From Tim Wilton
BP environmental specialist Michelle Horsfield was surprised that the underwater detonation of an old naval mine could knock people off their feet on a boat 2 kilometres away (9 November, p 50, UK edition, and newscientist.com/article/mg22029421.200).
However, water, unlike air or rock, is an incompressible medium. Hence, the shock waves, even at 2 kilometres, would have been 2 to 3 times as great as the equivalent for ground-borne vibration. Underwater detonation is usually the safest and most practical disposal method, although, as Horsfield witnessed, not risk-free.
Horsley Woodhouse, Derbyshire, UK
