being stretched and bent much like a diving board when someone stands on its end. The numerous fresh fractures around the drill site supported this notion. The freezing point of water is higher when under conditions of reduced pressure. Therefore, with an elevated freezing point, meltwater inferred to be at zero degrees celsius flowing down the side of the hole would encounter freezing conditions. The question at present remains unanswered. This happens when doing research. While engaged in the main objective of the study, many other observations and questions present themselves. Sometimes the answers to these questions are simple. Sometimes pursuing the answer involves more research. There is no finality to the conclusions that come about as the result of science research.
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