Kilauea is one of several active volcanoes on the island of Hawaii, the archipelago’s largest. Found in the island’s southeast corner, it has been erupting continuously since 1983. But by May of this year, a new eruption sequence had commenced, with two focal points: a flank area known as the lower east rift zone, a point where the volcano’s surface is gradually splitting apart, and the Halema’uma’u crater to the west at Kilauea’s summit.

Christina Neal, the scientist-in-charge at the Hawaiian Volcano Observatory and the study’s lead author, said this confluence of big volcanic events that went on for months meant that this eruption was “truly unprecedented in the modern record.” In fact, this was the largest such eruption from this rift zone in the last 200 years.

The collapse in April of the Pu‘u ‘O‘o crater, located in the east rift zone, may have coincided with the breakdown of a subterranean barrier. That could have allowed magma at the site to flow through an established pathway toward the lower east rift zone.

On May 2, the Halema’uma’u summit crater’s lava lake — a persistent pool of bubbling lava inside the crater — began to drain, and cracks appeared in the rift zone. The next day, the first fissure of many appeared in the Leilani Estates Subdivision, and lava began to flow, prompting the evacuation of thousands of residents.