Senior Geologist, Maria Celi V. Kennedy of the Geosciences Division conducted a geological investigation in response to the request made by the local government of Calamba City last June 3, 2014 concerning the appearance of a sinkhole located at Barangay Makiling, Calamba City. The situation had been considered as immediate concern. Ms. Kennedy was accompanied by local officials of Calamba City, Laguna headed by Barangay Chairman Atty. Soliman Lajara. Reportedly, the sinkhole is adjacent to Makiling Day Care Center
Location of the collapsed ground relative to the green building – Makiling Day Care Center. The cavity is less than a meter away from the concrete fence (blue structure). It is temporarily covered on all sides with wooden planks to deter anyone accesss to the danger zone. 14° 09′ 14″ N; 121° 08′ 15″ E
The observation in the area disclosed that the sinkhole has an opening of 3 × 2 meters and a depth of roughly 8 meters. The area is underlain by Taal Tuff, as confirmed on the unpublished geologic map of MGB. There are no geological structures such as fault or jointing in the area. Several creeks and tributaries drain the area, the biggest is the Siam-Siam River which drains to the east on Laguna de Bay. The topography of the area is relatively flat and the soil is predominantly sandy. There are localized ponding of water roughly 150 meters from the area. During the investigation it was found that an extension of the Makiling High School is constructed approximately 50 meters from the sinkhole. The residents stated that there are also water pumps installed in the vicinity of the area.
Other than earthquake and tectonic movement, collapse may be a result of natural phenomenon or human activities. It is recommended that an advanced geotechnical study be conducted to further understand the cause of the collapse. Meanwhile, the natural opening poses danger to the people, especially to the children attending the Makiling Day Care Center. It is highly recommended that the said opening be isolated by fence to avoid access in the area and DANGER ZONE signages be posted until safety measures by a structural engineer is implemented. Since the area is in the vicinity of inactive Mt. Makiling, assistance from the DOST-PHIVOLCS could be advantageous. Further studies for the adjacent areas that will undergo land development should give emphasis on geotechnical data and the inclusion of geological hazard assessment.