A powerful earthquake that struck the Philippines this week, killing at least 61 people, has lifted the seabed by as much as 2 metres (6.6 feet), exposing coral and harming marine life, according to the country's environment department.
Coastal Uplift Phenomenon
Residents first reported the geological phenomenon known as “coastal uplift” two days after the quake, which extended the shoreline by up to 200 metres in some areas, the department said on Sunday. The 7.8-magnitude earthquake off southern Mindanao island on Monday also left at least 40 people missing, based on updated figures from the disaster agency.
The Philippine Institute of Volcanology and Seismology explained that a shift in the Cotabato trench “pushed upward part of the coastlines of Sarangani and Davao Occidental provinces … exposing the bottom of the sea that was originally submerged.” The mapped uplift measured approximately 2 metres.
Environmental Impact
A team dispatched to the area discovered “long stretches of shoreline, coral reef and seagrass beds have been exposed,” the environment department said. Images from the department's regional office showed large areas of exposed coral with dead fish and other aquatic life on top. The department noted that “these exposed corals and seagrass beds had begun dying off alongside their resident organisms such as reef fishes, eels, clams, and shells.”
An official who spoke to Agence France-Presse on Sunday said they could not yet determine the exact extent of the affected area due to the size required for a full survey. Residents initially reported the seabed changes out of concern that they might be poisoned by fumes from decaying sea life.
Seismic Activity Context
The Cotabato trench, located as close as 50 kilometres (31 miles) off the coast of southern Mindanao, is prone to frequent seismic activity, including a “swarm” of thousands of mostly small earthquakes recorded in January.
