By Yereth Rosen
ANCHORAGE, Alaska, March 8 (Reuters) - A remote Alaska volcano that has been restless since last summer belched ash in a small, short explosion, scientists said on Thursday, but the cloud was not expected to impact commercial airline traffic.
Meanwhile, a second volcano that has not erupted in recorded Alaska history is experiencing a swarm of earthquakes for which scientists have yet to determine a cause.
The explosion was at Cleveland Volcano, located on an uninhabited Aleutian island 940 miles southwest of Anchorage.
While the exact size of the ash cloud it produced is unknown, it was believed to be small, as was a cloud the resulted from a similar explosion at the volcano in December, said Steve McNutt, a University of Alaska Fairbanks seismologist who works at the Alaska Volcano Observatory.
That cloud rose to less than 20,000 feet, lower than the levels used by large commercial jets, McNutt said.
The observatory maintains no on-site monitors at remote Cleveland, so it relies on mostly satellite imagery for news about the volcano's activities. But poor weather conditions are currently blocking satellite images of Cleveland, McNutt said.
Despite their distance from population centers, Cleveland and other volcanoes in Alaska's Aleutian chain pose potential risks to commercial air traffic because they lie below a well-used route between North America and Asia.
Meanwhile, another Alaska volcano that has not erupted in hundreds of years is now the site of frequent small earthquakes, a phenomenon that has so far puzzled scientists.
The Alaska Volcano Observatory has issued a notice about increased seismic activity at Mount Iliamna, located in Lake Clark National Park, on the west side of Cook Inlet and 130 miles southwest of Anchorage.
The site, which usually has a couple of small earthquakes a week, now is experiencing "a couple dozen" a day, McNutt said. That activity has been ongoing for about three months, he said.
So far, scientists have not seen signs of gas emissions, ground deformation or unusual heat at the Iliamna, McNutt said. Other than the swarm of earthquakes, he said, "We have not seen any of the tell-tale signals that magma is moving."
The USGS plans to conduct a research flight next week to sample the air around Iliamna for gases, McNutt said.
Iliamna, which rises to 10,016 feet, has had no known eruptions since Alaska recorded history began in the late 18th century, McNutt said. There is geologic evidence that it erupted 500 to 1,000 years ago, he said. (Editing by Dan Whitcomb and Paul Thomasch)