If there were an Olympic medal for hydrothermal systems, Norris Geyser Basin would bring home the gold.
Temperatures in its subsurface hydrothermal reservoir are the highest anywhere in Yellowstone National Park – more than 570 degrees. Norris is the most dynamic geyser basin in the Park and its more than 500 hydrothermal features are the most diverse. Among them is Steamboat Geyser, the world’s tallest. Recently, Norris has been competing with Yellowstone Caldera for the title of fastest mover in the Park — and winning. A new study used ground “changes to the surface of a volcano that occur due to magma movement underneath the surface. Most volcano deformation can only be detected and measured with precise surveying techniques such as with a Global Positioning System (GPS), tiltmeter, Interferometric Synthetic Aperture Radar (InSAR), or an Electronic Distance Meter (EDM).” Deformation data collected by GPS and also via satellite by a technique called InSAR concluded that an intrusion of magma deep under Norris two decades ago set the stage for much of what’s happened there since, including the wild (by geologic standards) roller-coaster ride that might have ended, or at least paused starting in 2018.
From 1996 to 2004, an area more than 18 miles across centered near Norris, just outside the north caldera rim, rose as much as 4.7 inches at an average rate of 0.6 inches per year. The area subsided about 2.8 inches in the next several years, but uplift resumed in mid-2013. From late 2013 to early 2014, Norris rose at the highest rate ever measured in Yellowstone —more than 5.9 inches per year. For comparison, the highest uplift rate ever measured inside Yellowstone Caldera is about 2.8 inches per year during 2004–2005.
The record-setting Norris uplift ended abruptly when a magnitude 4.9 earthquake, the largest in Yellowstone since the 1970s, struck the Norris area on March 30, 2014. Rapid uplift quickly reversed to subsidence that ended in 2015. But a third uplift episode, this one at an average rate of about 0.8 inches per year, began in early 2016 and continued through 2018. The net result was that Norris stood about 5.5 inches higher in 2018 than it did in 1996. Since early 2019, the area has subsided about 1 inch, but Norris still stands 4 to 5 inches taller than it did at the turn of the century.
Considering the area that’s been moving is larger than the city of Chicago, those numbers are impressive. But what’s more remarkable is the story that scientists have been able to piece together about what’s been going on under the surface.
Modeling of InSAR and GPS data suggests the 1996–2004 uplift was caused by an intrusion of magma about 8.7 miles beneath Norris. When magma intrudes the crust, it cools, crystallizes and releases gases that had been dissolved in the melt. Gas escape lowers pressure in the magma, causing the surface to subside. That’s probably what was going on at Norris from 2005 to mid-2013. But rising gases can become trapped under an impermeable layer of rock, causing the kind of rapid uplift seen at Norris from late 2013 until the M 4.9 earthquake in March 2014. It seems likely the quake created microfractures that allowed gases to escape upward again, resulting in subsidence that ended in 2015. The third uplift episode from 2016 to 2018 suggests rising gases became trapped again, this time at a slightly shallower depth. Modeling indicates the source depth for the 2013–2014 uplift was about 2 miles deep, compared to about 1.1 miles for the 2016–2018 episode.
Should you worry? In a word, no. Activity like this is probably common at Norris and, at other times, under the caldera, too. What’s different is that we now have the tools to detect and model Yellowstone’s ups and downs better than ever before. For the first time, we’ve been able to track an entire episode of magma intrusion, degassing and gas ascent to the near surface. For those in the know, like you, that’s awesome — not alarming.
Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory.
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