What PHIVOLCS’ alert levels mean and how to prepare under each stage

Taal Volcano on Sunday had a phreatic eruption, sending ash to as far north as Metro Manila and parts of Central Luzon.

In a matter of hours on Sunday afternoon to evening, the Philippine Institute for Volcanology and Seismology raised the alert level from two to four.

Here's what the alert levels mean and how the public should prepare under each:

Alert level 1

• Low-level seismicity, fumarolic, other activity
• Magmatic, tectonic or hydrothermal disturbance
• No eruption is imminent.

Alert level 2

• Low to moderate level of seismicity, the persistence of local but unfelt earthquakes
• Ground deformation measurements above baseline levels
• Increased water and/or ground probe hole temperatures
• Increased bubbling at Crater Lake
• There is a possible magmatic intrusion that could eventually lead to an eruption. However, if the trends decline, the alert level may be lowered to level 1.

Alert level 3

• Relatively high unrest
• Seismic swarms, including the increasing occurrence of low-frequency earthquakes and/or harmonic tremor (some events felt)
• Sudden or increasing changes in temperature or bubbling activity or radon gas emission or crater lake pH
• Bulging of the edifice and fissuring may accompany seismicity
• Should the trends continue during alert level 3, PHIVOLCS warns of a hazardous eruption within days or weeks.

Alert level 4

• Intense unrest
• Continuing seismic swarms, including harmonic tremor and/or “low-frequency earthquakes” which are usually felt
• Profuse steaming along existing and perhaps new vents and fissures
• Hazardous eruption may be possible within days.

Alert level 5

• Base surges accompanied by eruption columns
• Lava fountaining or lava flows
• During alert level 5, hazardous eruption in progress. Extreme hazards to communities west of the volcano and ashfalls on downwind sectors.

—NB, GMA News