I took a hike to Mendenhall Glacier the other day. As a person who is very interested in the geology of glaciers, it was a really amazing experience. I know a considerable amount about glaciers and can identify the landforms they leave behind with relative ease. Living in the upper Midwest means I’ve been surrounded by moraines and drumlins and eskers and all sorts of outwash features my entire life. Now I finally get to come face to face with a glacier.
The hike was very rugged at times and there was even a rope involved at one point. It was much more a ‘user maintained’ facility once it branched from the main trail for that valley.
The closer I got to the wall of ice, the younger the vegetation became. Mendenhall Glacier has been in steady retreat since the 1950’s and land that has been buried for centuries or millenia is slowly being exposed. This new land is at first sterile and devoid of life. But as time passes and seeds have time to find thier way into places with enough nutrients to support growth, everything starts getting greener. Close to the ice, the land looks like a construction site. Grasses and small shrubs fill the gaps between in exposed bedrock a few hundred yards down valley. The brush gets very dense where the soils have had time to develop. They slowly give way to conifer forests where the trees are larger the further you are from the ice. It’s a wonderful display of forest succession.
Then there was the main event.
The expanse of solid ice is remarkable. It awed me to think I was standing on a thousand winters’ worth of snow. Though it filters the visual spectrum to make it appear blue, the ice is actually clear. As you walk the surface, it crackles like small bubble wrap. Scattered around are oblong holes that vary in size from “oh, neat” to “holy crap!” I didn’t venture far on the ice for lack of appropriate gear and the very real danger of crevasses. Unlike falling through the ice on a lake where there is water immediately below the surface, breaking through on a glacier might mean a tumble of hundreds of feet.
You’ll notice the surface is generally very dirty. The big rocks are obvious, but there’s also a thin veneer of mud over most places. All of this stuff was once inside the ice, but that ice has melted leaving this debris behind. Imagine all of those rocks and all that dirt randomly distributed in a vertical space extending another 300 feet above you. It’s a large-scale version of what we see every spring as piles of roadside snow melt away and start looking dirty as the sand mixed with it remains.
A short distance up-ice is a magnificent ice cave. Here a tributary stream flows from the side of the valley and plunges beneath the ice. For 60 or 70 yards, a person can easily walk in and watch this tributary join other meltwater beneath an opening in the glacier.
I have to nerd out for a bit and talk about eskers. An esker, for those who haven’t done any hiking in the Kettle Moraine, is a long, narrow ridge made of sand, gravel and cobble that is formed by water flowing underneath a glacier. This ice cave demonstrates exactly how they form. This stream of water is currently walled in by ice on either side, so as it flows, sediment is accumulating inside. When the ice melts away, the water will flow someplace else and leave behind this narrow line of gravel and rock. Next time you stand on an esker, imagine this sight around you because that’s exactly what it would have looked like during the late Pleistocene.
I can nerd out further and mention this particular location is not going to preserve an esker. The land is far too steep and the accumulated sediment will erode away not long after the ice retreats from here. But if this was flat ground, an esker would indeed remain.
Being inside the ice means you can see all of the debris that the glacier is transporting. Everything from flecks of dust to giant boulders. It demonstrates how glaciers move material. It’s not so much an enormous bulldozer as it is an enormous conveyor belt. The ice grabs onto these rocks and drags them along with it. The material is released where ever the ice that holds it melts.
Up close, the ice looks more like frozen smoke. It’s very smooth where it’s melting and it is extremely hard. Glacial ice forms as layer after layer of snow builds up and compresses into ice as air is squeezed from it by the weight of the snow and ice above it. Again we see this on a small scale every winter in the pile of snow next to your driveway. By the time March rolls around, the base of that pile is solid ice. Simply add a lot more snow and a lot more time to get a glacier.
There is so very much more I could talk about when it comes to glaciers and how fantastic it was for an Earth Sciences nerd to be snooping around on one. Suffice to say I enjoyed myself a lot and it was well worth the difficult hike to reach it.
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