LANDSLIDE AND FAULT RELATED HAZARDS IN THE NORTH-CENTRAL PORTION OF MANKAYAN MUNICIPALITY, BENGUET PROVINCE

by

Berroya, Mary Antonette A., Fernando, Alvin, Espejo,
Benigno Cesar Jr. and Mantaring, Eleazar
Mines and Geosciences Bureau
North Avenue, Diliman Quezon City


A B S T R A C T

 

The north-central portion of Mankayan Municipality, roughly within the boundaries of the mining claim of Lepanto Consolidated Mining Corporation (LCMC), was assessed for actual and potential geologic hazards that may cause harm to people and damage to property. Focus was mainly given to the susceptibility of the area to mass movements and partly to fault-related/seismic hazards (particularly in the dam area).

Results of the study show that almost the entire study area is susceptible to different types of mass movement, particularly as it has been subject to intense landsliding in the past. This is evident from the extensive distribution of ancient landslide deposits in the area. In fact, most of the recent landslides result from the reactivation of old landslides. Example of this is the Colalo landslide of July 1999 which occurred within old landslide deposits. The situation is the same in the case of Mankayan Poblacion. The sites of LCMC old tailings pond (TP #s 2, 3 and 4) are also old landslide area.

Creeping is a common phenomenon and does not appear to be lithologically-controlled (i.e., it is observed in all lithologies). Noteworthy is the presence of creep in the area where the present Colalo Elementary School is located and in Bgy. Palatong, the proposed relocation site for the people affected by the mass movement in Mankayan Poblacion.

Finally, it was also found out from the investigation that numerous large-scale faults traversed the area where the operating tailings dam (TP # 5) of the LCMC is located. This has serious implication on the integrity of the structure.