Main Crater Lake Research Articles

Remote Characterization of the 12 January 2020 Eruption of Taal Volcano, Philippines, Using Seismo-Acoustic, Volcanic Lightning, and Satellite Observations

ABSTRACT 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 m3) was vaporized and incorporated into the volcanic plume within the first 12 hr of the eruption.

Diffuse CO2 degassing precursors of the January 2020 eruption of Taal volcano, Philippines

On January 12, 2020, Taal volcano in Philippines erupted, 43 years after its previous eruption in 1977. This eruption was preceded by diffuse CO2 degassing precursory signals. Significant temporal variations in diffuse CO2 emission from Taal Main Crater Lake (TMLC) were observed across the ~ 12 years reaching high CO2 degassing rates in 2011 and 2017, with values typical of plume degassing volcanoes. In addition to these CO2 surveys at the TCML, soil CO2 efflux continuous monitoring was implemented at Taal volcano since 2016 and a clear increasing trend of the soil CO2 efflux in 2017 was observed. These geochemical observations are most simply explained by magma recharge to the system, and represent the earliest warning precursor signals to the January 2020 eruptive activity.

Analysis of the 2020 Taal Volcano tephra fall deposits from crowdsourced information and field data

After 43 years of dormancy, Taal Volcano violently erupted in January 2020 forming a towering eruption plume. The fall deposits covered an area of 8605 km2, which includes Metro Manila of the National Capital Region of the Philippines. The tephra fall caused damage to crops, traffic congestion, roof collapse, and changes in air quality in the affected areas. In a tropical region where heavy rains are frequent, immediate collection of data is crucial in order to preserve the tephra fall deposit record, which is readily washed away by surface water runoff and prevailing winds. Crowdsourcing, field surveys, and laboratory analysis of the tephra fall deposits were conducted to document and characterize the tephra fall deposits of the 2020 Taal Volcano eruption and their impacts. Results show that the tephra fall deposit thins downwind exponentially with a thickness half distance of about 1.40 km and 9.49 km for the proximal and distal exponential segments, respectively. The total calculated volume of erupted fallout deposit is 0.057 km3, 0.042 km3, or 0.090 km3 using the exponential, power-law, and Weibull models, respectively, and all translate to a VEI of 3. However, using a probabilistic approach (Weibull method) with 90% confidence interval, the volume estimate is as high as 0.097 km3. With the addition of the base surge deposits amounting to 0.019 km3, the volume translates to a VEI of 4, consistent with the classification for the observed height and umbrella radius of the 2020 main eruption plume. VEI 4 is also consistent with the calculated median eruption plume height of 17.8 km and sub-plinian classification based on combined analysis of isopleth and isopach data. Phreatomagmatic activity originated from a vent located in Taal Volcano’s Main Crater Lake (MCL), which contained 42 million m3 of water. This eruptive style is further supported by the characteristics of the ash grain components of the distal 12 January 2020 tephra fall deposits, consisting dominantly of andesitic vitric fragments (83–90%). Other components of the fall deposits are lithic (7–11%) and crystal (less than 6%) grains. Further textural and geochemical analysis of these tephra fall deposits contributes to better understand the volcanic processes that occurred at Taal Volcano, one of the 16 Decade Volcanoes identified by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) because of its destructive nature and proximity to densely populated areas. The crowdsourcing initiative provided a significant portion of the data used for this study while at the same time educating and empowering the community to build resilience.

The 2010 seismovolcanic crisis at Taal Volcano (Philippines)

Typical eruptions of Taal Volcano in the Philippines are frequent and violently explosive. The last devastating phreatomagmatic eruption from 1965 to 1977 resulted in the death of about 200 persons. For this and other earlier events, no warnings of impending eruptions were issued. Since this time, volcanic crises involving episodes of seismicity, deformation, gas release, temperature change, etc., have occurred frequently. Each of these did not, but possibly could have, evolved into an explosive eruption. One such event occurred between April 2010 and March 2011. This paper reports various types of geophysical data (electric/magnetic field, ground temperature, seismicity and ground deformation) taken during this period of activity together with the current state of geophysical knowledge about the volcano in order to throw light on activity evolution. While the 2010 seismovolcanic crisis was preceded by unusual changes in electric field, ground tilting and uplift, the major signals from all data were concomitant with the evolution of the crisis. On April 20, 2010, felt earthquakes first started to occur. The numbers increased sharply after April 29 with repeated pulses of seismicity that ended finally in March 2011. Overall, we can identify three periods of seismic activity, from April 20 to August 4–8, from August 4–8 to November 18, and from November 18 to March 28, 2011. Although only a single tiltmeter was in operation, it recorded three phases of deformation that correspond generally with the pulses in seismic activity. Phase 1 appears to correspond to inflation at a depth of about 5 km just to the NW of Main Crater Lake from April 20 to June 11, 2010. This resulted in an eastward tilting of the northern flank of the volcano. This apparently triggered rapid but shallower inflation (Phase 2) in the hydrothermal region of the volcano under the northern edge of Main Crater Lake from June 11 to July 13 just to the SE of the initial deeper source as indicated by northward tilting of the volcano’s northern flank. Progressive deflation began after July 13. By March 28, 2011, the deformation state recovered to the pre-crisis level and felt seismic activity ceased. Apparent related changes in seismicity, tilt, magnetic and electric fields occur during smaller NS inflations in the Phase 3 deflation—Phase 3a (July 13 to August 4–8), Phase 3b (August 4–8 to November 18) and Phase 3c (November 18 to March 28, 2011). These likely result from interrelated stress change, fluid/gas migration and thermal activity at depth and in the hydrothermal system. The rapidity of changes in the state of the volcano over a matter of hours during this entire process indicates rapid communication occurs between processes at depth and in the hydrothermal system and this could easily result in the dramatic evolution to violent phreatic explosions with little warning.

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.

First study of the heat and gas budget for Sirung volcano, Indonesia

With at least four eruptions over the last 20 years, Sirung is currently one of the more active volcanoes in Indonesia. However, due to its remoteness, very little is known about the volcano and its hyperacid crater lake. We report here on the first measurements of gas and heat emissions from the volcano. Notable is the substantial heat loss from the crater lake surface, amounting to 220 MW. In addition, ~17 Gg of SO2, representing 0.8% of Indonesian volcanic SO2 contribution into the atmosphere, ~11 Gg of H2S, ~17 Gg of CO2, and ~550 Gg of H2O are discharged into the atmosphere from the volcano annually. The volatiles degassed from Sirung magmas are subjected to hydrothermal fluid-rock interactions and sulfide depositions, initiated by the disproportionation of SO2. These processes lead to distinct gas compositions and changing lake water chemistry (in the sub-craters and the main crater lake). However, the occurrence of SO2-rich fluids and strong gas flux appear to highlight a rapid fluid transfer to surface, avoiding re-equilibration with lower temperature rocks/fluids in the conduits.

Electromagnetic Observations at Taal Volcano

The electromagnetic (EM) method first applied to monitor the activity of the Taal Volcano from 2005 consists of repeatedly surveying total magnetic intensity (TMF) and continuously measuring EM fields. The EM observation system was greatly improved through the SATREPS project summarized in this paper. The resistivity structure is investigated in the project using the magnetotelluric (MT) method. The MT method revealed a large hydrothermal reservoir just beneath the center of Volcano Island. The existence of this reservoir explains several things – the special features of the devastating 1911 eruption, i.e., that it was magmatic-hydrothermal, together with the geochemical characteristics of Main Crater Lake, especially the absence of SO2gas. The reservoir’s formation process provides useful suggestions for understanding the volcano’s past eruption cycle.

Geochemical evidence of magma intrusion inferred from diffuse CO2 emissions and fumarole plume chemistry: the 2010–2011 volcanic unrest at Taal Volcano, Philippines

We report herein significant increases in the diffuse CO2 emission through the lake and soils of the Taal Volcano Main Crater (Philippines), during a volcano-seismic unrest period in April 2010–June 2011. Monitoring of CO2 emissions from the Taal Main Crater Lake and soils in the fumarole areas started in 2008 with a collaborative project between ITER and PHIVOLCS. In August 2010, the total diffuse CO2 emission from the Taal Main Crater Lake increased almost three times from a previously measured baseline emission value ∼1,000 t day−1 to 2,716 ± 54 t day−1. This increase occurred during anomalous seismic activity which started in April 2010. The highest CO2 emission value in the crater lake was measured in March 2011 at 4,670 ± 159 t day−1 when the volcano was still showing signs of unrest. Significant changes in the CO2/SO2, CO2/H2O, and SO2/H2S ratios in the fumarole gases suggest the occurrence of a magmatic injection several weeks before the onset of the volcano-seismic unrest period. These observed changes in the CO2 emission rate and the fumarole gas composition as the result of magmatic activity were likely caused by magma moving from a deep reservoir to a shallow reservoir.

Electrical resistivity tomography study of Taal volcano hydrothermal system, Philippines

Taal volcano (311 m in altitude) is located in The Philippines (14°N, 121°E) and since 1572 has erupted 33 times, causing more than 2,000 casualties during the most violent eruptions. In March 2010, the shallow structures in areas where present-day surface activity takes place were investigated by DC resistivity surveys. Electrical resistivity tomography (ERT) lines were performed above the two identified hydrothermal areas located on the northern flank of the volcano and in the Main Crater, respectively. Due to rough topography, deep valleys, and dense vegetation, most measurements were collected using a remote method based on a laboratory-made equipment. This allowed retrieval of information down to a depth of 250 m. ERTs results detail the outlines of the two geothermal fields defined by previous self-potential, CO2 soil degassing, ground temperature, and magnetic mapping (Harada et al. Japan Acad Sci 81:261–266, 2005; Zlotnicki et al. Bull Volcanol 71:29–49, 2009a, Phys Chem Earth 34:294–408, 2009b). Hydrothermal fluids originate mainly from inside the northern part of the Main Crater at a depth greater than the bottom of the Crater Lake, and flow upward to the ground surface. Furthermore, water from the Main Crater Lake infiltrates inside the surrounding geological formations. The hydrothermal fluids, outlined by gas releases and high temperatures, cross the crater rim and interact with the northern geothermal field located outside the Main Crater.

In situ cone penetration tests at the active Dashgil mud volcano, Azerbaijan: Evidence for excess fluid pressure, updoming, and possible future violent eruption

Active mud volcanism is a global phenomenon that represents a natural hazard by self-igniting eruptions and the continuous emission of methane gas in both marine and continental settings. Mud domes are often found in compressional tectonic settings such as the Caucasus orogenic wedge. Dashgil mud volcano, the most prominent of >200 features in Azerbaijan, has erupted vigorously in historic times. For several years, we have observed variations in the activity of Dashgil dome, including transients in methane flux, build-up of extrusive mud cones on the main feature, and flexural polygonal cracks adjacent to the main crater lake and new mud cones. In spring 2007, we carried out in situ CPTU (Cone Penetration Testing with Pore Pressure measurement) experiments in the crestal area of Dashgil. Our data suggest that the central portion of the crater lake, which hosts the conduit for gas (and possible mud) ascent, shows both low sediment shear strength (<5–20 kPa) and excess pore fluid pressures between 15 and 30 kPa supra-hydrostatic at 1 m sub-bottom depth. In situ cone resistance as a measure for undrained shear strength is as low as 150 kPa in the conduit, whereas the mud is found rather stiff in all other testing locations (300–700 kPa, probably a result of deeply buried shales of the Maikop formation parts of which now liquefy and ascend). Pore pressure is low in the centre of the conduit, probably because of rapidly migrating gas. It increases to 30 kPa at the lake bottom and deep flank, then decreases upslope on the lake flank, and reaches hydrostatic values at the crater rim. From the overpressured region beneath the fluid-filled crest of Dashgil dome, combined with the other observations, we suspect to currently witness an ongoing period of updoming. The presence of sintered mudstones from explosive eruptions in 1908 and 1928 (and most likely before) suggests that a similar violent activity may occur in the near future.

Combined electromagnetic, geochemical and thermal surveys of Taal volcano (Philippines) during the period 2005–2006

Since 1572, 33 phreatic to phreatomagmatic eruptions have occurred on Taal volcano (Philippines), some of them causing several hundred casualties. Considering the time delay between two consecutive eruptions, there is an 88% probability that Taal volcano should have already erupted. Since 1992, several phases of seismic activity have been recorded accompanied by ground deformation, opening of fissures, and surface activity. The volcanic activity of Taal appears to be controlled by dike injections and magma supply, buffered by a hydrothermal system that releases fluids and heat through boiling and subsequent steaming. In early 2005, a multidisciplinary project was launched for studying the hydrothermal activity. To map the hydrothermal system, combined surveys were carried out to investigate self-potential, total magnetic field, ground temperature and carbon dioxide soil degassing, along with satellite thermal imaging of the Main Crater Lake. The elevated temperatures and high concentrations of carbon dioxide, as well as electromagnetic anomalies, indicate large-scale hydrothermal degassing. This process is enhanced along the tectonic features (e.g., crater rim and faults) of the volcano, while active fissures opened along the E–W northern flank during the 1992–1994 seismic activity. Heat and fluids from the hydrothermal system are essentially released in the northern part of the crater, which is bounded to the South by a suspected NW–SE fault along which seismicity seems to take place, and dikes are thought to be intruded. During the January 2005 surveys, a new seismic crisis started, and the felt earthquakes prompted spontaneous evacuation of hundreds of inhabitants living on the volcano. Repeated surveys show changes of self-potential, total magnetic field, and ground temperature with time, without any noticeable spatial enlargement. These observations suggest that the northern flank located between the crater rim and the 1992–1994 fissures is connected with a deep thermal source in Main crater and is reactivated during seismic crises. This sector could be subjected to flank failure.

フィリピン・タール火山・主火口湖の磁気および水深測量：序報

A geomagnetic and topographic survey of the Main Crater Lake (MCL) on Volcano Island, Taal volcano, the Philippines, was conducted to identify the eruption mechanism of the volcano. A mound at the lake bottom was found near the northern part of MCL, which was not present at the 1986 survey. Called mound M, it was formed between 1986 and 2008 during a period of new fumarole activity, which started on the northeastern shore of MCL in the early 1990's. A geomagnetic survey found no Total Magnetic Field (TMF) anomaly corresponding to the mound, which implies that mound M is non-magnetic. The site coincides with the location of a high-temperature area detected by the ASTER satellite during the early 2005 volcanic crisis. The mound M might contain chemicals (chloride or sulphide?) deposited from volcanic gas. Two continuously-recording proton magnetometers were set up at two geothermal areas on Volcano Island. Recordings of TMF variations obtained over six months on Volcano Island showed excellent stability and precision for monitoring the volcanic activity.

The age of the Kaali meteorite craters and the effect of the impact on the environment and man: evidence from inside the Kaali craters, island of Saaremaa, Estonia

The Kaali meteorite impact crater field, which consists of a 110 m diameter main crater and eight satellite craters on the island of Saaremaa, Estonia is a unique object as its meteoritic origin is well proven, it lies in a densely populated area and fell in the relatively recent past. The precise age of the impact that generated the craters is still disputed. We investigated the basal sediment section from the main crater lake, Kaali jrv, consisting of crushed and in-washed dolomite diamiction. AMS dating of terrestrial macrofossils from these sediment layers places the age of the impact at 1690�1510 B.C. The age is about 1000 years older than revealed from the impact marker-horizon in a contemporaneous peat sequence 6 km northwest of the Kaali crater. The pollen, diatom and chemical data suggest the instant formation of a shallow hard-water lake environment in the main crater depression after the impact, and a rapid post-impact sedimentation of crushed dolomite dust. Archaeological evidence on the crater slopes points to human activity around 700- 200 B.C., indicating that the crater ring wall was inhabited by Bronze Age people soon after the impact event, and the structure of the main crater is mimicked in nearby ar- chaeological sites.

Geochemical and isotopic evidence for seawater contamination of the hydrothermal system of Taal Volcano, Luzon, the Philippines

The hydrologic structure of Taal Volcano has favored development of an extensive hydrothermal system whose prominent feature is the acidic Main Crater Lake (pH 3500 mg/kg) and low SO4/Cl ratios (<0.3). The Br/Cl ratio of most samples suggests incorporation of seawater into the hydrothermal system. Water and dissolved sulfate isotopic compositions reveal that the Main Crater Lake and spring discharges are derived from a deep parent fluid (T approximate to 300 degrees C), which is a mixture of seawater, volcanic water, and Lake Taal water. The volcanic end member is probably produced in the magmatic-hydrothermal environment during absorption of high-temperature gases Into groundwater. Boiling and mixing of the parent water give rise to the range of chemical and isotopic characteristics observed in the thermal discharges, Incursion of seawater from the coastal region to the central part of the volcano is supported by the low water levels of the lakes and by the fact that Lake Taal was directly connected to the China sea until the sixteenth century:. The depth to the seawater-meteoric water interface is calculated to be 80 and 160 m for the Main Crater Lake and Lake Taal, respectively. Additional data are required to infer the hydrologic structure of Taal, Geochemical surveillance of the Main Crater Lake using the SO4/Cl, Na/K or Mg/Cl ratio cannot be applied straightforwardly due to the presence of seawater in the hydrothermal system.