Ever-watchful eyes from space warn of more and more hazards down here on Earth. Satellites track hurricanes, measure movement from earthquakes and even show hotspots on volcanoes that are about to erupt.
The latest method of leveraging satellite data involves peering beneath the surface of volcanoes to monitor changes in the ground's mineral structure, which might warn of impending and possibly deadly mudflows. The so-called soft spots are not tied to visible volcanic activity, so there is typically little warning before they break loose.
"This is the frightening part about it," said Michael Sheridan, a University at Buffalo volcanologist who has forged the new use of an old observational technique. "These volcanoes don't even have to erupt. They just sit there and a part of it comes roaring off."
At a meeting of the American Geophysical Union this week, Sheridan explained how he uses a spectral analysis technique (first developed in the 1970s to search for economically useful minerals) to look for soft, comparatively worthless minerals that signal a possible collapse is coming. The method cannot make specific forecasts for when a catastrophe might occur.
Unseen changes
Under the surface of an otherwise benign volcano, groundwater is warmed by rising magma, Sheridan explains. Pockets of magma continually heat water to form a circulation system. The system leaches out soluble elements and retains, or precipitates, less soluble minerals. Over time, and under certain parts of the mountain, solid rock can turn to soft clay or sulfates. Sheridan notices the soft region as a different colored pixel on a satellite image.
"They form real zones of weakness," Sheridan said in an interview. "As the volcano continues to grow, building layer on layer, it becomes unstable."
The resulting collapse can lead to a wall of mud that travels as far as 80 miles, wiping out whole towns and villages, Sheridan said. During heavy rains from Hurricane Mitch in 1998, a sudden mudflow in Nicaragua killed 1,600 people.
"Nicaragua was a real eye-opener," Sheridan said. "There was such a small catchment basin where the rain accumulated, but because the conditions were favorable for this kind of event, a massive, tragic mudflow resulted. These areas are at extremely high risk if people are living nearby."
The volcanologist and his colleagues have a few other danger spots picked out. They have mapped soft spots on Pico Orizaba, the highest mountain in Mexico, and on Colima, the country's most active volcano. Hundreds of thousands of people live in the paths of possible danger.
Washington State residents, especially those around Mt. Rainier, might do well to pay attention to Sheridan's research, too.
"There's a lot of pressure in the Seattle and Tacoma areas to start new developments that extend right up into the mountains, but people are building subdivisions in areas that, in the not too distant past, were overcome by mudflows," he says. "People are not willing to accept the concept that this is a really dangerous area."
The method for finding soft spots is limited by the current resolution of satellites, Sheridan said. A more finely tuned measuring device, mounted aboard aircraft, has proven useful. But permission to fly over volcanoes is not always granted by local governments. Sheridan hopes that the higher-resolution scanners will find a place aboard future satellites.
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