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Research about Philippines

Source-linked reports with geographic coverage including Philippines.

At least 19 recordsLinked to original sources
USGS2023

Remote characterization of the 12 January 2020 eruption of Taal Volcano, Philippines, using seismo-acoustic, volcanic lightning, and satellite observations

On 12 January 2020, an eruption began on the shores of the Main Crater Lake (MCL) of Taal Volcano—a caldera system on the southern end of Luzon Island in the Philippines. Taal, one of the most active volcanoes in the Philippines, is located 30 km south of Manila—a major metropolitan area with a population of 13.5 million people. Eruptive activity intensified throughout the day on 12 January, producing prolific volcanic lightning, ashfall, and a sustained plume that reached 16–17 km altitude. The chronology of events was well documented by the Philippine Institute of Volcanology and Seismology and the Tokyo Volcanic Ash Advisory Center. The wealth of data collected during the eruption provides a unique opportunity to investigate how the combination of different remote sensing methods may complement local observations and monitoring. Remote systems tend to provide lower resolution data but are also less likely to be compromised by the eruptive activity, thus providing continuous records of eruptive processes. Here, we present a postevent analysis of the 12 January activity, including data from long‐range lightning, infrasound, and seismic arrays located at distances up to several thousands of kilometers from the volcano. By combining these datasets, we distinguish five phases of activity and infer a major shift in eruption behavior around 12:00 on 12 January (UTC). The remote observations suggest that the most of the water within the MCL ( ⁠∼42 million m 3⁠ ) was vaporized and incorporated into the volcanic plume within the first 12 hr of the eruption.

Taal Volcano↗
USGS2022

Eruption dynamics leading to a volcanic thunderstorm— The January 2020 eruption of Taal volcano, Philippines

Advances in global lightning detection have provided novel ways to characterize explosive volcanism. However, researchers are still at the early stages of understanding how volcanic plumes become electrified on different spatial and temporal scales. We deconstructed the phreatomagmatic eruption of Taal volcano (Philippines) on 12 January 2020 to investigate the origin of its powerful volcanic thunderstorm. Satellite analysis indicated that the water-rich plume rose >10 km high before creating lightning detected by Vaisala's global lightning data set (GLD360). Flash rates increased with plume heights and cloud expansion over time, producing >70 flashes min –1 . Photographs revealed a highly electrified region at the base of the umbrella cloud, where we infer strong convective updrafts and icy collisions enhanced the electrical activity. These findings inform a conceptual model with overlapping regimes of charge generation in wet eruptions—initially due to ash particle collisions near the vent, followed by thunderstorm-like electrification in icy regions of the upper plume. Despite the wide reach of Taal's ash cloud, most of the lightning occurred within 20–30 km of the volcano, producing thousands of hazardous cloud-to-ground flashes over a densely populated area. The eruption demonstrates that volcanic lightning can pose a hazard in its own right, embedded within the broader hazards of explosive volcanism in an urban setting.

Taal volcano↗
USGS2021

A petrological and conceptual model of Mayon volcano (Philippines) as an example of an open-vent volcano

Mayon is a basaltic andesitic, open-vent volcano characterized by persistent passive degassing from the summit at 2463 m above sea level. Mid-size (<0.1 km3) and mildly explosive eruptions and occasional phreatic eruptions have occurred approximately every 10 years for over a hundred years. Mayon’s plumbing system structure, processes, and time scales driving its eruptions are still not well-known, despite being the most active volcano in the Philippines. We investigated the petrology and geochemistry of its crystal-rich lavas (~50 vol% phenocrysts) from nine historical eruptions between 1928 and 2009 and propose a conceptual model of the processes and magmatic architecture that led to the eruptions. The whole-rock geochemistry and mineral assemblage (plagioclase + orthopyroxene + clinopyroxene + Fe-Ti oxide ± olivine) of the lavas have remained remarkably homogenous (54 wt% SiO2,~4 wt% MgO) from 1928 to 2009. However, electron microscope images and microprobe analyses of the phenocrysts and the existence of three types of glomerocrysts testify to a range of magmatic processes, including long-term magma residence, magma mixing, crystallization, volatile fluxing, and degassing. Multiple mineral-melt geothermobarometers suggest a relatively thermally buffered system at 1050±25 °C, with several magma residence zones, ranging from close to the surface, through reservoirs at ~4–5 km, and as deep as ~ 20 km. Diffusion chronometry on >200 orthopyroxene crystals reveal magma mixing timescales that range from a few days to about 65 years, but the majority are shorter than the decadal inter-eruptive repose period. This implies that magma intrusion at Mayon has been nearly continuous over the studied time period, with limited crystal recycling from one eruption to the next. The variety of plagioclase textures and zoning patterns reflect fluxing of volatiles from depth to shallower melts through which they eventually reach the atmosphere through an open conduit. The crystal-rich nature of the erupted magmas may have developed during each inter-eruptive period. We propose that Mayon has behaved over almost 100 years as a steady state system, with limited variations in eruption frequency, degassing flux, magma composition, and crystal content that are mainly determined by the amount and composition of deep magma and volatile input in the system. We explore how Mayon volcano’s processes and working model can be related to other open-vent mafic and water-rich systems such as Etna, Stromboli, Villarrica, or Llaima. Finally, our understanding of open-vent, persistently active volcanoes is rooted in historical observations, but volcano behavior can evolve over longer time frames. We speculate that these volcanoes produce specific plagioclase textures that can be used to identify similar volcanic behavior in the geologic record.

Mayon volcano↗
USGS2021

Formation of dense pyroclasts by sintering of ash particles during the preclimactic eruptions of Mt. Pinatubo in 1991

Dense, vitric, dacitic pyroclasts (dacite lithics) from the 1991 preclimactic explosions of Mt. Pinatubo were analyzed for their vesicular and crystal textures and dissolved H 2 O and CO 2 contents. Micron-scale heterogeneities in groundmass glass volatile contents (0.9 wt% differences in H 2 O within 500 μm) are observed and argue that parts of the dacite lithics equilibrated at different depths before finally being constructed. Greater vesicularities and larger and greater number densities of vesicles are observed in groundmass glass around phenocrysts compared to groundmass glass away from phenocrysts, similar to textures produced in experiments that sintered bimodal distributions of particles. Furthermore, increasingly greater proportions of stretched and distorted vesicles are observed in lithics from the later explosions, which parallels the increasingly shorter reposes between explosions. Finally, micron-sized crystal fragments are ubiquitous in groundmass glass of all dacite lithics. The textures, together with the variable volatile contents, lead us to propose a model that the dacite lithics formed by rapid and repetitive sintering of ash particles derived from a variety of depths on the conduit walls above the fragmentation level. We speculate that sintering of conduit material produced impermeable layers that retarded gas flow through the conduit, causing pressure to build until the cap failed and the next explosion occurred.

Mount Pinatubo↗
USGS2021

Marine ecotourism for small pelagics as a source of alternative income generating activities to fisheries in a tropical community

Overharvest has led to marine ecosystem degradation and declining fishery catches in many tropical communities. To allow stocks to recover and provide increased flows of food and income, reductions in fishing effort are necessary. The development of Alternative Income Generating Activities can help to reduce the economic reliance of coastal communities on fishing, potentially reducing pressure on fish stocks. Here we assess the local conditions which have enabled the creation of Alternative Income Generating Activities to fishing based on marine ecotourism in Moalboal, Philippines. Importantly, while marine ecotourism typically centers around charismatic megafauna, a combination of nearshore fringing reefs, the establishment of nearshore marine protected areas and the occurrence of a massive herring aggregation provide a large tourism draw to this community. Using a combination of regional and local economic statistics and stakeholder surveys, we implement an economic valuation of the Moalboal marine ecotourism for 2018 and compare this valuation to an independent estimate of the extractive value of the herring aggregation. The Moalboal case indicates that a combination of strong community engagement in the governance of the ecotourism resource, a network of locally managed marine protected areas and the retention and distribution of economic benefits within the local community have led to a significant marine ecotourism sector. We contextualize these conditions into a set of potential enabling conditions for marine ecotourism as an Alternative Income Generating Activity to fishing to contribute insights to diversifying livelihood opportunities beyond extractive fishing for coastal communities in the tropics.

Moalboal, Cebu Island↗
USGS2020

GIS-Modeling of island hopping through the Philippines demonstrates trade-offs migrant grey-faced buzzards during oceanic crossings

Migration can be costly with consequences that can influence population trajectories. These costs and consequences are especially heightened during over-water travels, which can be high-risk events for birds. We created spatial models to evaluate potential migratory responses of “oceanic”, island-hopping grey-faced buzzards that encounter variation in landscape parameters and weather as they move through and out of the Philippine archipelago. We constrained the modeled routes to enter the island chain at Basco and to use one of four potential exit points in the south of the country, either Balabac, Bongao, Balut Island, or Cape San Agustin. We used all possible combinations of our three external parameters (stopover sites, water crossings and wind direction) to model alternative migratory routes for each of the four exit points (n = 20 migratory routes). Modeled grey-faced buzzard routes were between 1,582 and 2,970 km. Routes overlapped over eastern and central Luzon, along a leading line created by the Sierra Madre Mountains. Routes also overlapped and suggested unavoidable over-water crossings between Mindoro and Palawan, Negros and Zamboanga del Norte, and Leyte and Surigao. Our models suggest that the optimal migratory strategy for these birds is to find the shortest route to an exit point with the greatest possible access to stopover habitats and fewest open-water crossings under wind resistance. Understanding how each of these external factors affected the geography and characteristics of the migratory routes helps us to understand the context for different migratory strategies of birds that face dangerous open-water crossings on migration.

Journal of Engineering, Environment and Agricultur↗
USGS2008

Establishing major permeability controls in the Mak-Ban geothermal field, Philippines

Recent updating of the conceptual model of the Mak-Ban (Bulalo) geothermal field verified both structural and stratigraphic controls on permeability and connectivity in the reservoir. Two silicic units within the predominantly andesitic production zone were identified from borehole logs, core and drill cuttings. Whole rock chemical data and petrographic analysis confirmed two rhyolite units that consist of partially welded ash-flow tuffs and lava with primary devitrification and vapor-phase alteration textures typical of subaerial rhyolites. U/Pb dating of zircons from the units showed two distinct episodes of silicic volcanism at 352 ± 16 ka and 501 ± 12 ka, respectively. A recent drilling campaign allowed the running of more gamma ray (GR) in tandem with PTS logs. The logs validated the presence of two units with high GR response generally coinciding with permeable zones just below the interpreted top of the reservoir. Naphthalene disulfonate tracer testing defined a predominantly fault-controlled flow path of fluids from the edges of the field into the central production area. Fifteen to 25% of injected tracers were recovered in production wells over a five-year monitoring period. Peak arrival of tracer returns indicated average speeds between 0.1 to 1.3 m/hr, allowing for sufficient time for the fluids to heat up prior to re-emergence in production wells. Although faults are known to be important pathways in most geothermal reservoirs, the identification of specific structures with high connectivities in Mak-Ban provide an important insight on fluid migration from peripheral areas. This information is critical in preparing a reservoir management strategy for addressing the entry of cool marginal recharge into the center of the field.

Mak-Ban geothermal field↗
USGS2006

AMS Radiocarbon dating of paleosols intercalated with tephra layers from Mayon Volcano, southern Luzon, Philippines: A preliminary report

This paper presents the AMS 14 C dates of paleosols intercalated with tephra layers in the vicinity of Mayon Volcano, southern Luzon, Philippines. the obtained 14 C dates are almost consistent with the stratigraphy of the Mayon tephra group. On the basis of calibrated 14 C age of soil layer directly overlying the lowest ash layer, the oldest eruptive event must have taken place shortly before 20 cal kyr BP. This age is younger than the previous estimates for Mayon.

Mayon Volcano↗
USGS1994

The Nd-, Sr- and Pb-isotopic character of lavas from Taal, Laguna de Bay and Arayat volcanoes, southwestern Luzon, Philippines: Implications for arc magma petrogenesis

Following the amalgamation of a collage of pre-Neogene terranes largely by strike-slip and convergence mechanisms to form the Philippine islands, volcanic chains, related to oppositely dipping subduction zones, developed along the eastern and western margins of the archipelago. There is ample field evidence that this volcanic activity, predominantly calc-alkaline in chemical character, had commenced by the Oligocene. Volcanoes resulting from subduction along the Manila-Negros trench in the west (e.g. Taal, Laguna de Bay and Arayat) form a high-angle linear array, trending away from the MORE field on Pb-isotopic covariation diagrams; have the highest Sr- and lowest Nd-isotopic compositions, of the two chains (but nevertheless plotting above bulk earth on the 87 Sr/ 86 Sr versus 143 Nd/ 144 Nd covariation diagram); and exhibit Sm/Nd and Rb/Sr values that are lower and higher, respectively, than the estimated values for bulk earth. While the Sm/Nd and Rb/Sr characteristics are common to both chains, volcanoes associated with the Philippine-East Luzon trench have Pb-isotopic compositions that fall in the Indian Ocean MORB field and that require time-integrated evolution in a high Th/U environment. They also have higher Nd- and lower Sr-isotopic ratios. The source materials of Philippine volcanoes, therefore, have undergone varied recent enrichments in LILE, as indicated by the decoupling of isotopic and elemental ratios. These enrichments, particularly for the western volcanoes, cannot be entirely due to small degrees of partial melting in the mantle wedge, considering that they were accompanied by elevations in radiogenic Pb. Elevated Pb ratios are best explained by the introduction of subducted, continentally derived sediments. The sedimentary component in the western volcanoes is probably the South China Sea sediments derived largely from Eurasia. That this component is not available in the Philippine-East Luzon trench is reflected by the fact that the eastern volcanoes have higher Nd- and lower Sr-isotopic ratios as well as less radiogenic common Pb.

southwestern Luzon↗
USGS1992

A basalt trigger for the 1991 eruptions of Pinatubo volcano?

The eruptive products of calc-alkaline volcanos often show evidence for the mixing of basaltic and acid magmas before eruption (see, for example, refs 1, 2). These observations have led to the suggestion3 that the injection of basaltic magma into the base of a magma chamber (or the catastrophic overturn of a stably stratified chamber containing basaltic magma at its base) might trigger an eruption. Here we report evidence for the mixing of basaltic and dacitic magmas shortly before the paroxysmal eruptions of Pinatubo volcano on 15 June 1991. Andesitic scoriae erupted on 12 June contain minerals and glass with disequilibrium compositions, and are considerably more mafic than the dacitic pumices erupted on 15 June. Differences in crystal abundance and glass composition among the pumices may arise from pre-heating of the dacite magma by the underlying basaltic liquid before mixing. Degassing of this basaltic magma may also have contributed to the climatologically important sulphur dioxide emissions that accompanied the Pinatubo eruptions.

Pinatubo volcano↗
USGS1992

The 1991 eruptions of Mount Pinatubo, Philippines

Recognition of the volcanic unrest at Mount Pinatubo in the Philippines began when steam explosions occurred on April 2, 1991. The unrest culminated ten weeks later in the world's largest eruption in more than half a century.

Mount Pinatubo↗
USGS1989

Geology of the Zambales ophiolite, Luzon, Philippines

The Zambales ophiolite of western Luzon, Philippines, exposes a typical succession of basalt flows, diabasic dikes, gabbro and tectonized harzburgite. The age established by limiting strata is late Eocene. Lack of evidence of thrust faulting and the general domal disposition of the lithologie units indicate that the ophiolitic rocks are exposed by uplift. Highly complex internal layered structures within the complex are related to processes developed during formation of the ophiolite and the Zambales ophiolite may be one of the least disturbed (by emplacement) ophiolitic masses known. The exposed mass trends north and the upper surface plunges at low angles (a few degrees) to the north and south. The chemistry and composition of the rocks in the northwest part of the Zambales area (Acoje block) is distinct from that in the southeastern segment (Coto block). The Acoje block, according to Evans (1983) and Hawkins and Evans (1983), resembles (on a chemical basis) arc-tholeiite series rocks from intra-island arcs and the rocks in the Coto block are typical back-arc basin rock series. The present writer believes that the ophiolite composes a single genetic unit and that the changes in composition are the result of changes that took place during the initial formation. The gabbro probably formed below a spreading center in an elongate, in cross section, V-shaped, magma chamber. The gabbro is estimated by the writer to be less than 2 km thick and may be less than 1 km in places. Numerous erosional windows through the gabbro in the northern and eastern side of the Zambales area show that the gabbro remaining in those areas is likely to be only a few hundred meters thick. Harzburgite is exposed to a depth of about 800 m in the Bagsit River area and this may be the deepest part of the ophiolite accessible for study on which there is any control on depth. A transitional zone, about 200 m thick lying between the gabbro and harzburgite, is composed of serpentinized dunite. Commonly the dunite contains disseminated sulfide minerals and at the Acoje Mines, platinum-group elements. A compositional layering within the gabbro is in places cumulate in the lower part of the unit but may have formed by nucleation higher up on the relatively steep sides of the magma chamber. A widespread gneissic banding in the gabbro forms large mappable structures which are many times more complex than is the disposition of the major rock units. These structures are believed to be the result of extensive slumping in the magma chamber. The structure produced by the cumulate layering merges with the gneissic banding, commonly without discernible change in attitude. This tectonic layered structure crosses the gabbro-peridotite boundary at any angle without seeming to disturb the original rock distribution. At greater depths below the boundary (ca. 800 m), the harzburgite contains low dipping banding, which probably reflects the result of differential movement within the mantle. Chromite occurs almost exclusively in a zone that generally lies no more than 200–300 m below the gabbro-peridotite boundary. Refractory-grade chromite is found in this zone below the olivine gabbro in the Goto block and as low-grade metallurgical grade chromite below norite in the Acoje block. At Acoje Mines the chromite is present in layers in dunite, which the writer interprets as being distributed in a zone along the gently dipping (ca. 25°) gabbro-peridotite boundary. The steeply dipping (ca. 60–80 ° ) individual layers lie en echelon along the boundary at an angle (ca. 50 ° ) to the contact. At Coto the chromite forms large discontinuous masses in the lowest dunite and in the uppermost harzburgite. Except for the chromite present as layers at Acoje, the regional tectonic layering crosses the chromite deposits without structural deviation. The chromite deposits and associated peridotite may be cumulate in origin, but have been modified to such an extent that cumulate textures are generally obliterated. The angle of repose of cumulate layers in the Acoje area and in the Coto block dip towards each other raising the possibility that the Zambales area may contain the relics of a spreading center. Initial emplacement of the Zambales ophiolite took place by uplift and the ultramafic portion was exposed to erosion in the earliest Miocene or late Oligocene. Submergence of some of the ophiolite followed the previous uplift and on the west side of the Zambales Range submergence of several kilometers is indicated. Final emergence appears to have taken place in Pliocene or Pleistocene time by block uplift and areas of greatest uplift closely conform to the present topographic surface.

Tectonophysics↗
USGS1969

Nuées Ardentes of the 1968 Eruption of Mayon Volcano, Philippines

Mayon Volcano, southeastern Luzon, began a series of explosive eruptions at 0900 April 21, 1968, and by May 15 more than 100 explosions had occurred, at least 6 people had been killed, and roughly 100 square km had been covered by more than 5 cm of airfall ash, blocky ash flows, and a lava flow. All material crupted was porphyritic augite-hypersthene andesite. Explosions from the summit crater (elevation 2460 m) ejected large quantities of ash and incandescent blocks to a height exceeding 600 m and produced ash-laden clouds which rose to heights of 3 to 10 km. Backfall of the coarser material fed nuées ardentes which repeatedly swept down ravines on all sides of the volcanic cone. The velocity of one nuée ardente ranged from 9 to 63 m per sec. The largest nuées descended to the southwest and reached as far as 7 km from the summit. An aa lava flow also descended 3 1/2 km down this flank. The nuées ardentes deposited pyroclastic flows that contained large breadcrust-surfaced blocks averaging about 30 cm across, but occasionally reaching 25 m in greatest dimension. These blocks were still very hot in their interiors several days later. Surrounding the pyroclastic flows is a seared zone as much as 2 km wide, but averaging a few hundred meters, in which vegetation is charred and splintered, but over which only a thin layer of airfall ash was deposited.

Mayon Volcano↗
USGS1967

Changes in surface temperature at Taal Volcano, Philippines 1965-1966

Taal Volcano erupted in September 1965 ending a dormant period of 54 years. A quiescent interval of 9 months followed, terminated by new eruptions in July 1966 at the same site. Aerial surveys with a scanning infrared radiometer were made at three periods during the quiescent interval and twice following the July 1966 eruption. The survey technique yields a quasiphotographic image of the radiant temperature of the volcanic terrain. Results indicate that the principal changes in surface temperature stemmed from changes in convective heat transfer by hydrothermal fluids. New hot springs developed along the structurally-controlled northwest and southeast flanks of the 1965 explosion crater. The northwest spring grew in size prior to the 1966 eruption, persisted through that eruption and has since maintained its discharge. The 1965 cinder cone meanwhile showed a persistent rim of hydrothermal activity with some shift in position of maximum discharge. The July 1966 eruptions took place on the rim about midway between two positions of maximum discharge.

Bulletin Volcanologique↗
USGS1962

Metallic spherules in tektites from Isabela, Philippine Islands

Iron-nickel spherules, as much as 0.5 mm in diameter, have been found completely embedded in some philippinites. The spherules consist mainly of kamacite with unidentified pink inclusions. The meteoritic origin of these spherules seems reasonable, suggesting that the tektites containing them were formed by asteroidal or meteoritic impact.

Isabela↗
USGS1958

Origin of manganese deposits of Busuanga Island, Philippines

The manganese deposits of Busuanga Island, Palawan, are tabular and broadly lenticular bodies which lie conformably within a thick sequence of deformed abort beds. The purpose of this study is to determine the probable mode of origin of the deposits. Similar deposits in other parts of the world have been described by others as products of several different genetic processes. Field and laboratory methods of research were employed in the course of the investigation. Detailed geologic mapping was done on the surface and underground, and many samples of rocks and ores were obtained. Later, intensive study of samples from four typical deposits and from the rooks in the surrounding areas was undertaken, using a variety of laboratory techniques. Microscopic study of thin sections and polished surfaces was supplemented by X-ray and chemical work. More than one hundred X-ray diffraction powder photographs were made to identify minerals, and qualitative chemical studies were made of a number of aamples by use of the X-ray spectrograph. In addition, quantitative chemical analyses were made of certain samples. Finally, published accounts of the occurrence and geological behavior of manganese and silica were consulted to aid in interpretation of the data at hand. Oherty layers in the manganese deposits are lithologically similar to the chart wallrooks and country rook beds. Radiolarian fossils are common in the chart and are also found in some ore specimens. Manganese content of the wallrocks and the country rock beds, however, in essentially nil. The manganese deposits contain mostly psilomelane-type oxides in their near-surface parts, and in the deepest mines this ore grades downward into siliceous protore. In three of the deposits studied, the protore consists mainly of braanite and quartz; in the fourth deposit, hausmannite and the silicate alleghatvite make up the milk of the protore. Some of the protoro is massive, but cherty stones are commonly well layered parallel to the wall rock structure. Grain size is very small, but, like the silica in the chert beds, becomes relatively coarse where the rocks are much deformed. No evidence of large-scale replacement or cross-cutting veins is found in the protores. It is concluded that the original manganiferous deposits were largely non-clastic or oolloidal marine sediments laid down in a reducing environment. The protorea were developed from these beds by processes of diagenesis and low-grade regional metamorphism. The protores were in turn altered to black oxide ore by near-surface agencies during the present erosion cycle. Particular interest is attached to the occurrence of alleghanyite and traces of pyroxmangite and hubnerite(?) in the protorea.

Busuanga Island↗