What are Ice Patches and
Why Do People Study Them?
When winter snows collect in places like the sheltered side of windblown boulders or a ridge, the snow can become thick enough to last through the summer. Over many years, more snow can collect, eventually becoming thick enough to develop ice at its core and large enough to be classified as an ice patch.

During the summer months when the weather is warm or even hot, ice patches provide a trickle of water that feeds tender young plants, and the patches offer a cool refuge for hoofed animals like deer or caribou or bison that are looking to escape biting insects — the insects avoid the cool air over ice patches. In the photos at right, you can see caribou, deer, and elk on ice patches.

In the past, human hunters followed the animals, and often killed them and butchered the them on the ice patch. Sometimes they left tools or a piece of clothing behind.

Unlike glaciers, ice patches don’t move — so anything that falls on top of one can, when it snows again, become covered with snow and eventually become encased and frozen within the patch. Things like fallen trees, fragments of plants, animal dung, the animals themselves, even artifacts discarded or lost by human hunters, gatherers, and travelers have become trapped within ice patches.

Illustration by Antoine Sandoval © 2014

Now climate change is melting ice patches and the ancient materials they hold are being released. In North America, the field of “ice patch archaeology” refers to the study of human-made materials—tools, pieces of clothing, etc.—recovered from these melting patches of ice. In Glacier National Park, the Blackfeet, Kootenai, Salish, and Pend d'Oreille tribes are working with scientists to survey ice patches and protect their ancient contents.

Click on one of these two tabs to learn more:

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Animals on ice patches: caribou (top, photo by Rob-Develice); mule deer (middle, photo by Rachel Reckin); elk (bottom, photo by Traute Parrie). The ice provides a refuge from biting insects and a place to cool off from warm summer temperatures.
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A moccasin found on a melting ice patch in the southern Yukon Territory.
Finding the Right Patch
There are thousands of ice patches in Glacier National Park, and Glacier’s Ice Patch Team established certain rules to help select which ones to study: (1) the patch is on a path where animals like deer and elk might walk, (2) it is on a slope that is not too steep for animals or people to walk on, (3) there are dark stains on it, and (4) it didn’t melt during Glacier’s warmest year in recent times—1998 (meaning it probably didn’t melt during warm years in past centuries). The team marked these ice patches targeted for study on satellite images and on computer maps. This allowed their locations to be loaded into Global Positioning System (GPS) devices, so that field teams could walk relatively easily to them, which is important in the rugged landscapes of Glacier National Park, where weather can change in minutes and researches can be caught in storms.
Surveying Patches
group surveys ice patch2
During their survey of ice patches, the team used GPS to map each ice patches’ side and lower edges, which allows them to see if they are melting from year to year. They photographed any artifacts or plant or animal remains they found and recorded the exact location of the find. They mounted fragile specimens plastic boards to protect them.

The team has found wood as old as 5,000 years, and from tree species that no longer are found around or above the ice patches and believes that its presence indicates treeline used to be higher at times when the climate was milder. The team also documents and collects any artifacts they find before placing them in a museum, and they analyze animal remains and animal feces. They can use that information to learn more about the ancient climates in which the animals lived.

Or click on one of these interactive activites:

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You can view an animation showing how artifacts become trapped in ice and then discovered. Click on the image above to view the animation.

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Examine an ancient bison skull found in one of Glacier National Park's ice patches. You can look at the skill in 3-D, rotating it and zooming in on any part of it. Click on the image to view the skull.