Scientists are on alert and closely monitoring the increasing activity with an Alaskan volcano.
The observatory detected elevated surface temperatures Jan. 24 at Cleveland's summit and satellite data obtained last week indicated that a growing lava dome on the floor of the summit crater had reached about 328 feet in diameter.
The summit crater itself is nearly 10 times that size, said Chris Waythomas of the U.S. Geological Survey.
Lava domes form a lid on a volcano chamber that holds magma.
When they grow big enough, lava domes can become unstable and collapse and the decompression of the magma chamber can lead to an explosion as the conduit inside the volcano suddenly becomes unsealed and gasses escape.
Development of a lava dome indicates sudden explosions of ash higher than 20,000 feet, a threshold for concern for international air carriers, could be produced with little warning.
The swelling lava dome led the observatory to change the volcano's alert level to "orange," indicating heightened or escalating unrest.
Cleveland Volcano, situated on the western half of uninhabited Chuginadak Island, is one of the most active of the volcanoes in the Aleutian Islands, about 940 miles southwest of Anchorage.
It is a stratovolcano, composed of alternating layers of hardened lava, compacted volcanic ash, and volcanic rocks.
Cleveland's last major eruption was 12 years ago, in which three explosive events occurred in February 2001 that produced ash clouds as high as 39,000 feet. The volcano has had burst of smaller plumes nearly every year since then.
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