Quezon City, Metro Manila – The Mines and Geosciences Bureau (MGB), as spearheaded by the Lands Geological Survey Division (LGSD), has recently launched an pioneering web application that seeks to automate preliminary sinkhole detection as a tool to support the Bureau’s karst subsidence susceptibility mapping, especially during post-disaster geohazards assessments. The application, that is currently being tested in the Central Visayas region, integrates manual digitization and automated geospatial analysis of available satellite data.
The manual digitization component entails the identification of sinkholes using the 1:50,000-scale Topographic Maps of the National Mapping and Resource Information Authority (NAMRIA) to establish a baseline and facilitate cross-referencing with the results of automated analyses. Meanwhile, the automated process analyzes available Digital Elevation Models (DEMs) and satellite images to delineate potential sinkholes and detect ground movement through changes in topography as well as ground deformation. The workflow established to generate preliminary sink depth maps for MGB’s karst subsidence susceptibility assessment are used as reference.
The outputs generated are initially screened to filter out non-geological anomalies (e.g., man-made features) and are further evaluated by MGB Geologists during field validation. This application is seen to reduce the processing time for initial sinkhole detection during emergency hazard assessments and, consequently, aid in a more efficient mapping of karst subsidence due to sinkhole collapse.
MGB’s karst subsidence hazard assessment and mapping is an on-going activity that was launched after the 2013 Bohol Earthquake exposed several sinkholes in southwestern Bohol. Currently, the MGB produces karst subsidence hazard susceptibility maps based on remote sensing and interpretation of available DEMs, establishment of a sinkhole inventory through field geological and geomorphological assessments, spatial analysis, and supplemented by geophysical survey using Ground Penetrating Radar (GPR). Various studies and initiatives led by the MGB have been and are being undertaken to further enhance its mapping methodology.
