VOLCANO MONITORING PRACTICAL Predicting volcanic eruptions is a hazardous and stressful business. If an eruption has occurred and was not predicted then the volcanologists get the blame for not giving any warning; if an eruption is predicted but never occurs then the volcanologists are even more unpopular for crying wolf. You form part of a emergency volcanic hazard task force whose main aim is to predict when an eruption may occur and to ensure that the safety of the local inhabitants is assured. Mount Philatubo has been under observation for a number of years. Monitoring has taken place using seismometers and tiltmeters. A hazard zonation map is also available for the volcano. There has recently been an increase in the seismic activity in the area and the local Volcano Observatory Unit, which studies the readings, are a bit anxious. Naturally worried by the recent results the Director of the Observation Unit has decided to call in the volcanic hazard task force. Your mission is to: l l predict when the possible eruption might occur, based on daily reports; to use the correct alert levels at each stage; l advise the local authorities about which local villages and towns should be evacuated if an eruption proves to be imminent. Alert levels are shown opposite (based on communications established during the eruption of Mount Pinatubo). It should be remembered that if your team calls a Level 2 alert then the authorities would expect an evacuation of the immediate area. If a Level 3 alert is called then the authorities would expect an eruption within 2 weeks. If you call a Level 4 alert you had better be right! You must also pay attention to the stand-down procedures. The future of the task force depends on your decisions. Good luck. Volcano 4 Hazard alert levels established for communication at Mt. Pinatubo Alert Level Criteria Interpretation 0 Background; quiet No eruption in the foreseeable future 1 Low-level seismic, fumarolic and other unrest 2 Moderate level of seismic and other unrest, with positive evidence for magma involvement 3 Relatively high and increased unrest, including numerous shallow volcanic earthquakes; accelerating ground deformation; increased vigour of fumarolic activity; gas emission 4 Intense unrest, including harmonic tremors and/or many long-period (low frequency) earthquakes Stand-down Procedures In order to protect against the calm-before-the-storm phenomena, alert levels will be maintained for the following periods after activity decreases to the next lowest level: From Level 4 to Level 3: wait 1 week From Level 3 to Level 2: wait 72 hours Magmatic, tectonic or hydrothermal disturbance; no eruption imminent Probable magmatic intrusion; could eventually lead to an eruption If trend of increasing activity continues, eruption possible within 2 weeks Eruption possible within 24 hours 5 Eruption in progress Eruption in progress (Table from Ewert, J.W. & Newhall, C.N. Volcanic crisis in the Philippines: the 1991 eruption of Mount Pinatubo, http://vulcan.wr.usgs.gov/vdap/pina_yrbk-1991.html)
Hazard Zonation Map for Mt. Philatubo and Vicinity Pyroclastic flow deposit Ocean Broughton Poggs 10 5 1 10 Mudflow prone area Isopach line for ashfall deposit (cm) 15 Ready Token 20 25 30 15 20 25 30 Slad 40 50 Mt. Philatubo Tuffley Boddington Fiddington 10 5 1 Thrupp N 10 km
Volcano 4 Summary Sheet Date of activity report Alert level Towns evacuated Any other comments?
Thursday 6 May Volcano 4 Over the past few weeks there has been a gradual increase in seismic activity; generally short period, high frequency quakes. At 15.45 an earthquake, magnitude 4.2, hit the area. Worried that this might be caused by the volcano reawakening, your team flies over Mount Philatubo to observe if there has been any activity. No new activity, or change in deformation is observed during the flight. Are the tremors related to the volcano? Friday 21 May Volcano 4 Earthquake frequency and amplitude is increasing. Another flight over the volcano reveals that a new lava dome has extruded on the western side of the vent. The lava forming this dome is viscous and is similar to that which commonly forms large pyroclastic eruptions. This is consistent with the deposits formed by previous eruptions. Sunday 26 June Volcano 4 Harmonic tremors are recorded all morning. At 17.50 Mount Philatubo starts erupting. This eruption is very small and results in a minor eruption column of ash, rising 0.5km into the air.
Wednesday 30 June Volcano 4 Minor ash eruptions have continued intermittently for several days. The seismic activity has decreased and the eruptions have died down. Was the volcano just degassing? Monday 5 July Volcano 4 Analysis of the tiltmeter readings have shown that the northern flank of Mount Philatubo is inflating fairly rapidly. Accompanying this rise has been a constant seismic harmonic tremor. Wednesday 7 July Volcano 4 The inflation of the flank has grown considerably. An aerial fly-by shows that the lava dome within the vent has also increased and is building up against the western wall of the crater.
Thursday 14 July Volcano 4 Seismicity has increased; still mainly harmonic tremors. Observations reveal that the lava dome has increased in size quite dramatically and has risen above the level of the western crater wall. There has been no significant increase in the bulge on the northern flank of the volcano. Sunday 17 July Volcano 4 At 16.35 the lava dome collapsed, forming an extensive Merapi-type pyroclastic flows down the western flank of Mount Philatubo, destroying the town of Slad. Seismicity has not decreased and there has been no deflation of the northern flank bulge. The seismic activity has changed from harmonic tremors to a series of high frequency, short period quakes. Tuesday 20 July Volcano 4 A large earthquake hit the area (5.6), causing failure of the northern flank of the volcano and an explosive eruption from the main vent. All the towns on the northern side of the volcano (e.g. Ready Token and Broughton Poggs) have been completely destroyed.