ICELAND’S GLACIER HIDES A DRAMATIC LANDSCAPE LIKE ANOTHER PLANET
When we look at an Icelandic glacier, we see a white expanse, glacier tongues and deep crevasses. But hundreds of metres beneath the ice, an entirely different world exists. There are mountains, deep valleys, volcanic ridges, calderas, waterways and even entire lakes. Some of these features are so deep that their floors lie hundreds of metres below sea level.
Scientists obviously cannot simply visit this hidden landscape. They explore it using radar measurements that can penetrate the ice and bounce back from the rock or water beneath it. Thanks to these measurements, we now have a surprisingly detailed picture of what Iceland looks like beneath its largest glaciers.
And in many places, it is a landscape that would look nothing like a place a glacier had ever passed over.
What Lies Beneath Iceland’s Glaciers? There Is No Flat Surface Beneath the Ice
The idea that there is more or less flat rock beneath a glacier is far removed from reality.
Radar measurements have revealed that beneath Iceland’s glaciers are deep valleys, high plateaus, long ridges and extensive volcanic structures. Some valleys were carved by the glaciers themselves over thousands or tens of thousands of years, while others are associated with older volcanic and tectonic activity.
For example, radio-echo sounding beneath the western part of Vatnajökull has revealed long subglacial ridges and valleys. Some extend for tens of kilometres, with their floors lying far below the surrounding terrain.
Vatnajökull National Park says that subglacial mapping has revealed previously unknown landforms, volcanic systems, drainage basins and routes through which glacial floods can flow. Some outlet glaciers in southern Iceland have also carved valleys whose floors reach as much as 260 metres below present sea level.
In other words, there is more than just “rock” beneath the ice.
There is a landscape.
VATNAJÖKULL
Iceland’s largest ice cap and one of Europe’s most remarkable glacial systems
Feature | Details |
Area | Approximately 7,500 km² |
Share of Iceland’s land area | Approximately 7% |
Average ice thickness | Approximately 380 m |
Maximum measured ice thickness | Up to 950 m |
Highest point | Hvannadalshnúkur – 2,110 m above sea level |
Type | Ice cap |
Number of outlet glaciers | Dozens |
Largest outlet glacier | Breiðamerkurjökull / Brúarjökull, depending on the parameter used |
Beneath the ice | Valleys, ridges, volcanoes, calderas, lakes and drainage systems |
Active volcanoes beneath the ice | Approximately 7 central volcanic systems |
Formation of the present continuous ice cap | Approximately 1,000–1,500 years ago |
Continuous ice cap at the time of Iceland’s settlement | Around AD 874 |
Holocene maximum | At the end of the 19th century |
National park | Since 7 June 2008 |
Note: The area and volume of Vatnajökull are changing over time as the ice cap retreats and loses mass due to warming. The national park gives an area of approximately 7,500 km² for 2023; over the past century, the glacier has lost more than 15% of its volume.
950 METRES OF ICE
In some places, almost one kilometre of ice lies between us and Iceland’s actual bedrock. Radar measurements beneath Vatnajökull have revealed that this enormous layer does not rest on a flat floor. Instead, there is a complex landscape of deep valleys, volcanic structures and, in some places, subglacial lakes.
Systematic radar mapping of the bed beneath Vatnajökull began in 1980, and researchers have now measured approximately 10,000 kilometres of profiles across the ice cap.
An important correction to some older material: 2,110 metres is not the “height of the glacier”, but the elevation of Hvannadalshnúkur, Iceland’s highest peak, which lies on the edge of Vatnajökull in the Öræfajökull massif.
How Can Scientists Measure Something Through Hundreds of Metres of Ice?
The principle is actually quite simple.
Scientists use radio-echo sounding, a form of radar sounding. The instrument sends a radio signal through the ice. Part of the energy is reflected from the boundary between the ice and the underlying bedrock, and the instrument records the returning signal.
The time it takes for the signal to travel there and back can then be used to determine the thickness of the ice.
When measurements are repeated across the entire glacier, they produce something resembling a topographic map – except that instead of showing the surface landscape, it reveals what lies beneath the ice.
Radar measurements have been carried out on Vatnajökull since the 1970s. The data have made it possible to create a digital model of both the glacier surface and its bed.
The result is remarkable: scientists can digitally remove the ice and see what the landscape would look like if the ice were not there.
These data are also the basis for the visualisations used in this article.
This is not fantasy. The shape of the landscape is based on actual radar measurements. The colours and final appearance, however, are an artistic reconstruction.
Öræfajökull: A Giant Volcano Hidden Beneath the Ice
One of the most fascinating examples can be found in southeastern Iceland.
Beneath the Öræfajökull glacier lies a huge volcanic caldera covering approximately 14 km².
Today, its floor is covered by ice. At its deepest points, the ice is approximately 540 metres thick, and the caldera contains around 4.3 km³ of ice.
If we removed the ice, we would not find an ordinary mountain meadow.
We would see a vast volcanic depression.
And even more remarkably, radar surveys have revealed another, smaller caldera inside the main one. It covers approximately 6 km², and its floor is about 150 metres deep.
Scientists have also identified an older, heavily eroded caldera north of the present summit of Öræfajökull.
Beneath the ice, there is therefore something we would never expect at first glance: an entire system of ancient volcanic structures.
What Would Such a Landscape Look Like?
If we removed the ice from Öræfajökull, the landscape beneath it would not resemble a simple flat surface.
We can imagine it as a combination of Icelandic volcanic mountain terrain, deep valleys and extensive volcanic depressions.
In some ways, it might vaguely resemble the landscape around Landmannalaugar – not because of specific colours or individual mountains, but because it would be a rugged volcanic terrain of ridges, valleys and volcanic rocks of different ages.
It certainly would not be another Landmannalaugar.
The actual landscape beneath a particular glacier has its own geological history, and its shape is the result of a combination of volcanic activity, tectonics and long-term erosion.
The Glacier Does Not Just Cover the Landscape. It Reshapes It.
Ice is not simply a blanket laid over an already finished landscape.
A huge mass of ice moves slowly and, as it moves, acts like a gigantic grinder. It breaks off rock, grinds down the bedrock and gradually deepens valleys.
The result can be deep subglacial troughs.
At Öræfajökull, for example, researchers have mapped troughs extending as much as 220 metres below present sea level. According to scientists, carving some of these features at the current rate of sediment erosion would take more than 4,000 years.
Some valleys are therefore older than the present form of the glacier.
And the glacier continues to reshape them.
There Are Lakes Beneath the Ice, Too
One of the most remarkable discoveries is the existence of subglacial lakes.
Water can accumulate beneath the ice, for example where a depression in the bedrock traps it. In Iceland, however, geothermal heat also plays an important role.
A typical example is the Skaftá area of Vatnajökull.
Beneath the so-called eastern Skaftá cauldron lies a subglacial lake. Approximately 200 to 400 metres of ice lie above it. Heat from geothermal activity keeps water beneath the ice in a liquid state. The water gradually accumulates and can then be suddenly released.
Scientists have monitored the lake using radar measurements for several years.
Its area has varied from approximately 0.5 to 4.1 km² in different years.
During one period of observation, researchers estimated the volume of water at approximately 250 billion litres. A subsequent flood released roughly 320 billion litres of water from the area.
And this brings us to one of the most dramatic phenomena in Icelandic nature.
Water Can Disappear Beneath the Ice Within Hours
When a subglacial lake fills up, a jökulhlaup – a sudden glacial outburst flood – can occur.
Water begins to flow beneath the ice and may create or enlarge its own pathway.
On the surface, however, there may be no obvious sign of what is happening for some time.
The water is flowing beneath hundreds of metres of ice.
This is one reason why some Icelandic rivers can be so unpredictable. Their source is not necessarily limited to what we can see on the surface. Some of the water may originate or move deep beneath the glacier.
At Grímsvötn, one of Iceland’s best-known subglacial lakes, similar processes occur. Research has shown that water can accumulate there for several years before being released in a huge flood that travels beneath Skeiðarárjökull towards the coast.
A Subglacial River Can Have an Entirely Different World Above It
Even more remarkable is the fact that a hidden drainage network exists beneath the glacier.
It is not a simple river like those on the surface.
Water can flow through channels, in thin layers between the ice and bedrock, or through spaces created by melting. Its routes can change depending on the amount of water, pressure and season.
Models of Vatnajökull, for example, show an extensive subglacial drainage system and suggest that some water may also be transported through underground aquifers.
Beneath the ice, there is therefore an entire hydrological system that is completely invisible from the surface.
And Beneath It All Lies an Iceland We Do Not Know
Perhaps the most fascinating thing about the whole story is that the glacier conceals a landscape that would be extraordinary in its own right.
There are subglacial ridges.
Deep valleys.
Volcanic calderas.
Ancient volcanic structures.
Lakes.
Rivers.
And places where the bedrock lies far below present sea level.
All of this lies beneath the surface on which hundreds of metres of ice are currently moving.
So What Would We See If the Ice Disappeared?
There is, of course, no simple way to find out. We cannot simply “move the glaciers aside” and look underneath them.
But radar measurements allow us to create a relatively accurate reconstruction.
And it reveals something far more fascinating than an empty black surface.
There is a real landscape hidden beneath Iceland’s glaciers.
In some places, it resembles a volcanic mountain range.
Elsewhere, a deep mountain canyon.
Beneath Grímsvötn lies a world of subglacial lakes and volcanic structures.
Beneath Öræfajökull lies a huge caldera.
And beneath some outlet glaciers are deep valleys whose floors lie tens or even hundreds of metres below sea level.
A glacier is therefore not the end of the landscape.
It is its lid.
And every time the ice retreats, it reveals a small part of a world that has been hidden from human eyes for thousands of years.
Sources
Vatnajökull National Park – Glaciological ResearchInformation on radar mapping of the subglacial terrain, hidden valleys, volcanic structures and drainage basins. [Vatnajökull National Park – Glaciological Research]
Magnússon et al. – Removing the Ice Cap of Öræfajökull Central VolcanoStudy reconstructing the bedrock, calderas, ice thickness and subglacial valleys of Öræfajökull.
Björnsson – Surface and Bedrock Topography of Ice Caps in IcelandResearch using radio-echo sounding to map the bedrock beneath Iceland’s ice caps.
Flowers, Björnsson & Pálsson – New Insights into the Subglacial and Periglacial Hydrology of VatnajökullResearch into the subglacial drainage system of Vatnajökull.
Einarsson et al. – Development of a Subglacial Lake Monitored with Radio-Echo SoundingDetailed research into the subglacial lake beneath the Skaftá cauldron.
Nature Communications – Subglacial Water Flow and Ice Dynamics During Glacial Lake Outburst FloodsRecent research into the Grímsvötn subglacial lake and the mechanisms behind jökulhlaups.
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