Glacial motion can be difficult to predict. In 1986, the Hubbard Glacier in Alaska's Russell Fjord suddenly began to surge at the rate of 30 feet / 9 meters per day, creating a sizeable lake at the mouth of the fjord.

The Tokositna Glacier, on the south side of Alaska's Mount Huntington, sometimes begins to surge down the mountain with loud rumblings and snapping sounds as the ice moves and breaks.

And the massive glaciers of western Greenland, where 90% of North Atlantic icebergs come from, are among the fastest moving in the world - moving up to 4½ miles / 7 km per year.

But the record for the fastest glacial surge goes to the Kutiah Glacier in Pakistan. In 1953, it raced more than 7½ miles / 12 kilometers in three months, averaging about 367 feet / 112 meters per day. Watch out!

Finding the reasons for a glacier surge can be difficult. It could be climate change, earthquakes, or even the build-up of melting water beneath the ice.