@misc{indiciaef27a87faacea,
  title = {Geology of El Chichon volcano, Chiapas, Mexico},
  author = {W. A. Duffield and R.I. Tilling and R. Canul},
  year = {1984},
  url = {https://pubs.usgs.gov/publication/70014011},
  note = {Source identifier: 70014011}
}