A 7.8-magnitude earthquake that struck off the southern Philippines earlier this week has dramatically reshaped stretches of coastline, raising the seabed by as much as two metres and exposing vast areas of coral reef and seagrass beds to open air — killing the marine life within them. The quake, which hit near the Cotabato trench off the coast of southern Mindanao island, has killed at least 61 people, with around 40 still missing, according to the country's disaster management agency.

The Philippine Institute of Volcanology and Seismology confirmed that a shift in the Cotabato trench — a deep underwater fault system that runs as close as 50 kilometres from Mindanao's southern shore and is a well-known zone of frequent seismic activity — pushed sections of the seabed upward, extending shorelines by as much as 200 metres in some areas. The country's environment department, which dispatched survey teams to the affected provinces of Sarangani and Davao Occidental, said long stretches of reef and seagrass habitat had been lifted clear of the water. Photographs from the department's regional office showed wide expanses of exposed coral, with dead fish, eels, clams, and other reef organisms scattered across the newly emerged surface.

Residents in affected coastal communities were the first to notice the changes, raising alarms two days after the quake — initially out of concern that fumes from decomposing sea life could pose a health risk. Officials acknowledged that the full extent of the ecological damage remains difficult to determine, given the scale of the affected coastline and the logistical challenges of conducting a comprehensive survey.

The phenomenon, known as coastal uplift, is a recognised consequence of major seismic events along subduction zones and thrust faults, where one section of Earth's crust is forced upward relative to another. The Cotabato trench, which had already recorded a swarm of thousands of small earthquakes earlier this year, sits within one of the most seismically active regions in Southeast Asia.

The environmental toll underscores the dual nature of powerful earthquakes in coastal zones: beyond the immediate human casualties and structural damage, they can permanently alter marine ecosystems that local fishing communities depend upon. Coral reefs, which take decades to form, cannot survive prolonged exposure to air. Authorities have not yet provided a timeline for ecological assessment or recovery efforts, but the scale of the uplift suggests that significant portions of the affected reef may be beyond recovery.