Energy partition in the 1982 eruption of El Chichon volcano, Chiapas, Mexico

Abstract

The 1982 eruption of El Chichon volcano, Chiapas, Mexico has been extensively investigated from various standpoints, including seismicity, tephra geology, atmospheric effects and tectonic structure. In this paper, the six largest of a series of explosions are isolated, considering various sources of information. Then, the seismic energy released by volcanic earthquakes and tremor is estimated using seismograms of low magnification in order to avoid saturation of seismic wave amplitudes. The explosion kinetic energy is evaluated by two methods: one by the initial velocity of the ejecta and the other by the air wave data recorded at a distance. Both the results are roughly coincident. The thermal energy is classified into two components: that transferred by volcanic ejecta and that consumed by convective clouds. The thermal energy released by the explosions is very large compared with that of mechanical energy, such as the seismic energy and explosion kinetic energy. After the last major explosion of April 4, A-type volcanic earthquakes swarmed till the end of April. Their occurrence rate decreased with time in an aftershock-like sequence. These earthquake swarms may have been due to post-eruptive readjustment of the stress field within and near the volcano. Such seismic activity contrasts with other examples of similar major eruptions, which were followed by growth of lava domes in the new craters after the paroxysmal eruptions. The 1982 eruption of El Chichon volcano has not been followed by the growth of a lava dome within the newly formed crater.