Taal Volcano

Etymology

As of 1821, the Taal Volcano was also called Bombou.

Geography

Taal Volcano and Lake are wholly located in the province of Batangas. The northern half of Volcano Island falls under the jurisdiction of the lake shore town of Talisay, and the southern half to San Nicolas. The other communities that encircle Taal Lake include the cities of Tanauan and Lipa, and the municipalities of Talisay, Laurel, Agoncillo, Santa Teresita, Alitagtag, Cuenca, Balete and Mataas na Kahoy.

Permanent settlement on the island is prohibited by the Philippine Institute of Volcanology and Seismology or PHIVOLCS, declaring the whole Volcano Island as a high-risk area and a Permanent Danger Zone (PDZ). Despite the warnings, poor families have settled on the island, risking their lives, earning a living by fishing and farming crops from the rich volcanic soil.

Vulcan Point

The crater lake on Volcano Island is the largest lake on an island in a lake on an island in the world. Moreover, this lake contains Vulcan Point, a small rocky island that projects from the surface of the crater lake, which was the remnant of the old crater floor that is now surrounded by the 2-kilometre (1.2 mi) wide lake, now referred to as the Main Crater Lake. Vulcan Point is often cited as the largest third-order island (island in a lake on an island in a lake on an island) in the world, though this is also claimed to be an unnamed Canadian island located within Victoria Island.

Therefore, Taal has an island within a lake, that is on an island within a lake, that is on an island: Vulcan Point Island is within Main Crater Lake, which is on Volcano Island, which is within Taal Lake, which is on the main Philippine Island, Luzon.

Recent activity

Although the volcano has been quiet 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 pots and mud geysers on parts of the island. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) regularly issues notices and warnings about current activity at Taal, including ongoing seismic unrest.

2011

2010

2009

2008

Geological history

Taal Volcano is part of a chain of volcanoes along the western side of the edge of the island of Luzon, which were formed by the subduction of the Eurasian Plate underneath the Philippine Mobile Belt. Taal Lake lies within a 25–30 km (16–19 mi) caldera formed by explosive eruptions between 140,000 and 5,380 BP. Each of these eruptions created extensive ignimbrite deposits, reaching as far away as where Manila stands today.

Since the formation of the caldera, subsequent eruptions have created a volcanic island within the caldera known as Volcano Island. This 5-kilometre (3.1 mi) island covers an area of about 23 square kilometres (8.9 sq mi) with the center of the island occupied by the 2-kilometre (1.2 mi) Main Crater with a single crater lake formed from the 1911 eruption. The island consists of different overlapping cones and craters of which forty-seven have been identified. Twenty six (26) of these are tuff cones, five are cinder cones and four are maars. With its highest Elevation at only 311 m (1,020 ft), Taal is one of the lowest volcanoes in the world.

Eruption history

There have been 33 recorded eruptions at Taal since 1572. The first eruption of which there is any record occurred in 1572, the year the Augustinian friars founded the town of Taal on the shores of the lake (on what is now San Nicolas, Batangas). In 1591, another mild eruption took place featured by great masses of smoke issuing forth from the crater. From 1605 to 1611, the volcano displayed such great activity that Father Torna de Abreu had a huge cross of anubing wood erected on the brink of the crater.

Between 1707 and 1731, the center of activity shifted from the Main Crater to other parts of Volcano Island. The eruptions of 1707 and 1715 occurred in Binitiang Malaki crater (the cinder cone visible from Tagaytay City). Minor eruptions also emanated from the Binintiang Munti crater on the westernmost tip of the island in 1709 and 1729. A more violent event happened on September 24, 1716, when the whole southeastern portion of the crater (Calauit), opposite Mount Macolod, was blown out. The 1731 eruption off Pira-Piraso or eastern tip of the island created an island. No studies had been done to determine whether Napayon or Bubuin Island was formed in the eruption, or just a pumice raft.

Activity returned to the Main Crater in 1749, and it was remembered for being particularly violent (VEI = 4). Then came the great 200-day eruption of 1754, the greatest eruption of Taal which is described below.

Taal remained quiet for 54 years except for a minor eruption in 1790. Not until March 1808 did another big eruption occur. While this outbreak was not as violent as the one in 1754, the immediate vicinity was covered with ashes to a depth of 84 centimetres (33 in). It brought great changes in the interior of the crater, according to chroniclers of that time. "Before, the bottom looked very deep and seemed unfathomable, but at the bottom, a liquid mass was seen in continual ebullition. After the eruption, the crater had widened and the pond within it had been reduced to one-third and the rest of the crater floor was higher and dry enough to walk over it. The height of the crater walls has diminished and near the center of the new crater floor, a little hill that continually emitted smoke. On its sides were several wells, one of which was especially remarkable for its size."

On July 19, 1874, an eruption of gases and ashes killed all the livestock on the island. From November 12–15, 1878, ashes ejected by the volcano covered the entire island. Another eruption took place in 1904 as a result of which a new outlet was formed in the southeastern wall of the principal crater. The Last eruption from the Main Crater was in 1911 which obliterated the crater floor creating the present lake. In 1965, a huge explosion sliced off a huge part of the island, moving activity to a new eruption center, Mount Tabaro. Eruptions have also been recorded in 1634, 1635, 1641, 1645, 1790, 1825, 1842, 1873, 1885, 1903, 1966, 1967, 1968, 1969, 1970, 1976 and 1977. Some of the major eruptions are described below:

The 1754 eruption

Taal Volcano's greatest recorded eruption occurred in 1754 which lasted from May 15 to December 1. The following is the narrative account of Fr. Buencuchillo, parish priest of Sala, and stationed at Taal at that time:

1911 eruption

One of the more devastating eruptions occurred in January, 1911. During the night of the 27th of that month, the seismographs at the Manila Observatory commenced to register frequent disturbances, which were at first of insignificant importance, but increased rapidly in frequency and intensity. The total recorded shocks on that day numbered 26. During the 28th there were recorded 217 distinct shocks, of which 135 were microseismic, while 10 were quite severe. The frequent and increasingly strong earthquakes caused much alarm at Manila, but the observatory staff was soon able to locate their epicenter in the region of Taal Volcano and assured the public that Manila was in no danger, as Taal is distant from it some 37 miles (60 km).

In Manila in the early hours of January 30, 1911, people were awakened out of their sleep by what they at first took for loud thunder. The illusion was heightened when great streaks of lightning were seen to illumine the southern sky. Those who investigated further, however, soon learned the truth. A huge, fan-shaped cloud of what looked like black smoke rose to a great height. It was crossed and crisscrossed with a brilliant electrical display, which the people of Manila at first took for lightning. This cloud finally shot up in the air, spread, then dissipated, and this marked the culmination of the eruption, at about 2:30 a. m.

On Volcano island, the destruction was complete. It seems that when the black, fan-shaped cloud spread, it created a blast downward that forced hot steam and gases down the slopes of the crater, accompanied by a shower of hot mud and sand. Many trees had the bark shredded and cut away from the surface by the hot sand and mud blast that accompanied the explosion and contributed so much to the loss of life and destruction of property. The fact that practically all the vegetation was bent downward, away from the crater, proved that there must have been a very strong blast down the outside slopes of the cone. Very little vegetation was actually burned or even scorched. Six hours after the explosion, dust from the crater was noticeable in Manila as it settled on furniture and other polished surfaces. The solid matter ejected had a volume of between seventy million and eighty million cubic metres (2.5×10⁹ and 2.8×10⁹ cubic feet) (VEI = 3.7). Ashes fell over an area of 2,000 square kilometres (770 square miles), although the area in which actual destruction took place measured only 230 square kilometres (89 sq mi). The detonation from the explosion was heard over an area more than 600 miles (970 km) in diameter.

Death toll

The eruption claimed a reported 1,335 lives and injured 199; although it is known that more perished than the official records show. The seven barangays that existed on the island previous to the eruption were completely wiped out. Post mortem examination of the victims seemed to show that practically all had died of scalding by hot steam or hot mud, or both. The devastating effects of the blast reached the west shore of the lake where a number of villages were also destroyed. Cattle to the number of 702 were killed and 543 nipa houses destroyed. Crops suffered from the deposit of ashes that fell to a depth of almost half an inch in places near the shore of the lake.

Observations on the Volcano Island after the eruption

Volcano Island sank from three to ten feet as a result of the eruption. It was also found that the southern shore of Lake Taal sank in elevation from the eruption. No evidences of lava could be discovered anywhere, nor have geologists been able to trace any visible records of a lava flow having occurred at any time on the volcano back then. Another peculiarity of the geologic aspects of Taal is the fact that no sulphur has been found on the volcano. The yellow deposits and encrustations noticeable in the crater and its vicinity are iron salts, according to chemical analysis. Slight smell of sulfur was perceptible at the volcano, which came from the gases that escape from the crater.

Changes on the crater after the eruption

Great changes took place in the crater after the eruption. Before 1911, the crater floor was higher than Taal lake and had several separate openings in which were lakes of different colors. There was a green lake, a yellow lake, a red lake and some holes filled with hot water from which steam issued. Many places were covered with a shaky crust of volcanic material, full of crevices, which was always hot and on which it was rather dangerous to walk. Immediately after the explosion, the vari-colored lakes had disappeared and in their place was one large lake, about ten feet below the level of the lake surrounding the island. The crater lake gradually rose until it is on a level with the water in Taal Lake. Opinions after the creation of the lake that the presence of the water in the crater has a tendency to cool off the material below and thus lessen the chances of an explosion or make the volcano extinct, but the preponderance of expert opinion was otherwise.(The subsequent eruption in 1965 and succeeding activities came from a new eruptive center, Mount Tabaro.)

Ten years after the eruption, no changes in the general outline of the island could be discerned at a distance. On the island, however, many changes were noted. The vegetation had increased; great stretches that were formerly barren and covered with white ashes and cinders became covered with vegetation.

1965 to 1977 eruption

The most recent period of activity lasted from 1965 to 1977 with the area of activity concentrated in the vicinity of Mount Tabaro. The 1965 eruption was classified as phreatomagmatic, generated by the interaction of magma with the lake water that produced the violent explosion that cut an embayment on Volcano Island. The eruption generated "cold" base surges which traveled several kilometers across Lake Taal, devastating villages on the lake shore and, killing about a hundred people. That eruption, in particular, led to the recognition of base surge (one of the American geologists who witnessed an atomic bomb explosion as a soldier and visited the volcano shortly after the 1965 eruption, compared it to an atomic base surge) as a process in volcanic eruption, which are now called pyroclastic surges when relating to volcanoes. The population of the island was evacuated only after the onset of the eruption. Precursory signs were not interpreted correctly until after the eruption.

After nine months of repose, Taal reactivated on July 5, 1966 with another phreatomagmatic eruption from Mount Tabaro, followed by another similar eruption on August 16, 1967. The Strombolian eruptions which started five months after on January 31, 1968 produced the first historical lava fountaining witnessed from Taal. Another strombolian eruption followed a year later on October 29, 1969. The massive flows from the two eruptions eventually covered the bay created by the 1965 eruption, reaching the shore of Lake Taal. The last major activities on the volcano were the phreatic eruptions of 1976 and 1977.

Eruption precursors at Taal

Other possible precursors

Volcanologists measuring the concentration of radon gas in the soil on Volcano 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 the magnitude 7.1 Mindoro earthquake on November 15, centered about 50 kilometres (31 miles) 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.