Crater lake overflow causes flooding; no volcanic activity

The overflow of Maughan Lake, the crater lake at Parker volcano, followed heavy rains associated with a passing typhoon and caused flashflooding in NW-flank communities on 6 September. A team from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) was dispatched to determine whether the overflow was caused by volcanic activity. Although no volcanic alert was declared, PHIVOLCS recommended that the crater area should be considered off-limits because of instability of the crater walls. Fieldwork on 8-9 September revealed that the flood was channel-confined along the NW-flank Alah River, which drains the crater lake, from 1,000 m down to 540 m elevation (Barangay New Dumangas, T'boli, South Cotabato Province). Below this point it was transformed into a sheetwash. The floods killed more than 60 people, destroyed 300 homes and nine bridges, and displaced 50,000 people.

Aerial observations on 11 September indicated that two or three landslides, indicated by escarpments, had occurred along the Alah River prior to the crater lake outbreak. The total mass displaced appears to have been sufficient to have dammed the upper reaches of the river. The crater wall was well-vegetated and without landslide scars, although underwater landslides may have contributed to the rise and subsequent overflow of the lake. The overflow breached the blocked river channel, sending an estimated ~10-15 x 10⁶ m³ of lake water down the river, lowering the lake by 1 m. No turbidity or color change was observed in the crater lake, indicating that there had been no volcanic explosion. On 9-10 September PHIVOLCS installed seismometers in T'boli, 12 km NW of the crater at 540 m elevation, and at Tobolok, ~4 km NW of the crater at 1,300 m elevation. No volcanic seismic events were recorded through 11 September.

Information Contacts: Ernesto G. Corpuz, Philippine Institute of Volcanology and Seismology (PHIVOLCS), 5th & 6th Floors Hizon Building, 29 Quezon Avenue, Quezon City, Philippines; United Press International.

Information is preliminary and subject to change. All times are local (unless otherwise noted)

September 1995 (BGVN 20:09) Cite this Report

Crater lake overflow causes flooding; no volcanic activity

The overflow of Maughan Lake, the crater lake at Parker volcano, followed heavy rains associated with a passing typhoon and caused flashflooding in NW-flank communities on 6 September. A team from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) was dispatched to determine whether the overflow was caused by volcanic activity. Although no volcanic alert was declared, PHIVOLCS recommended that the crater area should be considered off-limits because of instability of the crater walls. Fieldwork on 8-9 September revealed that the flood was channel-confined along the NW-flank Alah River, which drains the crater lake, from 1,000 m down to 540 m elevation (Barangay New Dumangas, T'boli, South Cotabato Province). Below this point it was transformed into a sheetwash. The floods killed more than 60 people, destroyed 300 homes and nine bridges, and displaced 50,000 people.

Aerial observations on 11 September indicated that two or three landslides, indicated by escarpments, had occurred along the Alah River prior to the crater lake outbreak. The total mass displaced appears to have been sufficient to have dammed the upper reaches of the river. The crater wall was well-vegetated and without landslide scars, although underwater landslides may have contributed to the rise and subsequent overflow of the lake. The overflow breached the blocked river channel, sending an estimated ~10-15 x 10⁶ m³ of lake water down the river, lowering the lake by 1 m. No turbidity or color change was observed in the crater lake, indicating that there had been no volcanic explosion. On 9-10 September PHIVOLCS installed seismometers in T'boli, 12 km NW of the crater at 540 m elevation, and at Tobolok, ~4 km NW of the crater at 1,300 m elevation. No volcanic seismic events were recorded through 11 September.

Information Contacts: Ernesto G. Corpuz, Philippine Institute of Volcanology and Seismology (PHIVOLCS), 5th & 6th Floors Hizon Building, 29 Quezon Avenue, Quezon City, Philippines; United Press International.