Sheets P D, 2004. Apocalypse then: social science approaches to volcanism, people, and cultures in the Zapotitan Valley, El Salvador. Rose W. I., Bommer J. J., Lopez D. L., Carr M. J., Major J. J. (eds), Natural Hazards in El Salvador. Bolder, Colorado, Geological Society of America Special Paper 375, pp 109–120. Siebert, L. Kimberly, P., and Pullinger, C.R, 2004, The voluminous Acajulta debris avalanche from Santa Ana Volcano, western El Salvador, and comparison with other Central American edifice-failure evens, in Rose, W.I. et al., Natural Hazards in El Salvador. Boulder, Colorado, Geological Society of America Special Paper 375, pp 5–23.