One of my favorite parts of being in Greenland is seeing the fingerprint of glacial ice virtually everywhere. During the Last Glacial Period (~110,000 through 11,000 years ago), the Greenland Ice Sheet expanded to cover the entire landmass. Now, in the present Interglacial Period, the ice sheet has shrunk and exposed large areas of land that were formerly covered by ice. Accordingly, abundant glacial landforms are visible around the coastal areas of Greenland, and the IGERT students spent a day last week exploring them.
Glaciers are powerful agents of erosion. They can remove huge masses of material from the landscape through both scraping/scratching the underlying rock surfaces (a process called abrasion) and freezing to rock surfaces and pulling off large pieces (a process called plucking). Glacial erosion leads to distinctively-shaped bedrock forms that are often sculpted and smoothed.
The material eroded by glaciers is carried through the ice as if on a conveyor belt, and is then deposited in a location in the down-ice direction from the material’s source. Most sediment deposited by glaciers is called glacial till; this material contains a mix of grain sizes (everything from clay to large boulders), is not sorted or layered, and often contains a mix of rock types that do not match the local bedrock. Glacial till is sometimes deposited in narrow ridges at the end and along the sides of a glacier. These ridges are called moraines and are useful for marking past positions of the glacier’s end, or terminus. Generally, younger moraines in Greenland, especially those deposited during a recent cold period called the Little Ice Age (~1450-1850 AD), are unvegetated and fresh. Conversely, older moraines in Greenland deposited during the ice recession after the Last Glacial Period are more weathered.
To complete our study of glacial landforms and processes, we ventured up on the edge of the ice sheet at the end of the dirt road from Kangerlussuaq. Alas, this small area of the ice appears to be stagnant and is no longer flowing (although, fortunately, this also means that it is not crevassed and is therefore safe to walk on). The IGERT group spent a beautiful, sunny afternoon walking on the ice, examining the complex system of meltwater streams flowing on top of the ice sheet’s edge, and seeing sediment embedded in the ice that has been transported from Greenland’s interior.
An important point to remember is that glacial features are visible in most northern areas of the United States too, including around Dartmouth! Next time you find yourself going for a walk in the woods or driving along the road in an area covered by ice during the Last Glacial Period, don’t forget to look for these fingerprints of lost ice. That piece of bedrock you’re standing on could preserve scratches, or striations, formed as an ice sheet several miles thick flowed over the exact area you’re currently standing!