Taal as seen in 1856

LATEST NEWS: TAAL Volcano is getting restive again, spewing 6-meter high geysers of mud and boiling water since Feb. 18, 1999. Reports of contiuned activity were issued in early August. -- more


CONTENTS
[Taal vent system]
[volcanic hazards]
[Taal Workshop 1995]
[virtual fieldtrip]

History
[19th cent. German travelers on Taal]
[pre-1911 eruptions by S. Maso]
[Eruptions 1965-1977]
[References] - [Links]
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.

Location

part of Taal map of Saderra Maso, 1911,
click on map for enlargement (98kB)
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.

Taal as the Decade Volcano for the Philippines Thirty three eruptions have been recorded since 1572 at Taal, mostly on Volcano Island. The impacts of these eruptions were largely confined to the intracaldera area. Occasional violent activity, however, such as the 1754 plinian eruption, affected the entire region, including what is now the Metro Manila area with fallout. Some activity, such as the 1749 eruption, were accompanied by crustal disturbance and strong earthquakes, which generated ground fissures and pronounced subsidence that extended across Taal lake.

The caldera has a long, but little known history of catastrophic explosive volcanism affecting much larger areas, including the Metro Manila area. The eruptions, one to two orders of magnitude larger and more devastating than those of Mount Pinatubo, have deposited massive ignimbrites, including the deposits of turbulent pyroclastic flows, and widespread tephra fall units in recent geologic time. Accompanying this volcanism has been extensive volcaniclastic sedimentation, dominated by deposition of hyperconcentrated streamflows and lahars in low-lying subaerial and shallow marine environments.

The Philippine Institute of Volcanology and Seismology's (PHIVOLCS) choice of a Decade Volcano from among the 200 volcanoes in the Philippines rests on Taal's obvious and dangerous attributes:

  • frequent activity
  • greatest number of elements at risk,
  • high population density of the region
  • complicated and little understood volcanology
  • excellent accessibility.

In addition, quite recently, the Philippine Government designated the region as a favored site for setting up new industries and infrastructures, hence, there is a need for detailed knowledge of potential hazards.

Thus, although momentarily sidelined by events at Pinatubo, the rationale for Taal as a Decade Volcano remains unperturbed even with the occurrence of one of this century's largest eruptions some 140 km NNW of Taal.


Taal Vent system

1976 crater

Looking into the 1976 crater, which exposes the 1968/69 plug
Taal caldera is envisaged as being composed of two adjacent calderas in a SW-NE striking graben setting largely controlled by the intersection of regional structures. Gravity profiles exhibit a high plateau-shaped anomaly, modeled as a graben structure underlain by a thick dense igneous intrusion (Yokoyama et al., 1975). Fault bounded caldera walls are more pronounced on the north rim, forming the Tagaytay Ridge with 600 m relief.

Taal is not a strato-cone, but has a low profile, pre-caldera construction topography, now blanketed by ignimbrite sheets. Taal lake has been the site of major eruptions of an unusual type of ignimbrite of andesitic composition, previously referred to as base surges (Geronimo, 1988).


Volcanic hazards


Rick measuring the lake temperture

Ricardo Seda of PhiVolcs measuring the water temperature of Lake Taal
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.


Taal Workshop Oktober 1995 During the Taal Workshop held at Tagaytay, on the caldera's rim, a number of major questions were identified [modified from Summary Report, compiled by R.Torres]:
  1. What is the overall structure of Taal Volcano?
    • Is Taal activity still related to subduction along the Manila Trench?
    • Does a large body of magma exist a depth and affect the stress field inside the caldera?
    • What is the influence of regional tectonic structures and activity to volcanic activity?
    • What is the current caldera structure and volcano feeder system?
  2. What is likely to happen next at Taal and how can we anticipate it?
    • What are the likely precursors for renewed activity?
    • How do eruptions proceed and when do we say that the activity is over?
    • Are improvements and refinements necessary for existing hazard maps? If so, what is required?
  3. Is Taal still capable of producing caldera-forming eruptions?
    • What types of caldera-forming eruptions happened in the past?
    • What was their magnitude (volumes of erupted material, areal extent of deposits)?
  4. What are the weak links in the disaster mitigation chain?
    • What types of information are required?
    • How and to whom is information to be diseminated?

As a consequence of the review of current knowledge of the volcano and identified information gaps, a number of projects were identified, that would be desirable:

Hazard Mitigation

  • Integration of volcanic hazards in the school curiculum
  • Regular training for local officials including field exposure tours, drills, skills
  • Brochures and popular science materials

Monitoring

  • Ground deformation
thin section photograph of Taal lava

Thin section of Lava showing phenocrysts of partially oxidized olivine (ol), clinopyroxene (px) mantled by olivine and plagioclase (pl).
Geology/Petrology
  • Establish a chronology of eruptions at Taal
  • Determine the seismic structure underneath Taal caldera and vicinity
  • Improve current knowledge of magma geochemistry and petrology
  • Active fault mapping (compilation of historical accounts, remote sensing etc.)



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