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3 August, 2000

August 3 , 2000

Matanuska Glacier, Alaska

The next dye tracing test has been put on hold as we wait for a shipment of dye to arrive. With the quantity that we have on hand we decided to let the others use whatís left. We plan to use much larger quantities in our next series of tests and it made sense to wait. In the meantime I continue to help Bob Bigl with the drilling team. Today was spent moving the sleds over some relatively rough ice and rocks to a new drill site. It was hard work as we had to chop lots of ice in some places to allow the sleds to pass.

In addition to working on the dye tracing project and occasionally helping people like Bob Bigl and Greg Baker I have helped Justin Pearce, Ben Cashman and Josh Lawson with a variety of tasks dealing with the day to day collection of water samples from a variety of vents. They were hired by Cold Regions Research and Engineering Lab to collect these samples during this summer melt season. They have been collecting samples from North Vent, Little River, two of the Mammoth vents and also from the main stream that drains South Vent. Samples of roughly 450 milliliter are taken in two hour intervals from each site. Back at camp the actual volume of each sample is recorded and the sediment is filtered from it. Using a special type of filter the sediment is sandwiched between two pieces of filter paper which have been weighed in advance of being used. These sandwiched sediment samples are then dried in an oven and weighed again to determine the mass of sediment that each water sample contained.

The mass and volume information can be used along with the flow rate of the water at stream gauging stations to calculate the flux of sediment out of the glacier. With this information the total mass of sediment for the season can be determined. When applied over the surface area of the glacier an approximate rate of erosion resulting in suspended sediment can be estimated. Data collected in the past suggests an abrasion rate of approximately one millimeter per year.

Recall from July 28 that this sediment called glacial flour is produced by abrasion of the underlying rocks by the basal till layer. There are other erosive processes at work on the bottom as well such as the plucking of bedrock and the subsequent movement and breakup of those larger pieces into smaller ones. By the time this material reaches the terminus there is a variety of parcticle sizes from sediment up to small pieces of stone.

In addition to his CRREL duties Justin Pearce is also collecting data for his Masters thesis project. It is Justinís hypothesis that vents are discharging more than just suspended sediment. Justinís research is looking at the flow of the larger parcticles such as sand and small rocks that may be discharging as well. Using a special type of sampling devices he manages to catch these parcticles for further analysis. The parcticles are sorted by size and the total mass and the mass of each parcticle size is recorded. I have seen Justin wading waist deep into these rushing, cold waters to collect his samples. Heís managed to only fall in once and he gives a good first hand account of how cold these meltwaters are.

At a later date he will have access to the discharge records of the streams draining the glacier. By using similar analysis techniques he will hopefully yield similar sorts of conclusions that were made about suspended sediment erosion. Heís hoping to be able to correlate vent discharge rates with suspended sediment flow and the larger parcticles that heís studying.

Marvin Giesting

Bob Bigl carefully maneuvers one of the sleds over an ice ridge.

Occasionally it is necessary to use the winch on the ATV to get up and over the ridges. At the top the sled must be carefully balanced and braced into a locked position while the hitch is reattached.

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