The dome now fills the floor of the crater at Cleveland Volcano, 940 miles southwest of Anchorage.
The Alaska Volcano Observatory on Tuesday raised the volcano's alert level to watch status. The threat level was dropped on Aug. 30, but raised against after a persistent thermal anomaly started Saturday. Observatory officials say in a news release that's when the lave dome likely started growing again.
The dome was 262 feet in diameter on Aug. 30, but is now about 394 feet in diameter.
Officials say if that continues, lava flows could start on the flanks of the volcano. The growing dome also increases the possibility -- but doesn't ensure -- an explosive eruption.
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