Secrets of ‘mystery sandwich’ beneath Yellowstone revealed in new map

A geyser erupts in Yellowstone National Park. It is supplied with boiling water by a network of underground fluid pathways heated by magma. (Image credit: Shutterstock)

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The underground “plumbing system” of superheated water that feeds Yellowstone National Park’s geysers and other hydrological features has been mapped in stunning detail – and the results could fill a major knowledge gap that experts have described like a “mystery sandwich”.

Yellowstone is home to the world’s largest hydrothermal system, which contains approximately 10,000 hydrothermal features, including geysers, hot springs, mud pots and steam vents, according to the National Park Service (opens in a new tab). These above-ground features are fed by a network of subterranean waterways which are superheated by subterranean magma, causing water to rise to the surface. However, researchers know very little about this underground network, or plumbing system.

“Our knowledge of Yellowstone has long had a gap underground,” study co-author W. Steve Holbrook, head of the geosciences department at Virginia Tech University, said in a press release (opens in a new tab). “It’s like a ‘mystery sandwich’ – we know a lot about surface features from direct observation and a fair amount about the magmatic and tectonic system many miles from geophysical work, but we don’t really know what that’s in the middle.”

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In the new study, researchers attached a giant electromagnet, known as SkyTEM, to a helicopter, then circled hundreds of times over Yellowstone to scan the ground below. The magnet consists of an 82-foot-wide (25-meter) loop of charged wire that generates a powerful electromagnetic field. Because different types of materials, such as rock or water, react differently to the magnetic field, the researchers were able to create subsurface maps of large sections of the underground hydrothermal system for the first time.

Researchers fly the SkyTEM magnet over Yellowstone National Park. (Image credit: SkyTEM)

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Map hydrothermal pathways

The method of investigation used by the team, called transient electromagnetism (TEM), involves inducing an electric current through the ground by switching the electromagnet on and off in the air. An electromagnet produces an electromagnetic field when an electric current passes through a loop of coiled wire, like the SkyTEM magnet. When the electric current stops flowing through the wire, the electric charge moves from the electromagnetic field to the ground below. The electrical charge dissipates through the ground causing fluctuations in the electromagnetic field which can be measured by the researchers above.

Underground waterways show up clearly in the resulting maps because water is a much better conductor of electricity than rock, lead author Carol Finn, a US Geological Survey researcher, told Live Science in an email. Thus, an electric current induced in water dissipates faster than the current in rock. The mapping technique could also differentiate magma from bedrock because they have slightly different properties. magnetic properties, Finn said. This allowed the team to see how magma and water interact to create impressive geological features on the surface.

An example of one of the maps created using the SkyTEM magnet. The blue and green areas are subsurface fluid pathways below surface hydrothermal features. Yellow and orange are rock and dark red is magma. (Image credit: W. Steven Holbrook)

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This method allowed the researchers to create high-resolution maps down to depths between 492 and 2,296 feet (150-700 m) and low-resolution maps down to a maximum of 1.5 miles (2.5 kilometers ), Finn said. However, the researchers believe the hydrothermal system may extend up to 5 km below the surface, meaning they only mapped the upper half of Yellowstone’s plumbing system.

In total, the team covered about 2,500 miles on their research flights. However, the technique was sensitive enough to detect only the largest fluid pathways. “It’s like imagining a city’s water supply and distribution lines, but not the individual lines supplying a given home or the difference in pipes between your kitchen and your bathroom,” Finn said.

Scientists already know a lot about the surface hydrothermal features of Yellowstone, thanks to decades of detailed observations and chemical samples. The researchers also have a good idea of ​​the tectonic plates and fault lines deeper underground, as the park’s frequent earthquakes provide ample opportunity to study this. For example, in July 2021, a swarm of over 1,000 earthquakes rocked Yellowstone, Previously reported Live Science. However, the researchers “missed the precise links between magma-heated deep water and varied surface features,” Finn said.

With the new maps, researchers can now see how waterways interact with magma to supply the superheated water that creates the geysers and hot springs above. As a result, the team now has a better idea of ​​the inner workings of some famous features, including the Old Faithful geyser and the Grand Prismatic Spring, Finn said. The maps also show that individual surface features can be connected to other separate features up to 9.7 km (6 miles), according to the release.

The Grand Prismatic Spring is one of many surface hydrothermal features in Yellowstone fed by the network of underground fluid pathways. (Image credit: Shutterstock)

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However, the maps also showed that the geysers and hot springs, which can vary widely in size, shape, color, chemical composition and volatility, were fed by remarkably similar underground pathways. “Our work shows that most thermal features are located over buried faults channeling hot water and that flow paths are similar across Yellowstone regardless of local spring chemistry,” Finn said.

This finding suggests that chemical mixing or geological differences closer to the surface are responsible for the diversity of surface features seen in the park.

The researchers said the huge amount of map data they collected could tell a lot more about the park.

“The dataset is so large that we have only scratched the surface with this first article,” Holbrook said in the release. “I look forward to continuing to work on this data and seeing what others find as well. It will be a set of data that will keep yielding.”

And many scientific disciplines should benefit from it. For example, microbiologists can study whether subsurface characteristics influence the biodiversity of microbial lifeforms living in geysers and hot springs. Geologists will be able to map the distribution of magma to better understand the past volcanic eruptions, and hydrologists will be able to learn more about the differences between how hot water and cold water flow underground. Researchers can also study how clay sediments block hydrothermal pathways that could lead to pressure buildups and explosions, which are a safety issue in the park, Finn said.

In the future, deeper sensing electromagnetic data could help reveal the rest of the hydrothermal network and provide researchers with a “comprehensive view of the system,” Finn said.

The study was published online March 23 in the journal Nature (opens in a new tab).

Originally posted on Live Science.

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