A Year Later: Analyzing the 2022 Kusiong Debris Flow and Landslides through Fieldwork

Around midnight of October 28, 2022, a deadly landslide caused by Severe Tropical Storm Paeng (Nalgae) devastated Sitio Tinabon in Barangay Kusiong, Maguindanao del Norte. Based on barangay records, the landslide killed 24 people and injured 68; all of them were residents of the relocation site at the foothills of Mt. Minandar, the source of the debris flow. UPRI-NOAH previously delineated the extent of the debris flow and other landslides in the vicinity using remote sensing analysis. A year after the event, from November 17 to November 22, 2023, the UPRI-NOAH, in collaboration with the Caraga State University Department of Geology, organized a fieldwork to assess and further understand the mechanism of the disaster.

Mt. Minandar, the origin of the 2022 landslide caused by Severe Tropical Storm Paeng, that affected Sitio Tinabon, Barangay Kusiong, Maguindanao del Norte (left). Boulders found within the identified alluvial fan were measured for deposit analysis (right).

The researchers conducted geological fieldwork that included rock sampling, boulder measurements, and channel profiling. A drone survey was also conducted to create a Digital Elevation Model (DEM) of the landslides in Sitio Tinabon for deposit analysis. Additionally, the locals were interviewed about the timeline of events and previous disasters that affected their barangay. Kusiong was also among the hardest hit by the 1976 Moro Gulf earthquake that caused a tsunami which killed 5,000 to 8,000 individuals. Coincidentally, during the team’s fieldwork, a moderately strong ground shaking (approximately Intensity IV in the PHIVOLCS earthquake intensity scale) was felt in Brgy. Kusiong during the Magnitude 6.8 Offshore Davao Occidental earthquake on November 17, 2023 – demonstrating the seismicity within the region.

The researchers held an exit interview with the officials of Barangay Kusiong at their barangay hall, presenting the team’s initial findings based on their six-day fieldwork. These findings included the discussion of the geology of Mt. Minandar that influenced the occurrence of the landslide, the validation of the disaster timeline through interviews, and lastly the team’s recommendation with regards to sinkholes: houses along its axis should be relocated. For evacuation protocols, officials may consider monitoring the rainfall by installing a rain gauge in the area.

The residents of Kusiong fled their homes heading upstream to avoid the flooding; unfortunately, they were hit by a debris flow coming from the mountains. Multi-hazard approach should be employed as opposed to the more common single-hazard assessment which may communicate better the whole hazard situation. In the NOAH website, these landslides are identified and mapped.

The main channel where a fast-moving slurry of rocks, mud, and water flowed downstream from Mt. Minandar to Sitio Tinabon (left), the remnants of an elementary school partially buried in debris flow deposits (middle), and an 8-meter deep sinkhole that appeared coincident with the event (right).
Exit interview with the officials of Barangay Kusiong, Maguindanao del Norte.