Turbulence leads to early rain of ash

9:11pm, January 2, 2002

From San Francisco, at the 2001 fall meeting of the American Geophysical Union

A new aerodynamic analysis suggests that small particles of ash in a turbulent volcanic plume can fall nearer their source than researchers had thought.

On Aug. 18, 1992, Mount Spurr–a 3,374-meter-tall volcano about 125 kilometers west of Anchorage, Alaska–sent a plume of ash more than 10 km into the sky. The cloud passed directly over Anchorage and dropped a two-nickel-thick layer of sand-sized ash particles there. Another 125 km downwind, the particles that blanketed the ground were smaller and came primarily in two disparate sizes–the larger was about 90 micrometers across, and the smaller was about 20 m.

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