Ozone concentrations increase in the mid-stratosphere (the top region of the volcanic cloud), by up to 12% at around 27km.

Lower level of volcanic cloud is at, say, 20,000 feet.

He inhaled on his pipe, and puffed up a volcanic cloud from the hissing bowl.

The volcanic cloud above them was fainter still.

I daresay they are more like what we should call volcanic clouds.

So far, the agency has issued 14 bulletins about the volcanic cloud, its direction of movement and its expected path.

There is huge concern for the effects of the volcanic cloud on the tourist industry.

"The rain comes from those same volcanic clouds and must be full of ash and debris."

At one time in human history, it would have seemed typically a volcanic cloud.

Phoenix were almost no-shows themselves, as they too encountered travel difficulties due to the volcanic cloud hovering over northern Europe.