(Adds ash fallout alert, witness account, byline)
By Terray Sylvester
PAHOA, Hawaii, May 17 (Reuters) - An explosive eruption sent ash spewing 30,000 feet (9,144 meters) into the air above Hawaii's Kilauea volcano on Thursday and residents of the Big Island were warned to shelter in place as the plume engulfed a wide area, authorities said.
"Hawaiian Volcano Observatory reports that an Explosive Eruption at Kilauea's Summit has occurred," County of Hawaii Civil Defense said in a phone alert. "The resulting ash plume will cover the surrounding area. Shelter in place if you are in the path of the ash plume."
"The wind may carry the ash plume north toward Kau, Volcano, Mt. View, Kea'au and as far as Hilo. Protect yourself from ash fallout," another phone alert warned.
The eruption could not be heard in the village of Pahoa, some 25 miles (40 km) down the volcano's east flank, but the air smelled of sulfur and there was a smoky-looking haze of ash, a Reuters reporter in the village said.
The powerful, steam-driven blast was expected to spew large amounts of volcanic ash and smoke from Kilauea's crater. The volcano has destroyed 37 homes and other structures in a small southeast area of the island and forced around 2,000 people to evacuate their homes.
Geologists had warned explosive eruptions could begin once Kilauea's falling lava lake descended below the water table, allowing water to run on to the top of the lava column and create a steam-driven blasts.
The powerful explosions could hurl "ballistic blocks" the size of small cars across a distance of more than half a mile (1 km) and shoot pebble-sized projectiles and debris up to a dozen miles, the USGS has warned.
Such an eruption could not only shroud large areas of the Big Island in volcanic ash and smog but also other Hawaiian Islands and potentially distant areas if the plume reaches up into the stratosphere and ash is carried by winds.
Kilauea, one of the most active volcanoes in the world, last experienced explosive eruptions in 1924. (Reporting By Andrew Hay in Taos, New Mexico; Editing by Tom Brown)
Our Standards: The Thomson Reuters Trust Principles.