31 July, 2000

July 31, 2000

Matanuska Glacier, Alaska

The beautiful weather we had yesterday remained to provide a nice clear sky all night long. For the first time I was able to spot a few stars although it’s still too light to see any but the brightest. We had not had such a clear night since the first week I was in camp. The distant snow capped peaks that are visible up Glacier Creek were very bright and scenic as the sun slowly dipped over the horizon. The scene was one that you wish could be preserved and experienced over and over. Although it doesn’t get totally dark, the absence of the sun always serves to cool things down whether it’s from the setting of the sun or daytime cloud cover. By morning the air felt quite cool and a good frost was on the stove as I made my morning coffee. By mid-morning we were off to town for yet another day of grocery shopping, laundry and showers.

Ben stayed behind and set up the ISCOs for yet another dye experiment. This time we decided to go farther up the glacier and pour into the moulin that we originally used with our salt experiments. We have gotten repeatable results with our first series of dye tests and now it’s time to build on those results a bit with a new experiment. It will be interesting to see what comes out of the samples when we analyze them tomorrow.

In many of the pictures I’ve included in these journals it has been obvious that there is a lot of rocks and debris on the surface of the glacier here. The Matanuska is a bit unusual in the extent and spreading of debris near the terminus. This debris which includes large boulders, gravel and sand is called a moraine. There are several basic types of moraines.

A “lateral moraine” runs parallel to the glacier and lines both sides of it. They are generally created by two processes: 1) a build up of debris between the sides of the glacier and the bases of the surrounding mountains from rockslides off the mountain slopes and 2) abrasion of sediment and plucking of rocks and boulders from the side valley walls by the glacier itself.

A “medial moraine” is created whenever two ice flows merge. As the glaciers meet, a pile of debris from each glacier’s lateral moraine is pushed up in between them. These are easily recognized in pictures or from the air as a ribbon of black material running down the middle of the glacier. There can be more a number of medial moraines on a glacier if several flows come together at different places along the path of the glacier.

An “end or recessional moraine” is created at the terminus as the ice melts and deposits rocks and debris. These can form if the terminus of a glacier remains essentially in the same place for a long period of time. If this moraine is the farthest down the valley it is called the “terminal moraine”. The terminal moraine of the Matanuska Glacier is near Elmendorf Air Force base near Anchorage and was produced beyond the confluence of the Matanuska and Knik Glaciers about twelve to fourteen thousand years ago. There are no distinct recessional moraines between this terminal moraine and about four miles from the present terminus. This suggests to geologists that it retreated rapidly back to near the present location. Currently the glacier is receding at about ten meters per year.

Marvin Giesting

You can see a large and a small medial moraine as well as the lateral moraines in this picture. The medial moraines spread out near the terminus of this glacier. The green area in the foreground is stagnant ice and supports wooded vegetation. As you move across the moraine you get into the active ice which has many flowers growing near the stagnant ice. Still farther across the debris is too rocky or thin to support any vegetation.

In this area near North Vent you can see the forested stagnant ice as well as flowers growing on the active ice.

It looks like a moonscape out on the moraines. You can barely see the white ice off in the distance.

The supraglacial debris thins out more and more as you move a cross the moraine toward the englacial (white) ice. Notice the rough angular edges to this material.