Valley Glaciers

Valley glaciers tend to be offshoots from ice fields or ice caps that follow the path of least resistance… through existing valleys. There are many of these throughout the world. You can easily tell a valley that was glaciated at some point in the past. The valley tends to have a flat bottom and high sides, forming a "U" shape. Those valleys carved by rivers are "V" shaped. A glacier is really just a river of solid ice, that slowly carves its way through an existing space, picking up rocks and other debris as it goes. This shapes the valley floor as the large heavy glacier slowly carves out its path.

Many of today's glaciers are valley glaciers in mountainous areas.  Glaciers begin in large fields of ice near the top of the mountains, and once they get heavy enough, they begin their slow descent. Eventually the ice gets so heavy that the bottom layer melts slightly, mixing with dirt, rocks and other debris. This slick layer makes it easier for the glacier to move down the slope. Meanwhile, new snow falls at the top, continuously refilling the ice field. The glacier continues on its way, carving out the floor and walls of the valley. Boulders and sediments get picked up in the ice of the glacier, which in turn carve even more of the existing valley into a different shape as the glacier proceeds to advance. This lifting of large items into the glacier is called plucking. Abrasion is the process of carving out the bedrock.

If you've ever seen a large boulder left all by itself somewhere it doesn't seem to belong, it was probably left there by a melting glacier. These lone boulders are called erratics.

A cirque is formed when a glacier carves away all the softer stone, leaving only the hard rock behind. This forms a bowl shape.

Hanging valleys occur where a glacier erodes a portion of the mountain either faster or slower than the surrounding areas. You'll find these near the top of mountains for the most part. You'll notice that they form near streams that are part of the river drainage system for the mountain. Sometimes, after the glacier is long gone, you'll see these hanging valleys make spectacular waterfalls.

Staircase lakes are a series of small lakes that are "stacked" on a mountainside. The soft materials were removed by a passing glacier, leaving only the hard rock behind, which effectively closed off each lake bed.

After a glacier melts away, the debris it carried is left behind. This is called moraine. Ground moraine is the debris left on the ground after the glacier melts. Lateral moraine is caused by the sides of the glacier, forming ridges along the sides. Ablation moraine is the boulders and other materials the glacier scraped from the mountain. Medial moraine forms in the middle of a glacier where two lateral moraines are swept together. Finally, push moraine is ground debris that is gouged out and pushed in front of the glacier.

As you can see, valley glaciers have very distinct features, though they may leave different signs behind. They are responsible for many of the valleys we now live in all over the world.