Preparation - Monitoring

• Steam emissions from side of volcano

  2nd April 1991
• Scientists from the Philippines Institute of Volcanology and Seismology (PIVOLCS)


  • Arrived and began onsite monitoring
• 10km radius danger zone


  • Declared around the volcano
• United States Geologic Survey (USGS)


  • Arrived with seismometers, tilt meters and other equipment
• USGS monitoring


  1. Monitored the current activity on the volcano

  2. Around 40-150 earthquakes were occurring each day

  3. Sulphur dioxide levels rose from 500 tonnes per day to 5000 tonnes per day in 5 weeks
• USGS field studies


  1. Examined the eruption history of the volcano

  2. Looked for evidence of where previous lahars and pyroclastic flows had travelled

  3. Discovered the volcano four or five times in the past 2000 years, indicating that an eruption here was likely to be explosive in nature