http://www.c3.lanl.gov/~cjhamil/SolarSystem/raw/volc/ash1.htm (Einblicke ins Internet, 10/1995)An exploding volcano blasts molten rock and ash into the air with tremendous force. The heaviest fragments fall back to the ground usually within a few kilometers of the vent but the dust size ash fragments continue to rise into the air forming a hugh billowing cloud of ash. This is the most common type of activity produced by explosive eruptions.The largest eruptions spew ash for hours at a time. Some continue erupting ash for several days to weeks. The ash clouds can be enormous, reaching more than 30 kilometers above a volcano in only 30 minutes. Once in the air, particles of ash drift with the wind. The smallest particles may be carried hundreds of kilometers downwind from a volcano, filling the sky with a dark cloud of ash as far as the eye can see.