The Challenge of Fire and Ice
Studying volcanoes is challenging at the best of times, but when they are buried under a massive ice cap, the difficulty multiplies. Direct observation is impossible, and traditional ground-based monitoring equipment is difficult to install and maintain
in such harsh, remote environments. Yet, ignoring them isn't an option. An eruption under the ice can have dramatic consequences, from triggering catastrophic meltwater floods known as 'jökulhlaups' to releasing vast plumes of ash that can disrupt global air travel. Scientists need a way to keep watch from a safe distance, which is where a new generation of sophisticated tools comes in.
An Eye in the Sky
Satellites have revolutionized how we monitor our planet, and subglacial volcanoes are no exception. Orbiting hundreds of kilometres above Earth, these instruments provide a persistent, wide-area view that ground sensors cannot match. They don't just take simple pictures; they use a variety of advanced techniques to detect the subtle, and sometimes not-so-subtle, signs that a hidden volcano is stirring. From detecting tiny changes in the ground surface to sensing pockets of heat, these orbital sentinels are our first line of defence in understanding and preparing for potential eruptions.
Mapping Millimeter-Scale Movements
One of the most powerful tools in the satellite arsenal is Interferometric Synthetic Aperture Radar, or InSAR. This technique involves a satellite bouncing radar pulses off the ground and measuring the signal that returns. By comparing two images taken at different times, scientists can detect minute changes in the ground surface, with an accuracy of just a few millimetres. As magma moves and collects beneath a volcano, it often causes the ground above to swell or deform like a balloon. InSAR can map this inflation across the entire ice sheet, revealing the shape and depth of the magma chamber below. This provides a crucial early warning that a volcano is 'breathing' and may be building towards an eruption.
Case Study: Bárðarbunga in Iceland
The 2014-2015 activity at Iceland's Bárðarbunga volcano, which lies beneath the vast Vatnajökull ice cap, is a perfect example of InSAR in action. As seismic activity began to increase, scientists used satellite radar data to monitor the situation. The InSAR images revealed that the surface of the ice was sinking by up to half a metre a day. This was a clear sign that the magma chamber deep below the caldera was deflating, feeding magma into a dyke that was spreading horizontally away from the volcano. This information was vital for Icelandic authorities, allowing them to track the magma's movement and correctly anticipate that the eventual eruption would occur outside the glacier, which helped mitigate the risk of a major glacial flood.
Sensing Heat and Gravity
Besides tracking movement, satellites can also detect other tell-tale signs of volcanic activity. Instruments can measure the surface temperature of the ice, looking for 'hot spots' caused by geothermal heat from below. A recent NASA-led study identified a significant heat source, believed to be a mantle plume, beneath West Antarctica's Marie Byrd Land, which may explain some of the instability and melting observed in the ice sheet there. Furthermore, other satellites can measure minute changes in Earth's gravity field, which can be affected by the movement of magma deep underground. By combining these different data streams, scientists can build a more complete picture of what is happening miles beneath the frozen surface.
