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Geology of Grand Teton National Park

Grand Teton National Park Geology

This image shows Schoolroom Glacier which lies at the head of the South Fork of Cascade Canyon. The mountains can be seen in
An image of Schoolroom Glacier below Hurricane Pass. Grand Teton National Park contains glaciers, lakes, and mountains. NPS.

Geologic History

The towering mountains of Grand Teton National Park contain some of the oldest rocks in North America, but the forces that lifted the Teton Range are geologically recent. The processes of metamorphism, mountain building, and glaciation are all part of the geologic history of the Teton Range.

Approximately 2.7 billion years ago seafloor sediments and volcanic debris were buried up to 20 miles deep due to the collision of tectonic plates. The heat and pressure from the collision changed the sediments and volcanic debris into a metamorphic rock called gneiss, a type of rock where light and dark minerals are separated into distinct layers. The rocks along the trail to Inspiration Point, one of the most popular trails within the park, are composed of gneiss.

This image shows metamorphic rocks in Grand Teton. Warped rocks are shown, and glaciers can be seen on the mountain.
Left – Banded and contorted layers within the metamorphic rock gneiss at Grand Teton National Park.
Right – Mount Moran contains basement rock, diabase, and sedimentary sandstone. NPS
A Tetons sunrise in Antelope Flats.
A Tetons sunrise in Antelope Flats. Anna Chalfoun/USGS

Magma infiltrated cracks and weak zones in the gneiss 2.5 billion years ago, cooled slowly and formed the igneous rock granite. Many of the highest peaks within the Teton Range are made of granite, including Grand Teton, Middle Teton, Mount Owen Teewinot, and Mount Moran. Other peaks contain granite and gneiss, where the granite cross-cuts the gneiss.

A stratigraphic column of units found in the core of the Teton Range within Grand Teton National Park
A stratigraphic column of the units found in the core of the Teton Range within Grand Teton National Park. NPS.

About 775 million years about iron-rich magma squirted into vertical cracks in the granite and gneiss, subsequently cooling and formed dikes, made of a rock called diabase. Mountain Moran contains a dike that is 150 feet wide that extends out from the face of the mountain 200 feet. Diabase is less resistant to erosion than gneiss and so is less easily eroded, allowing the diabase to extend out of the mountain.

Lying on top of the igneous and metamorphic rocks are sedimentary rocks that formed when global sea levels rose 510 million years ago. First the beach sands of the Flathead Sandstone were deposited and subsequently limestones were deposited in shallow seas. Finally, mudstones were deposited on a deeper ocean floor. Fossils are found within these seafloor rocks, including trilobites, stromatolites, corals, and shells.

A tectonic plate subducted under the west coast of present-day North America beginning 120 million years ago, generating mountains farther inland. Around 70 million years ago mountain building reached the Rocky Mountains and Gros Ventre Range, causing large blocks of bedrock to be thrusted upwards. Eruptions of lava from volcanoes occurred throughout the region as the Rocky Mountain uplift ended, and leftover heat from these events caused the Earth’s crust to expand, eventually causing it to break. These blocks of the Earth’s crust slide past each other on faults, such as the Teton Fault.

 

 

 

A view of the Grand Tetons over a grassland area.
A view of the towering Teton Range  from behind Jackson Lake Lodge. Scott Horvath/USGS

Approximately 10 million years ago the Teton Fault began to move triggering  a series of earthquakes. This movement tilted the mountain block upward, while down-dropping the valley block. These were large earthquakes, up to a magnitude 7.5, and offset the Earth’s surface by up to 10 feet. The total offset on the Teton fault is almost 30,000 feet. The Teton fault can be seen from the Cathedral Group Turnout on the Jenny Lake Scenic Loop. The last major earthquakes to occur on the Teton Fault were 4,800 and 8,000 years ago, but this fault is still active and can produce major earthquakes.

Grand Teton National Park is located near Yellowstone National Park. Beneath Yellowstone is a hotspot, a surface-level expression of a mantle plume. The Yellowstone hotspot erupted west of the Teton Range five million years ago, triggering earthquakes and causing further uplift along the Teton Range. The Yellowstone hotspot has erupted three times between two million and 640,000 years ago, and on top of Signal Mountain in Grand Teton National Park deposits from these eruptions can be seen by park visitors.

Earth’s climate began to cool significantly two million years ago causing glaciation within Grand Teton National Park, including the last two glacial advances, the Pinedale and the Bull Lake glaciations. The Pinedale occurred 50,000 to 14,000 years ago and formed Jackson Lake. The Bull Lake glaciation occurred 200,000 years ago and buried Jackson in 1,500 feet of ice. Much of the striking scenery within Grand Teton National Park was sculpted by glaciers. These glaciers have carved out channels across the valley floor, washed away soil, and have in turn affected the ecology seen today within Grand Teton National Park. Unglaciated stream drainages are V-shaped, and the glacial events transformed these drainages into U-shaped valleys.

 

Glaciers Today

Today more than eight feet of snow coat Grand Teton National Park during the winter. Snow begins to melt in the spring, but some snow remains all year long. This snow accumulates, and the weight of the accumulate snow compresses to  become ice. Since this compacted ice is so heavy, the ice sheet starts to slowly slide downhill where the land is sloped, forming a glacier where snowfall exceeds melting. As the glaciers move, they scrape the rocks below and that  rocky material is carried downslope within and on top of the glacial ice. This material is deposited at its terminus, or end point, creating ridges of unsorted sediment called moraines.

An image of the Middle Teton glacier on the northeast flank of the Middle Teton. There is white, compacted snow and rock.
An image of Middle Teton Glacier. Glaciers such as this provide late-season water, sustaining downstream ecosystems. NPS. 

There are as many as 11 active glaciers with Grand Teton National Park, ten of which are named. The named glaciers are as follows: Teton, Middle Teton, Teepee, Schoolroom, Petersen, Falling Ice, Skillet, and East, Middle, and West Trip Glaciers. Several glaciers can be seen from the road, including Teton Glacier, Falling Ice Glacier, and Skillet Glacier. Today many of the glaciers within Grand Teton National Park are retreating, and some of these glaciers may have lost enough ice volume to stop flowing. If a glacier is no longer flowing, it is not considered to be an active glacier.

Glaciers also play a crucial role in the hydrology of Grand Teton National Park. The snowmelt from glaciers provides late-season water to downstream ecosystems, sustaining a variety of wildlife and plants.

 

Research within Grand Teton National Park

Mapping of Geologic Features Within Grand Teton National Park

The U.S. Geological Survey has mapped the geologic features within Grand Teton National and produced a detailed geologic map.  In addition, the U.S. Geological Survey has researched the geologic history of Grand Teton National Park, investigating the formation of these mountains. Through this research, scientists have described each geologic unit within the park. A detailed description of the stratigraphic units within Grand Teton National Park can be found here.

Glacial Research

Glaciers are affected by temperature and precipitation and glacial changes are indicators of climate change. Since the late 1800s, all the glaciers within Grand Teton have retreated other than the exception of a period from the mid-1970s to mid-1980s. The first survey of Grand Teton National Park glaciers occurred in the late 1920s. Today scientists measure how much the glaciers within Grand Teton National Park are retreating by using ground and aerial photos from the last 90 years taken at the same time of the year.

Two images side by side of Schoolroom Glacier. The left is from 1987 and  is a larger glacier. The right is from 2007 and the
Two images from the same place of Schoolroom Glacier 20 years apart. The left image is from 1987 and the right is from 2007. The glacier has decreased in size from 1987 to 2007. NPS.

Scientists are focusing on monitoring Teton, Middle Teton, Schoolroom, Petersen, and Falling Ice glaciers and study every year how much is melting and what climatic factors affect these changes. Starting in 2014 scientist and climbing rangers have taken hundreds of GPS measurements of Middle Teton and Schoolroom each year to quantify the change in the amount of ice. Additionally, daily images from cameras allow scientists to see how much ice loss occurs. This time-lapse video by the National Park Service shows the snowmelt of Middle Teton Glacier over the summer of 2016.

On the left scientists use GPS to record change in glacial extent. They are climbing on top of the mountain. On the right is
Left: Scientists use GPS to record change in glacial extent of Schoolroom Glacier. Right: Teton Glacier feeds this glacial lake. NPS.

Eventually the glaciers within Grand Teton National Park may cease to exist, but it is currently not known when this will happen due to multiple variables such as size, shape, and slope. Climatic models of Wyoming predict increased rainfall and decreased snowfall in the winter and warmer temperatures during the summer within Grand Teton National Park.

Hydrologic Research

The water quality within Grand Teton National Park is vitally important to maintaining a healthy ecosystem within the region. The alpine and sub-alpine ecosystems supply water for human recreation, consumption, agriculture, and industry in the area surrounding Grand Teton National Park. The rivers within the park are designated as Outstanding Natural Resource Waters and the Snake River and its tributaries are protected under the Wild and Scenic Rivers Act. The U.S. Geological Survey monitors the water the within the Greater Yellowstone Region, of which Grand Teton National Park is a part. Scientists measure several different water-quality indicators, such as major ions and nutrients, conductivity, dissolved oxygen, pH, and water temperature. The water quality within Grand Teton National Park meets the requirements of the Clean Water Act.

The U.S. Geological Survey is also conducting research using remote sensing, where scientists use satellites or high-flying aircrafts to obtain geologic information. This technique allows scientists to estimate water depth and over time observe how the Snake River changes.

An image of the Teton Range from Oxbow Bend. The Snake River can be seen, along with flowers.
A view of Mount Moran and the Snake River from Oxbow Bend. The oxbow is created over time as erosion and soil deposits change the course of the river. Credit: Carrie McIntosh/USGS-VSFS intern
Grand Tetons National Park
In this image Grand Teton, the highest peak in the range, towers over a heard of bison. Phil Stoffer/USGS
Grand Tetons National Park
The Snake River runs through Grand Teton National Park and is important for the plants and animals within the park. Phil Stoffer/USGS

 

References and More information on Grand Teton National Park

https://pubs.er.usgs.gov/publication/70023715

https://pubs.er.usgs.gov/publication/70160345

https://pubs.usgs.gov/pp/0516e/report.pdf

https://www.nps.gov/grte/learn/nature/geology.htm

https://pubs.usgs.gov/of/2004/1216/tz/tz.html

https://www.nps.gov/grte/planyourvisit/upload/geology-access.pdf

https://www.nps.gov/grte/learn/nature/glaciers.htm

https://www.nps.gov/grte/learn/nature/glaciermonitoring.htm

https://www.nps.gov/parkhistory/online_books/grte/grte_geology/sec3.htm

https://earthobservatory.nasa.gov/images/87843/grand-teton-national-park

https://www.nps.gov/grte/planyourvisit/upload/glaciers-access.pdf

https://www.nps.gov/grte/learn/nature/geology.htm

https://irma.nps.gov/DataStore/DownloadFile/624838

https://mrdata.usgs.gov/geology/state/sgmc-lith.php?code=5.7 

https://pubs.usgs.gov/of/2004/1216/m/m.html

https://data.usgs.gov/datacatalog/data/USGS:59fb5d77e4b0531197b1638b