Title Bar: Illustrated Glossary of Alpine Glacial 
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Unconsolidated material (till) deposited along the sides of an alpine glacier.

Freeze-thaw weathering of alpine valley walls results in rock debris falling on the surface of valley glaciers. This rock debris constitutes lateral moraines, thus lateral moraines form ridges of rock debris on top of existing alpine glaciers parallel to the valley walls. As glaciers melt, this debris may be left behind as a ridge of unconsolidated rock debris along the valley side.

The photograph on the left shows a proglacial lake in front of Grinnell Glacier. The edge of the glacier is on the very left edge of the photo. Off in the background, some snow and ice can be seen leading up to the Salamander, another glacier. To the right of this ice and at the far end of the lake, you can see a ridge of gray-colored, unconsolidated material. This material forms a lateral moraine which extends off the right side of the photo.

Photo: lateral moraine

Photo: K.A. Lemke. Used with permission.

Photo: lateral moraine

Photo: R. Schukar. Used with permission.

The photograph on the right shows a closer view of this lateral moraine. The difference in the color of the moraine deposits is most likely due to the degree of weathering: the yellower material has been exposed longer than the grayer material. The deposits are unsorted and consist of material ranging from silt-sized particles, sometimes called glacial flour, to large boulders (compare some of the rocks to the person in the photo). In both of these photos you are looking toward the northwest.
Topographic map: lateral moraine On the topographic map, north is toward the top of the map. Upper Grinnell Lake is the proglacial lake in the photo. The thin band of ice leading away from Upper Grinnell Lake to the Salamander appears on the map and the photo. Both Grinnell Glacier and the Salamander appear much larger on the map than in the photos. The map is dated in 1968, while the photos were taken in 1993. These glaciers have been retreating since the eruption of Mt. St. Helens in 1980. The lateral moraine appears on the topographic map as brown speckles. Other moraines are also evident on the map.
| More Examples of Lateral Moraines |

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All commercial rights reserved. Copyright 2010 by Karen A. Lemke. Earlier copyright 2002 by Karen A. Lemke, and 1998 by Karen A. Lemke and Linda Freeman.
Last updated June 2010 KAL.