Friday Facts: Alaska Glaciers, Talk the Talk with these 27 facts about Alaska Glaciers.
One of the most instantly fascinating parts of Alaska for me, were and still are the incredible glaciers. I will share a little of the information I have accumulated over the years in Alaska, living about 6 miles from the Chisana Glacier, and you will be able to talk the talk with anyone interested in glaciers.
- In the modern world about 10% of land area, 5,791,532.4 square miles (roughly 15,000,000 square kilometres) is covered by glaciers, but during the last Ice Age glaciers covered about 32% of the total land area.
- In the United States, glaciers cover over 75,000 square kilometers (28,957.6 miles), with most of the glaciers located in Alaska.There are nearly 100,000 glaciers in Alaska, and most of them don’t have names.
- Washington and Alaska are the only two states in the United States which get a significant percentage of their water supplies from glacial sources. In Washington State, glacial melt water provides 1.7 trillion litres (470 billion gallons) of water every summer.
- In total Alaska’s glaciers empty over 50,000 billion gallons of water into streams and rivers every summer. That’s half of all the water that flows into the worlds oceans!
Glaciology is the study of glaciers, or more generally ice and natural phenomena that involve ice.
“We must go beyond textbooks, go out into the bypaths and untrodden depths of the wilderness and travel and explore and tell the world the glories of our journey.“~ John Hope Franklin
Glaciers tell stories of the earth’s history. Glaciers shape the earth’s surface as they move and form valleys, mountains and other large formations.
- Within the Wrangell St. Elias National Park boundaries is enclosed the nations largest glacial system. Glaciers cover over 25 percent, or approximately 5,000 square miles, of the park. In summer, these glaciers contribute a significant portion of the rivers’ high runoff and heavy sediment load. During the winter, glacial melt ceases and many rivers run with clear water.
Some notable park glaciers include:
- The massive Bagley Icefield is 127 miles long, 6 miles wide, and up to 3,000 feet thick!
- Flowing over 75 miles and calving into the sea with a face 6 miles wide, the Hubbard Glacier near Yakutat is the longest tidewater glacier in Alaska, and is actively advancing!
- The Malaspina Glacier is North America’s largest piedmont glacier (formed at the base of a mountain rather than enclosed by a valley), and covers an area larger than Rhode Island!
- The world’s longest interior valley glacier, the Nabesna Glacier, is over 75 miles long.
Most of Alaska’s glaciers have been retreating over the last century, and research shows that the rate of recession has increased significantly in recent years.
Areas of study within glaciology include glacial history and the reconstruction of past glaciation. A glaciologist is a person who studies glaciers. Glaciology is one of the key areas of polar research.
- A glacier is an extended mass of ice formed from snow falling and accumulating over the years and moving very slowly, either descending from high mountains, as in valley glaciers, or moving outward from centers of accumulation, as in continental glaciers.
There are two general categories (types) of glaciation which glaciologists distinguish: alpine glaciation, accumulations or “rivers of ice” confined to valleys; and continental glaciation, unrestricted accumulations which once covered much of the northern continents.
- Alpine – ice flows down the valleys of mountainous areas and forms a tongue of ice moving towards the plains below. Alpine glaciers tend to make the topography more rugged, by adding and improving the scale of existing features such as large ravines called cirques and ridges where the rims of two cirques meet called aretes.
- Continental – an ice sheet found today, only in high latitudes (Greenland / Antarctica), thousands of square kilometers in area and thousands of meters thick. These tend to smooth out the landscapes.
There are two “zones” of glaciers:
- Accumulation, where the formation of ice is faster than its removal.
- Wastage or Ablation, where the sum of melting and evaporation (sublimation) is greater than the amount of snow added each year.
Glacier flow exceeds ablation, and the terminus extends farther down valley than previously
Wastage of the glacier through sublimation, ice melting and iceberg calving.
Calve Process of ice breaking off at a glacier’s terminus
- Ablation zone
Area of a glacier in which the annual loss of ice through ablation exceeds the annual gain from precipitation.
Crevasse formed near the head of a glacier, where the mass of ice has rotated, sheared and torn itself apart in the manner of a geological fault.
Bowl shaped depression excavated by the source of a glacier.
Movement (of ice) in a constant direction.
A post-glacial lake in a cirque.
(Terminal) material deposited at the end; A deposit of rock debris shaped by glacial flow and erosion (Ground) material deposited as glacier melts.
A large crack in the surface of a glacier produced by the stress of glacial flow.
The lower end, or snout, of a glacier.
Glaciers, perennial accumulations of ice, snow, sediment, rock and water, respond to changes in temperature, snowfall and geologic forces. Several components make up a glacial system: the ice and sediment contained in the glacier; the valleys, fiords and rock features it flows over, on, or around; and the deposits left by its retreat or advance.
Moisture-laden air masses from the ocean are forced to quickly rise when they collide with the high mountains of the Wrangell and St. Elias Ranges. As the air rise, it cools and releases its moisture in the form of deep snowfall. New snow layers create pressure on existing layers of snow and ice.
This process, “Firnification,” (yes, that is actually a word!) slowly squeezes out the air pockets and changes fluffy snow into a dense granular snow (like corn snow). After the first season’s melt, snow becomes firn. As it is compressed further, firn eventually becomes ice.
As the snow collects over many years, an ice field forms. Icefields feed glaciers. When thick enough, ice will begin to flow down-slope, eventually filling valleys, sometimes flowing all the way to the sea.
- The Bagley Icefield which runs along the crest of the Chugach Range for about 120 miles, is the largest sub-polar icefield in North America. It covers most of the core of the Chugach Mountains and nourishes dozens of valley glaciers that drain down both sides of the range.
Glaciers form where more snow falls than melts. A glacier’s accumulation area, located at higher elevations, accrues a wealth of snow and ice.
The ablation area, located at lower elevations, loses ice through melting (down-wasting) or calving. A glacier’s terminus or face advances when more snow and ice amass than melt, and it retreats when melt exceeds accumulation.
When melt equals accumulation, a glacier achieves equilibrium and its face remains stationary. Whether the glacier’s face is advancing or retreating, glacial ice persistently glides down-valley.
Coerced by gravity, ice pursues the path of least resistance. Ice depth and bedrock angle influence the rate of glacial flow.
Glaciers contain two zones of ice flow.
- The zone of plastic flow, ice closest to the bedrock, experiences extreme pressure from the weight of the ice above and conforms to the anomalies in the bedrock.
- The zone of brittle flow, the upper 150 feet of glacial ice, lacks this pressure and reacts in-elastically to the bedrock features, forming elongated cracks called crevasses which fluctuate with the glacier’s flow.
Glaciers leave an impressive footprint on the landscape, carving the rock as they retreat and leaving behind steep topography and fiords where the ice once held sway.
Flooded seacoasts and rising water levels are the legacy of their retreats, as are the ecological changes on the landscapes around the glacier’s edge. Glaciers also have cultural impacts, in that their activity has affected human settlement, migration, and subsistence over thousands of years.
Cracked pieces of rock, plucked or torn from the bedrock, are carried with other debris in and on the glacier. This debris scrapes the valley walls and floors, leaving grooves and striations. Rock debris is crushed and ground into fine grains, called rock flour.
Hikers should not attempt to cross glaciers without proper equipment including crampons, ropes and ice-axes. Even the gravel covered moraines will turn slick and dangerous during or after a rain.
Pioneer Outfitters has been exploring the glaciers that surround us and guiding guests and clients over, around and through the massive ice since 1924. As the miners crossed the glaciers with laden horses to answer the call to mine the gold in the area during the Last Historic Gold Rush, we cross the ice to experience the land that has been frozen for eons and to answer the call of Adventure.
Do you want to have an Adventure and explore the glaciers with us? Let us know!