The Philippines is home to a significant number of volcanoes, making it one of the most volcanically active nations globally. The archipelago contains approximately 300 volcanoes, 24 of which are officially monitored as active by the Philippine Institute of Volcanology and Seismology (PHIVOLCS). This high concentration of volcanic activity stems directly from the country’s unique position along the Pacific Ring of Fire.
The Geological Reason for Volcanic Activity
The intense geological activity in the Philippines results from its location along the Pacific Ring of Fire, a vast zone of frequent earthquakes and volcanic eruptions. This region is characterized by the convergence of several major tectonic plates. The Philippine archipelago is situated at the complex boundary where the oceanic Philippine Sea Plate meets the continental Eurasian Plate.
The denser Philippine Sea Plate is forced to slide beneath the lighter Eurasian Plate in a process known as subduction. This downward movement occurs along deep oceanic features, such as the Philippine Trench to the east and the Manila Trench to the west. As the subducting plate descends, the immense pressure and heat cause the water trapped within its rock structure to be released.
This released water significantly lowers the melting point of the surrounding mantle rock, generating molten material known as magma. Because magma is less dense than the solid rock around it, it begins a slow ascent toward the surface. The rising magma eventually breaches the crust, forming the chains of volcanoes that define the Philippine landscape.
Classifying Active and Dormant Volcanoes
Volcanoes in the Philippines are formally classified by PHIVOLCS based on their eruptive history. An Active Volcano is defined as one that has erupted within historical times (documented accounts) or within the last 10,000 years (the Holocene period). The classification also applies if a volcano shows signs of magmatic unrest, such as seismic activity and ground deformation, even without a recent eruption.
Dormant and Extinct generally refer to volcanoes that have not erupted within the Holocene period. A dormant volcano has the potential to erupt again, while an extinct one is considered unlikely to become active again. However, the distinction is difficult, as the 1991 eruption of Mount Pinatubo occurred after centuries of quiescence, demonstrating that a long period of inactivity does not guarantee safety.
Mayon Volcano in Albay is the country’s most active volcano, possessing a near-perfect conical shape resulting from its frequent eruptions. It has had over 50 documented eruptions since 1616, often exhibiting Strombolian activity and pyroclastic flows.
Taal Volcano, located in Batangas, is the second most active, situated within a large caldera filled by Taal Lake. Its eruptions, including a significant one in January 2020, are often highly explosive due to magma interacting with the lake water.
Kanlaon Volcano on Negros Island is the most active in the central Philippines, experiencing at least 30 recorded eruptions, mostly mild ash emissions. Bulusan Volcano in Sorsogon is also frequently active, known for sudden, steam-driven explosions called phreatic blasts.
How Volcanic Activity is Monitored
PHIVOLCS is the government agency responsible for the continuous surveillance of the nation’s volcanoes. Monitoring is carried out using a variety of specialized instruments designed to detect subtle changes in the volcano’s state. A network of seismographs records volcanic earthquakes, which often increase in frequency and intensity as magma moves beneath the surface.
Another method is the measurement of ground deformation, which tracks the swelling or inflation of the volcano’s edifice as magma accumulates inside. This is often done using GPS stations and tiltmeters that measure slight changes in the ground slope. Scientists also analyze gas emissions, specifically tracking the output of sulfur dioxide (SO2), since an increase in gas release can signal magma rising close to the surface.
PHIVOLCS communicates the status of a volcano through a standardized Alert Level System ranging from Level 0 to Level 5. Level 0 signifies quiet, background activity with no eruption foreseen. Level 1 indicates low-level unrest, where activity is slightly above the norm but an eruption is not imminent.
A rise to Alert Level 3 means that magma is close to or at the crater, suggesting an eruption is possible within days or weeks, requiring pre-emptive evacuation of high-risk zones. The highest designation, Alert Level 5, indicates that a hazardous eruption is already in progress, characterized by events like lava fountaining, base surges, or extensive lava flows.