Wednesday, November 11, 2009

Mayon Volcano Alert Levels




No Alert. Quiet.

All monitored parameters within background levels. No eruption in foreseeable future.

Entry in the 6-km radius Permanent Danger Zone (PDZ) is not advised because phreatic explosions and ash puffs may occur without precursors.


Abnormal Low level unrest.

Slight increase in seismicity.

Slight increase in SO2 gas output above the background level.

Very faint glow of the crater may occur but no conclusive evidence of magma ascent.

Phreatic explosion or ash puffs may occur. No eruption imminent.

Activity may be hydrothermal, magmatic or tectonic in origin.

No entry in the 6-km radius PDZ.


Increasing Unrest - Moderate unrest.

Low to moderate level of seismic activity.

Episodes of harmonic tremor.

Increasing SO2 flux.

Faint / intermittent crater glow.

Swelling of edifice may be detected.

Confirmed reports of decrease in flow of wells and springs during rainy season. Unrest probably of magmatic origin; could eventually lead to eruption.

6-km radius Danger Zone may be extended to 7 km in the sector where the crater rim is low.


Increased Tendency Towards Eruption - Relatively high unrest.

Volcanic quakes and tremor may become more frequent.

Further increase in SO2 flux.

Occurrence of rockfalls in summit area.

Vigorous steaming / sustained crater glow.

Persistent swelling of edifice. Magma is close to the crater.

If trend is one of increasing unrest, eruption is possible within weeks.

Extension of Danger Zone in the sector where the crater rim is low will be considered.


Hazardous Eruption

Imminent Intense unrest.

Persistent tremor, many "low frequency"-type earthquakes.

SO2 emission level may show sustained increase or abrupt decrease.

Intense crater glow. Incandescent lava fragments in the summit area. Hazardous eruption is possible within days.

Extension of Danger zone to 8 km or morein the sector where the crater rim is low will be recommended.


Hazardous Eruption

Hazardous eruption ongoing.

Occurrence of pyroclastic flows, tall eruption columns and extensive ashfall. Pyroclastic flows may sweep down along gullies and channels, especially along those fronting the low part(s) of the crater rim.

Additional danger areas may be identified as eruption progresses.

Danger to aircraft, by way of ash cloud encounter, depending on height of eruption column and/or wind drift.

Revised 25 January 2001

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