Tyler O'Neal, Staff Editor EARTH SCIENCES

Miami researchers shine a light on hazards of Earth's largest volcano

Researchers find that a large earthquake could set off an eruption of Hawaii's Mauna Loa volcano

Scientists from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science analyzed ground movements measured by Interferometric Synthetic Aperture Radar (InSAR) satellite data and GPS stations to precisely model where magma intruded and how magma influx changed over time, as well as where faults under the flanks moved without generating significant earthquakes. The GPS network is operated by the U.S. Geological Survey's Hawaii Volcano Observatory.

"An earthquake of magnitude-6 or greater would relieve the stress imparted by the influx of magma along a sub-horizontal fault under the western flank of the volcano," said Bhuvan Varugu, a Ph.D. candidate at the UM Rosenstiel School and lead author of the study. "This earthquake could trigger an eruption." Standing 9 kilometers tall from the base on the seafloor to the summit, Mauna Loa is the largest volcano on Earth.

The researchers found that during 2014-2020 a total of 0.11 kilometers3 of new magma intruded into a dike-like magma body located under and south of the summit caldera, with the upper edge at 2.5 - 3 kilometers depth beneath the summit. They were able to determine that in 2015 the magma began expanding southward, where the topographic elevation is lower and the magma had less work to do against the topographic pressure. After the magma flux waned in 2017, the inflation center returned to its previous 2014-2015 horizontal position. Such changes of a magma body have never been observed before.

"At Mauna Loa, flank motion and eruptions are inherently related," said Varugu. "The influx of new magma started in 2014 after more than four years of seaward motion of the eastern flank - which opened up space in the rift zone for the magma to intrude."

The researchers also found that there was a movement not associated with an earthquake along a near-horizontal fault under the eastern flank, however, no movement was detected under the western flank. This led the researchers to conclude that an earthquake under the western flank is due. Motions along near-horizontal faults under the flanks are essential features of long-term volcano growth.

Will the volcano erupt in the near future? "If magma influx continues it is likely, but not required," says Varugu. "The topographic load is pretty heavy, the magma could also propagate laterally through the rift zone".

"An earthquake could be a game-changer," said Falk Amelung, a professor at the UM Rosenstiel School's Department of Marine Geosciences and senior author of the study. "It would release gases from the magma comparable to shaking a soda bottle, generating additional pressure and buoyancy, sufficient to break the rock above the magma."

According to the researchers, there are many uncertainties. Though the stress that was exerted along the fault is known, the magnitude of the earthquake will also depend on the size of the fault patch that will actually rupture. Additionally, there are no satellite data available to determine movements prior to 2002.

"It is a fascinating problem," said Amelung, "We can explain how and why the magma body changed during the past six years. We will continue observing and this will eventually lead to better models to forecast the next eruption site."

Standing 9 kilometers tall from the base on the seafloor to the summit, Mauna Loa is the largest volcano on Earth. In the 1950 eruption, it took only three hours for the lava to reach the Kona coast. Such rapid flows would leave very little time to evacuate people in the path of its lava. Another large eruption of Mauna Loa occurred in 1984.

The combination of earthquakes and eruptions is nothing unusual. The 1950 eruption was preceded by a magnitude 6.3 earthquake three days prior and was followed by a magnitude 6.9 earthquake more than a year later. The 1984 eruption was preceded by a magnitude 6.6 earthquake 5 months prior.

The satellite data were acquired by the Italian Cosmo-Skymed satellites in the framework of the Geohazard Supersites and Natural Laboratories (GSNL) initiative of the Group on Earth Observation (GEO), an international umbrella organization to enhance the use of Earth Observation for societal benefits. Several space agencies pool their satellite resources to enable new studies of hazardous volcanoes. Other volcano supersites include the Icelandic, Ecuadorian, and New Zealand volcanoes as well as Italy's Mt. Etna.

Europe's space freighter Automated Transfer Vehicle Jules Verne burning up over an uninhabited area of the Pacific Ocean at the end of its mission

Tyler O'Neal, Staff Editor EARTH SCIENCES
CREDIT ESA

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Simulations show Earth's deep mantle may have proton rivers made of superionic phases

Tyler O'Neal, Staff Editor EARTH SCIENCES

Pierfranco Demontis said in 1988, "Ice becomes a fast-ion conductor at high pressure and high temperatures," but his prediction was only hypothetical until recently. After 30 years of study, superionic water ice was verified experimentally in 2018. Superionicity may eventually explain the strong magnetic field in giant planetary interiors.

What about Earth, whose interiors are also under extreme pressure and temperature conditions? Although three-quarters of Earth's surface is covered by water, standalone water or ice rarely exists in Earth's interiors. The most common unit of "water" is hydroxyl, which is associated with host minerals to make them hydrous minerals. Here, a research group led by Dr. Qingyang Hu, Dr. Duckyoung Kim, and Dr. Jin Liu from the Center for High-Pressure Science and Technology Advanced Research located in China, discovered that one such hydrous mineral also enters an exotic superionic phase, similar to water ice in giant planets. The results are published in an academic journal.

"In superionic water, hydrogen will get released from oxygen and become liquid-like, and move freely within the solid oxygen lattice. Similarly, we studied a hydrous mineral iron oxide-hydroxide (FeOOH), and the hydrogen atoms move freely in the solid oxygen lattice of FeO2," said Dr. He, who conducted the computational simulation. Earth's mantle might be electrified by superionic minerals

"It developed into the superionic phase above about 1700°C and 800,000 times normal atmospheric pressure. Such pressure and temperature conditions ensure a large portion of Earth's lower mantle can host the superionic hydrous mineral. These deep regions may have rivers made of protons, which flow through the solids." added Dr. Kim.

Guided by their theoretical predictions, the team then tried to verify this predicted superionic phase in hot FeOOH by carrying out high-temperature and high-pressure experiments using a laser-heating technique in a diamond anvil cell.

"It is technically challenging to recognize the motion of H atoms experimentally; however, the evolution of O-H bonding is sensitive to Raman spectroscopy," said Dr. Hu, one of the lead-authors. "So, we tracked the evolution of the O-H bond and captured this exotic state in its ordinary form."

They found that the O-H bonding softens abruptly above 73,000 times normal atmospheric pressure, along with ~ 55% weakening of the O-H Raman peak intensity. These results indicate that some H+ may be delocalized from oxygen and become mobile, thus, weakening the O-H bonding, consistent with simulations. "The softening and weakening of the O-H bonding at high-pressure and room-temperature conditions can only be regarded as a precursor of the superionic state because high temperature is required to increase the mobility beyond the unit cell," explained Dr. Hou.

In superionic materials, there will be an obvious conductivity change, which is robust evidence of superionization. The team measured the electrical-conductivity evolution of the sample at high-temperature and pressure conditions. They observed an abrupt increase in electrical conductivity around 1500-1700°C and 121,000 times normal atmospheric pressure, indicating the diffusive hydrogen had covered the entire solid sample and thus, entered a superionic state.

"The pyrite-type FeO2Hx is just the first example of superionic phases in the deep lower mantle," remarked Dr. Liu, a co-lead author of the work. "It is very likely that hydrogen in the recently-discovered dense hydrogen-bearing oxides that are stable under the deep lower mantle's high P-T conditions, such as dense hydrous phases, may also exhibit superionic behavior."