* Volcano had threatened to erupt for months
* Alaska Air cancels 19 flights
* Anchorage not touched by harmful ash so far (Adds geophysicist quotes, update on ash fall)
By Yereth Rosen
ANCHORAGE, Alaska, March 23 (Reuters) - Alaska’s Mount Redoubt volcano erupted for the first time in 20 years, threatening air traffic and nearby villages with a towering burst of ash, and more eruptions were expected.
The first blast occurred at 10:38 p.m. Pacific time on Sunday (0538 GMT Monday), the Alaska Volcano Observatory said. It was followed by four smaller eruptions.
The 10,197-foot (3,108-metre) volcano, in a sparsely populated area 106 miles (170 km) southwest of Anchorage, Alaska’s largest city with about 260,000 people, had been showing signs of a possible eruption for about two months. So far Anchorage has been untouched by harmful volcanic ash, which is drifting north from the volcano.
“We expect the pattern of this event to be similar to the 1989 and 1990 eruptions and the activity could continue along those lines for several weeks or several months,” said U.S. Secretary of the Interior Ken Salazar on a conference call.
The volcano last rumbled to life in December 1989, erupting multiple times over a period of almost five months, with ash from the first blast nearly downing a KLM jetliner.
Ash can hamper visibility, clog machinery, hinder breathing and damage wastewater systems, among other things.
Tina Neal, a geologist at the Alaska Volcano Observatory, said each of the five eruptions lasted 10 to 20 minutes, and the series ended around 4:31 a.m. (0831 GMT) on Monday.
“Each event sent up an ash cloud as high as 50,000 (15,200 meters) and possibly 60,000 feet (18,300 metres),” Neal said.
The observatory warned airlines to steer clear of the area. Anchorage-area airports are still open, but Alaska Air Group Inc (ALK.N) — the state’s leading carrier — said it had canceled 19 flights in and out of Anchorage so far.
“This is changing constantly, depending on how the winds blow,” said Alaska Airlines spokeswoman Marianne Lindsey.
The Drift River Oil Terminal, a holding point for crude oil near the foot of the volcano on the western shore of Cook Inlet, was shutting down temporarily.
“At this point in time we believe that everything is safe there,” Salazar said. The terminal was inundated by floods and mudslides during the 1989-1990 eruptions.
The terminal is owned and operated by Cook Inlet Pipe Line Co, which is partly owned by Unocal, now a part of oil giant Chevron Corp (CVX.N).
The bulk of the ash from the most recent eruptions was blown at the 30,000-foot (9,150-metre) level, and is not reaching significantly populated areas, Neal said.
Ash was confirmed in one community and reported in a few other spots along the Susitna Valley north of Anchorage, she added. Denali Park and Nikolai also experienced some ash fall.
“We should consider ourselves lucky today that we aren’t out sweeping up ash now (in Anchorage),” said John Power, a geophysicist at the Alaska Volcano Observatory.
“If Redoubt erupts again, next time the wind direction may be very different,” said Power, who expects more eruptions.
“The volcano is still restless,” said Neal. “We’ll be watching it very closely. It is highly unstable still and further eruptions are likely.” (Editing by Bill Rigby and Chris Wilson)