Satellites detect volcanoes heating up before they blow

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Satellites detect volcanoes heating up before they blow

Popocatépetl, a volcano near Mexico City, steams away in this false-color satellite image (making vegetation appear red).

Just as we can often spot the beginnings of an illness from a number of signs, there are symptoms of volcanic activity that can indicate a growing likelihood of eruption. Monitoring them can involve detecting surface changes and small earthquakes caused by the movement of magma inside a volcano, or measuring changes in gases emitted from vents. Signs like these are used to raise alerts and trigger evacuations, and they have saved lives. But they aren’t always perfect.

Japan’s Mount Ontake erupted in 2014 without warning, for example, killing more than 60 people. So additional methods for detecting volcanic activity are always welcome, especially if they involve subtler signs that could be overlooked. A new study from a Jet Propulsion Laboratory group led by Társilo Girona highlights the possibility that presently available satellite data could provide an entirely new way to warn of eruptions.

Heat is obviously a relevant parameter for volcanic activity, but it can be quite variable at the individual spots where you might set up a thermometer. If we could instead measure all the heat coming out of a volcano, it would be quite meaningful, since the majority of volcanic energy gets released as heat.

To attempt this, the team turned to thermal radiation data from NASA’s Terra and Aqua satellites. Combined, these two provide twice-daily passes with global coverage, and each measurement is integrated over a 1 kilometer by 1 kilometer pixel. There are five volcanoes that have both had significant eruptions since 2002 (when these satellites came online) and aren’t located on islands that are too small to span enough pixels for a good signal. These include Ontake in Japan, Ruapehu in New Zealand, Calbuco in Chile, Redoubt in Alaska, and Pico do Fogo in Cape Verde.

Increasing temperature trends were seen over the two- to four-year periods preceding each eruption—including Ontake’s surprise 2014 eruption. Temperatures only increased by 1°C or less in the lead-up to each event, but these were statistically significant trends and not just noise. The peak temperatures in each record were associated with an eruption.

Enlarge / Temperature records for each volcano show eruptions (black vertical lines) at the peaks.

The researchers say this might represent a combination of two processes. First, magma progressing closer to the surface—and releasing gases—could stimulate hydrothermal circulation, carrying heat to warm the surface from below. Second, if this pushes more moisture into the soil layer, the ground could emit thermal radiation more efficiently and so appear “brighter” to the satellites. Either way, these subtle changes seem easily detectable in the satellite data.

This provides another meaningful metric helping to fill out a complete picture of volcanic activity. It could also make it easier to study the total heat budget of a volcano—the balance of energy coming in from below, and when and where it all gets released. Combined with other monitoring tools, the satellite data could easily be used to increase the confidence of alert levels, placing short-lived events in a longer-term context. And the more symptoms we watch for, the less likely we are to miss important warning signs.

Nature Geoscience, 2020. DOI: 10.1038/s41561-021-00705-4 (About DOIs).

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