A team of scientists from Stanford University, led by geophysicist Paul Segall, tested friction laws in explaining Kilauea's collapse when the volcano erupted in 2018. The analysis confirms the scientific paradigm on how friction may have been involved in earthquake faults that led to the collapse of the Kilauea volcano's crater.

The highly simplified mathematical model of the collapse showed the right conditions for such collapse to happen and cause big, damaging eruptions of basaltic volcanoes, which could someday help in future hazard assessments and mitigation.

They published their study, titled "Repeating Caldera Collapse Events Constrain Fault Friction at the Kilometer Scale," in Proceedings of the National Academy of Sciences (PNAS).

Scientists Tested Laws of Friction to Understand Caldera Collapse During Kilauea Volcano Eruption in 2018
(Photo: Wikimedia Commons)
Kīlauea's 2018 lower Puna eruption. Lava fountains from Fissure 20 in Kīlauea Volcano's lower East Rift Zone. The photo was taken on May 19, 2018, at 7:37 AM, HST. USGS

How is Friction Involved in Kilauea's Collapse?

According to Stanford's news release, friction is found everywhere in nature and plays a critical role in controlling the collapse of Kilauea's crater and the rupture of earthquakes. Scientists have studied friction for centuries, yet they still do not comp[letley understand how it behaves in all situations.

When the Kilauea volcano erupted on April 30, 2018, lava suddenly drained from the crater, and its floor collapsed. Soon, new cracks opened, and molten lava began to spurt out, burning trees and power poles.

Scientists examined the slipping and sticking of the chunk of crust from the Kilauea volcano to determine friction at a much larger scale. They set out to develop a model of the collapse.

They noted that the collapse was like a sticky piston that did not happen in one smooth descent. The news release said that the collapse block by nearly eight feet would fall roughly every day and a half. But then, it would suddenly stop because the magma in the chamber below the caldera took away the support for the overlying rock. But eventually, the pressure becomes so low that it collapses like a sinkhole.

By the time the Kilauea eruption ended, the piston-like collapse had repeated 62 more times which triggered earthquakes as recorded by continuous GPS receivers and tiltmeters, Segall wrote in the abstract published in the American Geophysical Union.

The experiment shows that the kind of Kilauea volcano eruption could lead to a bigger drop in pressure, triggering a collapse event. Once that happens, the weight of the massive caldera block forces the magma to the eruption site as the pressure drops below.

"If not for the collapse, the eruption would have undoubtedly ended much sooner," Segall said in the news release.

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Friction Properties in the Lab Applies to Big Tectonic Faults

 The team discussed in the study the different ways the rock surfaces slip and slide past one another or stick at different speeds and pressure that are quite similar to laboratory experiments. It provides information about the slip-weakening distance, which is an important factor in earthquake mechanics that geophysicists use to calculate how faults become unstuck.

A study published in Geophysical Research Letters defines slip-weakening distance as a parameter that controls the evolution of a fault slip during an earthquake. It is where the frictional strength of a fault weakens and is important to understand rupture dynamics.

Laboratory experiments suggest that this distance is equivalent to the width of a hair spliced into a few dozen silvers, wherein a real earthquake estimate could indicate it to be as long as 20 centimeters.

The new model showed that friction evolution might have happened no more than 10 millimeters or less. However, friction properties were the same as measured in the laboratory, which tells scientists that it could be applied to big tectonic faults because they hold the true behavior observed in Kilauea's collapse.

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