Mountaineers + Reading Glaciers: Our Connection to Climate
Mountaineers see climate change. It’s shoved in our face as an observable fact. On approaches to mountains we deal with miles of moraine where maps show glacier. Once on route, we find that steep glacier headwalls, once covered by spongy neve, have become black ice. And with less neve, we see more rockfall, such as during the summer 2003 heat wave that closed Mont Blanc.
Non-mountaineers have heard that glaciers are vanishing worldwide, yet most have never actually seen a glacier. They’re often curious about our encounters with these climate-change barometers.
By simply looking at a glacier, a mountaineer can interpret the glacier’s condition and the local climate trend. We don’t need historical photos to understand what is happening. I’ve talked with glaciologists around Alaska. They agree these are the 5 key visual indicators of glacier health:
Snowcover: On stable, healthy glaciers, at least two-thirds of the surface are covered with snow at summer’s end. Before the first winter snowfall, the equilibrium line altitude (ELA), dividing the accumulation zone from the ablation zone, should be no more than a third of the way up from the glacier terminus — otherwise the glacier is losing volume. Glacier snowcover is often visible from a vantage point above the glacier. On this photo you can see the ELA high on the glacier separating clean snow above from the dirty, snow-free glacier ice below.
Ice Thickness: Glaciers lose ice through thinning — even more so than by receding — in response to warmer average temperatures. From a mountaineer’s perspective, your altimeter or GPS might register elevations lower than those shown on the map. Some glaciers, such as the Taku Glacier in Alaska’s Coast Range or the center of the Greenland ice sheet, have increased snowfall in their accumulation zones. This is because the warmer temperatures, while remaining below freezing, allow the air to hold more moisture and produce more snow.
Toe Shape: Receding glaciers have a relatively crevasse-free, sloping snout, like a wheelchair ramp, created by ice stagnating and melting in place. Healthy glaciers, like the Taku, have heavily crevassed, vertical or bulbous fronts.
Trim Lines: Thinning glaciers leave trim lines on the valley walls and rock faces that show the most recent long-term high ice level. As the glacier melts down, a visible line often remains on the valley wall between the vegetated and lichened terrain above and the freshly exposed moraine and lichen-free rock below. Like high water marks, trim lines surround shrinking glaciers worldwide. Most obvious are trim lines from the Little Ice Age that ended 100 to 150 years ago. Less healthy glaciers have trim lines far above the glacier surface.
Moraine: With less snowfall and warmer temperatures, the glacier conveyor belt slows and moraine accumulates on the glacier surface, sometimes until the ice is entirely covered. Thus, healthy glaciers havewhite-ice melt zones, while receding glaciers have moraine on the theirmelt zones. When the ice under the moraine melts, the mud, rock and boulders become ground moraine. Early successional species, such as moss and alder, grow on this newly exposed land in the wake of a receding glacier. In contrast, the vegetation in front of a healthy glacier is characterized by climax forest, with old-growth species, like hemlock.
Joe Stock is a mountain guide and photographer based in Anchorage, Alaska.