By  DANICA B. GUINTO             APRIL 13, 2015

The Mines and Geosciences Bureau Region IV-A (MGB IV-A) conducted a geological hazard investigation on December 10, 2014 of the landslide occurrence in Barangay Paang Bundok, Plaridel, Quezon Province. The landslide occurred during heavy downpour brought about by Typhoon Ruby. This is in response to the verbal request made by Provincial Disaster Risk Reduction and Management Council (PDRRMC) of Quezon Province last December 09, 2015 for the MGB IV-A to conduct assessment of the reported landslide area. Three (3) technical personnel conducted the investigation to determine the extent of affected area and to see if it is still safe for the evacuees to return home.

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Landslide occurred in Barangay Paang Bundok, Plaridel, Quezon during heavy rainfall brought about by Typhoon Ruby (International Name: Hagupit). Houses along the footslope are very susceptible to landslide hazard. (Height: 60 meters/ Width: 100 meters from crown to the houses)

 

 

 

 

The landslide occurrence is located near the Philippine National Railway (PNR) railroad in Barangay Paang Bundok about half kilometer southeast of the Plaridel Municipal Hall. The main landslide zone is situated at geographical coordinates N 13° 57’ 24.0-24.4” and E 122° 01’ 02.8-05.7”. The affected area is characterized by a rugged topography with very steep slopes naturally considered as landslide prone. The steepness of the slope was amplified by cutting some parts of the terrain to give way to the railway construction.  Houses built at the foot slope are occupying what is known as accumulation zone. This zone consists of landslide materials of mixed soil and cobble to boulder sized volcanic rocks which are relatively loose. The surface and subsurface water that flow along and under the slope respectively, had resulted to the soil oversaturation. The slope materials manifest continuous movement as represented by bulging at the foot slope.

Based on the previous geohazard assessment made by Mines and Geosciences Bureau Central Office (MGB CO), the area was rated as “very high” (critical area) in terms of susceptibility to landslide. The MGB IV-A technical personnel have reissued another threat advisory to the concerned barangay official to remind them of mass movements that may occur in the area and adjacent site particularly during typhoons and/ or intense rainfall event.

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Photos of the footslope bulging-an evidence of continuous movement of the materials along the slope.

The above assessment prompts this Office to recommend that the community on the foot slope be relocated to safer grounds. However, due to the nature of the slope more landslides may recur. To strengthen the slope, an appropriate engineering mitigating measure may be used and reforestation of the slope can help minimize the chance of another slope failure. Proper drainage must be installed to control and minimize the effects of surface and subsurface water. A buffer zone must also be established to control people from building houses and other infrastructures on the foot slope.