Crevasse. What phrase depicts open fractures in a glacier's fragile surface ice? Only $2.99 per month. Cirque. What word comes from an Icelandic word meaning "circle" or "wedge"?
A cirque is a deep, roughly circular depression in a glacier caused by the pressure of surrounding rock. The word comes from the Icelandic krirfa which means "a circle or wedge".
In mathematics, a circlerotation is a form of rotation where each point on the rotating object stays fixed relative to some other point on the object.
Circles are particularly useful in mathematics because many properties can be expressed easily in terms of circles. For example, if we divide a line segment into two equal parts, then the two new points will form a circle with the original segment as a diameter.
The word "circling" also has another mathematical use: A sequence of numbers or objects that forms a circle when plotted together on a graph or chart is called a cyclic sequence.
Cyclicity is the property of having a repeated pattern or cycle. In mathematics and physics, a phenomenon is said to have cyclic behavior if it occurs in a periodic sequence with a repeating pattern.
A crevasse is just a deep break in an ice sheet or glacier. The two main causes of glacial crevasses are gravity and pressure. As a glacier moves over rock, it grinds away the rock's surface material. This creates sharp edges that can cause damage to vehicles traveling on glaciers. When a driver hits a crater or hole in a glacier, they can be thrown out of their vehicles.
As a glacier melts from the inside out, water flows into voids left by retreating ice. If the surrounding rock is weak, such as in a glaciated valley, then it too will dissolve, leaving a vertical fissure in the ground known as a krummholz tree.
The word "crevasse" comes from the French for "crack," which is how early explorers described features on Earth they didn't understand. Crevasses were first seen on glaciers during the Renaissance era, when people began to explore northern Europe and America. They were amazed at the sight of deep cracks in the ice caused by rocks falling into them from above.
Today, scientists use radar studies, aerial photographs, and other methods to learn more about glacial crevasses.
According to these research, the ice near the surface (approximately 165 feet [50 meters] depending on location, temperature, and flow velocity) is hard and brittle. This topmost zone is the brittle zone, where ice breaks when it moves, causing enormous fissures along the top of a glacier known as crevasses.
The depth of the ice that is hard and brittle increases with increasing temperature. At very high temperatures, almost the entire volume of the glacier is considered to be the brittle zone.
Glaciers spread out from a central point called the core. The amount of space between the glaciers and the core tends to increase with distance from the center. The ice in this region is less dense than the ice closer to the core and therefore more likely to break off into separate pieces. These floating chunks are called icebergs. An average-size berg has an area of about 100 square yards (90 sq m). Smaller or larger pieces may be detached from time to time.
As you can see, the brittle zone of a glacier extends far below the surface. However, because most glaciers cover a large area, only a small part of their total length is found in one place. So, although they appear fragile, glacial bodies are actually strong enough to withstand considerable mechanical stress without breaking up completely.
The flowing ice in the glacier's center flows faster than the glacier's base, which grinds slowly along its stony foundation. Because of the glacier's varying speeds, stress builds inside the fragile top section of the ice. The glacier's surface splits, generating crevices known as crevasses. As more heat enters the rapidly melting ice, more water is absorbed into the glacier, which increases its volume and pushes the split ends farther apart. This process continues, until an iceberg breaks off.
There are two types of glaciers: those composed of snow and ice frozen into rigid blocks called "icebergs," and those made up of liquid water that flows under the influence of gravity called "rivers." Glaciers form when large quantities of rain or snow melt quickly from the surface of the planet. The resulting flood of water rushes down steep slopes, forming narrow bands of white ice that extend for hundreds of miles below sea level. Glacier ice has returned to the earth's surface three times in the past few million years. The first time was when continental plates drifted away from each other, opening up new land and creating more shallow oceans. The second time was when large parts of Antarctica froze over during the Ice Age. The third time is today.
Most glaciers contain some amount of salt because of the ocean water they once held near their source. As the glaciers move south toward warmer climates and lower levels of salt concentration, most of this water is released into the world's seas.
Polar glaciers are frequently frozen to their beds, making this technique unable to occur. Glaciers' uppermost sections are fragile. When the bottom section deforms due to internal flow, the higher piece may fracture, resulting in enormous fissures known as crevasses. This can happen even when the temperature is above 0°C (32°F), if the ice is very thin or the force applied is great enough.
In addition, sunlight heats the ground directly under the sun, causing it to expand and break up the glacier surface. As more heat reaches the base of the glacier, it too will begin to melt away.
The most important factor affecting the rate at which a glacier melts is its distance from the tropics. The further north it is, the longer the day is, and thus the more time there is for heat to melt the ice. In fact, all else being equal, every 10 degrees North brings about a 30% increase in melting.
Glaciers in the tropics aren't completely immune to decay. Over time, rain and snowmelt water may wash debris into the sea that later turns up on distant shores. But the main cause of death for tropical glaciers is not natural but rather human-made: glacier mining.
Miners look for places where the glacier is thickest, then they drill holes down to the bedrock below.
Glacier surging is a quasiperiodic oscillation between long periods of sluggish flow (tens to hundreds of years) known as the quiescent phase or quiescence and shorter periods of generally 10-1000 times quicker flow known as the surge phase, active phase, or surge. During glacial periods when ice covered most of North America and Europe, many glaciers surged.
The term "surging glacier" is usually applied to large bodies of ice such as Greenland's Ice Sheet or Antarctica's Glacier. However, smaller glaciers can also surge. An example is the Walker Glacier in Washington state, USA which has been observed to surge after heavy rainstorms. The cause of this behavior is not clear but may be related to changes in water pressure that allow more ice to slip over an underlying rock bed.
Surging glaciers move forward rapidly then stop for many years at a time before starting up again. This happens because the weight of the ice on top causes it to press down on the rock below which increases friction and prevents further movement. As the weight of the ice reduces the pressure against the rock, it becomes able to move again.
It is estimated that about one percent of all glaciers worldwide are prone to surge. In general, these are small glaciers located in mountainous regions where there is enough precipitation to produce snowpack. When the weight of the snowpack is removed, it allows the glaciers to surge.