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Alaska's Redoubt volcano stops shaking
by The Associated Press ANCHORAGE, Alaska -
The swarm of small shallow earthquakes that began April 5 at the Redoubt volcano has ended, and the shaking returned to background levels. The Alaska Volcano Observatory lowered the aviation code Monday from yellow to green. Eruptions from the 10,197-foot volcano early last year disrupted air travel, dusted Anchorage with ash and sent a mudflow that partially flooded the Drift River Oil Terminal.
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than 2 millimetres (0.079 in) in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact with water causing phreatomagmatic eruptions, and ejection of entrained particles during steam eruptions causing phreatic eruptions. The violent nature of volcanic eruptions involving steam results in the magma and solid rock surrounding the vent being torn into particles of clay to sand size. Volcanic ash can lead to breathing problems, malfunctions in machinery, and from more severe eruptions, years of global cooling.