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14 July, 2000

July 14, 2000

Matanuska Glacier, Alaska

This morning Ben and I measured the conductivity of the samples that were left to settle over night. It seems that this does provide a better method than shaking the bottles just before testing. There doesn’t seem to be nearly as much variation in the data and the graphs look much smoother as a result. Perhaps the suspended sediment interferes somehow with the instrument.

What we consistently seem to see in our data is a decrease in conductivity during the time we sample. This is expected to some extent because the melting on the glacier increases during the day and into the early evening. This added pure water slowly dilutes the subglacial drainage and drives the conductivity of the silty discharge from the vents down. We’ve been hoping to see a rise during this period which we could attribute to the salt. In spite of getting better readings by this method, we are still coming up empty handed. We think that either: (1) the salt is not dissolving in the conduits fast enough (2) there is too much dilution before it reaches the ISCOs (3) the moulin drains to different vents or (4) a combination of factors. We think we may proceed with the rhodamine dye experiments very soon.

After collecting more ISCO samples from the two vent stations we had some free time and decided to explore certain parts of the glacier. In parcticular Ben wanted to follow some cracks in the area of our moulin to see where they went and if something else was going on along their length. We both wanted to go higher up on the glacier than we normally do during our work just to explore the scenery and have a little fun.

With crampons on we made our way up the glacier and onto the white ice. In many places we saw all different shades of blue coming out of the ice. This occurs because the other colors of sunlight are being absorbed, but the blue is not. We’ve also seen black ice but that is due to no light coming out of the ice at all. The ice is black under the rock debris that’s scattered around the north part of the terminus. The rocks, sand and silt block the light from entering the ice at all. As a result, little or no light can reflect or scatter back to the surface. Mounds of black ice can be very difficult to cross. You can’t really see that there is even ice under there. It just looks like a pile of sand and rock much of the time. If you’re walking on it without crampons you’re sure to lose your footing and take a hard fall.

But where we were headed it was all nice clean white ice. Wherever there were cracks or narrow crevasses we would see many beautiful shades of blue. As we moved higher up the ice the surface texture changed noticeably and it got much warmer for some reason. Lower on the ice the surface seemed really granular and normal hiking shoes could almost suffice. But up high it took a very smooth,wavy, almost fish-scale type of appearance. You had to kick hard with the crampons to get secure footing. We were very careful to pick a route that would be forgiving should we slip. Something odd we both noticed was that the dimpled surface of ice seemed to have pink rings where the “ridges” of the dimples were. It sort of caused you to lose your depth perception to some extent. I think it was our eyes playing tricks on the bright reflective ice. We agreed that polarized glasses would have been helpful.

At one point we came to an impressive crevasse which groaned quite often and very mysteriously. The walls were probably serving to amplify the cracking sounds that travel through the ice. As I peered into its deep blue I wondered how far away some of these sounds could have originated. I managed to roll a rather large boulder off its perch and into the chasm below. It gave a deep thud with each bounce off the walls and finally a huge splash at the end. Judging from the sound and time I estimate it was about 100 feet down to the water (which we could not see). This thing was huge and we were very careful about our positions here. We continued up the glacier a bit more but were forced to turn back. The ice was no longer gently rolling but had become quite impassable. We had managed to go quite a distance up the glacier.

On our return down the glacier I stopped many times for a drink of the meltwater from the many rivulets. It was so delicious and of course ice cold. We also paid another visit to the glacial lake that Ben Cashman had shown us last week. As we hiked its northern icy shoreline I was looking for other routes to explore on the far side of the lake. I’m certain that we will get several more chances for these hikes. It was a good thing to get away from the work for just a short while. Tomorrow we will pick up the work once again. Till then.....

Marvin Giesting

You can see various shades of blue in this small crevasse. Also notice the smooth wavy appearance of the ice. We had to be extra careful of our crampon holds on this type of ice.

The boulder under my left foot was sacrificed to the deep crevasse below.

Beautiful reflection of seracs on the glacial lake. It was very peaceful here listening to numerous small streams dump into this lake from all around!

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