Challenge 06: Increase community resilience to ocean hazards
Permanent URI for this collectionhttps://repository.unesco.gov.ph/handle/123456789/25
Ocean Decade
Challenge 06:
Increase community resilience to ocean hazards
Enhance multi-hazard early warning services for all geophysical, ecological, biological, weather, climate and anthropogenic related ocean and coastal hazards, and mainstream community preparedness and resilience.
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- A synthesis and review of historical eruptions at Taal Volcano, Southern Luzon, PhilippinesDelos Reyes, Perla J.; Bornas, Ma. Antonia V.; Dominey-Howes, Dale; Pidlaoan, Abigail C.; Magill, Christina R.; Solidum, Renato Jr. U. (Elsevier BV, 2018-02)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 A comprehensive and critical review of published and unpublished references describing the 33 known historical eruptions of Taal may provide answers to knowledge gaps on past eruptive behavior, processes, and products that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.
- Local tide and geoid corrections significantly improve coastal retracked Jason sea surface heights in the PhilippinesFlores, Paul Caesar; Reyes, Rosalie; Amedo-Repollo, Charina Lyn; Rediang, Abegail; Alfante, Rey Mark; Bauzon, Ma. Divina Angela; Pasaje, Nikki; Bringas, Dennis (Science and Technology Information Institute, 2022-11-08)Retracking algorithms increase the accuracy of coastal sea surface height (SSH) measurements. However, it is still important to validate these retracking estimates with tide gauge (SSHtg) observations. We downloaded the freely available Jason altimeter SSH processed using the XTRACK-ALES algorithm, then detided the SSH using different tide models. The first model is the default tidal correction based on Finite Element Solution 2014 (SSHfes), and the second model is the T_Tide harmonic analysis of the nearest tide gauge (SSHaltimeter). SSHfes showed a very poor correlation (< 0.31) and very high root mean square error (RMSE, > 29 cm). In contrast, SSHaltimeter generally showed a very high correlation (> 0.91) and low RMSE (< 17.4 cm). A further quality check based on the average and standard deviation of the difference between the SSH readings (SSHfes – SSHtg and SSHaltimeter – SSHtg) also showed the superior performance of SSHaltimeter,which scored < 9.3 and < 16.5 cm, respectively; compared to SSHfes, which scored < 9.3 cm and > 27 cm for the same parameters. The poor performance from the SSHfes likely comes from the complex bathymetry and coastal geomorphology of the country, which is not accounted for in the FES. The Philippines generally has a narrow shelf, and the FES tide corrections may be related to deep-water tides rather than the shallow-water tides observed from tide gauges. Despite the high correlation and agreement between the SSHaltimeter and SSHtg, the rate of sea level rise from the SSHaltimeter in some sites is more than twice the rate from SSHtg, which indicates the possible influence of the vertical land movement.This study was supported by grants to R.B. Reyes by the Department of Science and Technology–Philippine Council for Industry, Energy, and Emerging Technology Research and Development through the Coastal Sea Level Rise Philippines Project. We also thank the anonymous reviewers for their feedback on how to improve the manuscript.
- Ground deformation analysis caused by post-2013 earthquake in Bohol, PhilippinesBauzon, Ma. Divina Angela I.; Reyes, Rosalie B.; Blanco, Ariel C.; Siringan, Fernando P. (Springer Science and Business Media LLC, 2022-08-16)After the 2013 Mw 7.2 earthquake that occurred in Bohol, the shoreline specifically in Loon and Maribojoc was observed to shift seaward due to ground uplift. This study analyzes the post-earthquake shoreline movement, specifically a 12 km coastal strip in Loon and Maribojoc, and ground deformation of the West Bohol area through Sentinel-1 image processing techniques. From October 2014 to April 2018, the DSAS linear regression shoreline rates were − 4.36 m/yr in Loon and − 1.69 m/yr in Maribojoc, indicative of a landward movement of 91.4% and 88.8% of shoreline transects in Loon and Maribojoc, respectively. PSInSAR revealed varying rates of VLM in the study area from October 2014 to December 2018 such that Loon and Maribojoc exhibit a subsidence rate of − 2 to − 8 mm/yr. The correlation between the shoreline retreat and the land subsidence in the study area is 87%, indicating a possible elastic rebound after the earthquake. The portion of Tagbilaran City on its northern side exhibits land subsidence of − 2 to − 6 mm/yr while its southern side exhibits land uplift of 0–2 mm/yr. The relative sea level fall from TGSL measurements indicates an uplift in the location of the tide gauge in Tagbilaran City.
- Shallow structures, interactions, and recurrent vertical motions of active faults in Lingayen Gulf, PhilippinesFlores, Paul Caesar M.; Siringan, Fernando P.; Mateo, Zenon Richard P.; Marfito, Bryan J.; Sarmiento, Keanu Jershon S.; Abigania, Maria Isabel T.; Daag, Arturo S.; Maac-Aguilar, Yolanda (Elsevier, 2023-06-01)The surface trace of the East Zambales Fault (EZF) and its associated faults in the Lingayen Gulf have been previously mapped but no other characteristics were reported. This study utilized seismic reflection, multi-beam bathymetry, and side scan sonar to characterize the offshore EZF in terms of magnitudes of vertical displacement. Sequence stratigraphy and radiocarbon dates provided age constraints on the recurrence interval within the Holocene. The EZF extends for ∼ 57 km into the gulf, follows a north-northwest trend, and bounds the karstic terrane (west) and fluvio-deltaic deposits (east). Sinistral motion is indicated by: 1) normal and reverse drag geometries, 2) reversal in the sense of throw with depth, 3) flower structure, and 4) right-stepping and the uplift of a pressure ridge named Pudoc Bathymetric High. The Central Lingayen Gulf Fault (CLGF), to the east of EZF, follows the same trend. The Lingayen Gulf Transverse Fault (LGTF), oriented east–west, forms a flower structure with the CLGF. The EZF, CLGF, and LGTF combined form the Lingayen Gulf Fault System, which divides the gulf into five fault blocks where uplift and subsidence locally occurred. A paleo-delta at −60 m yielded an age of 6.8 kyBP, indicating it was formed during the first Holocene highstand. With natural compaction considered, fault-associated subsidence of 46–53 m may have occurred. The average Holocene vertical displacement is 2.1–2.2 m, which translates to a recurrence interval of 320–270 years for the fault system. The faults can likely generate earthquakes with magnitudes 7.5 (EZF), 6.7 (CLGF), and 6.6 (LGTF).This work was supported by grants to F. P. Siringan by the Department of Science and Technology – Philippine Council for Industry, Energy and Emerging Technology Research and Development through the Mapping of Active Offshore Faults for Resilient Coasts Project; and the Department of Environment and Natural Resources – Biodiversity Management Bureau through the Coral Reef Visualization and Assessment - Deep Coral Mapping Project. We are thankful to Deo Carlo Llamas for the meaningful discussions about the current knowledge of the East Zambales Fault. We also thank the anonymous reviewers who provided significant insights for the improvement of this manuscript.