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

Abstract

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.

The 2020 Eruption and Large Lateral Dike Emplacement at Taal Volcano, Philippines: Insights From Satellite Radar Data

“…Taal has a history of frequent seismovolcanic crises and/ or surface activity which are interpreted as repeated magma recharge of its shallow reservoir (Zlotnicki et al, 2018). The sudden magma injection in 2019 might have been due to the pressure imbalance induced by the depressurization of the shallow storage zone, resulting from long-term diffuse degassing, as supported by: (1) the sequence of long-term deflation and short-term inflation detected by InSAR, and (2) the decrease in CO 2 flux measurements from 2015 to 2017 before rapidly rising from 700 T/day (background value) to 2400 T/day between February 2019 and the eruption day (Bernard et al, 2020).…”

“…The timing of events can be further constrained with the availability of seismic, GNSS, and petrological datasets. Nevertheless, current knowledge of Taal’s plumbing system from geochemical and geophysical studies (Alanis et al., 2013; Maussen et al., 2018; Yamaya et al., 2013; Zlotnicki et al., 2018), and CO 2 flux and temperature measurements from Main Crater Lake (Bernard et al., 2020), indicate that high‐flux of gases and volcanic fluids are transferred from the shallow magma reservoir to the hydrothermal system (Zlotnicki et al., 2018). This eventually leads to three possible scenarios, the hydrothermal system may: (1) have been heated, sealed and pressurized, (2) have accumulated magmatic gas resulting in a reduced boiling point and overpressurization of the system (Bernard et al., 2020), or 3) have been destabilized due to the injection of magma, either as small batches or through interaction with a large dike.…”

“…Nevertheless, current knowledge of Taal’s plumbing system from geochemical and geophysical studies (Alanis et al., 2013; Maussen et al., 2018; Yamaya et al., 2013; Zlotnicki et al., 2018), and CO 2 flux and temperature measurements from Main Crater Lake (Bernard et al., 2020), indicate that high‐flux of gases and volcanic fluids are transferred from the shallow magma reservoir to the hydrothermal system (Zlotnicki et al., 2018). This eventually leads to three possible scenarios, the hydrothermal system may: (1) have been heated, sealed and pressurized, (2) have accumulated magmatic gas resulting in a reduced boiling point and overpressurization of the system (Bernard et al., 2020), or 3) have been destabilized due to the injection of magma, either as small batches or through interaction with a large dike. It is worth mentioning that the volume of erupted tephra (i.e., ∼0.032 km 3 , VEI = 3) from 12–13 January 2020 (Martinez‐Villegas, 2020), is close to the estimated: (1) volume of products that can be initially involved if a phreatic eruption occurs at Taal due to the mechanically weak and mineralized materials in the northern part of Volcano Island (Zlotnicki et al., 2018) and (2) pre‐eruptive volume increase of the magma reservoir from 2019.…”

“…The phreatic‐phreatomagmatic eruption that occurred in Volcano Island was driven by an initial gas‐rich phase (Bernard et al., 2020) which further decreased the remaining gas in the shallow storage zone. The orientation of the lateral dike is also consistent with the pre‐existing fault structures along the NE‐SW‐striking Macolod Corridor extensional zone, and appear to have played a significant role during the diking event by promoting the opening in the direction of the minimum compressive stress and the propagation along the maximum compressive stress (Anderson, 1951; Cotterell & Rice, 1980; Delaney et al., 1986).…”

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

“…Most recently, a period of uplift between December 2014 and May 2015 was followed by VT swarms (Sayco et al, 2017). During this time, carbon dioxide partial pressure in MCL waters rose to above 0.25 atm, the highest since the beginning of continuous monitoring in 2013 (Bernard et al, 2017).…”