Mt. Aso (halfway between Kumamoto and Beppu) is one of the world's most active volcanoes and is Japan’s largest active volcano. The bowl-shaped caldera covers 380 square kilometers and has 50,000 living inside and on top of it. The most popular of Aso’s peaks, hissing and steaming Nakadake crater, can be reached by cable car and looks like a barren moonscape, with a crater rim lined with concrete shelters in case of an unexpected eruption.
Mt. Aso has been described as double-coned volcano but is best seen not as a single volcano but rather a complex of active vents in the center of a large caldera. Created by at least four catastrophic eruptions between 270,000 to 90,000 years ago, the huge caldera is 16 kilometers (10 miles) wide and 24 kilometers (15 miles long. The outer rim of the caldera consists of a series of undulating plateaus, which contains small communities, roads, and farms with grazing horses and cattle.
Within the caldera are the Five Mountains of Aso: 1) 1337-meter-high Mt. Eboshi-dake, 2) 1238-meter-high Mt. Nishima-dake, 3) 1216-meter-high Mt. Naka-dake, 4) 1408-meter-high Mt. Neko-dake, and 5) 1592-meter-high Mt. Taka-dake.
Most of smoke, high-temperature gases and sulfurous fumes emanate from Mt. Naka-dake. Scattered around the perimeter of Naka-dake's crater are heavily-reinforced concrete structures, where tourists can seek refuge should volcanic bombs suddenly begin flying out of the volcano. These were built after sudden eruptions in 1958 killed 12 visitors near the crater. Another eruption in 1979 killed three people, one kilometer away, in an area thought to safe. In 1989 and 1990 the cable car was closed by a series of eruptions.
Visiting Mt. Aso
The Naka-dake's crater is 100 meters deep and varies in width from 400 meters to 1,100 meters. It is possible to walk along the southern edge. Try to climb to the crater at night. It is spectacular enough during the day with all the smoke spewing out, but at night you can see lava, hidden during the day by smoke, hissing out of fissures inside the crater.
There are three major hiking trails from the base of the volcano to the top. There are also a number of trails between the Five Mountains of Aso. Near Naka-dake's crater is grassy meadow with two small lakes and visitors centers has displays on volcano geology and shows films of major eruptions. On the road from Mt. Aso to Beppu are more smoking volcanos, spas, and a geothermal energy plant which can be visited.
Mt. Aso volcano is part of a huge geo park where visitors can enjoy cycling, horse-riding, guided hiking across volcanic peaks, paragliding, camping, or even helicopter rides. In nearby towns you can sample local sakes and try specialties cultivated in the rich volcanic soil. Star gazing from inside the caldera is a popular activity. Myuken Ishiharaso, which was partly created by Japan’s renowned interior designer Takashi Sugimoto of Super Potato, playfully unites postmodern elements with traditional Japanese features – double glass walls, for example, filled to the ceiling with colored bottles. Some have walls made of stacked-up driftwood, or a polished granite rock weighing a ton; perfect for setting your cocktail glass upon.
Aso Volcano Museum is located at Kamikusa-senrigahama, Mt. Aso. It is a facility for learning everything about Aso: its volcanic activity, plants and animals, hot springs, grasslands, and more. In addition to touring the center, visitors can enjoy the nature of the surrounding area through the Volcano Experience Program. Location: Akamizu 1930-1, Aso City, Kumamoto Prefecture, Tel: 0967-34-2111; Hours Open: 9:00am-5:00pm (Admission allowed until 4:30pm), Closed Open daily throughout the year Admission: Requires a fee
Aso Grassland Conservation Centre houses two facilities, the Grassland Education Centre and the Grassland Information Centre, the Aso Grassland Conservation Centre is a site where visitors can learn about, study, and protect the grasslands of Aso through a variety of activities. The Centre offers a variety of services, including use for school education or excursions, consultation on educational program creation, dissemination of information on grasslands and tourism, and eco-tourism. Location: Ozato 656, Aso City, Kumamoto Prefecture, Tel: 0967-32-0100 (Tel:General counter) Hours Open: 9:00am-5:00pm, Closed End and beginning of year
Minamiaso Visiter Center is an activity site for the Aso region, the Minamiaso Visiter Center is a facility that introduces visitors to the attractions of Aso and offers opportunities to enjoy nature. The center houses staff who are experts in interaction with nature, letting visitors experience nature at any time. The center also engages in a variety of events, focused on the neighboring Aso-yasoen Garden. Location: Takamori 3219, Takamori Town, Aso County, Kumamoto Prefecture, Tel: 0967-62-0911; Hours Open: 9:00am-5:00pm, Closed Wednesdays (if coinciding with a national holiday, the next day)
Tourism at Mt. Aso
Websites: Kumamoto Prefectural Government kumamoto.guide ; Aso Volcano Disaster Prevention Council Aso Volcano Disaster Prevention Council Government National Park Site National Parks of Japan ; Map: Map: Crater map aso.ne.jp/~volcano Hiking Map best-hike-japan.co
Accommodation Areas: Minamiaso, Jigoku Tarutama, Senomoto, Uchinomaki Onsen, Waita Onsen Area, Tsuetate Onsen, Minamioguni Spa Village, Kuju Plateau, Chojabaru, Sujiyu, Yutsubo, Beppu Onsen, Takeda Spa Village, Yuhuin Yunohira Ryokan and Minshuku Japanese Guest Houses Japanese Guest Houses Budget Accommodation: Japan Youth Hostels Japan Youth Hostels Check Lonely Planet books
Getting There: The JR Aso Station is on the train line between Kumamoto and Bepphu. From there you can catch buses to a cable car station near the main crater. 1) From Haneda Airport in Tokyo it takes about one hour 45 minutes to get to Oita Airport. Take airport shuttle about 55 minutes to get to Yufuin Station (Yufuin Ekimae Bus Center). From there take a Sanko Bus Expressway Bus about 52 minutes to get to Kuju Tozanguchi (Chojabaru), the bus stop closest to Chojabaru Visitor Center 2) From Haneda Airport it takes about two hours to get to Aso Kumamoto Airport. Take a Miyazaki Kotsu Expressway Bus about 55 minutes to Takamori Chuo Station. From there take Takamori Chomin Bus about 10 minutes to get to National Park Resort Village Minamiaso, the bus stop closest to Minamiaso Visitor Center 3) From Haneda Airport in Tokyo it takes about two hours to get to Aso Kumamoto Airport. From there take a Sanko Bus Limited Express Bus about 50 minutes to get to Aso Station. Lonely Planet Lonely Planet
Aso-Kuju National Park
Established in 1934, Aso-Kuju National Park covers an area of 726.78 square kilometers in Kumamoto and Oita Prefectures. The park embraces Mt. Aso and its huge caldera and extends to the north into the Kuju Mountain Range and includes the grasslands surrounding them. Inside the park are fuming Mt. Nakadake crater, the beautiful volcanic cone of Komezuka, vast Kusasenri-ga-hama, and the crater floor and somma surrounding them. [Source: Ministry of the Environment Government of Japan]
Around Kuju Mountain Range in the middle of the park, there can be seen solfataric phenomena and scenery unique to volcanoes. There are many highlights, such as the vast grasslands of Kuju Plateau and and Handa Highland and scholarly important wetlands of Tadewara Moor and Bogatsuru Moor. In the north of the park, Mt. Tsurumi and Mt. Yufudake, which are the source of onsens, such as Beppu and Yufuin, boast beautiful mountain shapes. The ridges command a panoramic view from Beppu Bay and Yufuin Basin to Kuju Mountain Range.
Inside Mt. Aso’s caldera is central cone composed of the five peaks of Mt. Aso (the highest one is Mt. Takadake at 1,592 meters) and the crater floor and somma surrounding them. Although the scenery is rough around the volcano, the more you go away from the crater rim, the more you will see grasslands with many plants on a more pastoral landscape. Kuju Mountain Range is comprised of tholoid volcanic topography consisting of peaks, including Mt. Nakadake (the highest peak, 1,791 meters high), offers more diverse scenery.
There are volcanic plateaus formed by volcanic ash and other materials in its north and south, presenting magnificent grassland scenery. There also are many dips that have developed into a lot of moors by abundant spring water and rainfall. Such a contrast of volcano and grasslands is one of the major attractions for visitors to this park.
Plants and Animals in Aso-Kuju National Park
The ecology of Aso-Kuju National Park is roughly classified into three of solfataric wilderness where volcanic gas fumes; forests that spread over the mountain base; and grassland that is maintained by controlled burning and mowing. The solfataric wilderness has peculiar biota where animals and plants have adopted to the harsh environment. The forests, including secondary forest and natural forest among other types, foster a wide variety of animals and plants. The grassland shows different vegetation depending on usage and management by human, including tall-grass vegetation where Japanese silver grass is dominant by continued controlled burning and mowing, and short-grass vegetation where zoysia is dominant by pasturing of cows and horses, each presenting ecology that fosters specific animals and plants. Around the volcano, due to the effect of volcanic gas, characteristic plants, such as Rhododendron kiusianum and Cowberry, grow in clusters, presenting unique scenery. [Source: Ministry of the Environment Government of Japan]
The grassland area over the mountain base has been kept from becoming a forest through such activities as pasturing, controlled burning, and mowing for many years. The dominant species is Japanese silver grass, but precisely because it is kept as grassland, many rare endangered species such as Echinops setifer, Viola orientails, and Ehimeayame (iris) are preserved. It is a very important habitat for such plants. In the Tadewara Moor and other moors, you can see scholarly precious vegetation where Sawagikyo (balloonflower), Numagaya (grass), and other plants grow in clusters.
Viola orientalis bloom in April and May throughout the grasslands of the Aso region, producing a yellow carpet in the blackened remains after the grasslands have been burnt off. Rhododendron kiusianum is a member of the Azalea family found on bare volcanic mountainsides in Kyushu. The mountains are covered in pink when the flowers bloom in May and June. In the Kuju Mountain Range, this species is being overwhelmed by other species, and is dying out. Protective measures are underway. Echinops setifer is a rare plant that still remains. Spread from the continent to Japan in the Ice Age its spherical flowers bloom in azure blue in August and September. Leaves resemble those of the thistle, and have prickles. Found on grasslands. Susceptible to extinction as grasslands disappear.
Some of the characteristic creatures here are butterflies, including rare species that eat grass, such as Shijimiaeoides divinus (that eats Shrubby sophora) and Scarce Large Blue (that eats Great Burnet). Additionally, there live such insects as Kyushu-ezozemi cicada in forests and Daikoku-kogane (scarab beetle) on the grasslands. Many birds are grassland species, such as Meadow Bunting, Chestnut-Eared Bunting, Zitting Cisticola, Japanese Reed Bunting, and Black-Browed Reed Warbler, and there also are raptor species such as Eastern Buzzard and Japanese Sparrowhawk. Other creatures include Japanese Odd-scaled Snake and Tiger Keelback and the Japanese Giant Salamander, Spotted Salamander, and Kajika frog for amphibians.
Volcanic Features of Aso-Kuju National Park
Five Peaks of Mt. Aso refers to Mt. Takadake, Mt. Nakadake, Mt. Nekodake, Mt. Kijima, and Mt. Eboshi. The five peaks resemble the Buddha asleep face-up, and therefore, collectively referred to as "Reclining Buddha." Mt. Nakadake is an active volcano. Daikanbo is a peak that is a good lookout site that allows you to see the five peaks of Mt. Aso called "Reclining Buddha of Aso," and commands a view of surrounding vast grassland and also north side of the Aso caldera below your eyes. There is a parking lot from where you can walk to the lookout spot in about 10 minutes.
Nakadake Central Crater is rare in the world in a sense that visitors can look into the crater. You can go near the crater on foot, by ropeway or car. (Upon visiting, please check the "Information on restrictions for Aso Volcano Crater.") Kusasenri-ga-hama is a double crater in which the crater of about 400 meters was produced inside a crater of about 1 kilometers in diameter. There are two ponds and grasslands, which allow you to spend time in a relaxed way in the idyllic scenery. Komezuka is the most recently shaped among the Aso volcanoes. It was created about 3,000 years ago and has a beautiful cone shape as if you turned down a bowl. It is about 80 meters high and has a vestige of crater at the summit. (You can't enter here because of vegetation preservation.)
Komatsu Jigoku is natural fumarole zone where hot water, water vapor, and mud spout out. There is a walking trail, letting you enjoy the scenery while feeling the energy of the volcano close by. Kuju Plateau is a wide and gentle plateau formed by pyroclastic sediment. Pasturing is conducted in the idyllic scenery, and controlled burning is done in spring.
Natural Features of Aso-Kuju National Park
Mt. Kurodake Natural Forest stands out in an area where grasslands predominate. Mt. Kurodake is covered with natural forest up to the summit, with many Japanese beech and Japanese elm. Oike Pond, Shiramizu Spring and Kakushimizu located at the trail entrance are known as some of the best waters.
Kikuchi Gorge is a beautiful valley is located in the northwest of the somma and has various big and small streams and waterfalls. The water temperature is low even in summer, and the cool environment attracts a lot of visitors.
Shirakawa Headspring is one of the water sources of the Shirakawa River, a first-class river in Kumamoto City. Representing the cluster of springs in Minamiaso district, this headspring generates 60 tons of water a minute. It was designated as one of the best hundred waters of Japan selected by Ministry of the Environment.
Kuju Bogatsuru and Tadewara Moor are intermediate moors formed from the springs at the foot of Mt. Kujusan reflect the diverse topology and geology, with a wide range of plant and animal life. The intermediate moors formed in the mountains cover the greatest area in Japan, and are registered in the Ramsar Site.
Mt. Hiiji is popular among trekkers with the summit having a huge community of Rhododendron kiusianum. You can command a view of Bogatsuru Moor, which is a registered wetland under the Ramsar Convention. There are many onsen areas that are the gift of volcanoes and have been loved by local people and tourists from ancient times One of the Major Onsen Areas (Sujiyu Onsen, "Japan's best pelting hot water")
Chojabaru Visitor Center The entranceway to the Kuju area, the Chojabaru Visitor Center is a mini-museum that offers an easy-to-understand introduction to the nature of the area through models, specimens, photos, videos, and more. The Center is also connected to the nature trail that leads directly to the Tadewara Moor, letting visitors experience nature close-up through the changes of the four seasons. Location: Tano 255-33, Kokonoe Town, Kusu County, Oita Prefecture, Tel: 0973-79-2154; Hours Open: 9:00am-16:00 (closed at 17:00 from May to October), Closed 12/29-1/3
Mt. Aso Eruptions
Mt. Aso erupted in a big way 90,000 to 100,000 years ago, leaving the entire island of Kyushu covered in lava and ash. Such “massive eruptions’ occur once in 20,000 to 50,000 years. In the past 1,000 years there have been 15 “large scale” eruptions, in which over 100 million cubic meters of material was ejected during the eruption. Smaller but deadly eruptions occurred in 1958, killing 12 visitors near the crater, in 1979 killed, when three people were killed one kilometer away, in an area thought to safe. In 1989 and 1990 the cable car was closed by a series of eruptions.
Mt. Aso eruption from Nakadake in 2014 affected flights in southern Japan, Jiji Press reported: “The column of smoke rose to about 1,000 meters above the volcano...Japan Airlines rerouted one of its flights out of Tokyo International Airport at Haneda to Fukuoka Airport in neighboring Fukuoka Prefecture. It was originally destined for Kumamoto Airport, located about 20 kilometers west of the volcano. In addition, JAL canceled 14 flights, including one between Kumamoto and Osaka International Airport at Itami in Hyogo Prefecture. Volcanic activity also caused cancellations or reroutes of nine flights by Skynet Asia Airways, also known as Solaseed Air, and 12 flights by Jetstar Japan. ANA Holdings Inc.’s All Nippon Airways canceled 18 flights.” [Source: Yomiuri Shimbun, November 28, 2014]
An eruption in September 2015, sent of ash and smoke 2000 meters into the air, tourist scarmbling for the cars and raised question about the restarting of a nuclear plant not so far away. Reuters reported: “Mount Aso is one of the most active peaks in Japan but also a popular hiking spot. There were a handful of people at a parking lot near the peak but they were being evacuated safely, officials said on Monday. They said the eruption had come without warning. Kyushu Electric Power Co said the eruption would have no impact on its nuclear plants, one of which – the Sendai nuclear plant, roughly 100 miles (160 kilometers ) south of Mount Aso – was restarted in August. Television footage showed black smoke boiling into the sky and ash falling as much as 2.5 miles (4km) away, NHK national television said. [Source: Reuters, September 14, 2015]
Major Eruption at Mount Aso in 2016
There was a large eruption on Mt. Aso in 2016. Volcanic ash was sent flying more than 11,000 meters (seven miles) into the sky. The explosive eruption was accompanied by a shock wave carrying airborne ash. It was the first eruption of this type and scale since 1980. Based in part on wind directions, meteorologists warned of a heavy ash fall within 30 kilometers (19 miles) northeast of the mountain, with moderate and light ash falls forecast up to 250 kilometers away for a period of a few hours.
Reuters reported: “Police and municipal governments said there were no reports of injuries from the eruption, which began at 1:46 a.m. local time. “It was the first "explosive eruption" at the peak since January 1980, according to the meteorological agency. The agency raised the alert level for the volcano to level 3 on a scale of 5, telling people not to approach the mountain and warning of falling rocks. It also warned of falling ash in 10 prefectures. TV footage showed volcanic ash had accumulated on cars, houses and roads in the city of Aso and ash was falling as far as 320 km (200 miles) away, Japanese media said. [Source: Reuters, October 8, 2016]
“Farmers have reported that some vinyl greenhouses where tomatoes and asparagus were being grown 6-8 km (4-5 miles) away from the crater had been broken by ash and small rocks. A window was cracked by a falling rock at an Aso youth center about 5 kilometers (3 miles) away from the crater but there were no reports of injuries, an official at Aso city hall said. “"We are concerned that more damage on crops will be reported," the official said. Up to 29,000 households lost power shortly after the eruption but the problem was fixed in less than two hours, a spokesman at Kyushu Electric said.
Wired report: “ Although eruptions aren’t rare at Aso, the scale of this one was larger than usual. Makoto Saito, director of the Volcanology Division of the Japan Meteorological Agency, speculates that pressure from an accumulation of volcanic gases lead to this blast, as most eruptions from Aso do not produce plumes taller than 10 kilometers.. Blocks of volcano junk as large as trucks were spotted near the crater. However, the evidence suggests that this eruption was phreatic—that is, driven by gas and steam, not new magma...“Last fall another eruption of Aso generated some impressive pyroclastic flows. These eruptions from Aso also have a strong impact on the local economy that has already seen consequences of recent earthquakes as well as tourists stay away and crops are damaged. False rumors about the activity at Aso have not helped that situation.” [Source: Wired]
According to the Japan News: “At 9:52 p.m. Friday, a relatively small-scale eruption occurred, about four hours before the large-scale eruption early Saturday. At that time, a crater opened on the volcano, but the volcanic vent appears to have closed again shortly after 1:30 a.m. Due to the closure of the vent, water vapor and volcanic gases rapidly filled the underground space. It is likely this resulted in the explosive eruption with the mounting pressure. Experts warn that volcanic ash that fell and accumulated on mountain slopes can cause sediment disasters if there is torrential rain. According to Masato Iguchi, a professor of volcano physics at Kyoto University, when rain falls, volcanic ash and soil could form mudflows, which can flow down into rivers or valleys at high speeds. Due to this fear, he said people in residential areas in downstream regions need to be cautious. ““People cannot feel safe, even after the eruption has calmed down. I hope people will pay attention to weather information and others,” Iguchi said. [Source: Takako Sasamoto and Shotaro Demizu, Japan News, October 9, 2016]
Causes of the 2016 Mt. Aso Eruption
The October 2016 eruption at Mt. Aso was likely a phreatic eruption, in which underground water in the volcano was heated by magma to cause an explosion. “Signs of a phreatic eruption, such as volcanic earthquakes and minor tremors, have been observed since the beginning of October according to Takahiro Okura, a professor at Kyoto University's Aso Volcanological Laboratory, a research facility that observes the volcanic activities of Mt. Aso in Kumamoto Prefecture. “According to the Japan Meteorological Agency and other sources, an eruption occurred at around 9:50 p.m. about four hours before the main eruption. In the first eruption, a crater opened on the volcano, but closed for unknown reasons before dawn. Underground pressure rapidly increased due to the closure and likely led to the phreatic eruption. [Source: Yomiuri Shimbun, October 9, 2016]
The rapid build-up of volcanic gases and vapors rapidly underground and growing pressure are believed to have caused the large-scale explosive eruption on Mt. Aso in October 2016. “Concerning Mt. Aso, it is extremely rare for the height of the columns of volcanic smoke to exceed 10,000 meters ,” Makoto Saito, director of the Volcanology Division of the Japan Meteorological Agency said. “During Mt. Aso’s eruption in September last year, the height reached 2,000 meters.. This time, earthquake-like tremors were observed in nearby areas and volcanic ash fell on the Shikoku region, which is located far from Mt. Aso.[Source: Takako Sasamoto and Shotaro Demizu, Japan News, October 9, 2016]
Takako Sasamoto and Shotaro Demizu wrote in the Japan News:“The explosive eruption accompanied by large-scale air vibrations at Mt. Aso in Kumamoto Prefecture was the first of its type in 36 years. According to experts, the eruption was likely a phreatic explosion in which underground water was boiled by magma heat, which caused an explosion. Other types of volcanic eruptions involve underground magma that is directly discharged from the volcano. But Yasuo Miyabuchi, an associate professor of volcanic geology at Kumamoto University, who conducted on-the-spot research on Mt. Aso on Saturday, said traces of discharged magma were not found, and thus it is highly likely it was a phreatic explosion “The quantity of volcanic ash discharged this time could be at least 100,000 tons,” Miyabuchi said.
“Prof. Takahiro Okura of the Aso Volcanological Laboratory of Kyoto University in Kumamoto Prefecture, an expert on volcano physics, said it seems that ash deposits the size of pickup trucks were scattered across areas several hundreds meters away from the volcanic vent. Okura believed one reason for such a large-scale eruption is that underground pressure rapidly rose just before the eruption.”
It is not known if the large 7.0-magnitude Kumamoto earthquake in April 2016 played a apart in triggering the eruption. Scientists believe an underground magma reservoir likely expanded horizontally by 30 to 40 centimeters after the earthquake as a fault near the magma chamber shifted position because of the earthquake. The earthquake is thought to have made it easier for magma to move up from undergound.
Color Changes at Mt. Aso’s Active Crater Lake
According to a research paper entitled “Color change of lake water at the active crater lake of Aso volcano, Yudamari, Japan: is it in response to change in water quality induced by volcanic activity?” the crater lake in Nakadake changes colores based on different conditions. [Source: Shinji Ohsawa, lead author, Takeshi Saito, Shin Yoshikawa, Hideo Mawatari, Makoto Yamada, Kazuhiro Amita, Nobuki Takamatsu, Yasuaki Sudo, Tsuneomi Kagiyama, Limnology, December 2010, Volume 11, Issue 3, pp 207–215]
The abstract of the paper reads: “One feature of volcanic lakes influenced by subaqueous fumaroles existing at lake bottoms (called active crater lakes) is the remarkable color of their waters: turquoise or emerald green. The active crater lake named Yudamari at Mt. Nakadake of Aso volcano, Japan, takes on a milky pale blue-green. The particular blue component of the lake water color results from Rayleigh scattering of sunlight by very fine aqueous colloidal sulfur particles; the green component is attributable to absorption of sunlight by dissolved ferrous ions. An objective color observation conducted during 2000–2007 revealed that the lake water color changed from blue-green to solid green.
“The disappearance of the blue ingredient of the water color will result in diminution of aqueous colloidal sulfur from chemical analyses of lake waters sampled simultaneously. The aqueous sulfur is produced by the reaction of sulfur dioxide and hydrogen sulfide supplied from subaqueous fumaroles. However, its production efficiency decreases by domination of sulfur dioxide in the subaqueous fumarolic sulfur gas species with increasing subaqueous fumarolic temperature. The disappearance of blue ingredients from the blue-green color of the lake water may be attributed to activation of subaqueous fumarole activity.”
Image Sources: Volcano Research Center University of Tokyo, USGS
Text Sources: New York Times, Washington Post, Los Angeles Times, Daily Yomiuri, Times of London, Japan National Tourist Organization (JNTO), National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
Last updated August 2020