Although there was no eruption history in Taiwan, volcanic features are still significant in some areas such as Tatun volcano group (TVG) and Kueishantao (Turtle Island). For example, a lot of geothermal activities such as hot-springs and fumaroles are found in the TVG. Since the distance between Mt. Chihsin (the highest peak among the TVG) and the Taipei 101 skyscraper is less than 15 km, the potential volcano activity is not only an interesting scientific subject but also associated with the safety of more than 5 million of residents in the Taipei metropolis. Besides, possible complex volcanic disasters around the Turtle Island and some submarine volcanoes can’t totally be excluded in the future.
Based on the early dating result of volcanic rocks, the TVG was thought as an extinct volcano because the last volcanic eruption might be taken place in hundred thousand years ago. But the TVG is considered now as an active volcano, evident from a variety of new studies such as geochemical analyses, seismic observations, geodetic survey and volcanic ash age in the past decade. In particular, some interesting seismic behaviors have been found in the TVG recently. For example, several repeated seismicity with a period of ~18 minutes persistently occur more than tens of hours (Lin, 2017a). Those periodical earthquakes, like the heartbeat, are first reported at non-erupting volcanoes in the Earth. Besides, some volcanic sounds generated at the fumaroles are detected in the TVG (Lin, 2017b). It is further interesting to see that strong degassing process at two separated fumaroles produced alternative volcanic sounds (Lin et al., 2018a). This phenomenon is similar to that volcanoes are talking to each other. Also some very-long-period volcanic earthquakes are detected in the TVG (Lin and Pu, 2016). All of the seismic activities show the TVG with a lot of heat is still active.
Although a variety of observations suggest the TVG is active, it was hard to see whether magma reservoirs exist or not for a long time. Since S-waves can’t propagate through liquids, a magma reservoir that is basically filled by some molten magma would stop S-waves. In the meanwhile, some travel-time delays will be detected if P-waves propagate through a magma reservoir. Based on both ideas, we carefully examined the seismic data recorded at the TVG and eventually found both of the S-wave shadows and P-wave delay at a particular area (Lin, 2016). The estimated size of the magma reservoir is about one-quarter area of the Taipei City. It is the first to detect magma reservoir from both S-wave shadow and P-wave delay in the world.
In addition to S-wave shadow, S-wave will be totally reflected from the magma reservoir. Based on the both characteristics, we also identify the magma reservoir beneath the Turtle Island offshore the Ilan plain from both S-wave shadows and strong reflections (Lin et al., 2018b). This result confirms the Turtle Island is an active volcano. Although the Turtle Island is an offshore volcano, potential complex disasters might be concerned if it is erupting in the future. For example, the Ilan plain might be threatened by a tsunami that is generated by the partial collapse of the Turtle Island if it is erupting again.
It is often known “Fear tends to come from ignorance” by Patrick Rothfuss. Although both of the TVG and Turtle Island are active volcanoes, we don’t be panic. Unlike earthquakes, volcano eruptions are often predicted through the scientific monitoring methods and analyses. The prediction idea is simple because some anomalies might be detected as the magma is ascending from the deep crust to the surface. Those volcanic anomalies, including not only significant increase of seismicity, volcanic gases and temperature but also dramatically crustal deformation, provide some useful information to estimate the possible location, size and time before the eruption. Since 2011, the TVO (Taiwan Volcano Observatory at Tatun) has been established for monitoring possible volcano activities in the northern Taiwan area. We expect an eruption warming will be issued in probably one week or tens of days before the possible volcano eruption in the future.
Lin, C.H. (2016), Evidence for a magma reservoir beneath the Taipei metropolis of Taiwan from both S-wave shadows and P-wave delays, Scientific Reports, Vol. 6, 39500.
Lin, C.H. and H.C. Pu (2016), Very-long-period seismic signals at the Tatun Volcano group, northern Taiwan, J. Volcanology Geothermal Research, Vol. 328, 230-236.
Lin, C.H. (2017a), Probable dynamic triggering of phreatic eruption at the Tatun volcano group of Taiwan, Journal of Asian Earth Sciences , Vol 149, 78-85.
Lin, C.H. (2017b), Dynamic triggering of drumbeat seismicity at Tatun volcano group in Taiwan, Geophysical Journal International, Vol. 210, 354-359.
Lin, C.H., Y.C. Lai, M.H. Shih, C.J. Lin, J.S. Ku and H.C. Pu (2018a), Extremely similar volcano sounds from two separated fumaroles at the Tatun volcano group in Taiwan, Seismological Research Letters, Vol. 89, No. 6, 2347-2353.
Lin, C.H., Y.C. Lai, M.H. Shih, H.C. Pu and S.J. Lee (2018b), Seismic detection of a magma reservoir beneath Turtle Island of Taiwan by S-wave shadows and reflections, Scientific Reports, Vol. 8, 16401.