Glacier (noun, “GLAY-shur”)
This word describes a massive body of ice that moves slowly across land. Glaciers can be hundreds or thousands of meters (yards) deep. They form in places where snowfall does not completely melt each year. Over time, the weight of the snow piling up compresses the snow below, turning it to ice. At the very bottom, the ice becomes viscous, meaning it is able to flow and move.
Glaciers that form on mountains creep downhill. Big ice sheets on land, like the one covering most of Antarctica, move too. These ooze or slide outward from their centers. Most glaciers move at a crawl — advancing just a few centimeters (an inch or so) each day. But some move up to 50 meters (164 feet) in a day. That’s half the length of a professional football field.
Such huge masses of ice grinding across the land leave their mark. They can carry or push soil, rocks and big boulders. They can erode the land and gouge deep valleys. Dents and divots left by glaciers have filled with water to form lakes, such as the Great Lakes that border the United States and Canada.
Scientists estimate that glaciers cover around 10 percent of the Earth’s surface. Some glacier ice is just 100 years old. The oldest glacier ice in the world, though, in Antarctica, may be 1,000,000 years old. Glaciers contain much of the planet’s freshwater. But climate change is causing them to melt. Some are losing ice quickly, such as the ice sheet that covers Greenland. From 2006 to 2015, that ice sheet shed 278 billion tons of ice every year, on average. That water contributes to rising sea levels. And if glaciers disappear, people who depend on annual meltwater may be left high and dry.
In a sentence
A satellite launched in 2018 is keeping an eye on thinning glaciers from the sky.