Volcanoes and atom bombs

Photo of Matua volcano, Siberia, taken by NASA astronauts

Detonation of a thermobaric (fuel-air) bomb by the Russians.
Believed to be the largest of its kind ever detonated.

The New York times recently had a photo documentary of development of the atomic bomb. The photo below is of a "fuel-air bomb", often called a "vacuum bomb". This type of explosive uses oxygen from the surrounding air to increase the duration, and destructiveness, of the shock waves/fireball. They were first developed by the Germans during WWII, and are in use by modern military and in guerilla warfare (1993 World Trade Center bombing, 2002 Bali bombings).

Some volcanoes have eruptions that are "explosive" enough to produce shock waves.  These were first recognized by Perret during explosive eruptions of Vesuvius in 1906, and were later observed and analyzed quantitatively at Ngauruhoe, New Zealand (Nairn, I.A., Nature 259 (5540, pp. 190-192, 1976). On June 12, 2010, NASA astronauts were able to capture the photo at the left of an eruption of Matua volcano, Siberia.  You can't see the shock wave directly, but can see the hole that it punched through the cloud deck.  The rising ash plume has also pushed up a layer of moist air forming a pileus "cap cloud".  A pyroclastic flow is visible at the base of the column, descending toward 5 o'clock on the flank of the volcano.  Volcanologists use some of the same basic concepts about shock waves that were developed to analyze shocks from atomic bombs, and although we talk about the energy released in eruptions in terms of "kilotons" or "megatons". For example, I analyzed the energetics of the lateral blast at Mount St. Helens in 1980, and concluded that about 24 megatons of energy was released during the blast (Kieffer, S.W., Nature, 291, 568-570, 1981).