Computational tool helps forecast volcano slope collapses and tsunamis

For people living near volcanoes, the danger goes far beyond lava flows and ash clouds. Certain explosive eruptions can cause dramatic collapses from the sides of a volcano, such as those of Mount St. Helens, Washington and Anak Krakatau, in Indonesia. The latter sparked tsunamis blamed for most of the deaths of his historical eruptions in 1883.

But science and exact triggers behind such disasters remain largely unknown. To help scientists predict the collapse of the sides of the volcano, also known as flanks or slopes, Cholelle Wauthier, associate professor of the Penn State Geosciences department and the Director of HUB Computation Sciences at the Institute for Computing Sciences and Data Sciences, has led the development of new models that can assess the stability of a volcano.

Models, published in the Journal of Geophysical Research: Solid EarthCan help authorities and local communities by assessing the collapse potential long before the soil could yield completely and suddenly.

“The contribution of the magma under the volcano puts the crust under enormous pressure – much stronger than the pressure of the water,” said Wauthier. “It exercises enormous force on the rocks which can help to destabilize the volcano and to collapse. But we do not really know the exact conditions which would promote instability, and assess the trigger factors is quite complex.”

Relying in part from real examples of sliding volcales – including sites in Hawaii which have experienced the collapse – Wauthier and its research partners developed a way to predict how the slopes would react to the increase in magma in variable conditions. The magma is the melted rock which becomes of lava once it emerges on the surface of the earth. They also assessed where the surface shift would be more or less likely, in accordance with the expected changes of stability.

Their new models are based on the prior knowledge of the location of the magma. The magma rising under a volcano can force the shift on existing defects – fractured areas where two blocks of rock can move compared to the other. The shift in these places can finally collapse.

“If you have an idea of ​​which zone of the volcano is more likely to collapse, you can place ground sensors such as seismometers or a GPS to monitor a risky flank on a minute at a minute or an hour on time long before a collapse,” said Wauthier, who is also an affiliate of the Earth and Earthly Systems Institute.

To help make predictions, the research team has concentrated on fault dip or the angle of a flaw or rock fracture compared to the horizontal surface. The researchers found the ground more likely to give way to the slopes with shallow flaws below the surface, especially if the magma opens the crust under the top of the volcano. Like the batteries of blocks side by side on a slide in playgrounds, more decreases of vertical flags on more steep sides are also subject to instability, the researchers said.

They noted that the topography has a considerable impact on the predictions of the soil movement, a factor often neglected in other studies.

“This fundamental research can have useful applications to better assess the risks and areas of specific collapse of the volcano which are more sensitive to instability,” said Wauthier. “In the long term, pushing this type of research could help the communities adjacent to volcano by giving them time to prepare and evacuate before a collapse if necessary.”

Historically, she said, the collapses caused by volcanic activity have been particularly threatening for human life. When Mount St. Helens broke out in May 1980, its collapse removed the ceiling from its magma tank, causing an even more violent explosive eruption. In all, 57 people died in the eruption of Mont Saint-Hélens; 27 bridges and nearly 200 houses were destroyed.

A century earlier, the August 1883 eruption by Anak Krakatau – another example of volcanic collapse – led more than 36,000 deaths and ruined dozens of villages. Tsunamis waves were recorded more than 100 feet high.

After the collapse and eruption of the volcano in December 2018, more than 400 people died in the middle of a massive tsunami. Wauthier and his colleagues also studied this event, finding that the flank of the mountain had been slipping for years.

“These collapses can be very, very dangerous,” said Wauthier, whose research focuses on the attenuation of the natural risks of volcanoes, landslides and earthquakes, among others.

She said that the most explosive volcanoes form along the subduction arcs, where a tectonic plate is subdued or buried in another. Many volcanoes in the subduction area are located along the coasts, especially in Indonesia and along the hazard islands in Alaska. Volcanoes in Hawaii can also be unstable in places, although they are not as explosive as those in the subduction zones, Wauthier said.

Monitoring research can focus on strengthening model calculations and testing models in other variable conditions, she said.

The other contributors to the study are Judit Gonzalez-Santana, a former graduate student and postdoctoral scholar in the Wauthier group in geosciences in Penn; Jay Su Tung, assistant professor in geophysics at Texas Tech University; and Timothy Masterlark, professor of geology and geological engineering at the South Dakota School of Mines and Technology.