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APART from the enormous tortoises and wealth of other wildlife, the Galapagos Islands are home to thousands of people. Some 200 live on Isabella Island, the archipelago’s largest landmass, which they share with Cerro Azul, an active volcano. So when scientists picked up signals suggesting the volcano was stirring, they were justifiably worried.

The quiverings underneath the volcano were detected at the in Quito, Ecuador, in March. The scientists acted fast. First, to be on the safe side, they issued a warning to residents. Then they rang a team that they hoped could confirm if an eruption was imminent.

While most geoscientists rely on ground-based measurements to help interpret the planet’s inner manoeuvres and rumblings, the crack squad on the end of the phone thinks it has a faster, better method. Earth’s hidden activities manifest themselves as subtle bulges and dips on its surface. So, find a way to follow such movements, and we would open a new window into the realm below. That could help us discover hidden fault lines, track the underground course of magma streams and learn how earthquakes change the delicate balance of Earth’s tectonic plates. More importantly, it could save lives.

What happens in the bowels of the planet is a mystery, but we have a decent idea about the nature of the first few hundred kilometres beneath the surface. Tectonic plates, at most 250 kilometres thick, float on a layer of slowly flowing rock. Sometimes, those plates move suddenly against or away from each other, creating earthquakes. And at spots we call volcanoes, liquid rock spills onto the surface.

To study the plates and these hazards, geologists often use seismometers to detect vibrations, track surface movements by attaching GPS devices to the rock, or measure emissions of gases such as sulphur dioxide, which hint at magma on the move deep below. Each deployment of these methods generally gives us information on just one locality, meaning we can only monitor a tiny fraction of Earth’s surface.

But there’s no reason in principle why we can’t have a global picture. Enter, interferometric synthetic aperture radar, InSAR for short. This satellite-mounted radar technique, developed by NASA in the 1970s, bounces radio waves off Earth’s surface. From this, you can work out the distance between the instrument and the surface, and by comparing measurements taken days or weeks apart, visualise the average surface movement – to within a few millimetres.

Instruments like this have circled the globe aboard satellites since the early 1990s. But they didn’t cover the whole planet and the time between measurements was long.

Now “an incredible game changer” is on the scene, says geophysicist at the University of Leeds, UK. It comes in the form of the European Space Agency’s pair of , dedicated to continuous InSAR measurements. Analysing those readings is a UK research consortium called . “What makes it stand out is the attempt to eventually cover the whole world, if all goes to plan,” says of the University of California, Berkeley.

InSAR is handy for many things, including tracking ships and icebergs. But its promise in geoscience was demonstrated in 2014, after the first satellite, Sentinel-1A, was launched. The Icelandic volcano Bárðarbunga had begun to release magma, so COMET scientist , also at the University of Leeds, looked into it.

As lava began to shift in a chamber beneath the volcano’s crater, the team saw a bulge forming along a nearby surface rift. Using InSAR images, they followed the bulge as it , eventually coming to the surface and spraying out lava equivalent to more than half the volume of Mount Everest. The long, convoluted path the lava took was a big surprise, says Hooper.

By November 2016, Sentinel-1B was in action too, meaning both satellites could be called upon when a magnitude-7.8 earthquake struck near Kaikoura, New Zealand.

Normally, earthquakes are relatively simple. Even a magnitude-8 quake might only rupture a few segments along a single fault line. But the Kaikoura one ruptured an interlinked network of 12 faults – some sliding towards each other, others thrusting apart. “It’s probably the with modern tools and it has completely changed the way that we think about earthquakes,” says Wright. The find is prompting seismologists to re-evaluate earthquake hazard models, which state that if several interconnected faults did rupture, they would do so in separate earthquakes, with each creating the strain necessary for the next.

Hidden faults

Until quite recently, we had surface deformation data for only a handful of earthquakes. And since quakes may only repeat once every 10,000 years in some places, we haven’t yet seen the range of ways they can play out. But with COMET, there should be records for perhaps 40 quakes every year.

One implication is that COMET could discover hidden fault lines. Our maps of these lines are based on records of quakes, but these sometimes happen where we’ve never seen them before. One example is the magnitude-6.6 quake that hit Bam, Iran, in 2003, killing more than 26,000 people. Data from Sentinel-1 should allow the COMET team to spot things like this in advance.

Bulge-watching could also help us decide what action to take, as was demonstrated by that incident in the Galapagos. When the Ecuadorian researchers got through to COMET, they wanted to know what was going on. “We were able to send back a result within about 12 hours,” says Wright. There was certainly something brewing below Isabella, but thankfully the analysis showed magma was moving 5 kilometres beneath the ground, meaning an imminent eruption was unlikely.

The tortoises and the local people were safe, but there are plenty more threats around the world. Obviously active volcanoes such as Santorini in Greece and Mount Etna in Italy are permanently watched. “But many others are not monitored, especially those in the developing world,” says , a volcanologist at the University of Oxford. Yet sometimes they do blow, as was the case with Japan’s Mount Ontake in 2014, which killed 60 people, and Calbuco, Chile, in 2015, when thousands were evacuated. Then there are “zombie volcanoes”: those that are deforming but aren’t watched, because they haven’t erupted in many thousands of years.

The solution might simply be to monitor them all. That’s what Mather and the other COMET scientists are planning. The satellites are already collecting images of most of the planet’s surface, including every land volcano. For now, the team is processing a backlog of data and putting it into . The next step is to develop an algorithm to parse the data in real time and flag up any suspicious bumps so a warning can be issued. This should be running by the end of the year.

The system might not work in all cases, says of Cornell University in New York, because deformation is difficult to detect under heavy vegetation, for example. But fieldwork can fill those gaps, which will be a relief to Mather. She finds visiting volcanoes awe-inspiring, with fire fountains thundering and clinking lava flowing past, while the ground pulses with energy.

Put the satellites and fieldwork together and it will usher in an “era of global volcanology”, says Pritchard. Monitoring volcanoes over time will allow us to build up a database and match specific patterns with actual eruptions. “We want to be able to say: ‘The volcano is showing these symptoms – what’s the likelihood of an eruption?’,” says Mather. If we can do that, it truly will be a game changer.

This article appeared in print under the headline “Earth’s pulse”