Geologists and geophysicists say that Mount Toba, which erupted thousands of years ago, turning into Lake Toba, still contains a dangerous magma chamber and its activity needs further study.
Indonesia Geological Experts Association president Rovicky Dwi Putrohari said the magma chamber could be observed in a study conducted by researchers recently. Rovicky added that researchers used the tomography method to detect the magma chamber.
Researchers said the Mount Toba magma chamber was located at a depth of between 20 kilometers and 100 kilometers.
"The method was used in the early stage of the study. Our researchers were able to find the location and dimensions of the magma chamber of Mount Toba. Later research will find out the potential volume of magma in the volcano for triggering an eruption," Rovicky told The Jakarta Post on the sidelines of a joint conference between the Indonesian Geological Experts Association and Indonesian Geophysics Experts Association in Medan, North Sumatra, recently.
Around 800 geologists and geophysicists took part in the conference, including scientists from Australia, France, Malaysia, Singapore and the United States.
Rovicky said that during the three-day conference several studies related to the Mount Toba eruption were presented by experts, including Craig A. Chesner, from the Eastern Illinois University in the US.
Rovicky explained that based on Chesner's study in 2011, it was concluded that the current Lake Toba was the result of four previous eruptions.
The first eruption took place around 1.2 million years ago at the northwest end of Lake Toba, the second was around 840,000 years ago south of Lake Toba, encompassing Parapat and Porsea, the third eruption occurred around 500,000 years ago at the northern end of the lake between Silalahi and Haranggaol, and the fourth eruption occurred some 74,000 years ago which resulted in the present state of Lake Toba, with Samosir Island in the middle. Its depth is estimated at 500 meters.
Rovicky said Mount Toba was regarded as a super volcano as it had a huge magma chamber, which, if it erupted, would leave a massive caldera, like Lake Toba today.
Rovicky added that the magma chamber inside the volcano could erupt any time if the Sumatra fault line reactivated.
The Sumatra fault line bisects Sumatra Island from the northwest in Aceh to the south in Lampung. The fault line runs through Mount Toba.
"A quake could reactivate the magma chamber which is so far dormant. That's why we believe Mount Toba could erupt again at any time. When it will be, we don't know. Thorough and continuous research is needed to find that out," said Rovicky.
Andi M. Adiwinata, from the Indonesian Geophysics Experts Association, said the scientist who detected the presence of the magma chamber in Mount Toba was Sri Widyantoro, from the Bandung Institute of Technology. Andi added that the detection was carried out using the tomographic technique.
Andi said Mount Toba had currently attracted the attention of local as well as foreign researchers thanks to its massive and devastating eruptions in history. He said a joint team of Indonesian scientists had been formed from relevant institutions, including the Indonesian Institute of Sciences (LIPI) and the Meteorology, Geophysical and Climatology Agency (BMKG), to conduct mitigation studies regarding the latest condition of Mount Toba.
"The researchers are currently working to find out how big the potential threat from Mount Toba is. Despite being categorized as inactive, its development needs further monitoring," said Andi, adding that besides Mount Toba, 129 active volcanoes in Indonesia were also being monitored.