Volcanic activity detected beneath Turtle Island (Gueishan Island, 龜山島) and the Datun Volcano Group (大屯山火山群) prove that they are active groups, Taiwan Volcano Observatory Director Lin Cheng-horng (林正洪), who is also an earth science researcher at Academia Sinica, said yesterday.
An active volcano is defined as having a magma reservoir or having erupted in the past 10,000 years, Lin said as he told a news conference about his team’s research over the past decade at the observatory on Datunshan (大屯山) in Taipei’s Yangmingshan National Park.
Almost no geologists in Taiwan thought the volcano group might be active about 15 years ago, as earlier studies had suggested its latest eruption might have occurred about 100,000 years ago, he said.
Photo: Lu Chun-wei, Taipei Times
However, his team has documented the existence of magma chambers beneath Datunshan through the variations in primary waves (P waves) and secondary waves (S waves) of earthquakes since the observatory was set up in 2011, he said.
S-waves cannot penetrate a magma reservoir, which also slows the transmission of P-waves — and both phenomena have been observed in the areas beneath Datunshan and Turtle Island, Lin said.
The island, which is about 10km off the coast of Yilan County, is only populated by military personnel, he said.
Volcanic eruptions under the island were more likely than under Datunshan and might trigger small-scale tsunamis off the coast of Yilan, he said.
However, there is no reason for the public to panic, because volcanic eruptions, unlike earthquakes, can be forecast by monitoring increases in the concentrations of carbon dioxide and sulfate ions, he said.
Lin’s team found that several magnitude 4 earthquakes in Taichung and in Hualien County in 2015 triggered regular “tremors” — or as Lin said, “heartbeats” — beneath Datunshan every 18 minutes for more than a day after each quake.
The team is likely to have been the first to have documented such “regular” quake activities, but its monitoring of such activity was later discontinued.
The team’s findings were published in Scientific Reports, the Journal of Volcanology Geothermal Research and other journals between 2016 and last year.
While there have not been any volcanic eruptions in Taiwan during its recorded history, identifying new evidence about earlier volcanic activities is still exciting, he said.
He expects to improve the volcanic surveys on Turtle Island, where there are fewer monitoring devices, he said.
Volcanologists from around Asia are to meet in Taiwan in October for the 4th field camp of the Asian Consortium of Volcanology, which has previously been held in Japan and Indonesia, he added.
Lin said he was originally interested in earthquakes, but switched to volcanology about 15 years ago after visiting Japanese volcanologists.
The workings of lava and gaseous substances of volcanoes was more attractive than the breaks or fault lines of seismology, he said.
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