Yellowstone volcano’s last caldera-forming eruption may have gone off some 640,000 years ago but the volcanic caldera is still very much active today. Up to 3,000 earthquakes strike the Yellowstone area in the northwest US each year and the national park’s various thermal features have a habit of erupting unannounced. As a result, working in the Yellowstone caldera can be extremely dangerous for US Geological Service (USGS) geologists.
Yellowstone is home to more than 10,000 hydrothermal features, including 500 geysers – more than half of all the geysers in the world.
USGS geologists keep a watchful eye on these features, measuring the slightest of changes in their size, spread and activity.
But getting up close and personal with the features is considered too risky, and has unexpectedly killed park guests in the past.
In 2016, Colin Scott, 23, died after taking an illegal dip in one of Yellowstone’s closed off hot springs.
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According to an incident report, Mr Scott’s remains were dissolved by the acidity and scorching temperatures of the water.
Yellowstone’s deputy chief ranger Lorant Veress said at the time Yellowstone is “a very unforgiving environment”.
Ten years earlier, in 2006, a six-year-old boy suffered serious burns after falling into hot water that had erupted from West Triplet Geyser.
The jets of water spewed by these geysers can reach boiling temperatures of more than 120C (250F).
Since Yellowstone was established in 1872, more than 20 people have died from burns after falling into hot springs.
Because of these dangers, USGS geologists are having to rely on innovative technology to keep track of Yellowstone’s shifting features.
The USGS said: “Given that historical photos might not be able to capture very small changes, how can more precise measurements be collected?
“Walking up to an active geyser is very dangerous given the unstable ground and often unpredictable eruptions of thermal waters – people who approach or walk on thermal features have been severely injured and even killed.
“Even with safety in mind, scientists walking in thermal areas can cause damage to these delicate features, which Yellowstone National Park has pledged to protect ‘for the benefit and enjoyment of the people.’
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“Taking measurements and obtaining imagery from a safe distance is thus important both for resource protection and safety.”
Aerial photography can be a useful tool when measuring features such as the Mammoth Hot Springs.
Between 2013 and 2016 alone, the popular tourist attraction rose by more than six feet.
The technique used in this case is known as structure-from-motion (SfM) photogrammetry and can provide a precise scale of an object.
The USGS also turns to 3D photography to create digital models of Yellowstone’s active features from a safe distance.
In 2019, geologists constructed 3D models of Castle Geyser, Giant Geyser, Lone Star Geyser, and Old Faithful.
The USGS said: “Obtaining the needed photography for the models required walking a circular path around these features with a camera.”
Then, with the aid of aluminium scale bars near each feature and GPS data, geologists were able to track any changes down to less than a millimetre.
Despite all of the activity that goes in the Yellowstone caldera, geologists do not suspect it is in any way a sign of another major eruption in the future.
The biggest known Yellowstone volcano eruption went off about 2.2 million years ago.