Measuring Volcanic Eruptions from Space: Uniting Geophysical and Geochemical Data

When volcanoes erupt, they spew lava, ash, and gas into the atmosphere and over the surrounding landscape. The impacts of volcanic eruptions in populated areas are well documented, since scientists can monitor gas emissions and collect physical samples with relative ease. However, a significant fraction of Earth’s volcanoes are remote, making direct observation challenging.

Some researchers have therefore turned to space-based techniques, collecting data from satellites. In a new paper published in the journal Nature Communications, DCO collaborators Brendan McCormick Kilbride, Marie Edmonds (both at the University of Cambridge, UK), and Juliet Biggs (University of Bristol, UK), analyzed several sets of satellite data in order to reconcile, for the first time, geophysical and geochemical models of magma composition [1].

“We’ve known for some time that when many volcanoes erupt we see a change in elevation, like the volcano has deflated, and we can measure this change using satellite observations,” said Edmonds, co-Chair of DCO's Reservoirs and Fluxes Community. “We also know that volcanic eruptions produce gas plumes rich in sulfur dioxide, which we can also measure from space. However, what’s been a bit of a mystery is how these two datasets fit together. We couldn’t spot a pattern.”

By measuring how much a volcano deforms throughout an eruption, scientists can make an estimate of the volume of material previously contained within the magma chamber. These measurements, however, were at odds with the mass of sulfur dioxide measured in the erupted gas plume.

“We were seeing way more sulfur dioxide than we would expect for the volume of materials expelled during an eruption,” said first author McCormick.

The team therefore began modeling what was going on beneath the surface. They found that if more gases like sulfur dioxide and carbon dioxide are present in magma, they change its physical properties. Magmas with high concentrations of these volatiles are not homogenous. Instead, the gases clump together, creating bubbles. These bubbly, spongy magmas are a lot more compressible than magmas without bubbles, partially explaining why many large eruptions rich in sulfur dioxide show only limited changes in ground deformation.

The authors also suggest that in eruptions with huge gas emissions, a fraction of pure gas could collect at the top of the magma chamber prior to eruption making the ratio of erupted gas to eruption volume even larger.

“What we’ve done here is build a model of volcanic eruptions that could explain several aspects of volatile rich magmas,” added McCormick. “We’ve shown that our model is consistent with several datasets. If we can confirm this relationship between sulfur dioxide output and eruption volume, we come closer to being able to use satellite data alone to investigate some of Earth’s most remote volcanoes.”

“These data also tell us a lot about the Earth system,” added Edmonds. “As we refine our model, and integrate data from DCO’s DECADE volcano monitoring stations, we’ll generate a much more accurate picture of deep volatile cycles, including the deep carbon cycle.”

Image: Okmok volcano in the Aleutian Islands, Alaska, one of the volcanoes analyzed in the study. Credit: Christina Neal, Alaska Volcano Observatory, USGS (source)

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