How can archaeological finds survive inside or beneath massive glaciers? Well, they can’t! The constant movement of the ice crushes the artefacts and eventually dumps the sad remains at the mouth of the glacier. When you hear about exciting discoveries from glaciers, these finds tend to be relatively recent, like missing airplanes or WW1 soldiers.
Luckily for glacier archaeologists not all ice in the high mountains moves. We would have made much fewer finds if it did! Non-moving fields of ice may be attached to glaciers, and are good places to look for artefacts. Ice patches, isolated non-moving accumulations of ice, also exist and are excellent contexts for the preservation of artefacts, once lost in the snow.
Glacier or ice patch?
The basic difference between a glacier and an ice patch is that a glacier moves, while an ice patch does not move much (but read below). Ice masses can switch between being ice patches and glaciers over time. During a colder climate, like “the Little Ice Age”, ice patches could increase in size to a point where they became sufficiently thick (25-30 m) to start moving and turn into glaciers. Essentially all glaciers have started as ice patches.
The ice in the larger ice patches can deform due to the pressure from the overlying ice. This process is very slow, compared to the fast movements of glaciers. The lower ice layers are compressed and stretched, which can lead to very finely laminated ice. If the topography below the ice patch is flat, as in the photo above, the lamination will be quite even. On the other hand, if the topography is uneven, the stratigraphy will be more undulating, sometimes leading to strange and beautiful layering in the ice (see photo below).
Ice patches as archaeological sites
Even when ice is not moving or deforming only very slowly, as a find spot it provides special challenges for archaeologists. Ice patches react quickly to changes in climate, mainly winter precipitation, summer temperature and wind, and prevailing wind direction and strength during the winter season. Even if objects were originally lost in the snow, most of them have melted out of the ice at some time or times in the past, and been recovered by snow and ice. This is the reason why most artefacts are found on the ground and not on the surface of the ice. Objects are only found on the ice when the melting reaches ice layers previously untouched by melting.
Finding artefacts melting out of the ice they originally were encapsulated in happens only when old ice melts. Such finds are therefore quite rare.
Many finds are displaced by meltwater and/or wind, and parts of the same object may be found several hundred meters apart. The distribution of finds on the sites is thus difficult to interpret. Are the artefacts found where they were originally lost or are they displaced?
A major factor for the preservation of an artefact found at an ice patch is the length of exposure. This factor is often correlated with the distance of the find spot from present day ice – the further away from the ice, the poorer the preservation. This may appear self-evident, but sometimes local conditions around the find spot may be beneficial to artefact survival. This could, for example, be a large boulder that has collected extra snow, and provided shadow.
Different types of artefacts also preserve differently, depending on the material they are made of. Arrowheads made of stone or metal preserve well, but are hard to spot among the stones, if there is not an associated arrow shaft. Wood, birch bark and bone preserve best of the organic materials, while sinew, hide and textile deteriorate more rapidly.
The landscape surrounding ice patches also varies a lot. Some ice patches are situated in a landscape with active processes, for instance steep slopes where rocks move. Others are in flatter areas with active permafrost. Such active geomorphological processes offer poor preservation conditions for artefacts.
A lot more research is needed to gain a deeper understanding of what the finds recovered from the glacial ice can tell us about past human activities on the sites.