Formation of Sinkholes

The #NationalMuseumPH is one with the nation in the observance of a month-long National Disaster Consciousness Month (NDCM) this July. 

This year’s theme “Sambayanang Pilipino, Nagkakaisa tungo sa Katatagan at Maunlad na Kinabukasan” advocates for unity towards resilience and sustainable development. For today’s #DignayanBiyernes feature, let us talk about a landform that can have devastating consequences when triggered for collapsed – sinkholes.

Sinkholes are cavities in the ground that are common in areas underlain by limestone and other rocks that can naturally be dissolved by percolating groundwater. When rainfall interacts with the atmosphere, and as well as when it seeps through the soil, it absorbs carbon dioxide creating slightly acidic water. This acidic water moves through the voids and cracks underground, slowly dissolving the limestone and creating a network of cavities. Over thousands of years, these cavities become larger forming cave systems.

Sinkholes are formed when the land above collapses or sinks into these cavities or when the surface materials are carried down into the cavities. Many natural sinkholes cannot be prevented. The land usually stays intact for a while until the cavities get too big. If there is not enough support for the overlying land, then a sudden collapse usually happens.

The October 2013, 7.2 magnitude earthquake in Bohol triggered the collapse of close to 100 sinkholes on the island. Following this event, the Mines and Geosciences Bureau (MGB) expanded its geohazard assessment mapping to include subsidence susceptibility assessment due to sinkhole collapse in areas underlain by limestone.

Sinkhole collapse is unpredictable and rarely happens, but when it does, may lead to damages to infrastructure, cause high economic losses, evacuation, and displacement of residents, and loss of lives.

Text and image by the NMP Geology and Paleontology Division

© 2022 National Museum of the Philippines