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24 July, 2000

July 24, 2000

Matanuska Glacier, Alaska

The great weather has stayed with us for yet another day. It was a beautiful day to be on the ice a long time and the sunshine felt warmer than ever today. We had another couple of REU students assisting us with our work today, Isaac Larsen and Jessica Allewalt. At one point I had to go help Isaac get out of some muck that he got stuck in. We were sampling from a different vent than we had before and it comes out about 50 feet from the shoreline of some very wet loess beds. Loess is the very fine sediment formed by the scraping rocks in the glacier. It is easily suspended in water (glacial flour) and makes the waters very gray. It forms thick layers as it settles around the lake formed by the Mammoth Vents. Earlier this month these beds had been under water but the recent cooler weather has reduced melting and the resulting water levels are down significantly. In certain parts it will hold you up really well but in others it seems to suck you right in. I was standing taking a picture near the edge today when all of a sudden my right foot sunk all the way to the knee, covering my boot completely. Oddly enough the other foot had plenty of support that I could get myself out. Itís very interesting to walk on and rubber boots are a must. Of course thereís the uncertainty of whether or not it will hold you up in some spots and occasionally you must backtrack and try to pull yourself out. Sometimes as you walk you see the color change as you plant your foot. Iíve noticed this before on beaches at the ocean where the sand is very wet. The odd thing is it appears as though your foot causes the loess or sand to dry up somehow. In other places you can stand on one foot and with the other foot actually create waves in the loess, sort of like standing on Jello. Sometimes it tends to form long narrow cracks underfoot as you apply pressure. There are loess deposits all over the place here, some of which have been deposited many years ago, and when itís dry it gets blown easily by the wind. The vehicles we use here are constantly covered with this fine powdery material. It would be impossible to keep up with a daily car wash!

We are now using just two ISCO water samplers again and they are both sampling the Mammoth Vent area. We decided to remove the ISCO from Mammoth-4 and move it to Mega Vent. This vent is also in the Mammoth collection of vents but has a pretty high discharge and we want to see if dye is also coming out there as well. We wanted to keep one existing ISCO on Mammoth-1 and take samples more frequently (every five minutes instead of ten) in order to get a more well defined graph, especially near the two hour mark which gave several little rises in the first dye run. We decided to start the sampling a half hour later since we didnít see any dye in the first half hour of samples before. We hope that by adding the extra half hour at the end that maybe we can determine whether or not all the dye has left the system without actually taking more samples than before. If we still see dye in the last samples then we will sample for a longer time period the next time.

A pretty nice frazil ice terrace has formed at Mammoth-4. In fact the frazil ice there is starting to become a real problem with the water samplers. In my July 18 journal I included some pictures of the ice that had frozen onto one of the collectors. Today they had a really tough time getting it dislodged from the ice. Ben Cashman actually walked out onto the ice terrace to try to break it free with a pole. At one point the ice he was on slowly began to tip over and he quickly jumped back to the safety of the glacierís ice edge.

Tomorrow we will begin to analyze the samples taken today and go to town for groceries, laundry and showers. It will be interesting to see if we duplicate the result at Mammoth-1 and if Mega Vent seems to be connected as well.

Marvin Giesting


Isaac Larsen tried to dig himself out of the muck but it was too much. A lateral moraine from a previous advance of the glacier can be seen in the background. It is the low flat green ridge extending the full length of the picture.


Water flows over the frazil ice terrace that has formed at Mammoth-4.


Looking over the low, wet loess deposit toward the Mammoth Vent area and the glacier. The highest part of this is maybe four inches above the water level.


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