Report on Mayon (Philippines) — 20 June-26 June 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 20 June-26 June 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Mayon (Philippines). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 20 June-26 June 2001. Smithsonian Institution and US Geological Survey.
13.257°N, 123.685°E; summit elev. 2462 m
All times are local (unless otherwise noted)
A large, pyroclastic-flow producing eruption began at Mayon on 24 June at 1245. The first signs of heightened volcanic activity occurred on 19 June when tremor began that was associated with increased lava extrusion. SO2 emission increased to 6,000 metric tons on 19 June in comparison to an average of 1,700 metric tons per day the previous week. In addition, intense incandescence was observed at the dome and slight inflation was detected. By 23 June lava was rapidly flowing SE along the Bonga Gully towards the town of Mabinit, reaching 3.4 km from the volcano's summit. The same day at 1909 lava fountains rose at least 50 m above the summit crater rim. Due to the increase in activity PHIVOLCS raised the Alert Level to 4 (hazardous eruption possible within days).
On 24 June a series of strong explosions produced ash clouds that rose up to 1 km above the volcano and drifted to the N. At 1245 a pyroclastic flow descended about 4 km SE down the Bonga and Buyuan gullies, generating an ash cloud that ascended to 2.3 km. Beginning at 1644 explosions sent ash clouds to ~5 km above the summit crater. The largest eruption produced an ash cloud that rose to 10 km above the volcano. Ash generated from the pyroclastic flows and from the summit eruptions drifted to the NE towards the town of Malilipot. PHIVOLCS increased the Alert Level to 5 (hazardous eruption in progress) and the danger zone was extended from 7 to 8 km in radius. PHIVOLCS also announced that all areas within the declared danger zone should be immediately evacuated. The areas at greatest risk were near the Mabinit, Bonga, Matanag, and Buyuan gullies. After the large eruptions on 24 June a lull in activity occurred until at least 0630 on 26 June. This interval was marked by a decrease in seismic activity and only three small explosions. PHIVOLCS maintained Alert Level 5 due to the possibility of more explosive volcanic activity.
News agencies reported that ~25,000 residents near the volcano were evacuated on 24 June. Many returned to their homes the following day despite the evacuation order. There were no reports of injuries directly from the eruptions. On 25 June area airports were closed. News articles noted the possibility that rain from a tropical storm in the area could mix with ash and generate dangerous lahars. The provincial government declared a state of calamity in affected areas.
Geologic Background. Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.