When snow accumulates over a period of many years (that is, it doesn’t melt away after one season), the buildup creates a thick deposit in which the overlying mass tends to compress the lower snow layers into solid ice. During this, the individual snowflakes change into granules, which fuse into crystals of ice. Often, the air between the flakes becomes trapped, thereby creating air bubbles within the ice crystals. In polar areas, this produces huge and massive ice caps that can overwhelm and cover the entire landscape, including even mountains. Eventually, the ice mass thickens to the point where it begins to move due to a combination of gravity and the shape and slope of the ground surface. On steeper slopes this can occur when the thickness of the combined snow and ice reaches 15 m (50 feet) in depth. This is often referred to as glacial ice. If the flowing ice is constrained by mountains, valley walls, or other land surface formations, it is known as a glacier. You can see quite a few Arctic glaciers on our Arctic travel.
Glacial ice is the world’s largest reservoir of fresh water, albeit in solid form. Nearly 99% of all glacial ice on Earth is contained within the huge ice sheets in the polar regions. In fact, this volume of ice is so large that if the ice sheets of both Greenland and Antarctica were to melt, it would cause sea levels to rise about 70 meters (230 ft). In addition to Antarctica, Greenland, Canada, Iceland, and Svalbard, there are also significant glaciers scattered around the world outside of polar regions, including Alaska and Chilean Patagonia. They are found on every continent, except Australia, and some even occur in tropical zones, but only on high mountains where low temperatures can endure. Many of these glaciers are so extensive, they accumulate and store H2O in what is known as the Accumulation Zone and release it as meltwater elsewhere as it flows downhill in the Ablation Zone. This can be a very important source of water for plants, animals when other sources are lacking.
Glacial flow speeds vary greatly. The record is held by Greenlands's Jakobshavn Isbrae, which generally moves at the rate of 20 to 30 meters (66 to 100 ft) per day. As glaciers flow downhill, the internal ice deeper than 50 meters (160 ft) behaves like a plastic and becomes deformed. The upper region, which is under less pressure and is more rigid, behaves like a brittle solid and is known as the Fracture Zone. Here is where one encounters the infamous crevasses. The depth of the crevasses and width of the crack openings are dependent upon the shape and slope of the underlying substrate, as well as the speed of flow. Crevasses seldom extend more than 50 meters (160 feet) below the ice surface, but can sometimes extend much deeper…perhaps as much as 330 meters (1,000 feet). Below this depth, the plastic deformation of the pressurized ice is too extensive to create cracks. Crevasses make travel over glaciers extremely dangerous, because heavy snow falls can form fragile snow bridges that hide the crevasses from view until too late.
Glaciers can have a significant effect on the land forms over which they flow. In some areas, we can easily see evidence of past glacial action…such as scratches and gouges left behind on the bedrock, specific shapes or configurations of valleys, and diagnostic piles of rock, pebble, and sand debris (known as moraines) that were bulldozed by moving ice. These remnant signs of glacial action were produced primarily by rock particles being moved along with the ice and eroding the terrain. As glaciers flow over the bedrock's surface, the ice has a tendency to pick up pieces of rock (a process known as ‘plucking’) that are broken loose through freeze expansion. As the rocks are carried along in the bottom of the ice, they act like abrasive grit in sandpaper. The same process occurs along the edges of the ice flows, when rocky debris comes loose from the mountain sides and gets incorporated into the ice load. The rocky particles themselves may become pulverized during this grinding and form extremely fine grains known as rock flour. This material is so fine that it will escape with the meltwater and stay in suspension within the liquid water, thereby giving it a milky appearance.
Most polar glaciers and many temperate glaciers actually flow all the way to the sea, where they can be easily viewed from boats. In fact, the fjords that they often inhabit are simply flooded valleys that were created or modified by the glaciers themselves. This is the norm for glaciers in the Svalbard Archipelago. These so-called Tidewater Glaciers can be quite fascinating, because they frequently break off, or calve, at their terminal ends and create impressive ice bergs. There is usually much ice debris around the faces of Tidewater Glaciers to be seen on an Arctic cruise and the combined actions of ice movement and meltwater streams, which agitate the subsurface waters, create good feeding regions for wildlife, such as sea birds, cetaceans, and pinnipeds. We seek out these sites to offer Zodiac cruises, kayak expeditions, and wildlife viewing in spectacular settings.
Glaciers are greatly affected by long-term climatic changes, such as average annual temperatures and amounts of precipitation. This makes the easily observable changes in ice movements, accumulation, ablation, etc., one of the most sensitive indicators of climate change. Such observations have been going on for a long time. Since 1850, after a worldwide cold period known as the Little Ice Age, glaciers throughout the Northern Hemisphere retreated significantly until 1950. Then, a slight cooling trend caused many glaciers, especially in high mountains, to advance for more than 30 years. However, since the mid-1980s, nearly all the glaciers in the Northern Hemisphere have been on the retreat. This fact alone is not greatly significant with regards climate change, but the fact that many these glaciers are dramatically thinning (undergoing a mass balance loss of ice) is considered a very significant observation. When a glacier is reduced in size to a critical point, it stops flowing and becomes what is known as a static glacier. We observe many such glaciers nowadays, and their continuing meltwater outflows create complex network braided rivers and stratified alluvial deposits.
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