LETTER : Volcanic fire and brimstone

From Dr David A. Rothery

Sir: The fears among scientists about the possibility of a much bigger volcanic eruption still to come on Monserrat are not that it will "spew deadly lava", as stated in your report (23 August). Lava is rarely deadly. A lava flow may destroy buildings in its path, but it almost always moves slowly, usually advancing on a narrow front, and it can be walked away from.

The real threat to life on Monserrat is of a wide-spread ground-hugging flow of volcanic ash that could be generated by a major explosive eruption. These hot avalanches travel at more than 100km per hour, and it was one of these that obliterated the town of St Pierre, along with its 28,000 inhabitants, on the nearby island of Martinique in 1902.

So far, the most vigorous current activity on Monserrat has been ash thrown a few thousand metres into the air, dispersed by the wind and falling slowly to the ground. An air-fall deposit such as this should not be referred to as an avalanche, because the process of emplacement and the hazard it represents are both quite different. The fine dust in an airfall is a respiratory hazard, if ash is allowed to accumulate thickly on roofs it can cause them to collapse, and it may kill crops and other vegetation.

Yours faithfully,

David A. Rothery

Department of Earth Sciences

The Open University

Milton Keynes

24 August