The Kilauea volcano on Hawaii’s big island has been acting up for weeks. But on Thursday, all hell seemed to break loose when new fissures began to open in the volcano’s East Rift zone, sending lava shooting into the air and causing molten rock to carve a path through the thickly forested Leilani estates residential area.

The eruptions, which lasted for about two hours, are getting attention both because of the absolutely bonkers footage and because they prompted mandatory evacuations in several subdivisions. As volcanologist Erik Klemetti pointed out over at Discover Magazine, there haven’t been eruptions in this relatively well-settled area of the East Rift zone since the mid-20th century. But that doesn’t mean we should be surprised by the new activity.

“Since the 1950s is a very short time for a volcano,” Concord University volcanologist Janine Krippner told Earther. “This is pretty normal.”

To understand why, let’s talk about some basic geology. Kilauea is a shield volcano powered by the same magma hot spot that built the entire Hawaiian island chain. The Pacific tectonic plate moves across the hotspot like a saucepan being slowly dragged across a flame, causing magma to bubble up in different places. Kilauea will eventually go dormant, but right now, it’s still in its fiery youth with 90 percent of its surface less than a 1,000 years old.

Because it’s one of the most active volcanoes in the world, Kilauea is heavily monitored by the U.S. Geologic Survey (USGS), whose Hawaii Volcano Observatory maintains several 24/7 webcams trained on the summit and East Rift zone. The USGS also uses a smorgasbord of equipment to monitor surface deformation, subsurface seismic activity, and gaseous outbursts, all of which can indicate that magma is moving around beneath the surface, and potentially priming the volcano for new eruptions.

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A map of the magma intrusion and earthquake activity in the East Rift Zone following the collapse of Pu‘u ‘Ō‘ō’s crater floor on April 30.
Image: USGS

Thanks to all these monitoring tools—plus all of our accumulated knowledge about what Kilauea has done in the past—the USGS had a hunch a new fissure might open up in the East Rift zone. As Live Science reported, the East Rift zone’s Pu‘u ‘O‘o vent began to inflate with magma in mid-March before the crater floor collapsed on April 30. According to the USGS, this “signal[ed] an intrusion of magma along the middle and lower East Rift Zone.”

As magma pushed into new areas to the east, a swarm of small earthquakes ensued. These culminated in a magnitude 5 earthquake on Thursday, shortly before the new eruption began.

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“This [eruption] is largely because of increased seismic activity,” Krippner said.

Fortunately, the USGS was able to notify the appropriate authorities that some serious shit was likely to go down, prompting evacuation orders from the Hawaii County Civil Defense at 5 p.m. local time on Thursday. By around 6:30 p.m., the fissure had quieted down. No new activity has been reported since, and no fatalities have been reported.

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Krippner thinks this fairly positive scenario is largely due to advances in monitoring that allowed scientists to spot warning signs of the outburst early. The last time there was activity in this part of the East Rift zone, that might not have been possible.

“It’s pretty amazing seeing how far volcanology has come in recent years,” she said.