HR: 0830h
AN: V51F-0353    [PDF]
TI: Comparing the Hazards From Large Volcanic Eruptions and Impacting Asteroids
AU: * Mason, B G
EM: bgm21@cam.ac.uk
AF: University of Cambridge, Department of Earth Sciences, Downing Street, Cambridge, CB2 3EQ United Kingdom
AU: Pyle, D M
EM: dmp11@esc.cam.ac.uk
AF: University of Cambridge, Department of Earth Sciences, Downing Street, Cambridge, CB2 3EQ United Kingdom
AB: Explosive volcanic eruptions and asteroid impacts leave craters that allow direct comparison of the scale and frequency of these severe events. We have compiled data on large volcanic eruptions over the past 45 million years, and used this to develop an improved quantitative assessment of the frequency of large volcanic eruptions, and to make a comparative assessment of the relative likelihood of the Earth being affected by severe volcanic eruptions, and impact events of equal severity. In terms of volcanic activity, the expected frequency of explosive eruptions involving $>$ 10$^{15}$ kg of rock lies between 1.3 and 22 events per million years. For the events that form terrestrial craters with diameters of order 10 - 25 km, the thermal energy release (during a volcanic eruption) is of the same order of magnitude as the kinetic energy release (from an asteroid impact), and ca. 10$^{21}$ - 10$^{22}$ J (2 $\times$ 10$^{5}$ - 2 $\times$ 10$^{6}$ Mt equivalent of TNT). Over the past 5 Ma, volcanic activity dominates the production rate of craters $<$ 45 km diameter. This suggests that over short timescales ($<$ 1 Ma), destructive volcanic eruptions are more frequent than impact events of a similar energy. A better comparison of the primary effects of both phenomena may be realised by considering the area destroyed by shock waves (impactors) or hot pyroclastic deposits (volcanoes). Using simple scalings, we show that the primary area destroyed by an impactor is about ten times that for an eruption. Using this area as a measure of severity, we can show that for events with a return period of 100,000 years or less, there are considerably more eruptions of a given severity than there are impact events. Impactor events only dominate for return periods of $>$ 200,000 - 500,000 years. We conclude that smaller ($<$ 10$^{12}$ kg, $<$ 1 km diameter) near-earth orbiters pose a significantly smaller hazard to humans than the regional effects of large (10$^{14}$ - 10$^{15}$ kg) volcanic eruptions.
DE: 1600 GLOBAL CHANGE (New category)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting