- Part of the Andes fold mountains which resulted from the subduction of the Nazca plate beneath the South American plate.
- The volcano had been dormant for 69 yrs, but erupted 7 times in previous century.
- 13th November 1985 at 9.00pm local time an eruption of VEI scale 3 sent andestic ash over 30km into the atmosphere.
- Summit was covered by glacier and large meltwater valleys lead away in a radial pattern.
- Nearest major town was Amero, of 28,000 people over 40km away.
- Rivers swollen due to previous heavy rainfall.
- Pyroclastic flows produced rolled down the volcano helping to melt the summit…