Geology
Although Glacier National Park currently has 27 modern glaciers, it gets its name from the monstrous glaciers that have carved out its terrain 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 roadcuts originally started out over one billion years ago as deposited layers of mud and sand. Today, these rocks are sandstone, limestone, and mudstone. These rocks formed during the Precambrian period, before plants or animals existed on earth. These Precambrian rocks are believed to have been undisturbed for about 65 million years, until the Rocky Mountains began to form.
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 Precambrian rock on top on younger and softer Cambrian rocks.
It is unusual to find older rocks on top of younger rocks. One of the best places to see the effects of the Lewis overthrust is Chief Mountain.
Most of the rocks found in Glacier are Proterozoic sedimentary rocks that were deposited 1600-800 million years ago. What is unique about these rocks is that they have preserved a lot of 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. A glacier is essentially a river of ice that forms when more snow falls in the winter than is melted in the summer.
The building up of snow presses down on the snow beneath and forms ice. The ice on the bottom becomes soft and flexible, thus allowing it to be able to move. Today, all glaciers in Glacier National Park are receding.
Glaciers are powerful destroyers and creators. Many typical features evident of glacial existence are found in Glacier National Park.
Besides 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.
West Glacier, MT Weather
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