You’re coming to Iceland and have been told that stepping foot onto a moving glacier is a once in a lifetime experience. You’re really excited about it and have seen the pictures of the incredibly blue ice, the bottomless crevasses and captivating textures and features in these moving giants. You can’t wait to go explore this icy wonderland. But before we do that, let me ask you something; what actually is a glacier?

Made of ice, sure. But that’s only part of it. Let me explain further. A glacier must meet certain criteria to be deemed a glacier;

  • It must have been formed from condensed snow. Usually over hundreds of years of accumulation to squeeze out all the air and turn it into ice.

  • It has to be a certain width and depth. The numbers are regularly debated, but the short answer is that it must be heavy enough to move under its own weight. That generally means about 100 metres of pressure. The width is negligible but anything over 60 metres wide is usually recognized as a glacier.

  • It has to be able to move under its own weight. This one is the most important and indeed most interesting features of a glacier so I’ll elaborate further below;

The phenomenon of ice as big as a city perpetually moving out towards the sea is as beautiful as it is baffling. Without using technical terms like plasticity, regelation or actual density measurements let me explain further;

Some glaciers move so slowly that you can’t see them move, except over a long period. The Sólheimajökull glacier flows just a few cm a day at it’s terminal face. Others flow so quickly that a thunderous ice avalanche is a daily occurrence, like on the Falljökull glacier as it pours off the side of a cliff.

Falljökull Glacier | Jökulsárlón Glacier Lagoon 2 Day Tour | Hidden Iceland | Photo by Amy Robinsson

So how does it happen?

Most people will sheepishly say ‘gravity’. Which is technically true. Gravity forces the ice from a higher to a lower ground. But then gravity is the force that pushes all things on earth. But this doesn’t fully explain how glacier ice, despite its weight and density, can flow over broken volcanic rock, drift over flat open plains, or ride up and sometimes over mountains.

The more astute observer will say that melt water from the glacier gives it lubrication underneath to slide. Again, technically true. It relates to what experts will refer to as a ‘wet glacier’. So this explains glacial movement in the warm summer months of Iceland. But how do glaciers in Antarctica, Greenland, and Icelandic winters move when the temperature is almost always below zero?

Falljökull Glacier | Hidden Iceland | Photo by Jonny Livorti

Here is the magic part.

Ice is the only natural substance on earth that is less dense than it’s liquid counterpart (water). It’s due to how the individual hydrogen and oxygen atoms bond with each other which I won’t explain further here. In fact that’s why icebergs float.

Jökulsárlón Glacier Lagoon | Hidden Iceland | Photo by Norris Niman

So let’s connect that to a glacier that’s 100 metres thick. Then let’s add fresh snow on top adding even more weight to it.

When you add that much weight to something you squeeze out all the inconsistencies and empty spaces. The more you do that (in this case adding more snow) the more dense the ice gets at the bottom.

Now normally when a solid object is pushed to its maximum density it will simply smash, crack or break. Ice doesn’t do that. It does something much more magical. It compresses so much with the increased weight above it that it converts back to its most dense form….water.

So what I’m saying here is that when ice is put under enough pressure, the parts under the most the pressure at the bottom will turn back into a liquid. In effect creating it’s own lubricant which allows it to slide, even in the dead of the deep cold winter when water would usually be frozen.

In essence the glacier pushes itself. Pretty cool right?

The walk to Solheimajökull Glacier | Hidden Iceland | Photo by Norris Niman

You can learn more about the glaciers in Iceland, their changes over time and see them first hand by joining a number of our tours with our knowledgeable and passionate guides. If you have a day free then our South Coast: Fire & Ice tour takes you to the front of the Sólheimajökull glacier for some great views, as well as visiting the famed sights of the south. For those with a bit more time, and feeling adventurous, then join our Two Day Jökulsárlón Glacier Lagoon tour out to Vatnajökull National Park, where we hike right up to the ice fall on Falljökull glacier. If you are really short on time, or have youngsters under 10, then there is an amazing Glacier & Ice Cave Exhibition at Perlan, right in Reykjavík!


Ryan (1)

Hi, I’m Ryan Connolly; Co-Founder, Glacier Guide, and Marketing Manager of Hidden Iceland. I’ve guided in multiple countries around the world and stepped foot on all 7 continents. I’ve made Iceland my home for the past few years. My passion for science, the outdoors, nature, glaciers and volcanoes has led me to study many aspects of my adopted home, Iceland.


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