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19 July, 2000

July 19, 2000

Matanuska Glacier, Alaska

After more rain off and on throughout the night the skies cleared up once again and we had another beautiful day on the glacier. This morning Jeff Strasser took all the REU students out for a little bit of a tour and some Glaciology 101. I had no other plans for the day and Jeff graciously accepted when I asked to join them. I thoroughly enjoyed myself as I continued to learn more about glaciers and glacial features.

Also joining us this morning was Greg Baker from SUNY-Buffalo who came up with Jeff. Greg is a geophysicist and will be here for only a short while doing some seismic studies on the glacier. I hope to learn a little about what he’s doing as well and eventually report about what his experiments tell us about this glacier. While we were out on the ice he tested a device that uses blank shotgun shells to impart a shock wave of sorts into the ice. Eventually he will set up sensors to pickup the reflective signals that come from below. But today he was simply interested in seeing how well it might work on this ice. He seemed absolutely delighted with the result, picking up on subtle observations that we weren’t clued into. I was snapping a picture while he did it and then I noticed a sound all around me sort of like small pieces of ice were falling. And yet I was merely 10 feet from it when it fired and did not feel anything, not even a splash from the small puddle that surrounded the bore hole. Then I noticed that the sound was actually coming from ground level, caused by numerous squirts of water and air bubbles ejecting out of the many ice cracks in the vicinity as a result of the vibrations set up by the shell. It was very entertaining and interesting. I couldn’t resist saying what my students say after a neat demonstration, “Do it again!”

In the afternoon Jeff, Ben and I walked around looking at the moulins and vents and discussed how we might proceed with the dye tracing experiment. We decided to use a new moulin, one that is very close to Trail Vent, perhaps 150 yards or less away. The hope is that we can’t miss with this one since we will have four ISCO water samplers spread like a fan around the vents in this vicinity. Even though it won’t be able to tell us much about the subglacial drainage system due to the short distance traveled, it should provide a good test run to go through all our procedures and will give us an indication of maximum concentrations we should see when we eventually do move to a more distant moulin. We also think it could be interesting to compare the results of a short drainage run to a long one. At first we felt that it would definitely show up at Trail Vent and probably not at another location. However, the volume of water flowing into this moulin today appears to be much greater than what’s exiting Trail Vent. So it must be going somewhere else, either exclusively or in conjunction with Trail Vent. We think some will split off and go to the Mammoth Vent area. We’ll have two of those vents covered, most likely the ones with the larger discharges. With the cool weather of the past 8-9 days the flow at all vents has gone down drastically. Those with low flows at Mammoth may mix too much with water surrounding it in the basin to get good samples. We plan to dump the dye at 11:00 am and take samples every 5 minutes for two hours. We anxiously anticipate the results.

Marvin Giesting

One of the topics discussed during the morning walk with the REU students was ice cones. This was a big one at over three feet tall. The sand and silt at the top was wiped away and then rinsed with water to expose the perfectly clear ice beneath.

Greg Baker is about to set off the charge in his seismic gun.

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