Why do glaciers retreat?

Find out how some of Earth’s most impressive frozen features are disappearing

(Image credit: ArtTower/Pixabay)

Glaciers form in areas of snowfall where conditions are cold enough to allow snow to lie until it has frozen into ice. Ranging in size based on climate conditions and snowfall levels, many are the remnants of the last ice age, when frozen peaks covered over 30 per cent of all land. 

Referring to them as remnants gives the impression that these frozen spectacles are declining. Currently these thick ice blocks dominate 15 million square kilometres of our planet, but as human activity continues to increase global temperatures, glaciers are reverting back to water at a faster rate than they would naturally.

It’s not unusual for glaciers to be subjected to melting during their lifetime, but they run on a continuous snow budget. If they lose ice quicker than they receive their income of fresh snow, their mass begins to diminish and glaciers begin to retreat.

Glaciologists analyse the activity of glaciers year on year. Studying individual glaciers can provide insight into which are growing, which are sustaining their mass and which are retreating. This being said, specific locations come with their own patterns, and a glacier’s state depends heavily on its surroundings.

To an extent, glacial retreat is natural, and the causes of this can vary from temperature and evaporation to wind scouring. The build of these structures can often be season dependent, meaning a slight summer decrease is nothing to worry about, as the winter snowfall will make up for any mass lost as the season continues. Determining global glacier patterns for unnatural retreating requires long-term data to be analysed over a variety of locations.

Taku Glacier (Image credit: Melissa Mahon/Pixabay)

Melting Alaska's mightiest

Glaciers form high in snowy mountains, so it is no surprise that Alaska is an area bountiful in these colossal ice blocks. In fact, Alaska is home to the world’s thickest glacier, the Taku Glacier.

Towering a mighty 1,480 metres from its surface to the ground, scientists studying the block have stood in awe of its ability to appear unsettled by global warming. That was until recently. Glacial developments have always been used as a visual representation of our impact on Earth’s climate, but the world’s thickest was not only surviving, but thriving. The icy giant continued to expand, as it had been doing for nearly 50 years, seemingly unphased by the shrinking of its glacial neighbours. 

But now, by comparing aerial photos taken by NASA in August 2014 and then in August 2019, the glacier’s size is visibly reduced. In most natural glacier cases studied, they stop advancing for at least a few years before beginning their retreat, so this case has come as a surprise to many glaciologists.

A huge percentage of the world's fresh water is stored in glaciers.

The distance some glaciers can move in a day

North America’s longest glacier is almost twice as long as the English channel

One tenth of the world is covered in glaciers.

The estimated number of glaciers currently found on Earth

This article was originally published in How It Works issue 133, written by Ailsa Harvey 

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