CITY OF SAN FERNANDO – The Philippine Institute of Volcanology and Seismology (Philvolcs) clarified yesterday there were no indications that tons of lahar debris on the slopes of Mt. Pinatubo are poised to flow and bury parts of this province.
In an interview with Punto!, Phivolcs chief volcanologist Perla de los Reyes said a team of scientists who inspected the Pasig-Potrero River last Friday found the lahar embedded on the channel remained intact.
The river, which runs down from the slopes of Mt. Pinatubo, used to be an active lahar channel.
De los Reyes said the scientists inspected the river from the area of the Gapan-San Fernando-Olongapo Road downstream up to the so-called Delta 5 lahar monitoring station up the slopes of Mt. Pinatubo some 20 kilometers away.
Reports of lahar danger from the Pasig-Potrero caused some panic from local folk after some persons were reported to have shouted lahar was on its way to a packed local mall. The news was immediately contained by local officials.
Huge volumes of volcanic debris were deposited on the Pasig-Potrero channel during the series of lahar flows that followed Mt. Pinatubo’s big eruption in 1991.
The heavy rains brought by the recent southwest monsoon triggered fears of re-mobilization of these lahar deposits.
Last Friday, this city’s Mayor Oscar Rodriguez expressed fears that strong rains would push the volcanic debris downstream and bury southeastern portions of his city, as well as the towns of Minalin and Sto. Tomas.
He recalled that in the 1990’s, the entire town of Bacolor was literally buried by volcanic materials during the series of lahar flows from the Pasig-Potrero.
“There is no re-mobilization (of lahar debris). It was only water with siltation that flowed,” said De los Reyes.
De los Reyes said that the so-called transverse dike across the downstream portion of the Pasig-Potrero remained intact, although some 70 meters of the “tail dike” also in the lower parts of the river, was damaged.
“The tail dike was after all built to capture the volcanic materials flowing down. With no lahar materials flowing, the tail dike has served to dam up water instead,” she said.
The dikes are within the U-shaped megadike built starting 1997, to shield heavily populated communities from lahar flows.
De los Reyes said, however, that downward movement of lahar along the channel is possible during “torrential rains.” She said the recent rains brought by the southwest monsoon was not torrential and did not significantly disturb the deposits on the channel.
While she saw no immediate danger from lahar flow at the Pasig-Potrero, De los Reyes nevertheless noted that some people continue to live within the megadike system.
“It’s not for us to tell them to move out, but we must remember the megadike was built precisely to catch lahar flows within its system to protect outside communities,” she noted.
