Q. What is a glacier?
A. A glacier is a thick mass of ice that forms on the earth's surface from the accumulation, compaction and re crystallization of snow.
Q. How are glaciers formed?
A. Gradually, year after year, snow is transformed into ice. New layers of snow fall on top of existing layers of snow and ice; creating pressure, and a phenomenon known as firnification. This process transforms the snow into firn, which is much more dense and granular. As the firn is further compressed by additional layers of fresh snow, it becomes ice. Over the years, the ice becomes thicker and heavier, forming a field of ice. The forces of gravity take over and slowly, the ice field naturally begins to move, flowing down into the valleys and lower slopes of the mountains, and forming the tongues of the glaciers. In flatter areas, or areas with little surface melting, like Greenland and Antarctica, the formation of glacial tongues can take hundreds, or even thousands, of years.
Q. Why do glaciers move?
A. The enormous pressure placed on the ice crystals, as more and more layers amass, produces a plastic-like texture, and a composition which begins to move slowly, under the force of gravity. To be a bit more precise, the ice moves through two different processes:
Internal flow takes place when the structure of the ice crystals changes and heavier ice begins to place pressure on lighter ice. In some parts of the ice field, internal flow causes the ice surface to become more fragile, and produce cracks that can be very dangerous for hikers. Inside, the behavior is more plastic and the ice crystals slide over each other.
Basal slip movement results when the entire mass of ice turns over. When the base of the glacier takes on a liquid water film, this reduces the internal friction that naturally facilitates the movement of ice over the bedrock, causing basal slip. This happens frequently in temperate glaciers.
Q. Are there many glaciers in the world? Where are they?
A. Glaciers form in regions where the annual precipitation exceeds the amount of snow that melts and evaporates, in summer. This phenomenon is most often associated with areas near the North and South Poles, but glaciers can also be found in many mountainous areas, including mountains of Africa and South America. Today, only 10% of the Earth is covered with glaciers, but during the last ice age, that percentage rose to 30%. Currently, 91% of the total volume of glaciers, and 84% of the total area of glaciers, are within the Ice Fields of Antarctica.
The Antarctic Ice Sheet is huge! It covers almost 14 million Km² and contains 30 million Km³ of ice. The Antarctic Ice sheet represents almost 61% of all the fresh water reserves in the world! The next highest concentration is the Greenland Ice Sheet, which extends from the latitudes of 60° to 80°, covering approximately 1.7 million square Km. This ice sheet represents approximately 8% of the world's total glacier volume, and 14% of the glacier area.
In Patagonia, there was once a third Ice Sheet, extending from Puerto Montt through all of southern Chile, into Argentina. This ice formation reached its largest mass between 17,500 and 18,000 years ago, covering 480,000 Km² of land, with a mass of more than 500,000 Km³ Today, only about 4% of that mass remains; contained within the Northern and Southern Ice Fields that you can visit within the Undiscovered Patagonia Circuit. These Ice Fields comprise the third largest extension of continental ice in the world. The Northern Patagonia Ice Field consists of approximately 4,200 Km2 of ice, with 28 outlet glaciers; all within the boundaries of the San Rafael Lagoon National Park, in Chile. The Southern Patagonia Ice Field consists of 16,800 Km2 of ice, with 48 outlet glaciers entering the Patagonian channels of the Pacific Ocean, and lakes and rivers extending to the Atlantic. This natural wonder is protected through the Chilean National Parks of Bernardo O'Higgins and Torres del Paine, and Los Glaciares National Park, in Argentina.
Q. Why is glacier ice blue?
A. Despite the common belief, the blue color of glacier ice is not a result of age; at least not directly. The various shades of blue you can see in a glacier originate from the high compression of ice under the weight of snow, which prevents the formation of air bubbles. Over time, this pressure builds and more weight is added. The dense, heavy ice absorbs all of the colors of the visible light spectrum, including yellows and reds; transmitting only the blue. Of course, you cannot always appreciate this blue because, often, the densest, bluest ice, is hidden under a layer of snow, airier, white-colored firn, or the dirt and debris of the moraine.
Q. Is climate change affecting the glaciers?
A. In general, the size and melt rate of glaciers depends on the climate of the region in which they are situated. Part of glacier mass loss is due to the natural dynamics of the ice, in relation with this climate.
However, in climates with prolonged warming trends, ice melt has intensified. In recent decades, there have been increases in average temperatures and trends, as well as differences in rainfall patterns, produced in part by climate change. These changes have had a strong impact on the glaciers. Scientific studies indicate that almost all glaciers in the Southern Patagonia Ice Field are receding. For example, Glacier O'Higgins, the fourth largest in Patagonia, has experienced dramatic losses of ice mass in recent times. The front of this glacier remained in a stable position until the early twentieth century, when it began to decline at an increasingly rapid rate. By 1995, the front wall has receded approximately 14.6 Km; 11.5 Km of which, were lost between 1945 and 1980 (Casassa et al., 1997).
Q. Are all glaciers the same?
A. Each and every glacier is unique, but there are similarities that allow them to be categorized; normally, according to their size and relation to the topography. Here are some typical classifications:
- Large Ice Sheets or Caps: Large masses of ice that completely cover the terrain on which they stand, except, at times, the very edges of the land mass. There are two large Ice Sheets; one in Greenland and the other in Antarctica.
- Small Icecaps: Also cover large areas, but less than 50,000 km2 in size. The best known are those of Iceland and Svalbard.
- Ice Fields: Unlike the ice sheets or caps, ice-fields have a surface that is dome-shaped. Their flow is controlled by the topography of the land they cover. Examples include the Northern and Southern Patagonian Ice Fields, and parts of the Canadian Rocky Mountains.
- Valley Glaciers: Here, the ice does not completely cover the topography; rather, it is channeled through it. Valley Glaciers are found in mountainous areas, occupying the bottoms of some of the valleys, and discharging melts and freshwater releases to warmer areas.
- Cirque Glaciers: Small masses of ice that are located in the headwaters of mountain valleys and occupy depressions called cirques.
- Alpine Glaciers: The combination of the presence of Valley and Cirque glaciers forms another larger category, known as alpine glaciers.
Q. What are the effects produced by glaciers?
A. Glaciers have an enormous impact on the world in which we live; both locally, in the areas where they are situated, and globally. Worldwide, glaciers store almost 33 million Km³ of fresh water. This giant “ice cube”, helps regulate world sea levels. Imagine if all of that ice melted overnight. Water would flood down, through rivers and lakes, and the oceans of the world would rise dramatically!!! In fact, much of the current land mass would disappear under the rising tides.
In ice ages, more of the annual rainfall is held as ice, and the glaciers grow. Conversely, in periods with warmer climate trends, the ice sheets melt, raising the sea level worldwide, This is called eustatic change. Think of the world's glaciers like systems, with inputs and outputs, that interact with other natural systems, such as atmosphere, oceans, rivers, topography, and landscape.
At a local level, glaciers also influence other natural systems. In fact, you will probably experience one of these interactions during your time in Patagonia. Probably, when you are close to the Ice fields, you will notice that weather behaves "differently" than in the rest of Patagonia, or at your home. You will notice localized pressure changes that produce erratic rain and wind patterns. These weather patterns are being influenced by the outputs of the glacier systems nearby.
Also, glaciers are important geomorphic agents; which leave a giant footprint on their local environment. As the ice moves slowly over the terrain, behaving as a plastic material, it carves U-shaped valleys, bowl-shaped cirques, pyramidal horns, and jagged ridge lines. It grinds up and erodes the rock below, transporting and abandoning it in the form of sediment. As you travel through areas where the glaciers have disappeared, look you can often notice their footprints from the configuration of the land and the presence of erratic boulders and large rocks, left behind by ancient ice.
Still have questions? Talk to the guides and rangers you meet during your trip and look for these resources:
- Benn, Douglas I. and Evands, David J.A. 1998. Glaciers and glaciation. Arnold. Page 66-90
- Knight, Peter G. 1999. Glaciers. Stanley Thornes Ltd.
- "Formation and Characteristics of glacier ice." Encyclopedia Britannica. Academic Edition. Revised. August 10, 2011.
- "Glacier hydrology". Encyclopedia Britannica. Academic Edition. Revised. August 2, 2011.
- Derruau, Max. "The system of glacial erosion." In "Geomorphology". Section 3, Chapter 2. Barcelona: Ariel, 2nd Ed., 1991.
- Hambrey, Michael, Alean, Jürg. Glaciers. Cambridge University Press, 2004. ISBN 0-521-82808-2
- Mattern, Joanne. Antarctica: The world's largest glacier. The Rosen Publishing Group, 2004. ISBN 0-8239-6874-X
- Strahler, Arthur N. (1992, reprinted 1997) Physical Geology, chap. 18: Glaciers and glaciations of the Pleistocene, Barcelona: Ed ISBN 84-282-0770-4 Omega
- Tarbuck, E., 1999, Earth Sciences: An Introduction to Physical Geology, Madrid, Prentice Hall.
And for younger readers:
- Icebergs, Ice Caps, and Glaciers. Allan Fowler. 1997.
- Learning about the Earth: Glaciers. Colleen Sexton. 2008.
- Exploring Glaciers. Melody S. Mis. 2009.
- Glaciers. Larry Dane Brimner. 2000.
- Icebergs and Glaciers. Seymour Simon. 1999.
- Glaciers. Isaac Nadeau. 2006.
- Icebergs. Stuart A. Kallen. 2003.