Taal Volcano
From Wikipedia, the free encyclopedia.
| Taal Volcano | |
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 A cinder cone in an acidic lake on Taal Volcano |
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| Elevation: | 400 metres (1,312 feet) |
| Location: | Luzon, Philippines |
| Coordinates: | 14°0′7″ N 120°59′34″ E |
| Type: | Stratovolcano |
| Age of rock: | |
| Last eruption: | 1977 |
Taal Volcano is an active volcano on the island of Luzon in the Philippines. 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. Because of its eruptive history and location close to population centres, the volcano has been designated a Decade Volcano worthy of close study to prevent future natural disasters.
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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 Plate. 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, within which is another island.
Recent activity
There have been 33 recorded eruptions at Taal since 1572. 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. These generated base surges and cold pyroclastic flows, which travelled several kilometres across Lake Taal and devasted villages on the lake shore, killing several hundred people. The population of the island itself had been evacuated when the eruption began.
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
In light of its proximity to populated areas and violent eruptive history, Taal has been designated one of fifteen Decade Volcanoes, making at 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
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, 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
- 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
- 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
