Taal Volcano

Taal Volcano

Map showing major volcanoes of the Philippines

Taal Volcano is an active volcano on the island of Luzon in the Philippines. This is located in Talisay and San Nicolas in Batangas. It consists of an island in Lake Taal, which is situated within a caldera formed by an earlier very large eruption. It is about 50 km from the capital, Manila.

The volcano has erupted violently several times, causing loss of life in the populated areas surrounding the lake, the current death toll standing at around 5,000 - 6,000. Because of its proximity to populated areas and eruptive history, the volcano has been designated a Decade Volcano worthy of close study to prevent future natural disasters.

Geological history

Taal Volcano is part of a chain of volcanoes along the western side of the island of Luzon, all formed by the subduction of the Eurasian Plate underneath the Philippine Mobile Belt. Taal Lake lies within a 25–30 km caldera formed in four giant explosive eruptions between 500,000 and 100,000 years ago. Each of these eruptions created extensive ignimbrite deposits, reaching as far away as where Manila stands today.

Since the caldera formation, subsequent eruptions have built up the current Taal Volcano, on an island known as Volcano Island in the lake. This island covers an area of about 23 km², and is made up of overlapping cones and craters from many different eruption episodes. 47 cones and craters have been identified on the island. Volcano island contains a lake about 2km across, called Crater Lake, within which is another island.

Recent activity

Taal Lake and Taal Volcano taken from a boat.

Taal volcano's crater lake (in 2005)

There have been 33 recorded eruptions at Taal since 1572. A very devastating eruption occurred in 1911, which claimed more than a thousand lives. The deposits of that eruption is yellowish, fairly decomposed (non-juvenile) tephra with a high sulfur content.

The most recent period of activity lasted from 1965 to 1977, and was characterised by the interaction of magma with lake water, producing violent phreatic explosions. In particular, the 1965 eruption led to the recognition of base surge as a common process in volcanic eruption (due to the fact that one of the American geologists, who visited the volcano shortly after the 1965 eruption, had to witness an atomic bomb explosion when he was a soldier). The eruption generated base surges and cold pyroclastic flows, which travelled several kilometres across Lake Taal and devastated villages on the lake shore, killing some hundred people. The population of the island itself was evacuated only after the onset of the eruption. Precursory signs were interpreted correctly only after the eruption. Eruptions in 1968 and 1969 were characterized partly by Strombolian activity and produced a major lava flow that reached the shore of lake Taal. The 1977 eruption produced only a very minor cinder cone within the main crater.

A cinder cone in an acidic lake on Taal Volcano

Although the volcano has been dormant since 1977, it has shown signs of unrest since 1991, with strong seismic activity and ground fracturing events, as well as the formation of small mud geysers on parts of the island.

Eruption precursors at Taal

Taal Caldera 2005

In light of its proximity to populated areas and violent eruptive history, Taal has been designated one of sixteen Decade Volcanoes, making it a focus for research efforts and disaster mitigation plans. While seismic activity is a common precursor to eruptive activity, another useful indicator at Taal is the temperature of Lake Taal. Before the 1965 eruption began, the lake's temperature rose to several degrees above normal. However, the lake's temperature does not always rise before an eruption. Before some eruptions, the dissolution of acidic volcanic gases into the lake has resulted in the death of large numbers of fish.

Earthquake precursors in the Taal region

Satellite image showing Taal Lake with Volcano island within it

An interesting observation on Volcano Island was made in 1994. Volcanologists measuring the concentration of radon gas in the soil on the island measured an anomalous increase of the radon concentration by a factor of six in October 1994. This increase was followed 22 days later by a magnitude 7.1 earthquake on November 15, centred about 50 km south of Taal, off the coast of Luzon.

A typhoon had passed through the area a few days before the radon spike was measured, but when Typhoon Angela, one of the most powerful to strike the area in ten years, crossed Luzon on almost the same track a year later, no radon spike was measured. Therefore, typhoons were ruled out as the cause, and there is strong evidence that the radon originated in the stress accumulation preceding the earthquake.

References

1. Lowry A.R., Hamburger M.W., Meertens C.M., Ramos E.G. (2001), GPS monitoring of crustal deformation at Taal Volcano, Journal of Volcanology and Geothermal Research, v.105, p.35-47
2. Richon P., Sabroux J.-C., Halbwachs M., Vandemeulebrouck J., Poussielgue N., Tabbagh J., Punongbayan R. (2003), Radon anomaly in the soil of Taal volcano, the Philippines: A likely precursor of the M 7.1 Mindoro earthquake (1994), Geophysical Research Letters, Volume 30, Issue 9, pp. 34-1

External links

• Taal Volcano satellite image on Google Maps
• Information from PHIVOLCS
• VolcanoWorld page about Taal
• Global Volcanism Program information
• A home page for Taal from the Aachen University, containing historical accounts and a virtual excursion to volcano island