The volcanic pressure that preceded the 2018 Big Island eruption was building for years, but it was a relatively rapid and cascading succession of minor geologic processes that led to one of Hawaii’s most destructive events in 200 years, a new study has found.

The study by scientists with the Hawaiian Volcano Observatory and the University of Hawaii at Manoa also says HVO scientists correctly predicted the eruption in the weeks leading to the May 3, 2018, event but missed on its scale and location.

Published in the journal Nature Communications, the paper also discounts a previous scientific study that suggested excessive and prolonged rainfall led to the Kilauea eruption.

“The buildup of pressure was enough to explain the triggering of the eruption,” said Matthew Patrick, research geologist at the U.S. Geological Service’s Hawaiian Volcano Observatory and lead author of the new study. “There was no outside triggering mechanism needed.”

Using HVO data from before and during the 2018 eruption, the research team reconstructed the geologic events that preceded the historic changes that occurred across the volcano.

The research describes 10 likely cascading steps that led to the four-month eruption that spewed roughly 1 billion cubic yards of molten rock across the Lower Puna landscape.

But first, the paper said, the volcano was being primed for years by the ongoing movement of the mountain’s southern flank. The vast block of mountain has been slipping toward the ocean at around 3 inches a year, and this movement helped to stretch out and open up the island’s lower East Rift Zone to magma. It also helped to pressurize the entire system.

The cascade of events, according to the paper, was set in motion in late 2017 and early 2018 as a blockage developed in the vent supplying magma to the ongoing Pu‘u O‘o lava flows (step 1). That reduced lava outflow (step 2) and caused magma to back up and further pressurize the system (step 3), opening a pathway bypassing Pu‘u O‘o and sending large quantities of magma eastward and into the lower East Rift Zone (step 4).

Magma erupted in Puna (step 5), a process that put stress on Kilauea’s south flank, triggering a 6.9-magnitude earthquake (step 6). The sizable temblor relieved “confining stress” on the rift zone which, in turn, may have caused even more magma to flow to the eruption site (step 7).

The Puna eruption took in magma from the summit magma reservoir at a high rate (step 8), causing the collapse of the caldera floor (step 9) that led to small summit explosions (step 10) and maintained magma reservoir pressure to help sustain the new eruption.

This convoluted sequence links a relatively small change near Pu‘u O‘o to the destruction below, all enabled by an efficient hydraulic connection along the East Rift Zone, the paper says.

The eruption destroyed 716 homes in Lower Puna, forced the evacuation of 2,000 residents, covered 30 miles of roads, isolated 1,600 acres of farmland and caused damage estimated at more than $800 million.

HVO scientists failed to predict the larger eruption because the volcano was behaving in the same way it had been over the past several decades, which featured relatively small eruptions emanating from Pu‘u O‘o.

It had been 57 years since the last lower East Rift Zone eruption, and 43 years since the last major south flank earthquake.

“This form of tunnel vision, which gives less attention to the least likely outcomes, is a bias that can be overcome by considering the broader, longer history of the volcano,” Hawaii state volcanologist, UH earth sciences professor and co-author Bruce Houghton said in a release. “For Kilauea, this consists of widening the scope to consider the types of behavior seen in the first half of the 20th century and perhaps earlier.”

Added Patrick, “It’s a reminder to volcanologists to always have that broader picture in mind.”

Researchers at the University of Miami published a paper in April that concluded heavy and prolonged rainfall left the volcano’s subsurface rock weakened and more vulnerable.

But the latest work responds that high rates of widespread inflation and lava lake level rise in the weeks prior to the eruption indicate that increasing pressure from magma was the dominant driver, and outside triggers such as rainfall are not required to explain the eruption.

The new study, which adds to work that aims to reduce human and physical costs of the next eruption, was funded by the U.S. Geological Survey Volcano Science Center and a federal disaster research program. UH researchers were supported by the National Science Foundation.