The Setting
Over 1800 square miles (4660 sq. km) of the rugged Rocky Mountains are found within the boundaries of Waterton-Glacier International Peace Park. Two mountain ranges, the Livingston and the more easterly Lewis Range trend from northwest to southeast through Glacier. The Continental Divide follows the crest of the Lewis Range. Elevation varies from a low of 3150 feet (960 m) at the junction of the Middle and North Forks of the Flathead River (near the Lake McDonald valley to a high of 10,466 feet (3192 m) on Mt. Cleveland. There are 6 peaks over 10,000 feet (3050 m) and 32 peaks over 9100 feet (2770 m) found in Glacier National Park. The impressive mountains and valleys within the park are the result of approximately 1.6 billion years of earth history and a number of geologic processes, including, erosion, sediment deposition, uplift and thrust faulting and glaciation Waterton-Glacier is a geologic park. The geologic processes happened in three stages:

1. The sedimentation or deposition of the rock;
2. The uplift of the mountains; and
3. The glaciation or carving out of mountain valleys.

Waterton-Glacier has some of the oldest and best preserved sedimentary rocks found anywhere in North America. Usually, over time and with heat and pressure, sedimentary rock becomes metamorphic rock. For example, limestone becomes marble. It is quite unusual that this old rock still retains its sedimentary characteristics.

Ancient Sediments – 1.6 billion to 800 million years ago
The majority of the rocks forming the mountains of the Peace Park are the result of the deposition of sediments into an ancient inland sea that existed over 1600 million years ago during the middle Proterozoic Era. The ancient Belt Sea covered parts of present-day eastern Washington, northern Idaho, western Montana, and nearby areas in Canada. During the period of active deposition over 18,000 feet (5500 m) of sediment eroded from nearby highlands and were carried into the sea. Accumulation of sediment subsequently resulted in downwarping of the sea floor. Also, over time and as environmental conditions varied, a variety of different materials were eroded and washed into the Belt Sea. The result was alternating layers of sediments of differing composition. With time, and as the sediments accumulated, the heat and pressure created layers of quartzite, siltite, argillite, limestone, and dolomite. The sedimentary character of the rocks in Waterton-Glacier is clearly evident in the form of preserved mudcracks, ripples, and layers; the crystal structure of each formation has been slightly metamorphosed, creating what can accurately be called metasedimentary rock. The combined rock formations that occur in Waterton-Glacier are part of the Precambrian Belt Supergroup and are readily visible in the 33 percent of the park above treeline. Because of the age of these rock structures, no developed life forms are found as fossilized remains; instead only fossilized algae beds have been found.

Stromatolites – a fossil algae colony dating from the Belt Sea
Six species of blue-green algae that thrived in shallow parts of the Belt Sea played a significant role in the formation of the carbonate rocks of the park. They are mostly found in the Altyn and Helena (Siyeh) Formations. Stromatolites have shapes and internal structures very similar to blue-green algae that live in present-day seas less than 100 feet (30 m) deep. Sunlight allows algae to consume carbon dioxide from seawater and release oxygen in the process. There are two important results from this process:

1. When algae remove carbon dioxide from the seawater, fine particles of calcium carbonate are formed from a chemical reaction. The sticky ooze secreted by the algae also traps fine sediment precipitated from the seawater. Removal of carbon dioxide from seawater caused the formation of large quantities of calcium carbonate, which contributed to the great thickness of carbonate rocks in the park.

2. Oxygen is released into the atmosphere. This was a major factor in producing the oxygen-rich atmosphere that allowed development of oxygen-consuming life forms on earth.

An Intrusion of Magma - 750 million years ago
While most of the rock in the Peace Park is metasedimentary in nature, late in the Proterozoic some igneous rock in the form of lava flowed onto the sea floor. Additional igneous material was intruded between layers of limestone forming sills at an even later time. Today the igneous materials are evident as pillow lava formations (black basalt) in the Granite Park area (granite does not occur in the park) and as the Purcell Sill that runs through the Siyeh Limestone, a dark band of igneous rock (diorite) about 100 feet (30 m) thick. The heat of the intrusion forced out the dark organic matter from the surrounding limestone, recrystallizing it into white marble (metamorphic rock). The Purcell Sill is seen throughout the parks, for example on Mt. Siyeh and the north side of Mt. Cleveland in Glacier, and Mt. Blakiston near Red Rock Canyon in Waterton.

Lewis Thrust Fault – 60-70 million years ago
Approximately 150 million years ago, collision of crustal plates on what was then the western edge of North America resulted in the beginning of mountain building processes inland that would continue until about 60 million years ago. In the area that would become Waterton-Glacier International Peace Park, massive forces uplifted a slab of rock several miles thick, which slid east some 50 miles (80 km) over much younger rock. The Lewis Overthrust Fault is major evidence of the tectonic events that created the mountain scenes of present day Glacier and Waterton. However, numerous other events were occurring simultaneously; synclinal folding and other types of faulting are also evident in Waterton-Glacier. As a result of the uplift, erosive forces accelerated and over several million years removed the upper layers of material, exposing the rock formations evident in the park today.

Glaciation: The Ice Age – 2 million years ago
The geologic event that would define the landscape began with a global cooling trend approximately 2 million years ago. The Pleistocene Ice Age saw large ice sheets repeatedly advance and retreat throughout the temperate regions of North America until about 10,000 years ago. In the area that would become Waterton-Glacier International Peace Park, ice advanced and retreated until probably melting completely about 12,000 years ago. During the ice advances, the lower valleys were filled with glaciers and only the very tops of the higher peaks were visible. The "rivers of ice" sculpted the mountains and valleys into a variety of landforms associated with major alpine and valley glacial action. Even though the Ice Age glaciers are gone, the results of their passing are evident on the landscape. Massive u-shaped valleys, numerous cirque lakes or tarns, horns, cols, moraines, and aretes are but a few of the glacially carved landforms that contribute to the beauty of Waterton-Glacier International Peace Park.

Recent Glaciation – dating from about 6,000 years ago
Today, we are living in a relatively warm interglacial period. All remnants of the Pleistocene ice have disappeared. There are no active glaciers in Waterton Lakes National Park; however, the last survey in Glacier NP resulted in 25 named alpine glaciers. They are of relatively recent origin, having formed in the last 6,000 to 8,000 years. They probably grew rapidly during the Little Ice Age that started about 400-500 years ago and ended about 1850. However, they work in the same way as larger glaciers of the past.

A glacier forms when more snow falls each winter than melts the next summer. With alternating freezing and thawing, the snow becomes granular ice. As these layers build up, the ice recrystallizes, becomes denser, and eventually forms a massive sheet. The ice needs to be about 100 feet (30 m) thick for a glacier to form and have a surface area of at least 25 acres. (10 ha).

Ice near the surface of the glacier is often hard and brittle. Due to the pressure of ice above, the ice near the bottom of the glacier becomes flexible. This flexible layer allows the ice to move. Depending on the amount of ice, the angle of the mountainside, and the pull of gravity, the ice may start to move downhill. Once the ice begins to move, it is called a glacier.

As the ice moves, it plucks rock from the sides and bottom of the valleys. Rocks falling on the glacier from above mix with the glacial ice as well. Over long periods of time the sandpaper-like quality of the moving ice and rock scours and reshapes the land into broad U-shaped valleys, sharp peaks, and lake-filled basins.

Tree-ring studies indicate that retreat of the recent glaciation began about 1850. When Glacier National Park was established in 1910, there were more than 150 glaciers within the national park compared to about one fourth of that number now. Retreat rates appear to have been slow until about 1910. There was a period of rapid retreat during the mid- to late 1920s. This corresponds to a period of warmer summer temperatures and decreased precipitation in this region. Several of the larger glaciers separated into two smaller glaciers at this time. The Jackson and Blackfoot Glaciers separated as did the Grinnell and Salamander Glaciers. If the current rate of recession continues, it is estimated that there won't be any glaciers in Glacier National Park by 2030.


What sets our mountains apart?

  • There is a relatively flat lying Lewis Thrust sheet from which our mountains formed. The mountains of Waterton-Glacier are a result of one major fault and many minor ones, instead of many major and minor faults often found in mountain ranges, such as the front ranges of Banff and Jasper National Parks in Alberta. The fault extends from south of Marias Pass north 348 miles (560 km) to Banff NP, thrust in a northeasterly direction and coming to rest after millions of years. Most of the horizontal displacement occurred in the Waterton-Glacier area.
  • The ancient rocks of the Belt Sea that form our mountains have much less limestone (limestone is mainly a byproduct of sea life) and fewer fossils than the younger rock exposed in most of the Rockies.
  • The Lewis Thrust sheet was displaced about 50 miles (80 km), as opposed to thrust sheets in the rest of the Rockies that were displaced over much shorter distances.
  • The varied colors of the rock in the mountains, including the reds, greens and maroons are the result of small amounts of various iron minerals.
  • There is an abrupt transition of mountains and prairie. Although the disturbed subsurface rock structures typical of foothills are present here, they are covered by glacial debris.
  • Here is the oldest exposed sedimentary rock in the entire Rocky Mountain chain – 1.6 billion years old.

Last updated: May 18, 2015

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