Masato Iguchi (Professor, Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University)

Japan's most active volcano

An interview with
Masato Iguchi
Professor and Director
Sakurajima Volcano Research Center

Sakurajima: One hundred years on

A century on from the 1914 eruption at Sakurajima volcano, Kagoshima Prefecture in Kyushu, southwestern Japan, the threat of another eruption looms over the region. Throughout the 20th century and continuing today, Kyoto University has been developing novel methods to monitor eruptions and provide simulations that will be of vital importance in mitigating future disasters.

Masato Iguchi, Director of the Sakurajima Volcano Research Center and Professor at the Disaster Prevention Research Institute, reflects on the history of volcano studies at Kyoto University and looks to the future.

Molten lava erupts from Sakurajima volcano
© IPGGutenbergUKLtd/Thinkstock

First of all, there have been many recent news reports about Sakurajima and the increasing likelihood of there being another big eruption. What makes Sakurajima one to watch in particular?

Iguchi: Sakurajima is the most active volcano in Japan and one of the most active in the world. There are many different kinds of volcanoes across the world and some of the eruptions are quite big -- some bigger than Sakurajima. What makes Sakurajima stand out is the frequency of eruptions.

One hundred years ago, we had a big eruption called the Taisho eruption in 1914. This was the biggest eruption in the 20th century in Japan. After that, we had lava flow in 1946, and since around 1955, there have been frequent volcanic eruptions. A typical eruption involves ejection of volcanic material to a distance of around 3 km, and there's a large amount of volcanic ash. The peak of volcanic activity at the summit crater occurred in the 1970s. In this century, activity has declined at the summit crater but from 2006, we had new activity at a different crater called the Showa crater. Now, we have two craters -- the Minamidake summit crater and the Showa crater.

Click to open
Historical eruptions at Sakurajima

What can we learn from the frequency of eruptions at these craters?

Iguchi: Looking at data that goes back over the past century, we can see peaks in the annual number of explosions at Sakurajima. At Minamidake summit crater, for example, in 1974, there were more than 400 explosions. More recently, at the Showa crater, there have been more than 1,000 explosions both in 2010 and in 2011. And in 2013, volcanic ash elevation reached up to 5 km, which is very large-scale.

In your view, how likely is it that Sakurajima will erupt in the imminent future?

Iguchi: It is difficult to say and infer the time of the eruption. From our data, we can estimate the increase in the volume of the magma underneath. We now know that the magma volume is 90% full. It is almost comparable to the volume effused by the 1914 eruption. The magma is stored beneath Aira Caldera; there's a large magma chamber with a depth of 10 km. So, it means we must worry about a future big eruption.

How is it possible to tell that the magma volume is 90% full?

Iguchi: We can track vertical displacement around Aira Caldera. In 1914, the ground around Aira Caldera subsided by up to 80 cm -- this corresponds to the discharge of magma. After the eruption, the ground gradually uplifted. This uplift of the ground has been continuing for 100 years. Now, the level of the ground has reached nearly the same as before the 1914 eruption. It's being lifted up again by the magma to the former level.

How do you actually go about monitoring the magma chamber? What kind of equipment do you use?

Iguchi: We have many instruments at Sakurajima Volcano Research Center. We have ten seismic stations and nearly 20 ground deformation stations that can monitor activity. The ground deformation measurement is conducted by GPS or tiltmeters and other devices. We have some of the most sensitive sensors to detect eruption precursors such as water-tube tiltmeters and strainmeters in the underground tunnel.

When an eruption occurs, we can detect the precursor signal. Plans are underway to construct a new underground tunnel, now that Kyoto University has a new budget. The existing tunnel has a length of 200 m and the new tunnel will be built on almost the same scale. The new one will be set up on the northeastern side of Sakurajima so that we can monitor more of the area.

Is it unusual to be able to monitor the magma chamber in this way, compared to other volcano centers?

Iguchi: It is certainly not so common. The real importance is the history of the measurements. Usually at other volcanoes, there isn't such long-term measurement -- the data would go back about one or two decades. But southern Kyushu has a history as a military base. Geodetic measurements were recorded by the government. That is why we have long-term measurements going back 100 years. And Kyoto University started observations in the 1960s.

Now, I wonder if we could talk about your journey as a researcher. Were you always interested in studying volcanoes?

Iguchi: Yes, when I studied at Kyoto University as an undergraduate, I actually pursued geophysics. We conducted underground surveys. For example, I worked on technical studies of how to detect oil or minerals underground. I didn't imagine I would end up detecting underground magma!

I see; there must be a parallel between studying magma and other formations underground. What was it about Kyoto University that attracted you?

Iguchi: I'm not sure. When I was younger, Kyoto University was renowned for Professor Hideki Yukawa's achievements, for which he was awarded the Nobel Prize in Physics. Young students wanted to enter Kyoto University's Faculty of Science. It was a big influence and inspiration. On the other hand, I was not so clever. Other students were much more excellent than me.

What led to your specialization in volcanoes?

Iguchi: My mentor, Professor Kosuke Kamo, was the director of the Sakurajima Volcano Observatory at the time. He invited me; that was the reason. When I began to study volcanoes, I didn't know about volcanology at all. I started from zero. This was the start of my career in volcanology.

Today, more and more students are going to places like New Zealand and Hawaii to study volcanology. What would be your advice for students who want to study volcanoes in Japan?

Iguchi: The important thing is to see the volcanoes. Volcano studies are at almost the same level at these other universities. Fortunately, we have a lot of instruments here in Japan compared to other countries. We have some of the highest-level instruments in the world in our underground tunnels. Other volcano centers do not have such high-sensitivity sensors. They usually have borehole sensors, which are difficult to maintain in the long-term.

Compared to other universities, another big difference is that Kyoto University has its own observatory near the volcano. We actually have two volcano observatories: Sakurajima and the Aso Volcanological Laboratory (AVL). The AVL was established in 1928 and is the oldest volcanological observatory in Japan.

Prof Iguchi at the Disaster Prevention Research Institute

Do you spend most of your time at Sakurajima Research Center?

Iguchi: I hope to, but actually, I must attend many meetings and give lectures at Kyoto University and at other universities. I come to the Disaster Prevention Research Institute around twice a month. In addition, I give seminars at Kagoshima, which are open to the public.

It must be important to communicate with the residents of Kagoshima. What is life like for people who live near Sakurajima?

Iguchi: It's part of daily life -- the fall of volcanic ash. It's on the roads and on the farmlands. Sakurajima is famous for its daikon radish. As radish is a root vegetable, it's not affected as much by the ash. Also, in soil that contains volcanic ash, the drainage is good. This may be beneficial for fruit and vegetables. It's not so good for rice. That's why Sakurajima is well known for its daikon, tangerines, and purple sweet potatoes, but not rice. The staple crop is sweet potatoes.

What would be your key message to people who live near Sakurajima?

Iguchi: If we have an eruption similar to the 1914 eruption within ten or 20 years, the important thing is to develop simulation models and understand what happens in relation to the eruption. Being able to imagine the disaster is the most important thing to reduce potential damage.

What can be done to prepare for another eruption?

Iguchi: We need to keep in mind that volcanic ash may even reach Tokyo. In that case, all the airplanes will stop. It would be similar to or more serious than the Iceland volcano eruption in 2010. The population is not so dense in Iceland but in Japan, many people live near the volcano -- within 10 km. So, the volcanic disaster would be much more severe than for other countries.

This is why I frequently visit Indonesia. I'm working on a Science and Technology Research Partnership for Sustainable Development (SATREPS) program supported by the government, which encourages international collaborative research with a focus on global issues. Volcanic activity there is even more frequent than at Japanese volcanoes, so we can study more data and learn from more experiences. The other reason is that social conditions are similar to Japan as many people live beside the volcano, so we can learn from activities in Indonesia.

What are the challenges ahead?

Iguchi: Volcanoes are different to other natural disasters. In earthquakes, the ground shakes, tsunami involve the movement of water, and landslides involve the movement of land. Volcanic eruption actually involves ejection of new material from the Earth. The size of the volcanic disaster is directly related to the intensity of the eruption.

The most important thing is how to estimate and forecast the hazard of the eruption based on monitoring of volcanoes and simulations of dispersion and fall of volcanic ash. Then we can simulate the movement of the volcanic material. I hope the results of our disaster reduction system will be valuable for planning land use and for evacuation to prepare for future disasters.

Thank you very much for your time.


Published: 24 December 2014



Masato Iguchi was appointed Professor and Director of Sakurajima Volcano Research Center (SVRC) in 2012. He holds a concurrent position as Professor at the Disaster Prevention Research Institute (DPRI), Kyoto University. Apart from his extensive fieldwork and journal publications, he has co-authored numerous books including Volcanic Earthquakes and Tremor in Japan (2011). He is President of the Volcanological Society of Japan and a committee member of the Tokyo Geographical Society. Prof Iguchi frequently gives lectures for university students and members of the general public.

Additional information

To discover more about Prof Iguchi's publications, click here

For more information about the Sakurajima Volcano Research Center, click here


Interviews by Rieko Kawabata
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Kyoto University Research Administration Office (KURA)