Unusual Uplift at Yellowstone Volcano Was Caused by Magma Rising up Deep Beneath the Surface, Study Finds

In 2013, an area of the Yellowstone supervolcano started rising at an unusually high rate. Over the next two years, it rose by over 5.9 inches per year—the highest rate of uplift ever recorded inside the caldera. What was behind this was unknown.

Now, scientists have said this unusual period of ground deformation was the result of magma intrusion deep below the Norris Geyser Basin area. When magma rises, it pushes the rock above it up.

In a study published in the Journal of Geological Research-Solid Earth, researchers from the U.S. Geological Survey (USGS) looked at the event and found magma rising under the Basin was behind the uplift.

Their study, published in January, has been highlighted by the Yellowstone Volcano Observatory (YVO) in its weekly column, The Caldera Chronicles.

Ground deformation at Yellowstone is normal, with the land swelling, sinking and cracking as a result of the magma, fluids and gas moving around beneath it. It is normally only a few inches per year and can only be detected with sensitive instruments. Studying deformation allows scientists to monitor the volcano for any changes beyond the normal background movement, which may suggest something is happening deep beneath it.

The period of uplift at Yellowstone over 2013 and 2014 came to an abrupt end when a magnitude 4.9 earthquake hit the area. At this point, uplift switched to subsidence, and the ground started to sink. Uplift started again in 2016 and continued until the end of 2018. It now appears to have paused.

By analyzing GPS and radar data, researchers say this unusual ground deformation was likely the result of deep magma intrusion beneath the Norris Geyser Basin between 1996 and 2001. This was followed by the "volatile ascent and accumulation" at a level possibly just a few hundred meters (about 600 feet) below the surface. The magma that rose beneath the Basin appears to have got shallower between 2014 and 2016.

"Frequent eruptions of Steamboat Geyser since March 2018 are likely a surface manifestation of this ongoing process," they wrote. "Hydrothermal explosion features are prominent in the Norris Geyser Basin area, and the apparent shallow nature of the volatile accumulation implies an increased risk of hydrothermal explosions."

Steamboat Geyser, the tallest currently active geyser in the world, broke its own record for eruptions in 2019, producing 48 over the course of last year—16 more than the previous record set in 2018. Researchers say the shallow magma under the Norris Geyser Basin may suggest there is an increased risk of hydrothermal explosions in the area.

Dan Dzurisin, one of the study authors, wrote about the research in The Caldera Chronicles. He said the magma intrusion two decades ago appears to have set the stage for all the deformation recorded.

"Modeling...suggests the 1996–2004 uplift was caused by an intrusion of magma about 14 km [8.7 miles] beneath Norris," he wrote. "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... 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 [magnitude] 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."

He said this activity was common, so there is no reason to be concerned. "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."