Glaciers are masses of ice that move slowly across dry land. Though they are composed of solid ice, glaciers behave like a liquid, moving downhill as gravity exerts its will.
Glaciers are found in the polar regions in the form of giant ice sheets, ice caps, and icefields. They are also found across the planet in mountainous regions. As snow accumulates and compacts, it turns into dense glacial ice that eventually pushes its way down mountainsides, through valleys, and across coastal flats. Glaciers can scour the sides of rocks, transport debris across miles of terrain, and shape topography in stunning ways. In general, researchers classify glaciers according to their size, location, and appearance.
Here are 10 types of glaciers and the characteristics that make them unique.
Continental Ice Sheets
The largest bodies of glacier ice are called continental ice sheets. These are large expanses of glacial ice that cover entire landscapes. Ice sheets are more than 20,000 square miles in size.
In modern times, there are only two continental ice sheets on Earth, in Antarctica and Greenland. Of the two, the Antarctic Ice Sheet is larger, covering some 5.4 million square miles, or roughly the size of the United States and Mexico combined. Ice sheets once covered most of Canada and Scandinavia, as well.
Ice sheets are so massive that they cover nearly every topographical feature, except for the tallest mountains. Entire mountain ranges and valleys exist beneath the Antarctic Ice Sheet, which is as much as three miles thick in some places.
Ice Caps
Ice caps are similar to ice sheets, but are smaller in size. They measure less than 20,000 square miles. Still, these expanses of glacial ice are massive, and can cover topographical features like mountain ranges. Ice caps are dome-shaped and primarily found near the polar regions in areas of relatively high elevation. It’s important to note the ice caps are different than “polar ice caps,” a phrase commonly used to refer to Arctic sea ice.
The Vatnajökull Ice Cap covers about 8% of Iceland, making it the largest ice cap in Europe. It covers seven active volcanoes, as well as valleys and plains. The volcanoes release heat, which creates lakes beneath the surface of the glacier. These lakes can release violently, flooding the glacial rivers that flow out from the ice cap.
Icefields
Icefields look much like ice caps, except they are influenced by the underlying terrain of the area. While ice caps are dome-shaped and create their own topography, icefields tend to be flat. Icefields also are generally not large enough to cover entire mountain ranges. Instead, they usually cover the surrounding valleys, while the mountain peaks rise above the glacial ice.
Many types of glaciers are fed by ice sheets, ice caps, and icefields. For instance, the Harding Icefield in the Kenai Mountains of Alaska feeds more than 30 smaller glaciers. At 700 square miles, it’s the largest of the four icefields found in the United States.
Outlet Glaciers
When a glacier flows out of an ice sheet, ice cap, or icefield, it’s called an outlet glacier. Outlet glaciers flow downhill, where a gap between mountains forms a low point. As such, they are generally hemmed in on the sides by exposed bedrock.
Since they are the outflow of massive expanses of ice, outlet glaciers can be massive themselves. The Lambert Glacier in Antarctica is the world’s largest and fastest-moving glacier. It drains about 8% of the Antarctic ice sheet.
Valley Glaciers
A glacier found in a low-lying area below mountain peaks is called a valley glacier. They can form in several different ways. If an outlet glacier is not impeded by terrain, it can flow downhill and become a valley glacier. They can also form independent of outlet glaciers in high, mountainous regions.
Aided by gravity, valley glaciers can carve through bedrock and change the topography of an area over the course of millions of years. The result of the carving action is typically a U-shaped valley. Yosemite Valley is a classic example of the steep-walled, flat-floored valley carved by an ancient glacier.
Tidewater Glaciers
Tidewater glaciers form when valley glaciers flow for such a long distance that they eventually reach the ocean. Rather than smoothly meeting the water, tidewater glaciers often form tall cliffs that sit above the water level. These glaciers calve ice as they surge forward, creating icebergs.
The John Hopkins Glacier is a tidewater glacier in Alaska’s Glacier Bay National Park. It stretches 12 miles from its source in the mountains, and is one mile wide and 250 feet tall where it meets the sea. Harbor seals often use the icebergs created by the glacier as a mating and pupping habitat.
Hanging Glaciers
A hanging glacier begins high in the mountains and often will feed into a valley glacier. Rather than flowing uninterrupted, however, hanging glaciers stop abruptly, usually at a cliff. They then calve or feed valley glaciers through avalanches and icefalls. They can also trigger rockfall and landslides.
The abrupt movement of hanging glaciers can be dangerous and even deadly. In 2002, a hanging glacier on the slopes of Mt. Dzhimarai-Khokh in Russia surged forward, releasing ice and rock onto the Kolka Glacier. The sudden impact caused the Kolka glacier to fail, triggering an avalanche that barreled eight miles down the valley. It buried entire villages and killed 125 people.
Piedmont Glaciers
Piedmont glaciers form at the end of valley glaciers when they flow into wide, flat areas. Piedmont glaciers are marked by their wide, bulblike appearance and the large, low-lying areas they occupy.
Alaska’s Malaspina Glacier is the largest piedmont glacier in the world, covering about 1,500 square miles of coastal plain. The glacier’s surface is marked by ripples and folds where moraines or rock and soil have been incorporated into the ice. In this region of Alaska, glaciers often surge forward rather than flowing at a constant rate, creating this uneven appearance.
Cirque Glaciers
Cirque glaciers are found high in alpine regions, surrounded by walls of mountain peaks. Generally, cirque glaciers are formed of accumulated snow, rather than being fed by larger icefields. Snow accumulates in small depressions on the side of a mountain, eventually compacting into glacial ice. Over millions of years, the shifting glacier can erode these depressions, forming bowl-shaped valleys called cirques.
Wyoming’s Cirque of the Towers is one of the most dramatic examples of a glacial carved cirque. The glacier that carved the valley has receded, leaving behind a semi-circle of 15 jagged granite peaks.
Rock Glaciers
Rock glaciers are glaciers that are covered or filled with debris like rock and soil. All glaciers contain some amount of rock, accumulating as the glacier moves and shears debris from the surrounding terrain. But rock glaciers are marked by the increased amount of rock contained within them. In some cases, a rock glacier might contain more rock than ice. In other examples, small glaciers can be completely covered by rocks. Often, they are brown or gray, and look more like a mudslide than a glacier.
The Atlin Glacier is one example of a rock glacier that looks like a rockslide at first glance. The glacier clings to the side of Atlin Mountain in British Columbia, Canada. Due to the steep terrain and loose rock, the glacier accumulates enough rock as it flows to nearly obscure the ice entirely.
