1 August, 2000
August 1 , 2000
Matanuska Glacier, Alaska
Today I spent another long day on the ice, this time watching and helping Bob Bigl (sounds like beagle) drill holes through the ice to the bottom. Bob is an engineering technician with the Cold Regions Research and Engineering Lab and is quite fun to be around and talk to. He works out of the CRREL office in New Hampshire and was accompanied by Brian Harrington who’s an engineer at the same office. Drilling through the ice is obviously something that requires sophisticated equipment. It also takes quite an effort to get this equipment packed onto sleds and hauled over the rough terrain of the terminus area to the drill site. Bob seems to have designed quite an effective rig and has the transportation logistics down to a science. I am amazed at how efficiently his operation works.
His rig does not drill into the ice as we would think of it. Rather, it uses hot water to melt its way down and it does so very well. In preparation for “drilling” a small area is sprayed clean of all rocks and sediment. A hole is then chiseled into this clean ice that will serve as a reservoir for water that returns to the surface as new hot water is injected into the bore hole. Due to the flow rate of new water into the bore hole, the water that comes up is relatively warm and is pumped out of this reservoir hole in the ice back to a tub where it is filtered of any sediment before going through the boiler again. It is much more efficient to do this than to heat local surface meltwater which is always at the freezing point.
After the reservoir has been prepared the drilling is ready to begin. The drill tip is actually like a long brass plumb bob with a hole through the center. A coil of a special type of hose is attached to this and the hot water is pumped from the boiler through the hose to the drill tip. The water temperature is about 200 degrees Fahrenheit and comes out the point of the drill at around 400-450 pounds per square inch in a narrow stream. With that kind of pressure and temperature the ice is simply melted away in advance of the tip as it is lowered. It can easily drill over one meter per minute by this method.
During the drilling process a computer monitors everything that’s going on. The depth and loadcell are displayed on a real time graph. The loadcell reflects what sort of weight the drill rig is supporting. When the drill just hangs there it is simply recording the weight of the “drill bit” and whatever hose hangs below. When water is fired out the tip this load will decrease a bit. If they start to go through a debris band (small parcticles of rock, sand and sediment) the load gets even lower as the water has a harder time melting ice through these layers. The computer has digital displays for the water temperature entering the hose, the pressure of the water, the flow rate of water and the drilling rate.
Eventually the drill reaches the basal ice layer at the bottom. This layer is loaded with debris and the loadcell reflects this very well. At some point, whether at the bottom or even before, the ice will drain down into the bore hole to a certain depth. Back on July 7 I mentioned the possibility of a water table in the glacier down at some depth. It turns out that all glaciers have a water table. It can be found in any glacier by going down roughly 10 percent of the ice thickness. Due to the density differences of ice and water, 10 percent of ice will float above the water. This happens with ice cubes, icebergs and glacier are no different. The buoyant effect of the underlying water is partially the cause of the more rapid advance of glaciers during the melting season. Once the drill reaches the bottom water or a conduit connected to the bottom, the bore hole will drain down to the equilibrium point.
The holes that have been drilled so far have been done on the same line that Greg Baker used for his seismic tests. The holes have shown that Greg’s techniques for locating the bottom of glaciers works perfectly as the results of drilling has confirmed his earlier measurements. Several researchers are interested in what’s going on at the bottom of the glacier here. Once the holes are drilled a variety of sensors can be lowered into it for collecting data. In addition, Isaac Larsen is going to inject dye samples into some holes in a study similar to ours.
It’s odd how you discover new things sometimes. By the time everything was finished at the first hole it was already about 1:00. I had been battling the cold all day in spite of nice sunny weather. It occurred to me that there is ALWAYS a cold stiff wind barreling down the glacier valley. You only notice this if you’re out on the flat open sections of white ice. In other locations you can become shielded from the wind by mounds or ridges of rock and ice. If you’re fairly active you don’t notice the cold. But just stand around a lot and it really starts to penetrate into your core. Drilling over 100 meters required a LOT of standing around! Like so many other things here I just had to think about this briefly before realizing that it’s a density driven wind. Up higher on the glacier the ice is cooling the air which makes it more dense. This cold, dense air is simply sinking and flowing down the valley much like the glacier itself is. Once we left the ice and got back on dry land it was t-shirt weather and there was no noticeable wind at all.
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