Catastrophic flood hazards from crater lakes: Parker and Pinatubo volcanoes, Philippines

Abstract only.In a span of seven years, three catastrophic flood events ensued from the breakout of two crater lakes: two from Maughan Lake, the crater lake of Parker volcano, and one from Pinatubo volcano. The mechanisms of the three lake-breakouts differ significantly from each other. In September 1995, about 30 million m3 of water was suddenly released from Maughan Lake, resulting in large life and property losses. The breakout, which lowered the lake level by 10 m, was caused by the sudden removal of the material that had been damming the lake at its outlet along the Gao Creek. How the dam material was removed remains the subject of a criminal investigation. A result of the 1995 breakout was the destabilization of the slopes along the Gao Creek, which resulted in several large landslides that dammed the lake outlet anew. By January 1997, Maughan Lake had risen by more than 8 m, equivalent to an additional 24 million m3 of water. Maughan Lake broke out again in March 2002, hours after a M6.8 earthquake occurred offshore southwest of Cotabato City. The lake level was lowered by more than 9 m, and the total volume of water released was about 27 million m3. The debris flows and floods resulting from the breakout emplaced deposits that could be traced to at least 80 km along the Gao-Alah River. The breakout is believed to have been caused by the progressive weakening of the landslide dam due to the earthquakes, and/or to seiches that may have been produced along the blocked Gao Creek. The lake-breakout scenario at Pinatubo was anticipated as early as 1998, with the lake rising at ~10 m per year. Judging from the loose emplacement and low density of the uppermost layers of the deposits at the Maraunot Notch (the lowest part of the crater rim), Philippine Institute of Volcanology and Seismology (PHIVOLCS) and United States Geological Service (USGS) scientists predicted a potentially large lake-breakout lahar event that might inundate the town of Botolan, Zambales. In September 2001, while the lake was still 5 m below spilling level, the government decided to excavate a trench that would drain the lake at a scheduled time and prevent the accumulation of an additional 15 million m3 of water. However, miscommunication between scientists and engineers resulted in a trench that favored slow drainage of the crater lake. It was only in July 2002, during heavy typhoon rains, that the lake actually broke out, releasing about 65 million m3 of water and lowering the lake by 23 m. The floodwaters bulked up with sediments downstream to form lahars with a total volume of 165 million m3, reaching the Bucao Bridge but sparing the Botolan town proper. Without the 2001 trenching, the lahar volume could have been more than 200 million m3, perhaps enough to adversely affect Botolan. The 2002 Pinatubo crater-lake breakout was probably generated by channel-bed erosion at the Maraunot Notch, as predicted by commonly used dam-breach models. With the lake now draining through the Maraunot Notch over erosion-resistant dacitic bedrock, a catastrophic breakout by such mechanism is no longer expected. Lake-breakout, however, may be triggered by unpredictable events such as an eruption from the crater

Continuous CO2 flux monitoring at Taal Main Crater Lake

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Insights on Recent Ground Deformation of Taal Volcano based on continuous GPS Measurements

Six Global Positioning System stations around the active Taal Volcano caldera complex on Volcano Island (Philippines) detected an uplift event between December 2014 and May 2015. The greatest deformation was measured south of Main Crater Lake (MCL). The event preceded swarms of volcano-tectonic earthquakes (VTs) beneath Volcano Island. Along with seismicity, flux rates of CO2 dissolved in the waters of MCL rose gradually, reaching saturation point by March 2015. Taal Lake’s water level similarly increased. According to GPS observation data, Taal Volcano has slowly deflated since June 2015. Likewise, seismicity and water levels decreased to baseline levels by October 2015. Volcano deformation during this period of unrest is most consistent with pressurization of Taal Volcano’s hydrothermal system rather than direct magma processes, in agreement with seismicity and gas monitoring. We modeled the continuous GPS deformation velocities to estimate the location, depth and volume change of the deformation source before and after the episode of unrest. We inverted the deformation velocities using an analytical model that assumes an elastic, homogeneous and isotropic crus

Carbon dioxide in Taal volcanic lake: a simple gasometer open to the atmosphere.

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High CO2 enrichment in surface waters of MCL lake at Taal volcano, Philippines

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Evaluating magmatic volatile input in Taal volcano’s Main Crater Lake, using combined geochemical and hydro-acoustic techniques

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Geochemical characterisation of Taal volcano-hydrothermal system and temporal evolution during continued phases of unrest (1991–2017)

Taal volcano (Luzon Island, Philippines) has last erupted in 1977 but has known some periods of increased activity, characterised by seismic swarms, ground deformation, increased carbon dioxide flux and in some cases temperature anomalies and the opening of fissures. We studied major, trace element and sulphur and strontium isotopic composition of Taal lake waters and hot springs over a period of 25 years to investigate the geochemical evolution of Taal volcano's hydrothermal system and its response to volcanic unrest.Long-term evolution of Main Crater Lake (MCL) composition shows a slow but consistent decrease of acidity, SO4, Mg, Fe and Al concentrations and a trend from light to heavy sulphate, consistent with a general decrease of volcanic gases dissolving in the hydrothermal system. Na, K and Cl concentrations remain constant indicating a non-volcanic origin for these elements. Sulphate and strontium isotopic data suggest this neutral chloride-rich component represents input of geothermal water into Taal hydrothermal system. A significant deviation from the long-term baseline can be seen in two samples from 1995. That year, pH dropped from 2.6 to 2.2, F, Si and Fe concentrations increased and Na, K and Cl concentrations decreased. Sulphate was depleted in 34S and temperature was 4 °C above baseline level at the time of sampling. We attribute these changes to the shallow intrusion of a degassing magma body during the unrest in 1991–1994.More recent unrest periods have not caused significant changes in the geochemistry of Taal hydrothermal waters and are therefore unlikely to have been triggered by shallow magma intrusion. A more likely cause for these events is thus pressurisation of the hydrothermal reservoir by increasing degassing from a stagnant magma reservoir. Our study indicates that new magmatic intrusions that might lead to the next eruption of Taal volcano are expected to change the geochemistry of MCL in the same way as in 1994–1995, with the most notable effects being changes in temperature, pH, F and Si concentrations.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A synthesis and review of historical eruptions at Taal Volcano, Southern Luzon, Philippines

The Philippines is an area of persistent volcanism, being located in one of the most tectonically active regions in the world. Taal Volcano in Southern Luzon is the second most frequently erupting volcano of the 24 active volcanoes in the Philippines. A comprehensive and critical review of published and unpublished references describing the 33 known historical eruptions of Taal may provide answers to knowledge gaps on past eruptive behavior, processes, and products that could be utilized for hazard and risk assessment of future eruptions. Data on the prehistoric eruptions and evolution of Taal Caldera and subsequent deposits are limited. Only four caldera-forming events were identified based on four mapped ignimbrite deposits. From oldest to youngest, these are the silicic Alitagtag (ALI) and Caloocan (CAL) Pumice Flow deposits, the dacitic Sambong Ignimbrite (SAM), and the basaltic-andesitic Taal Scoria Flow, renamed Scoria Pyroclastic Flow (SFL). Except for SFL with 14C dating yielding 5380 ± 70 to 6830 ± 80 ky, there are no age constraints or estimates of extent for the three older deposits. A comprehensive review of the historical eruptions of Taal Volcano is the central element of this paper and includes all eruptions from AD1572 (the first known historic event) to AD1977. Eruption styles and the interplay between processes and products for each eruption are reinterpreted based on the narrative descriptions from all available accounts. A change of classification of eruption styles and eruptive products is undertaken for some events. At least nine reported eruptions were deemed uncertain including the AD1605-AD1611 event (more likely seismic swarms), the AD1634, AD1635, and AD1645 (may simply be solfataric or hydrothermal activity) events, and the AD1790, AD1825, AD1842, AD1873 and AD1903 events that were listed in recent published and unpublished documents but do not provide any details to describe and confirm the eruptions except for listing a default VEI of 2. Pyroclastic density currents brought devastating impacts to the communities around Taal during the AD1749, AD1754, AD1911 and AD1965 eruptions and remain the biggest threat in the case of renewed volcanic activity. Significant implications for aviation are implied by the narrative of tephra fall dispersal towards Manila, the central gateway of international aviation operation in the Philippines, during the AD1754 eruptions. The dispersal of tephra in the event of an explosive eruption at Taal towards Metro Manila would have catastrophic effects to transport, utilities and business activity, potentially generating enormous economic losses. Hazards from earthquake events associated with future volcanic activity may also have localized impacts. Occurrences of liquefaction phenomena as a consequence of severe ground shaking are interpreted during the AD1749, AD1754, and AD1911 eruptions. More work needs to be done to develop a comprehensive understanding of the hazards and risks associated with an explosive eruption at Taal Volcano, especially related to the older Quaternary caldera-forming eruptions that produced large-volume pyroclastic deposits that are extensively distributed and exposed. We acknowledge that there may be additional prehistoric eruptions where the eruptive products have not been preserved, recognized or reported. Events that cannot be verified or do not have sufficient details to confirm the eruption, have been downgraded to “uncertain”. Eruptions that are confirmed with identified dispersal and emplacement of tephra fall and other eruptive deposits, as interpreted from narrated records, could provide crucial information that may be utilized in hazard assessment.SCOPUS: re.jinfo:eu-repo/semantics/publishe

Carbon Dioxide in Taal Volcanic Lake: A Simple Gasometer for Volcano Monitoring

We report here an increase in the amount of carbon dioxide in Taal lake during the year preceding the January 2020 eruption. Starting in February 2019, the CO2 emissions from the lake increased from background value (700 t day−1) to a flux close to 2,400 t day−1 at the time of the eruption. We show that the lake acts as a highly sensitive gasometer where CO2 (aq) reflects the balance between CO2 supplied to the lake (by hot springs) and CO2 lost by diffusion at air-water interface. The lake waters are extremely enriched in dissolved carbon dioxide with pCO2 values as high as 0.35 atm (350,000 ppmV) equivalent to a CO2(aq) of 9.32 mmol l−1. The residence time of CO2 in the lake is around 1 week which allows for fast detection of change in magma degassing and makes carbon dioxide a very promising tool for volcano monitoring.SCOPUS: le.jinfo:eu-repo/semantics/publishe