Last year at this time, Kilauea was locked in the throes of the largest lower East Rift Zone eruption in more than 200 years. Since August the volcano has been uncommonly quiet.

That poses the question, When will it erupt again?

While Hawaiian Volcano Observatory scientists are predicting Kilauea’s caldera could erupt “within a few years,” at least one independent expert suggests the volcano might not come to life for perhaps a decade if Hawaii’s undersea volcano, Loihi, is a guide.

Jacqueline Caplan- Auerbach, a geology professor at Western Washington University, says the last known eruption of Loihi in 1996 has some remarkable parallels to the 2018 eruption of Kilauea.

Located 22 miles off the southwest coast of the island of Hawaii, Loihi’s summit rises from the ocean floor to about 3,000 feet below sea level. It is fed by magma from the same “hotspot” in Earth’s mantle supplying Kilauea. Loihi is not expected to rise above the sea surface for at least 10,000 years.

Caplan-Auerbach, a volcano seismologist, has studied Loihi since she was a graduate student at the University of Hawaii at Manoa in 1996. The former HVO scientist has conducted recent work using data from seismic instruments placed on the submarine flanks of both volcanoes.

As with Kilauea for three months in the summer of 2018, the 1996 Loihi eruption began with a large increase in seismic activity in the volcano’s rift zone before transitioning to its summit, she said. In both cases there was a long series of large earthquakes, according to Caplan-Auerbach.

Loihi experienced more than 100 magnitude-4 or larger earthquakes, while Kilauea was struck by more than 50 magnitude-5 or larger earthquakes.

“There were magnitude-5 earthquakes at Kilauea with regularity, almost daily,” she said. “That wasn’t the case at Loihi. There wasn’t a regular pattern, but there was an enormous number of earthquakes about magnitude 4 in size. Loihi is a much smaller volcano, about 10 times smaller.”

In both instances, swarms of earthquakes led to significant summit collapses, creating Pele’s Pit on Loihi and enlarging Halemaumau Crater at Kilauea. Although Loihi is a much smaller volcano, when scaled to the same size, the two are “strikingly similar,” she said.

It is rare to see this kind of caldera collapse in action, Caplan-Auerbach said, although it has been seen at volcanoes in the Galapagos Islands and Iceland.

In a presentation to the Seismological Society of America annual meeting last month, Caplan-Auerbach said she wondered whether this draining of the summit reservoir and collapse indicates a volcano has “done its time.”

Following its 1996 eruption, Loihi went silent, and the seismologist recorded very little seismicity during two missions deploying instruments in 1997-1998 and 2010-2011.

The seamount remained mostly quiet for nearly 20 years before gradually increasing seismicity leading to earthquake swarms in 2015, a possible indication Loihi is replenishing its magma reservoir, she said.

If the similarities between the two volcanoes offer a guide to future behavior, Kilauea might be quiet for a decade before becoming active again, Caplan-Auerbach suggested.

Why doesn’t she predict two decades or longer of Kilauea inactivity — like Loihi?

Caplan-Auerbach said the underwater volcano is on the edge of the hotspot, while Kilauea is more directly on top of it, which leads her to speculate that Kilauea would restore its magma more rapidly.

“I think the good news is that volcanoes tend to talk to us before they do anything truly dramatic,” she said. “So I think we will know when it restores its magma system.”

According to the Hawaiian Volcano Observatory, only infrequent periods during which no lava erupted at Kilauea have been recorded since the early 1800s, when written records of Hawaii volcanoes began.

The longest known silent period spanned 17 years from 1935 to 1952, ending with an eruption in the caldera.

None of the pauses on record followed the kind of collapse that occurred in 2018, HVO scientists said. After partial caldera collapses in 1840 and 1868, lava returned to the caldera within days to a few weeks.

Following partial caldera collapses, the first eruption outside the caldera took place on the East Rift Zone 17 years after the 1823 collapse, on the Southwest Rift Zone 28 years after the 1840 collapse and on the Southwest Rift Zone 52 years after the 1868 collapse.

“On the basis of these observations, we think it most likely that the next eruption of Kilauea will take place in the caldera within a few years, and that the next eruption on one of the volcano’s rift zones will be in a decade or longer. This prognosis assumes a return to Kilauea’s general style of behavior for the past 200 years,” HVO scientists said in their latest Kilauea Volcano Activity Notice.

Michael Garcia, a geology professor at the University of Hawaii at Manoa, called HVO’s prognosis reasonable based on the short historical record of Kilauea.

“Wish we had a longer record to base this ‘prediction’ on,” Garcia said in an email.

On a side note, he said, Kilauea’s neighbor, Mauna Loa, tends to erupt when Kilauea does not, and there are signs Mauna Loa is getting ready for its next eruption.

Between 2014 and 2017, HVO seismic stations recorded elevated rates of shallow, small-magnitude earthquakes beneath Mauna Loa’s summit, upper Southwest Rift Zone and west flank.

At the same time, HVO measured changes in the volcano’s ground surface consistent with the movement of magma into the volcano’s magma storage system.

A slight increase in the number of detected earthquakes at Mauna Loa was noted just over the past month, according to HVO’s Mauna Loa monthly update May 3.

“These are really exciting times,” Caplan-Auerbach said. “These are oddly quiet times — a new type of exciting for volcanologists in Hawaii.”