Ash cloud from Hawaii volcano sparks aviation red alert

Explosions intensified on Hawaii's Kilauea volcano on Tuesday, spewing ash and sparking a red alert for aviation for the first time since the latest eruption began 12 days ago.

Ash and volcanic smog, or so-called vog, rose up to 12,000 feet (3,657 meters) above Kilauea's crater and floated southwest, covering cars on Highway 11 with gray dust and sparking an "unhealthy air" advisory in the community of Pahala, 18 miles (29 km) from the summit.

An aviation red alert means a volcanic eruption is underway that could affect aviation by spewing ash into air routes, according to the US Geological Survey (USGS) website.

Lava flowing from giant rips in the earth on the flank of Hawaii's erupting Kilauea volcano threatened highways on Monday, raising the possibility officials may order thousands more people to evacuate before escape routes are cut off.

Lava from a huge new fissure tore through farmland towards a coastal dirt road that is one of the last exit routes for some 2,000 residents in the southeast area of Hawaii's Big Island.

More lava-belching cracks are expected to open among homes and countryside some 25 miles (40 km) east of Kilauea's smoking summit, possibly blocking one of the last exit routes, Highway 132.

A shift in winds was expected to bring ash and vog inland on Wednesday and make them more concentrated, said John Bravender of the National Oceanic and Atmospheric Administration (NOAA).

"We're observing more or less continuous emission of ash now with intermittent, more energetic ash bursts or plumes," said Hawaiian Volcano Observatory (HVO) Deputy Scientist-In-Charge Steve Brantley on a conference call with reporters.

The observatory warned the eruption could become more violent.

"At any time, activity may become more explosive, increasing the intensity of ash production and producing ballistic projectiles near the vent," the HVO said in a statement on the change in aviation alert level to red from orange.

Ash is not poisonous but causes irritation to the nose, eyes and airways. It can make roads slippery and if emitted in large quantities could cause electrical power lines to fail, said USGS chemist David Damby.