What is a Glacier?
Glaciers are made up of snow that compresses into ice over many years. What makes glaciers more than just ice is their significant size, which causes them to flow very slowly under the weight of their own magnitude. They can range in size anywhere from several hundred feet to hundreds of miles. Glaciers often take the topographical shape of their surroundings, which then creates the many different “types” of glaciers.
Two Types of Glaciers
There are fundamentally two types of glaciers: (1) Continental glaciers, or ice sheets, and (2) alpine, or valley glaciers. The first type are dome-shaped glaciers that flow from a central region and are relatively unaffected by underlying typography, now only found in Antarctica and Greenland. Secondly, alpine, or valley glaciers, flow down valleys and are typically constrained by the surrounding mountains. Beyond this, glaciers receiver their name-type based on where they are and how they interact with their surrounding environment. For example, if a glacier flows to the sea, it’s called a tidewater glacier. Below is a more full list of glacier types:
Piedmont Glaciers—Alphine/Valley glaciers that spill out onto plains.
Ice Sheets—Huge continental masses of ice and snow expanding over 50,000 square kilometers (19,305 square miles).
Ice Caps—Mini ice sheets, covering less than 50,000 square kilometers (19,305 square miles).
Icefields—Similar to ice caps, except flow is influenced by underlying topography, like an alpine glacier; typically smaller than ice caps.
Hanging Glaciers—A hanging glacier is when a glacier system retreats and leaves smaller glaciers hanging out alone.
Ice Aprons—small, steep glaciers that form an “apron” on the mountain.
Tidewater Glaciers—Glaciers that reach the sea and calve icebergs icebergs.
Ice Shelves—Occur when ice sheets extend over the sea and float on the water.
How Glaciers Form
Glaciers form by snow compression and ice formation. This requires an area where snow remains all year and accumulates enough to transform into ice. Over time, new layers of snow compress on top of older layers and begin a process by which the snow re-crystallizes. During this process, the snow compresses and becomes more dense over time, decreasing the amount of air pockets within the snow. Over the course of roughly a year, the snow becomes firn, a state in which the snow has become more dense but not yet compressed into glacier ice. Soon, the snow will transform from firn to glacier ice, a process that can take more than a hundred years.
Glacial Formations and Features
Snow falls in the accumulation area, usually the highest elevation of glacier. Further down the glacier, where most of the melting occurs, is the ablation area. When a glacier reaches equilibrium, it is accumulating as quickly as it is melting. A glacier advances when snowfall exceeds melting, and a glacier retreats when melting exceeds snowfall
Crevasses are deep cracks in the glacier. Moraines are created by rock debris carried and moved along by the glacier. Moraines can show areas of recession along the glacier. Medial moraines run down the middle, lateral moraines run along the sides, and terminal moraines run at the ends of a glacier. Glacial Till makes up moraines, being the the material directly deposited from glacial ice, being anywhere from fine particles to large boulders.
Kames are glacial deposits that take the form of hills. You’ll spot these along the Sterling Highway driving between Anchorage and Homer. Drumlins are small, elongated oval mounds or kills. Eksers are long ridges formed by meltwater, a mini-river that carved its way through the glacial ice. They often make their way down the length of the glacier. Outwash is a deposit carried by running water from the melting glacier.
Glaciers in South-central Alaska
There are 626 officially named glaciers in Alaska. The Alaska Almanac estimates 100,000 glaciers in Alaska, however, counting the number of glaciers is a bit misleading. Over time, the number of glaciers has risen. This is the result of a retreating glacier, for example, that results in several additional hanging glaciers. So, one glacier can split into three, for example. A more efficient method counts the number of square miles of glacial ice within Alaska, which is estimated at 34,000 square miles.
Kenai Fjords National Park
Two areas near Seward, Alaska contain most of the glacial area within Kenai Fjords National Park: (1) the Harding Icefield and (2) the Grewingk-Yalik Glacial Complex. The Harding Icefield is over 700 square miles in its entirety, one of the largest ice fields in the United States. The ice field contains at least 38 glaciers, the largest of which is Bear Glacier. One of the most popular glacier within Kenai Fjords National Park is Exit Glacier, which can be accessed at the end of the park’s only road.
Glaciers and Flightseeing
Over many years, glaciers have helped to form many of the beautiful valleys, ravines, and fjords that call Alaska home, whether across Kachemak Bay in the Kenai Mountains or in Katmai Park and Preserve. The massive glaciers that still inhabit Katmai are some of the amazing sights we get to see during our flights in and out of Katmai’s bear viewing country. We can also access the Kenai Mountains across the bay through a flight seeing trip. The Kenai Fjord National Park, including both the Harding Icefield as well as the Grewingk Glacier, are stunning sights to see from the air.
