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Alert level lowered at Mayon 2 January 2010

Posted by admin in activity reports, Mayon, Philippines.
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Things are calmer at Mayon: the declining trend in the volcano’s activity since 28 December has convinced Phivolcs to lower the alert level from 4 to 3, indicating ‘relatively high unrest’. Mayon bulletin no. 20, issued by Phivolcs on 2 January 2010, explains as follows:

The latest activity of Mayon still indicates that its overall state of unrest remains relatively high. However, this phase of unrest, characterized by moderate seismicity, high volcanic gas outputs and continuing glow of the summit are processes normally associated with very gradual return to the repose period. The volcanic system is expected to continue producing earthquakes and to vent a large amount of gases because fresh magma still resides along the whole length of the volcanic pipe and near the summit.

From 28 December to present, a declining trend in Mayon volcano’s activity was noted as reflected by the following observations:

1. No ash ejections were observed since 29 December. Steam emission was most of the time weak and white in color indicating considerable decrease in energy and absence of ash.

2. Majority of the type of earthquakes that were recorded during the past days were associated with rockfalls and rolling down of fragments from the lava deposits along Bonga gully and the advancing lava front.

3. Measured SO2 levels have also showed a decreasing trend from a maximum of 8,993 tons per day to 2,621 tons per day. The still high concentration of SO2 gas emission suggests that there is residual magma degassing at shallow depth.

In view of the above observations, PHIVOLCS-DOST is lowering the alert status of Mayon from Alert Level 4 to Alert Level 3 to reflect the overall gradual decrease of activity. Alert Level 3 means that there is less probability of a hazardous explosive eruption. However, the lowering of the alert level from 4 to 3 should not be interpreted that the unrest of the volcano has ceased. If there is resurgence in the volcano’s activity and the potential for explosive eruptions is perceived to be forthcoming, the alert level may be raised back to 4 but if there is noticeable downward trend in the monitored parameters, then the alert will be further lowered to Alert Level 2.

Even before the decision to lower the alert level was taken, Albay Governor Salceda was welcoming the decline in Mayon’s activity with characteristic enthusiasm: ‘It really looks like Mayon drops dead. This is the first time in its recorded history. It seems that God answered our prayers and saw the collective preparations of a united people’. However, this may be a little optimistic. Extended periods of variable activity – declines followed by upswings – are characteristic of Mayon’s eruptive history: the first half of 2001 was marked by episodes of decline and resurgence, accompanied by changes in alert level, leading to significant eruptions in June and July of that year. There may very well be more to come from Mayon.

Local farmer Pedro Balast, at 77 a veteran of 11 evacuations and several eruptions, has this to say: ‘I won’t go home yet, I will stay here for a while. Mayon should not be trusted especially that it suddenly dies down … eruption will come if there is a sudden lull’. Nevertheless, evacuees are heading home, although a 4-kilometre exclusion zone remains in place around the volcano.

For all our Mayon coverage: Mayon « The Volcanism Blog.

Mayon quieting downPhilippines Daily Inquirer, 1 January 2010
Farmer still wary of calm before the stormManila Bulletin, 2 January 2010
Mayon evacuees head home as eruption less imminent – GMANews.TV, 2 January 2010

Global Volcanism Program: Mayon – summary information for Mayon (0703-03=)
Philippine Institute of Volcanology and Seismology – website for Phivolcs

The Volcanism Blog