Environmental Engineering Reference
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2.11 (a) Volcanic eruptions and fatalities, 1800-2000
(plotted from data at Volcano Live). (b) Energies released by
Mount St. Helens eruption on May 18, 1980 (plotted from
Decker and Decker 1981).
loss at 200 GW, less than 0.5% of the global geothermal
flux. In contrast, Verhoogen (1980) put the maximum
volume of continental lava outpouring at less than 1
km 3 /a and estimated the highly uncertain rate of oceanic
eruptions at close to 4 km 3 /a. A global total of less than
5km 3 /a corresponds to heat loss of about 800 GW, still
no more than 2% of planetary heat flow. But power rat-
ings of individual explosions are huge: those of Tambora
and Pinatubo were put at about 400 TW, and that of
Vesuvius in 79 C . E . at 200 TW (Ritchie and Gates
2001). The main eruption of Mount St. Helens (1.9 EJ)
on May 18, 1980, lasted 9 h, prorating to 52 TW. An
eruption releasing 80 EJ in 10 h rates over 2 PW,
roughly equal to a magnitude 8 earthquake lasting 30 s.
Modern volcanologists have repeatedly used power
comparisons with nuclear bombs, whose energy is
expressed in equivalents of TNT. Mount St. Helens's
1.9 EJ equals 450 Mt TNT, or 27,000 Hiroshima
bombs. Such comparisons ignore different ways and
durations of energy release. Nuclear explosions produce
blinding light within 10 3 s and emit deadly IR radiation
0.2-3 s after the eruption, and their blast wave, contain-
ing about 50% of all latent energy, travels at initial veloc-
ities of 10 2 m/s (CCMD 1981). In contrast, the median
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