Glaciers in Iceland – Everything You Need To Know

Iceland is famous for its glaciers – in fact, around 11% of the country’s surface is covered by ice. The country certainly is aptly named. Iceland is home to the largest glacier in Europe, the magnificent Vatnajökull. In places it measures a kilometre thick and boasts around 30 outlet glaciers which extend from the main body of ice like knobbly white fingers. Some of Iceland’s most iconic visitor experiences, such as seeing the icebergs at Jökulsárlón Glacier Lagoon or riding snowmobiles on Langjökull, involve interacting with glaciers in some way.

So how much do you really know about glaciers? Here’s a brief guide which covers everything you need to know. 

What are glaciers?

To put it simply, glaciers are akin to frozen rivers. At the top of a glacier you’ll find what’s known as the zone of accumulation. This is where the rate of snowfall is greater than anything that’s being lost through melting. As the snow builds up, it is compressed under its own weight and turned to a substance called firn, which is a kind of granular snow. Eventually that firn turns into ice as the process continues.

At the bottom of the glacier, where the temperature is naturally warmer because of the lower altitude, you’ll encounter the zone of ablation. This is where the ice melts and in summer, the glacier may actually recede. Another cause of melting is where the ice comes into contact with water, particularly sea water as it contains salt. Icebergs will calve off the glacier if this is the case, such as happens in Jökulsárlón Glacier Lagoon.

How and why do glaciers move?

Glaciers move downhill because of gravity. Where the tongue of ice comes into contact with the rock of the valley or mountain below, friction occurs. Just as your hands get warmer if you rub them together, so too does the ice that’s being forced against the rock as it travels downhill. The heat that’s being created melts the bottom of the glacier slightly. This lubricates the glacier and helps it slip more easily over the land below.

Even if you get up on the glacier and hike, you won’t see the glacier moving as the rate at which it does so is too slow. However as the glacier moves over the landscape below, it can flex and crack. You’ll see the crevasses, deep cracks in the ice, which are formed as a result. Because of this, and also because up high the weather can be seriously bad, glaciers can be dangerous places and you shouldn’t head up onto one without an experienced guide.

What impact do Iceland’s volcanoes have on its glaciers?

Some of Iceland’s volcanoes are visible from above, such as the Fagradalsfjall volcano in Reykjanes which erupted spectacularly in 2021 and again briefly in 2022. Others however, are hidden beneath a glacier. Katla, potentially one of Iceland’s most dangerous volcanoes, lies beneath Mýrdalsjökull. In the centuries that Iceland has been settled, records show that Katla has erupted at least 20 times. 

Sometimes eruptions like this cause a glacial outburst flood which Icelanders call a jökulhlaup. Basically, the heat from the magma that’s being forced up beneath the glacier causes the ice to melt and a large volume of water is released, often suddenly. Grímsvötn, a volcano that sits beneath Vatnajökull, has also caused jökulhlaups to occur.