Glacier NP, Flathead Valley Geology

Glacier National Park currently has 27 modern glaciers, but its name comes from the monstrous glaciers that carved out its landscape tens of thousands of years ago.

Glacier National Park reveals some of the oldest sedimentary rocks in the country. The current rocks that are exposed in cliffs and road cuts originally started out over one billion years ago as deposited layers of mud and sand. Today, these rocks are sandstone, limestone, and mudstone.

The Lewis overthrust plays a leading role in shaping the landscape of Glacier National Park. Beginning over 170 million years ago, due to crustal plate movements, the Lewis overthrust pushed a large slab of ancient rock on top of younger and softer rocks.

Most of the rocks found in Glacier are sedimentary rocks that were deposited 1600-800 million years ago. What is unique about these rocks is that they have preserved their sedimentary features such as ripples, mud cracks, and raindrop impressions.

About two or three million years ago, the earth climate began to change and became cooler and wetter, creating several ice ages. The last ice age melted about 10,000 years ago. During these ice ages, huge glaciers formed.

Glaciers are powerful destroyers and creators. Many typical features evident of glacial existence are found in Glacier National Park. In addition to breathtaking lakes, keep your eyes peeled for:

• Horns: peaks formed by glaciers moving on all sides of a mountain.
• Cirques: a large bowl caved out at the head of a glacier.
• Aretés: formed when two glaciers flow on opposite sides of the same wall, creating a thin ridge.
• Hanging valleys: small valleys near tops of mountains formed by smaller tributary glaciers.
• Moraines: deposits of debris and rocks that the glacier had carried and left in piles as it melted.