New Zealand volcano erupts

The eruption of Mount Tongariro sent a dark ash plume into the sky (EPA)

A New Zealand volcano erupted with a brief blast of dark ash today, forcing the cancellation of flights but causing no significant damage. Schoolchildren and dozens of other hikers who were walking on trails along the mountain's base were safe.

The eruption of Mount Tongariro, its second in less than four months, sent a dark ash plume about 1.9 miles into the sky. Authorities issued a no-fly alert above the mountain located in the sparsely populated area of central North Island.

National carrier Air New Zealand advised travellers that some of its flights could be delayed or cancelled because of the eruption. Airline spokeswoman Brigitte Ransom said two flights had been cancelled by midafternoon.

The New Zealand Herald reported that about 100 middle-school students and teachers were safe after they were hiking on the Tongariro Track at the base of the volcano when it erupted. Dozens more adults hiking in the region were also uninjured.

Tongariro National Park has three active volcanoes, is a popular tourist destination and was the backdrop for many scenes in "The Lord of the Rings" movies.

Civil defence authorities were advising people in the region to remain indoors and shut their windows to avoid the ash, which could be a health hazard.

Tony Hurst, a volcanologist with GNS Science, said the eruption lasted about five minutes and was unexpected, although scientists had placed the volcano on a higher alert after it erupted in August for the first time in more than a century.

Hurst said the dark ash indicated that magma pressure deep underground caused the eruption. A steam-driven eruption typically produces white ash.

New Zealand lies on the Pacific Ocean's "Ring of Fire" and has frequent geothermal and seismic activity.