What Are Glaciers?
You’ve likely heard of them, but what are glaciers exactly? Well, simply put, a glacier is a densely packed body of ice and snow that is so heavy that it moves under its own weight. They can be thought of as a very cold and very, very slow moving rivers. The word glacier comes from the French word glace, which means “ice”, and indeed, glaciers are often informally referred to as “ice rivers.”
Types of Glaciers
There are two main types of glaciers: alpine glaciers and ice sheets.
Alpine glaciers are restricted to mountainous areas, where they move downward from the tops of mountains into valleys, sculpting unique features into the surrounding topography as they slowly creep across the surface. They occur on every continent, with the notable exception of Australia.
Ice sheets, by contrast, can form anywhere where it is cold enough to do so and do not require mountainous topography to occur. They form around a central dome and can spread out to cover incredibly vast areas. The largest ice sheets are referred to as continental glaciers and cover massive swaths of land including most of Greenland and Antarctica. A total of 99% of the surface area of glaciers are contained within these gigantic ice sheets.
How Do Glaciers Form?
Glaciers occur when snow builds up more quickly than it can melt away or be sublimated. As snow continues to build up on the surface, it gradually becomes increasingly dense and granular. When new, softer snow falls on top, it further packs the already denser snow underneath, creating a grainy type of ice called “firm.”
Over the years, the firm will continue to grow until it reaches a thickness of about 160 feet. At this point, the weight of the firm will cause the mass to collapse into itself, forming a thick sheet of ice. As this process continues, the ice will exert so much pressure that it will begin to move. Similarly, snow and firm will begin to melt regardless of the temperature, which makes the bottom of the glacier thicker and more mobile.
An ice sheet will move out and away from its dense center point, while an alpine glacier is pulled downhill by the forces of gravity. Most glaciers move only an inch or two a day. The rare kind of glacier that can sometimes move as fast as 150 feet over the course of 24 hours are called galloping glaciers.
Despite their slow moving speeds, glaciers are incredibly powerful phenomenon. They are capable of carrying massive chunks of rocks for miles. As these rocks are dragged along, they create huge gouges in the surrounding landscape. They are eventually deposited near the end of a glacier, in a repository referred to as a moraine. At the point where a glacier meets a body of water, huge chunks of ice break off in loud and dramatic fashion. These chunks of ice become icebergs.
Why Is Glacial Recession a Big Deal?
Present day glaciers are merely the leftovers of the last ice age, where glaciers were estimated to cover more than 60% of the earth’s surface. Familiar topographical landforms, such as lakes, are typically created in the hollowed out remains of these ancient glaciers. An ice age can only occur when cold temperatures are prolonged over the course of many years, and global warming has resulted in the disappearance of the glaciers at unprecedented speeds.
As glacial ice melts, these enormous masses increasingly end up in the ocean, where they are causing the sea level to rise at alarming rates. As the sea level rises, coastal land erodes and human populations living in these areas are becoming threatened. Meanwhile, the global balance of salt to freshwater is upset, contributing to drought and excess rainfall and generally exacerbating the effects of global warming.
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