Last updated on April 17, 2014 at 1:21 EDT

What is a Glacier?

June 14, 2013

Hi, I’m Emerald Robinson, and in this “What Is” video, we’re going to investigate a very unique formation of ice called a glacier.

A glacier is defined as a “slowly moving river of ice.” But not all masses of ice are glaciers. To qualify to be a glacier, ice must be at least six hundredths of a square mile in size, and over one hundred and sixty four feet thick. Earth’s largest glacier is Eastern Antarctica’s Lambert Glacier, which is about sixty miles wide, over two hundred fifty miles long, and over eight thousand feet thick.

Glaciers form in places where snow accumulates over a long period of time. As the snow gets deeper, the resulting weight and pressure turns the bottom layers of snow into ice. This high pressure, combined with the force of gravity, causes the glacier to move. Although most glaciers move very slowly, some move as fast as one hundred feet per day!

Glaciers exist on every continent, and play a major role in shaping the face of the earth through erosion. Water from the bottom layer of the glacier seeps into cracks in the earth where it freezes and expands, loosening rocks and boulders from the earth’s surface. These rocks are dragged along the glacier’s path. The earth beneath the glacier becomes smooth as smaller rocks and debris become frozen in the glacier’s lower layers, acting like sandpaper. Glaciers carve lakes and valleys, form natural dams, and create riverbeds.

The water that melts from a glacier’s surface is the largest source of fresh water on the planet. Although glacier melt, also called “retreat,” is a normal part of the water cycle, scientists have noted that glaciers are retreating faster and further than ever, and point to this as evidence of global warming.