Glaciers 101

By Grayson Carlile

Since our arrival at Camp 10 we have shifted gears from safety and expedition training to science . Our time has been spent developing our individual research projects and receiving lectures from an exceptional group of faculty. We are beginning to delve into the details of how the icefield functions.

So before we begin filling the blog with our research and theirs, we thought it appropriate to give a brief explanation of what a glacier is - how snow is transformed into the spectacular rivers of ice that we are wandering among this summer.

The rivers of ice we know as glaciers form from the accumulation of enormous quantities of snow.  Mendenhall Glacier, Alaska.  Photo by Adam Taylor

It all starts with the same snow you might have falling in your backyard during the winter. Most of us, however, do not have glaciers in our backyards, so there must be a few other criteria. Here is where snow quantity and local climate come into play. There has to be enough snowfall that summer temperatures will not melt it all away before the snow returns. Some of the snow that has accumulated has to persist through the entire year.

Then the process has to repeat itself...over, and over, and over again. As time goes on, individual snowflakes begin to metamorphose – their delicate, spindly structures gradually breaking down through a combination of melting, refreezing, and pressure from overlying snow. The resulting products are rounded ice granules called

firn. In the final step on the journey to becoming glacial ice, these firn granules meld into larger ice crystals that fit together like pieces in a three dimensional jigsaw puzzle.

The transformation of snow to glacial ice can take decades to centuries depending on the consistency (wet or dry) and quantity of snow that falls. Once the ice has formed, it can begin to take on the properties of a glacier. As mentioned above, glaciers are rivers of ice. By definition they are moving - pulled downhill by the force of gravity. So in order for the ice to become a glacier, something has to change within the ice in order for it to flow.

Once the ice is a few tens of meters thick, there is enough stress on the underlying ice that it begins to behave viscously - that is, similar to a fluid - and can finally deform and flow. To understand how this works, imagine a ball of silly putty. If you work it in your hands, applying pressure, you can get it to start stretching and slowly flowing. This is essentially what happens to the underlying ice in the 70 meters of accumulation. The pressure of the overlying ice brings it to a consistency that allows it to flow. Once it has reached this point, it begins to succumb to the force of gravity and flow down a valley or across a continent. In addition to this viscous flow, some glaciers such as those that exist in warmer climates, may also flow over the bedrock or sediments at their bases.

So while a reference to glaciers may conjure images of the Arctic or Antarctica in the minds of many, with the right conditions glaciers can form almost anywhere – from the summit of Mt. Kilimanjaro in Africa, to the South Island of New Zealand, to the Cascade volcanoes of Washington State. However, glaciers can and do behave differently in these various locations. Some places, such as Southeast Alaska, where precipitation and cool temperatures are widespread and rampant, cater to more than just a single glacier, producing complex networks of glaciers such as the Juneau Icefield. Here the Coast Mountains receive more snow than almost any other place on Earth. The vast distribution of enormous quantities of snow has created nearly 1500 square miles of glaciated terrain that drains the rugged mountains – flowing east into British Columbia and west into the salty waters of Alaska’s Inside Passage.