10 April 2017
Cebu City government were told to evacuate the families and relocate the structures within the “active” landslide area and encouraged the public to help revegetate the mountains of barangay Sirao.
The recurring landslide in sitios Langub and Tawagan is due to the complex mass movement in barangay Sirao caused by the remobilization of old landslide materials and overly saturated ground especially during rainfall.
Apart from the ten houses that were reported by the Cebu City Disaster Risk Reduction Management Office (CCDRRMO), the team from the Mines and Geosciences Bureau – Central Office (MGB-CO) indicated 40 more houses and structures that are along the path of the debris flow including the barangay hall and gym.
During the assessment conducted last March, a team of geologists led by Liza Socorro J. Manzano said that the tension cracks were striking and are progressing laterally and vertically in sitio Tawagan and in the slope of the Sirao Flower Garden. They have also observed several ground depression, sinkholes, and fractured cave systems that indicate active subsidence hazard.
The team found 22 sinkholes within Mt. Kan-irag, Mt. Pung-ol and Mt. Balisong with a depth ranging from 0.5 meter to three meters and a diameter of 0.5 to 250 meters.
The continuous movement or spalling-off of lose soil and rock materials from the slopes of Mt. Kan-irag is caused by its highly-fractured rocks and highly-weathered soil characteristics.
MGB gave a copy of an updated geohazard map to the Cebu City government and recommended for an immediate relocation of families within the identified critical areas and discouraged permanent habitation.
Active monitoring was also recommended in zones adjacent to the critical area.
Manzano also recommended that an evacuation protocol and plan should be established and residents must be made aware of the geohazard in their locality.
Construction of high-rise buildings are also discouraged along unstable slope and subsiding ground.
Areas declared as highly susceptible to subsidence and landslide should be free from permanent habitation. These areas may be designated for agro-forestry and other uses deemed appropriate by other agencies.
The phenomenon affecting barangay Sirao for three decades is a complex type of mass movement, a combination of subsidence and hillslope debris flows and may occur anytime.