Are glaciers dangerous?

Photograph of an ice avalanche on Kjenndal Glacier, NorwayAn ice avalanche tumbles down Kjenndalsbreen (Kjenndal Glacier) in Norway. —Credit: Jason Karaian

Glaciers usually are found in remote mountainous areas. However, some are found near cities or towns and sometimes present a problem for people living close by. On land, lakes formed on top of a glacier during the melt season may cause floods. At the terminus, or snout, of a valley glacier, ice falling from the glacier presents a hazard to hikers below. When ice breaks off over the ocean, an iceberg is formed. Some examples of these hazards are listed below.

Flooding caused by a glacier

Although it is not uncommon for a glacier to have a small lake of meltwater near its terminus, extreme melting or unusually fast melting can cause these lakes to overflow their barriers and cause flooding downstream. These are called glacial lake outburst floods.

More dangerous is the case when a glacier flows across a stream or river, creating a dam that can trap a large amount of water. In spring 1986, Hubbard Glacier in Alaska surged and blocked the outlet of Russell Fjord, entrapping a large lake. Over the summer, snowmelt continued to fill the lake. In October, the glacier-created dam gaves way. The fjord reconnected to the ocean, only after releasing an enormous gush of water equivalent to about 35 Niagara Falls.

In Peru in 1941, 6,000 people perished when a glacial lake suddenly burst through its dam, flooding the town of Huaraz below it. Since then, another lake has formed at the base of the glacier, but engineers have created artificial channels to prevent future flooding.

Avalanches from glaciers

Ice avalanches from glacier snouts have been recorded in the Swiss Alps for centuries, and they still occur despite attempts to prevent them. In 1965, the government of Switzerland was constructing a dam for a hydroelectric plant above the town of Mattmark. Without warning, an enormous mass of ice from the nearby Allalingletscher broke off. In mere seconds, the avalanche had rushed down the slopes and buried much of the construction camp, killing 88 workers.

The threat of icebergs

Icebergs that have broken off, or calved, from ice shelves and tidewater glaciers pose a significant threat to sea lanes worldwide. One of the most famous examples is the Titanic, which in April 1912 carried 1,503 passengers to a watery grave after colliding with an iceberg that ripped a large hole in the ship. Shipping lanes along the coasts of Greenland and Newfoundland are historically iceberg-infested waters.

Satellite images showing a large Antarctic icebergCalved in 2000, Iceberg B-15 was a massive iceberg that spent several years drifting off the coast of Antarctica. It disrupted the normal circulation of sea ice in McMurdo Sound; rammed into and knocked off the tip of the Drygalski Ice Tongue; and hindered travel routes for the regional population of Adelie Penguins. In 2005, the iceberg splintered into smaller bergs that finally started to drift north. As late as 2011, small remnants of the iceberg were spotted floating near Australia and New Zealand —Credit: NASA images courtesy Jeff Schmaltz, MODIS Land Rapid Response Team at NASA GSFC

Icebergs calved by glacial ice continue to present problems even today. In 1995, an enormous iceberg, over 80 kilometers (50 miles) long and 40 kilometers (25 miles) wide, broke away from the Larsen Ice Shelf in Antarctica. In March 2000, the largest well-documented iceberg in human history calved from the Ross Ice Shelf in Antarctica. Dubbed B-15, the iceberg measured 295 kilometers (183 miles) long and 37 kilometers (23 miles) wide. The iceberg drifted in the Southern Ocean for several years, gradually splintering into smaller pieces. Small pieces of the iceberg were spotted near New Zealand as late as December 2011.

Because large iceberg may threaten shipping routes, they are carefully tracked by satellite and aerial surveys.