Kilauea is one of five active volcanoes on the island of Hawaii.
Phreatic eruptions are "notoriously hard to forecast, and can occur with little or no warning", Hawaiian Volcano Observatory geologist Janet Babb said.
The lava lake in the crater has been dropping since May 2, which increases the chances for a phreatic explosion, but it will be hard to warn residents. The deflation on the ground as lava level falls is causing stress faults around the crater to move, resulting in the earthquakes. The ash cloud is drifting slowly northward from the Kilauea summit and ashfall may occur in Hawai'i Volcanoes National Park and Volcano Village.
Geophysicist with the US Geological Survey (USGS) Mike Poland said the explosion probably lasted only a few minutes and the ash accumulations were minimal, with only trace amounts expected near the volcano.
The Hawaii Fire Department reported "extremely risky air quality conditions due to high levels of sulfur dioxide gas in the evacuation area", civil defense officials said on Saturday. Much of the park remains closed.
"They said they slept through it". "We live on a volcano!" The lava seeping through fissures has forced the evacuation of almost 2,000 people 25 miles away near Leilani Estates.
Scientists forecast more eruptions and more earthquakes, perhaps for months to come, after the southeast corner of the island was rocked by a 6.9 tremor on Friday, the strongest on the island since 1975. There was no tsunami alert.
They warn: "There has been volcanic eruption on Hawaii's Big Island and some local residents have been evacuated".
Ash emerges from the Pu'u O'o vent on the Kilauea volcano last week. Communities downwind may receive ashfall and should take necessary precautions. The Pacific Tsunami Warning Center says there is no tsunami alert at this time. Kilauea has channels that flow underground.
Hawaii's Kilauea volcano erupted Thursday, the biggest explosion yet driving a plume of ash and debris 30,000 feet into the air and putting Big Island residents on further notice that a bigger blast could still be percolating in the volatile crater.
Part of the U.S. Geological Survey's Volcano Hazards Program, the Hawaii Volcano Observatory is perched on the rim of Kīlauea's summit caldera. The wind will carry the plume towards the south-east.
Instead, they will operate from a backup command center at the University of Hawaii at Hilo.
The Kilauea eruption is the latest since the Hawaii volcano began spewing ash and lava earlier in May, as fissures opened up along the volcano.