Understanding Our Earth: Glaciers (1977)

My home state of Alaska is sometimes called a paradise of glaciers. Huge masses of solid ice. They fascinated [music] me ever since I was a small boy. I guess that's [music] why I became a glacier scientist. In other words, a glaciologist. I make my living studying glaciers, how [music] they form, how they move, and how they affect the land and the oceans. That's an important part of understanding our Earth. As a boy growing up in Alaska, the first glaciers I saw were the type called valley glaciers, one of two types. They're formed high up in the tallest mountains of the world. We have several valley glaciers in the mountains along the coast of Alaska. And valley glaciers are especially [music] common in the Alps in Europe. This is where scientists first started to study glaciers, and that may be why this type is also called an alpine glacier. They're big, sometimes several hundred meters thick, >> [music] >> a couple of kilometers wide, and several kilometers long. I've studied these rivers of ice in several [music] parts of the world. They're also found in the high mountains of western Canada and the western United States and in the Andes Mountains [music] of South America. So, you can visit an Alpine glacier without traveling to Europe. For example, there's Deming Glacier on Mount Baker in Washington state. It's a typical Alpine or valley glacier, a huge river of ice formed in the valley of a high mountain and moving slowly down through the valley. You may have guessed that glaciers can form in high mountains because of the very cold temperatures here. It starts when a heavy winter snowfall builds up on the peaks and on the mountainsides. Summer is short and cool, and not all of the snow can [music] melt. Next winter, more snow covering what's left from the winter before and packing it down into ice. Some of the new snow melts in the summer, but each year more is left and packed down to become [music] ice. >> [music] >> Eventually, the layer of ice becomes so heavy that its own weight begins [music] to push it down through the valley. The movement you're seeing here actually takes much longer in a real glacier. A glacier rarely moves more than 2 m a day and often only a few centimeters a day. >> [music] >> As it moves over uneven ground, the ice may bend and crack. The cracks are called crevasses, and they may be more than 60 m deep. >> [music] >> They're interesting to explore, but dangerous. In warm weather, some of the ice on the glacier surface [music] may melt and flow into a crevasse, forming a stream of water under the glacier. This meltwater can carve a cave in the ice. So, a glacier is constantly changing as it moves slowly down a valley. But, we know that a glacier will also cause some changes in the valley and the mountains themselves. Even where a valley glacier has melted away, we can tell where it's been. Sometimes a mountain is carved by several valley glaciers into a rugged peak called a horn. This is the Matterhorn in Switzerland, probably [music] the most famous mountain of its kind. You've probably heard of the fjords of Norway. A fjord is formed when a glacier moves all the way to the ocean and carves a valley into the shallow seabed. I've seen [music] fjords like this in several parts of the world. The glacier that carved [music] this fjord in Norway melted away long ago, but in the northernmost part of Alaska, some valley glaciers still flow down to the sea. And huge pieces may break off [music] to form icebergs. Of course, most of the world's icebergs come from Greenland, but we do have some off northern Alaska. [music] Most of an iceberg, about 5/6, floats underwater. So, icebergs are much larger than they look and dangerous to ships. The reason [music] they float so low in the water is that glacial ice is much harder and heavier than ordinary ice. >> [music] >> I remember the iceman I used to see when I was a boy in Alaska. They collected [music] floating ice and sold it for use in homes and businesses. It was like regular ice, but better in one way. It melted much more slowly. But the largest icebergs don't come from valley glaciers. They come from a second and more extensive [music] type of glacier called a polar ice cap. There's one covering nearly all the land surrounding the South Pole. The continent of Antarctica. And in the north, ice caps cover Greenland and parts of several smaller islands. >> [music] >> In some places, the solid ice goes down more than 3 km. Those rock formations are actually the tips of mountains in Greenland. A couple of years ago, I spent a few months near the South Pole at a scientific station in Antarctica. Quite an experience, >> [music] >> but not exactly comfortable. I'm glad there are other ways to learn about the ice cap. Here in Alaska, for example, we found evidence that the glacial ice once covered much more land than it does today. These stones were rounded and polished by the action of the polar ice sheet. In Central Canada, more evidence. Rock surfaces left behind when the ice sheet passed through like a bulldozer, carrying away most of the topsoil. Further south, the deep fertile soil of the corn belt developed from silt deposited mainly by meandering rivers that formed as the ice sheet melted. And the gravel hills in New England are another kind of deposit left by the ice sheet. The hills are made up of pebbles and [music] coarse soil called glacial drift. Another type of hill here called a drumlin formed when glacial drift piled up on a knob of rock or clay. When the glacier moved on, it rounded the hill into an almond shape. Lake Michigan and the other Great Lakes formed as glaciers gouged out river valleys and filled them with glacial meltwater. And smaller lakes formed in basins scooped out by the ice sheet. Putting together all the clues from several parts of North America, we can get a good idea of what must have happened. More than 2 million years ago, as the climate turned colder, [music] several glaciers were formed. The glaciers grew and joined, spreading southward and covering about half of North America. Then, after many thousands of years, a warmer climate began to melt the ice cap. This pattern was repeated at least four times. >> [music] >> The ice cap has slowly been shrinking over the last few thousand years. And the valley glaciers have been shrinking, too. Sizing up the evidence, it looks like we're in a period between ice ages. But we have good reason to expect that the glaciers may start to grow again, and a new ice age might begin. Some think ice ages are triggered by unusually heavy snowfall over a period of time. Others say it has to do with periodic [music] changes in the Earth's orbit. We're looking for more information to help us predict when a new ice age may begin and what effects it will have. That's one reason why knowing about glaciers is an important part of understanding our Earth. >> [music] [music] [music]