HONOLULU (Reuters) – A small explosion of ash erupted from the summit of Hawaii’s Kilauea volcano early on Tuesday morning in a vertical plume some 15,000 feet (4,600 meters) high, the U.S. Geological Survey said, the latest outburst in a month of volcanic activity.

The agency warned that ash was drifting northwest and liable to dust anyone in the summit area. Hundreds of people have been ordered to leave the vicinity of the biggest eruption cycle in a century of one of the world’s most active volcanoes.

A news reporter takes pictures of the Kilauea lava flow that crossed Pohoiki Road near Highway 132, near Pahoa, Hawaii, U.S., May 28, 2018. REUTERS/Marco Garcia

Multiple fissures continue to spew up hot lava flows, which have blocked roads and damaged dozens of buildings on Hawaii’s Big Island.

One fountain of lava rose more than 200 feet (60 meters) at times on Monday, the Geological Survey said.

Officials are on high alert for occasional earthquakes, though none have been big enough so far to trigger a tsunami.

Lava has engulfed the heads of two wells that tap into steam and gas deep in the Earth’s core at the 38-megawatt Puna Geothermal Venture. Its operator, Israeli-controlled Ormat Technologies Inc, said it had not been able to assess the damag

So far no deaths have been blamed on the eruption, though a man’s leg was shattered when he was hit by a spatter of super-dense lava.

Residents fear the wells may be explosive. Officials have said the power plant is safe but lava has never engulfed a geothermal plant anywhere in the world, creating a measure of uncertainty.

Contingency plans have been made for a possible helicopter evacuation of up to 1,000 residents in a coastal area south of the fissures should their last exit route, be blocked by lava or become unsafe due to gaping cracks, County of Hawaii officials said.

At least 82 homes have been destroyed in the southeastern corner of Big Island and about 2,000 people have been ordered evacuated since Kilauea began erupting on May 3.

(Reporting by Jolyn Rosa; writing and additional reporting by Jonathan Allen; Editing by Scott Malone and Jonathan Oatis)