Saturday, February 2, 2008

Taal Volcano

Taal Volcano is located on the island Luzon, south of the Philippines' captial Manila. It has been selected as one of 15 Decade Volcanoes. There is currently no Taal-homepage by the Philippine Institute of Volcanology and Seismology's (PHIVOLCS), hence this is only an unofficial home-page (PhiVolcs' "blessing" is indicated by a link from the PhiVolcs-www-page to this site). Aside from information on Taal, this site provides information on and translations of 19th century work of German/Austrain scientists travelling the Philippines and exerpts from the famous work of Fr. Saderra Maso, who summarized the pre-1911 activity on the basis of historical ("hard-to-get-to") accounts.

Taal Volcano is located about 60 km SSE of Metro Manila, the capital of the Philippines. It is a complex volcanic system composed of a small volcanic island (Volcano Island), which has been the site of almost all historic activity, located within a 20x30 km lake-filled complex caldera(?) (Taal Lake, in older texts also called Lake Bonbon), one of the great volcano-tectonic depressions of the world.

The whole region surrounding Taal is at considerable volcanic risk. Taal Volcano is situated in a highly populated and rapidly growing agricultural and industrial region. Five towns are located around the lakeshore and 2 cities and 8 more towns are lined up along the caldera rim. Two large power stations are located 15 km and 17 km, respectively, from Taal Lake.

The geologic setting of Taal, and the variability of eruption sites and magnitudes, generates a diverse range of volcanic hazards, such as base surges, lava flows, ballistic fallout, ash and scoria fallout, toxic gases, acidic flashes from crater lake, lake tsunamis and seiches, lakeshore flooding, earthquakes, ground fissuring and subsidence, landslides and sectoral collapse, turbulent ashflows, and lahars.

Base surges were first documented during an eruption at Taal in 1965 (Moore et al., 1966). This particular hazard is the notorious cause of deaths and destructions both on Volcano Island and in lakeshore areas as surges can propagate over the lake without significant reduction in force.

Base surge eruptions in 1911 and 1965 blasted the villages to the west of the vent at Volcano Island, travelling 3 km across Lake Taal. In contrast, the aa lava flows erupted in 1968 and 1969 were confined within the embayment created by the 1965 eruption in the SW flank of Volcano Island and, apparently, did not pose a significant threat at that time. However, lava flows could be a serious hazard at Taal if erupted from a lakeshore vent and accompanied by violent hydrovolcanic explosions resulting from lava-lakewater interaction. The presence of a scoria cone at Boot, located east of Volcano Island, also suggests that eruptions along lakeshore areas are highly probable, although without historical precedence.

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