A glacier is a huge, thick body of ice that forms on land and then creeps, very slowly, down a mountain valley. It is not a frozen lake sitting still — though it looks still if you glance once. Year by year it slides, carrying rock with it, and it can be tens or hundreds of metres deep. Some glaciers reach the sea; many never do. People picture only the North and South Poles, but mountain glaciers sit in the Alps, the Himalaya, and many other high places. The ice is born from packed snow, pressed until it turns to ice. English borrowed the word from French in the 1700s (first recorded in 1744); at the root is Latin glacies, “ice”, though scholars are not sure where that Latin word itself began.