Geologic Activity

Gable Mountain, part of the Lewis Range, is located in the far northeast corner of the park.

NPS photo.

Glacier National Park is millions of years in the making. Its landscape is defined by geological processes. The park we see today began forming with the deposition of the Belt Sea (about 1,500 million years ago) and continued with periods of mountain uplift and glaciation. The shifts we see today are more subtle than what happened in the past, but Glacier has a dynamic landscape that is always subject to change. Weather, natural events, and time can transform the park we know today in ways we can’t always predict. Recent geologic activity includes:

• Erosion and sedimentation

• Landslides and rockslides

• Earthquakes

 

Stream channels and their effects on the park's geology can be seen in many places within the park. Avalanche Gorge, visible along the Trail of the Cedars hike, is an excellent example of the carving power of water.

NPS photo.

Erosion and sedimentation

Heavy spring snowmelts, precipitation, and stream runoff contribute to the movement of rock material and the continuous flow of stream channels. Eroded rock is flushed down steep mountain streams in the spring and re-deposited in flatter sections downstream. New stream channels are created through the powerful forces of water and rock. Riparian zones and floodplains along creeks and rivers are in constant change because of this annual process. The North Fork of the Flathead River and its tributaries are good examples.

 

Evidence of landslides can be seen at places like Slide Lake, located near Chief Mountain on the northeast side of the park.

NPS photo.

Landslides and rockslides

Numerous landslides and rockslides have happened throughout Glacier. These events are influenced by weaknesses in the underlying geology and climatic factors. In some parts of the park, highly fractured bedrock sits above weak sedimentary rocks. Repeated freeze and thaw cycles of changing seasons can additionally weaken these slopes, bringing them closer to collapse.

Notable recent activity includes a large rockslide off Chief Mountain in 1992; one near Napi Point in the 1950s; and a very large rock avalanche that dammed Otatso Creek to form Slide Lake around 1910.

 

The Lewis Range seen today was partially formed by fault activity along the Lewis overthrust over millions of years. The fault follows the eastern range front, near the east boundary of the park.

NPS photo.

Earthquakes

Many faults run through the park, creating the potential for earthquakes. However, most are older faults that are less active today, such as the Lewis overthrust. Compared to other areas of the western United States, earthquake activity doesn’t happen often and is usually minor. Southwest Montana has greater seismic potential compared to Northwest Montana, where Glacier is located.

 

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  Geologic Formations

  Glacier's sedimentary rock banding represents many ages.

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  Mountains

  Glacier's impressive mountains are a story of pressure, folding, uplift, and erosion.

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  Glacial Geology

  Once you know what to look for, viewing Glacier's landscape can seem like reading a textbook on the geologic effects of glaciation.