What are Ice Patches and Why Study Them?
When winter snows accumulate in places like the lee of windblown boulders, the snow can become thick enough to withstand summer temperatures. Over the years the old snow stratifies into layers of low-density, sometimes porous ice. In summer the ice patches provide a trickle of water that nourishes tender young plants. They also offer a cool refuge for hoofed animals fleeing biting insects. Human hunters follow the animals. Unlike glaciers, ice patches don’t move — so anything that falls on top of an ice patch can become encased and frozen, including fallen trees, fragments of lighter vegetation, animal dung, the animals themselves, and even artifacts discarded or lost from human hunters, gatherers, and travellers. The stable ice in these features exhibits little internal deformation or movement and can preserve otherwise perishable materials for millennia.

Illustration by Antoine Sandoval © 2014

Now climate change is melting perennial ice patches at high latitudes and high elevations, resulting in the release of ancient paleobiological and archaeological materials that, until recently, were in cryogenic-like stasis. In North America, the field of “ice patch archaeology” refers to the study of anthropogenic materials recovered in association with retreating snow and ice patches. Colleagues in Europe frequently refer to this field as “glacial archaeology,” in part because of archaeological finds in glaciated passes.

Stacks Image 62
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 predatory insects and a place to cool off from warm summer temperatures.
Finding the Right Patch
There are thousands of ice patches in Glacier National Park, and the team established certain characteristics to help select target ice patches: (1) if they are in likely traffic routes for ungulates, (2) if they are on slopes that can be traversed by animals and people, (3) if dark staining is visible, and (4) if the patches can be seen on aerial photographs from 1998, the warmest year in recent times. The project team then identified several target ice patches by examining historical documentation including aerial and satellite images from the park and the U. S. Geological Survey. In conjunction with the University of Colorado Boulder’s Institute for Study of Arctic and Alpine Research, the team was able to ortho-rectify images and put them into Geographic Information System format. This allowed data about the target ice patches to be input to Global Positioning System devices, so that field teams could walk relatively easily to their targets. This is important in the rugged, remote landscapes of Glacier National Park, with extreme weather shifts that can happen in minutes.
Surveying Patches
group surveys ice patch2
During survey, while examining the forefield, we also use GPS to map the ice patches’ lateral and lower margins. Recording the ice patch margins in this way allows for comparison of ice patch extent based on remotely sensed images as well as for direct comparison of melt from year to year. Any artifacts or paleobiological specimens (feces, unmodified wood, bone) found are photographed and their GPS coordinates recorded. Fragile specimens are mounted on ridged, hydrophobic and archivally stable plastic board (e.g., Coroplast) and held in place with plain cotton gauze bandaging or strips of unbleached muslin. A representative sample of paleobiological specimens are collected for paleoenvironmental context. Sometimes the volume of paleobiological material can be staggering. To date, in Glacier National Park, we have found wood as old as 5000 BP, and of species that no longer are found around or above the ice patches. We had originally speculated that some of the wood may have been transported to these locations by raptors for use in nest building, but that explanation now seems unrealistic based on GNP’s maps of known raptor nesting locations. A more parsimonious explanation holds the presence of this wood as indicative of a higher treeline during a more favorable climate. Any artifacts that are found are documented, collected, analyzed, and curated. Paleobiological specimens (e.g., animal remains, feces) are analyzed for isotopic and other information useful in characterizing ancient climates in which organisms lived.