by Paul Jaysent Fos, Romblon News/PR | Tuesday, 29 March 2016
Geoscientists from the Mines and Geosciences Bureau (MGB)-MIMAROPA recently validated the report of the Provincial Environment and Natural Resources Office (PENRO)-Romblon regarding the development of sinkhole along the active channel of Gabawan River in Bgy. Gabawan, Odiongan, Romblon. The bowl-like depression found on the riverbed of Gabawan was first observed on January 18, 2016 by small scale miners of sand and gravel operating in Sitio Bulwang. According to MGB-MIMAROPA geologists who inspected the site last January 26-27, 2016, the said depression had widened over time and has now an estimated diameter and depth of approximately 4.5 meter and of 1.7 meters, respectively. It is classified as a solution sinkhole formed on soluble bedrock that has thin or no overburden.
The subject sinkhole, which is now filled with water and river sediments appears to be the product of gradual dissolution of the underlying carbonate rock forming a natural depression at the surface. The fractures/joints observed on calcareous and tuffaceous sedimentary beds in the area serve as the conduits for the surface and subsurface waters to move through spaces resulting to dissolution of the soluble rock.
MGB-MIMAROPA investigating team explained that human activities, particularly sand and gravel quarry operation, may have triggered the development of sinkhole in Gabawan River. The excavation of stream sediments including the transport of extracted sand and gravel deposits, and removal of the overburden materials had exposed the underlying carbonate rocks to various forms of weathering.
Results of field assessment also showed that the condition of sinkhole has no imminent threat to the barangay. Its location is far from residential houses and existing infrastructures of Barangay Gabawan. Moreover, the sinkhole has only localized extent and appears only on the riverbed area with no signs of lateral propagation and deepening. Through time, the depression will be filled and sealed off with sediments.
In order to study the development of solution sinkholes in Bgy. Gabawan and its adjoining barangays, MGB MIMAROPA will pursue the conduct of ground subsidence/sinkhole mapping in areas covered by carbonate bedrock. This undertaking will utilize Ground Penetrating Radar (GPR) survey to detect solution cavities below the ground and to determine important indications of sinkhole and ground subsidence.
