Yu-Ming Lai

Although the Tatun Volcanic Group (TVG) looms over the metropolitan capital region of Taiwan, the threats it poses are only vaguely known. Here, as a first step toward improving understanding those threats, we investigate the Shamao complex, one of the youngest and smallest features of the TVG. Analysis of a high-resolution, LiDAR-based, Digital Terrain Model (DTM), augmented by sparse outcrops and a drill core, reveals an episodic, multi-event pyroclastic density currents (PDCs), particularly block-and-ash flow (BAF) succession rather than a single slump event. This demonstrates that the complex consists of overlapping West and East Domes and an older West Flow, which extends southwestward ~ 650 m from a source on the flank of the domes. High-precision ⁴⁰ Ar/ ³⁹ Ar analyses reveal that West Flow erupted at 196.4 ± 2.3 ka, long before the eruptions of East Dome at 24.2 ± 1.8 ka and West Dome likely soon thereafter. The three principal landforms of the complex consist of crystal-rich volcanic rocks with basaltic-andesitic to andesitic bulk compositions and limited Sr–Nd isotopic variations, grossly similar to other published data for the TVG. However, subtle differences in petrography and trace element geochemistry likely reflect differing mineralogy and melt fraction during magma extraction. Overall, our combined geomorphologic, geochronologic, petrologic, and geochemical approach suggests that the development of the Shamao complex involved intermittent magma extraction from one or more mush systems over 10–100 kyr timescale, in the Pleistocene.

Chihsing Volcano represents the youngest and highest edifice within the Tatun Volcano Group (TVG) of northern Taiwan, yet the timing and character of its recent magmatic activity have remained poorly constrained. This study integrates 40Ar/39Ar and 14C geochronology, mineral chemistry, whole-rock geochemistry, and Sr–Nd isotopes from drill cores to reconstruct late-stage evolution of the volcano. Our results establish a two-stage eruptive model for the Late Pleistocene to Early Holocene transition. The first stage (16–8 ka) featured magmatic eruptions producing calc-alkaline andesitic lava flows. 40Ar/39Ar ages (14.0 ± 2.2 to 11.6 ± 3.6ka) mark these as TVG's youngest reliably dated magmatic units, demonstrating persistence far later than previously recognized. Mineral thermobarometry and geochemistry indicate origin from a homogeneous 7–15 km deep crustal reservoir (1135–1184°C) with repeated recharge events producing thorough magma homogenization evidenced by narrow isotopic (εNd = +2 to +3) and geochemical ranges, and negligible crustal contamination. The second stage (~8 ka) transitioned to phreatic activity. 14C dating of crater-fill sediments confirms sedimentation initiation around 7.4 ka, with rates increasing from 0.02 to 0.17 cm/yr after 3.6 ka. Ongoing phreatic activity continues through residual magmatic heat driving pyroclastic density currents, tephra fallout, and landslides. These findings reveal a persistent magma supply system beneath the TVG and suggest that the potential for magmatic transport remains active. Consequently, future hazard assessments for the Taipei metropolitan area should integrate both phreatic and potential magmatic eruption scenarios.

Lateral collapses, also referred to as sector or flank collapses, are common in various types of volcanoes, particularly in island arc systems. Taiwan is situated in an active oblique collision zone, where the northern Luzon Arc converges with the Eurasian continental margin. Lutao volcano represents the last uplifted island that has not yet fully accreted into Taiwan, providing a unique opportunity to study volcanic evolution in the northern Luzon Arc during the collision process. This study focuses on the volcanic products of Lutao volcano, examining their spatial distribution and characterizing their occurrences. The seven recognized lithofacies are categorized into three lava coherent facies and four volcanic-breccia facies (one hyaloclastite, one lahar, and two pyroclastic density currents), distributed across four formations on Lutao Island. By integrating these findings with existing topographical data, we propose a revised eruption model, suggesting that the main eruption crater was located on the island’s eastern side and collapsed during the arc–continent collision. In addition, we extend this model to other island volcanoes now incorporated into Taiwan’s Coastal Range, further investigating the implications for volcanic behavior in these regions.

Sumatra is located at the western end of the Sunda Arc, which resulted from the subduction of the Indo-Australian Plate beneath the Eurasian Plate. In this study, we report detailed zircon U–Pb and Hf isotope data for Cenozoic igneous rocks from the entire island of Sumatra to better constrain the temporal and spatial distribution of arc magmatism. The new dataset, combined with literature information, identifies the following two magmatic stages: (1) Paleocene to Early Eocene (66–48 Ma) and (2) Early Miocene to Recent (23–0 Ma), with a 25 myr-long period of magmatic quiescence in between. The magmatic zircons show predominantly positive and high ε _Hf ( t ) values, ranging from +19.4 to +7.1 in western Sumatra, +17.1 to +1.6 in central Sumatra and +18.0 to +7.0 in eastern Sumatra, indicating an isotopically juvenile magma source in the mantle wedge along the western Sunda Arc. We explain the negative and low ε _Hf ( t ) values (+0.5 to −13.1) of young samples around the supervolcano Toba as evidence for the subduction of sediment. We argue for a change in the subduction processes, where the first magmatic stage ceased owing to the termination of the Neo-Tethyan subduction and the following stage corresponded to the modern Sunda subduction.

The Toba volcanic system in Indonesia has produced two of the largest eruptions (>2,000 km³ dense-rock equivalent [DRE] each) on Earth since the Quaternary. U–Pb crystallization ages of zircon span a period of ∼600 ky before each eruptive event, and in the run-up to each eruption, the mean and variance of the zircons’ U content decrease. To quantify the process of accumulation of eruptible magma underneath the Toba caldera, we integrated these observations with thermal and geochemical modeling. We show that caldera-forming eruptions at Toba are the result of progressive thermal maturation of the upper crustal magma reservoir, which grows and chemically homogenizes, by sustained magma influx at average volumetric rates between 0.008 and 0.01 km³/y over the past 2.2 My. Protracted thermal pulses related to magma-recharge events prime the system for eruption without necessarily requiring an increased magma-recharge rate before the two supereruptions. If the rate of magma input was maintained since the last supereruption of Toba at 75 ka, eruptible magma is currently accumulating at a minimum rate of ∼4.2 km³ per millennium, and the current estimate of the total volume of potentially eruptible magma available today is a minimum of ∼315 km³. Our approach to evaluate magma flux and the rate of eruptible magma accumulation is applicable to other volcanic systems capable of producing supereruptions and thereby could help in assessing the potential of active volcanic systems to feed supereruptions. Significance Understanding the thermal state of magma reservoirs before supereruptions is crucial for interpreting the processes leading to such catastrophic events. Here, we show that the two supereruptions of Toba were preceded and followed by protracted magma influx at relatively constant average volumetric rate over the past 2.2 My. This suggests that increased magma flux is not essential before supereruptions. Instead, long-term thermal maturation of the magma reservoir related to significant magma pulses primes the system for eruption. Importantly, our results indicate that significant variations of monitoring parameters, such as increased surface deformation or degassing, may not occur before supereruptions. Our method can be widely applied to other large silicic magmatic systems to evaluate their potential to feed a supereruption.

Gabbroic enclave in the Shihtiping ignimbrite was a shallow reservoir cumulate We identified three sub-stages magmatic processes at 4 Ma in the Shihti...

This study explored the effects of a collaborative computer-based concept mapping strategy on Geographic Science learning outcomes in junior high school students. A quasi-experimental approach was applied to a sample of 85 9th grade students. Class instruction lasted for five weeks, with two...