Explained: Why eruption of a tiny, ‘complex’ volcano is causing concern

Taal is currently at alert level 4, which means that a “hazardous eruption” could be imminent within a few hours to a few days. (Photo: AP)

In the Philippines, a volcano called Taal on the island of Luzon, 50 km from Manila, erupted on Sunday (January 12), spewing lava on the ground, and ash and smoke into the sky. Although Taal is a tiny volcano, the eruption has caused concerns in the Philippines. There are several reasons:

A complex volcano

Taal is classified as a “complex” volcano by the Philippine Institute of Volcanology and Seismology (PHIVOLCS). A complex volcano, also called a compound volcano, is defined as one that consists of a complex of two or more vents, or a volcano that has an associated volcanic dome, either in its crater or on its flanks. Examples include Vesuvius, besides Taal.

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The Taal volcano does not rise from the ground as a distinct, singular dome but consists of multiple stratovolcanoes (volcanoes susceptible to explosive eruptions), conical hills and craters of all shapes and sizes, as per NASA’s Earth Observatory. Taal has 47 craters and four maars (a broad shallow crater).

Unpredictability

Taal has erupted more than 30 times in the last few centuries. Its last eruption was on October 3, 1977. An eruption in 1965 was considered particularly catastrophic, marked by the falling of rock fragments and ashfall. Before that, there was a “very violent” eruption in 1911 from the main crater. The 1911 eruption lasted for three days, while one in 1754 lasted for seven months.
Because it is a complex volcano with various features, the kinds of eruption too have been varied. An eruption can send lava flowing through the ground, or cause a threat through ash in the air.

Location

Taal’s closeness to Manila puts lives at stake. The BBC quoted James White, head of geology at the University of Otago, as saying: “Metro Manila is a few tens of kilometres away with a population of over 10 million, and there are multiple cities within 30 km that have more than 100,000 people in each, not counting the smaller towns in between.”

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Since the events of Sunday, thousands living on the island have been fleeing their homes.

The volcano is currently at alert level 4, which means that a “hazardous eruption” could be imminent within a few hours to a few days. Hazardous eruptions are characterised by intense unrest, continuing seismic swarms and low-frequency earthquakes. Because the country is situated at the boundaries of two tectonic plates — the Philippines Sea Plate and the Eurasian plate — it is particularly susceptible to earthquakes and volcanism.