The world’s largest active volcano, Hawaii’s Mauna Loa, has started to erupt for the first time in nearly four decades, prompting volcanic ash and debris to fall nearby, authorities said Monday.

The eruption began at approximately 11:30 p.m. Sunday in Moku‘āweoweo, the summit caldera of the Mauna Loa volcano, inside Hawai‘i Volcanoes National Park on the Big Island. 

As of 2:43 a.m. local time, “the eruption continues at the summit of Mauna Loa,” according to the latest Hawaiian Volcano Observatory Status Report from the U.S. Geological Survey (USGS). “All vents remain restricted to the summit area,” the report said. “However, lava flows in the summit region are visible from Kona. There is currently no indication of any migration of the eruption into a rift zone.”

A rift zone is where the mountain is splitting apart, the rock is cracked and relatively weak and is easier for magma to emerge, according to the Associated Press.

The USGS warned that residents at risk from Mauna Loa lava flows should review their eruption preparations. Scientists had been on alert because of a recent spike in earthquakes at the summit of the volcano, which last erupted in 1984.

Portions of the Big Island were under an ashfall advisory issued by the National Weather Service in Honolulu, which said up to a quarter-inch of ash could accumulate in some areas. Mauna Loa is one of five volcanoes that together make up the Big Island of Hawaii, which is the southernmost island in the Hawaiian archipelago.