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Glacial Moraine

ice and moraine

The Matanuska Moraine

Features of a Glacier

Looking out on the Matanuska Glacier, you’ll see flowing fields of white ice, surrounded by what looks like mud and rock on both sides of that ice. In fact, those sections of rock are actually a part of the glacier as well, called the moraine. Underneath the rocks and mud are many layers of ice, just like what you can see on the other sections of the glacier. The moraine contains many of the same glacial features, including moulins, crevasses, and pools. So what makes the moraine so different from the bright white ice on a glacier?

What is Moraine?

rocky moraine and glacier cave

A view of this glacial cave exposes the ice that rests below the moraine

Moraine is a formation of debris gathered by glacial movement over time. Similar to how a river can carve out valleys and canyons, glaciers pick up bits and pieces of mountains and earth as they travel. Different from a river though, a glacier doesn’t sort the debris as it drops it to become moraine. When rivers deposit debris, the rocks and stones are sorted by size. The speed of the water determines how big the rocks are that it can carry. A glacier, however, carries everything along with it, and deposits debris of all sizes in the same location.

The Matanuska glacial moraine is composed lateral moraine. This rocky debris is located at the sides of the ice flow, and the terminal moraine, located where the glacier ends. The Knik glacier, located further south in Alaska by Anchorage, has a large medial moraine. This is created when two glaciers converged over time, with their lateral moraines flowing together in the center. Often, when looking at a glacier, you will notice that the lateral moraines tend to rise up higher than the glacier itself. This happens because the moraine shields the ice below from the sun. Thus, slowing down the melting of the glacier beneath the moraine. Glacier that is not covered by moraine will melt much faster than moraine-covered glacier.

Moraine also exists where glaciers used to be, but have since receded from. When a glacier completely melts away, the lateral, terminal, and medial moraines all remain in their place. This can result in glacial deposits all over the world. Further, leaving large boulders in unexpected places, such as in the middle of a field in the Midwest. Scientists often study the extent of terminal moraines to learn more about the size of glaciers at their maximum. The terminal moraine represents the furthest extension of a glacier.

The Power of Glaciers

a man walking across glacial moraine

These ice guides traverse the lateral moraine of the Matanuska Glacier.

Many other types of moraines exist in addition to those described here. Glaciers are powerful landforms that can cause bits of mountains to travel hundreds, or even thousands of miles. If you’re ever somewhere, and notice a boulder that seems rather out of place, think about the possibility of a glacier being the cause. And whenever you’re out on a glacier, remember that the dirt and rocks on the sides are more than just that. They are a super cool glacial phenomenon!

Author: Michelle Patten