The Yellowstone Volcano Observatory (YVO) and US Geological Survey (USGS) are the first line of defence against a Yellowstone eruption. For decades, the geological agencies have tracked ground deformation and seismic activity within Yellowstone National Park. Ground movement is a sure indicator of bubbling danger and often precedes an incoming eruption. In 1994 for instance, geologists noted rapid ground motion in the Rabaul caldera in Papua New Guinea before the volcano erupted.
According to the USGS, the ground deformation was so intense a local reef rose from the sea fast enough to strand fish out in the open.
A similar incident occurred in 1927 when Fernandina volcano in the Galapagos caused the coast to rise and trap a fishing boat above the water.
Geologist Beth Bartel has now said in this week’s edition of the USGS Caldera Chronicles, scientists monitor Yellowstone for such signs of activity.
She said: “At Yellowstone and other calderas, changes in deformation patterns from uplift to subsidence and back again are a common occurrence.
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“By studying these changes, we hope to learn more about the subsurface conditions that are causing the ground to move and also to monitor for changes that are not normal.
“Recognising the normal from the unusual is key for identifying the potential for future hazards volcanic activity.”
Yellowstone volcano’s last caldera-forming eruption went off an estimated 640,000 years ago and was powerful enough to cover most of the US in ash.
But the volcano has not been entirely dormant since and the Earth is a constant state of flux as tectonic plates shift, grind and pass over one another.
Ground movement is the principal reason why mountains and volcanoes exist, caused by colliding tectonic plates pushing the earth upwards.
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When magma pools near these points of collision volcanoes like Yellowstone are born.
The magma itself and the underground water systems it heats up also contribute to the movement of volcanic systems on the surface.
Motion caused by the change in pressure within a volcano’s “plumbing system” is known as deformation.
Precise instruments and GPS stations positioned around Yellowstone can trace this movement to get a better idea of what is happening below.
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Ms Bartel said: “Sometimes, motions are so large we can see them with our eyes.
“In the Spring of 1980, a bulge on the north flank of Mount St Helens was growing by more than a metre – about three feet per day, as magma pushed up into the mountain.
“While the exact magnitude of the motion was measured with precise ranging instruments, the growing bulge was clearly visible to the naked eye.
“Mount St Helens erupted on May 18, 1980, beginning with the collapse of that bulge.”
Thankfully at Yellowstone, all recent ground deformation has been absolutely minimal.
The USGS primarily uses GPS tools and Interferometric synthetic aperture radar (inSAR) to measure the shift in ground levels.
To date, the largest uplift recorded at Yellowstone over the last few decades was only about two inches (five centimetres) per year between 2005 and 2009.
Ms Berth said the largest uplift ever, by contrast, averaged about 25 inches (60cm) per year between 1982 and 1984 at the Campi Flegrei caldera in Italy.
