While there is no shortage of volcanos in Hokkaido and Japan, few feature fumaroles that are as easily accessible as those of Mount Io (Atosanupuri) in Akan-Mashu National Park in Eastern Hokkaido. With its 1500 fumaroles, it stands out with its barren beauty, while also facilitating a diverse biosphere in the surrounding area. In fact, the acidic ground around the mountain even helps alpine plants to thrive which usually only grow at a significantly higher altitude.
Given that I have been fascinated by volcanos for as long as I can remember, I know that I had to include Mount Io in my Hokkaido itinerary, and the volcano did not disappoint. It is a captivating environment in which a continuous symphony of steam tells stories of our planet’s restless energy.
Thanks to its easily accessible viewing area and a trekking tour that allows you to venture into a restricted area, Mount Io is the perfect place to observe the fumaroles surrounded by yellow needle-like sulfur crystals.
While the main observation area is already a fascinating place to visit, it is the guided trekking tour that offers a thrilling off-the-beaten-track adventure that few people have experienced. In fact, in 2022 only 196 hikers join the trekking tour during which one can see more of this stunning area while learning more about its history.
I was able to hike Mount Io (Atosanupuri) during a press trip organized by JTB. As always, all opinions expressed are my own.
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At a Glance: Mt. Io
Best Place to Stay: ANA Crowne Plaza Hotel Kushiro
Getting there: Take the JR Senmou Line to JR Kawayu Onsen Station or rent a car
About Mount Io (Atosanupuri)
Mount Io is an active volcano that is rich in sulfur and has over 1500 fumaroles. It is one of ten volcanos called ‘Mount Io’ in Japan, with four of them being in Hokkaido including one on the Shiretoko Peninsula.
However, there is only one Mt. Io that has the Ainu name Atosanupuri which translates to “naked mountain”. It received its Ainu name due to the lack of vegetation on the volcano, which stands in contrast to the vegetation-covered surrounding area.
While the volcano itself is bare, the surrounding area features a peculiar plant life thanks to the acidic ground where only the strongest plants survive. These plants include alpine plants that usually only grow above an altitude of 1000 meters including marsh Labrador tea.
The Atosanupuri volcanic group which includes Mount Io formed around 7000 years ago during an eruption on the east side of the Kusharo caldera. However, the geological forces only led to the mountain’s current form between 500 to 2000 years ago. Its summit is at a height of 508 meters.
Today, the volcano is observed 24 hours a day with the help of seismographs and tiltmeters that are used for elevation monitoring. It is currently at volcanic alert level 1, which means it is currently relatively safe to visit it. Nevertheless, you should always be careful as the steam can cause injuries, and follow the directions of officials including trekking guides.
Due to the sulfur, visiting Mount Io can be problematic if you have asthma and similar medical conditions.
The volcano is the source of the hot springs of Kawayu Onsen including the Kawayu Onsen public foot bath which has very acidic water with a PH level of 2. I recommend stopping here after your Mount Io trekking tour.
Sulfur Mining History
Nowadays, Mount Io is a protected natural site, but in the past, it served as a sulfur mine. In 1877, a rising national demand for matches and gunpowder, and therefore sulfur, led to the establishment of a commercialized mining business. Additionally, the sulfur of Mount Io was also used to bleach paper white in Kushiro. By 1898, the mining site had the highest sulfur mining gross in all of Hokkaido.
While the sulfur was initially transported by horse wagon, in 1887, a railway connection to Shibecha was built. Known as the Yasuda Line, it was the second railway line of Hokkaido and facilitated the development of the entire area.
After being transported to Shibecha town, the sulfur was subsequently transported to Kushiro via the river from where it was shipped.
However, the ability to mass transport sulfur led to a depletion of the sulfur resources of Mt. Io within 9 years. As a result, the railway directly to Mount Io was suspended in 1896. The sulfur mine of Mount Io was reopened from 1919 to 1944 and then again from 1951 to 1963 when it was closed for good.
Since then, most of the rail tracks have been removed, while some wooden parts of the old mine remain on Mount Io.
Fumarole Observation Area
If you do not want to hike but still want to see the fumaroles of Mount Io, you can do so from an observation area close to the parking lot. While it is still a short walk on uneven terrain, no hiking gear of any kind is required to get close to the fumaroles.
The dangerous areas of the main viewpoint are fenced off, but you should still be careful. Do not attempt to climb over the fence as the steam escaping the fumaroles has a temperature of 100°C.
If you want to expand your experience beyond marveling at the fumaroles and the neon-yellow sulfur surrounding them, you should enter the Iozan Rest House.
Aside from souvenirs, food, and drinks, they also sell eggs cooked in the steam of the fumaroles. While these eggs look rather normal and do not turn black like those of Owakudani near Hakone, it is cool to eat something cooked by the powers of nature.
‘Atosanupuri Trekking Tour’
If you are looking for an adventure that has you exploring more of Mount Io and its history, the Atosanupuri Trekking Tour is ideal for you. After being closed for more than twenty years due to a rockfall incident, the trail was reopened around three years ago as part of an ecotourism project.
The trail takes you through a restricted entry zone under the Ecotourism Promotion Law, and as such, you can only hike it while accompanied by a certified guide. Hereby, all guides are local residents and cannot accompany more than six hikers at a time.
The hike starts with a walk through a forest along the path of the former railway track. And while the main tracks have been removed, you will see some of them after cutting into the forest after around 1 km on the old railway path. Over the past 60 years, this remaining section of the tracks has been lifted by quick-growing birch, which makes it a rather peculiar sight.
As you continue walking through the forest in a single line, the trail crosses an old lava flow before it takes you to a monitoring station with a seismograph and elevation monitoring. This spot marks the beginning of the restricted zone so you have to put on the helmet.
While doing so, we were told about the evacuation route in case of an eruption alarm, and for a minute I could not help but question my decision to hike an active volcano with a lot of fumaroles. But ultimately, curiosity and the knowledge that the mountain is monitored 24/7 won.
The first noteworthy location in the restricted zone is the stopping point of the old rail tracks. While the tracks themselves were removed, the wood remains to this day as it does not rot in the absence of bacteria.
The hiking trail then has you climb up the mountain, and as you look around you, you see fumaroles surrounded by yellow-colored sulfur crystals all over the mountain.
As you gain elevation, the view slowly opens up, and the stark contrast between the bare Mount Io and the lush surrounding area becomes strikingly obvious.
After taking in the view, the trail keeps gaining elevation until you reach a split-off point from where you can reach the big crater also known as ‘Bear Trap’. Formed during the last eruption several hundred years ago, its lowest side is at a height of 350 meters and therefore marks the highest elevation of this Mount Io hike.
Having hiked to the summit of Mt. Meakan the previous day, I was likely rather spoiled in terms of what a crater can look like. Therefore, this crater admittedly felt somewhat underwhelming despite its size. In fact, it looks more impressive from a hundred meters away. After all, you only see a stone-filled crater while standing on the lower area of the crater rim.
Please be careful while near the edge. There is an old shrine to children who died here after falling into the crater while on a school trip. Take it as a warning reminder that even small drops can be dangerous and that it is vital to never walk right at the edge – especially, if the ground could be unstable.
My personal highlight of the Mt. Io hike comes shortly after descending from the crater rim. Known as F1, the biggest fumarole of Mount Io is more than an impressive sight. As you stand or sit on the ledge near it, you can safely observe the raw power of the earth and enjoy a great view of the neon-yellow sulfur crystals and the continuously emerging steam.
Funnily enough, it was the trails back down from this point, that ended up being the most challenging element of the hike as you follow a deer trail. Due to rain on the previous days, the earth slope had plenty of slippery sections and it was good to wear gloves and long sleeves as branches arch into the path. After all, “the deer do not care about the branches”, and as such they arch heavily onto the path.
Difficulty
The Atosanupuri Trekking Tour requires a moderate fitness level, as it is a 4.5 km long hike on uneven terrain with an elevation gain of around 200 meters. While the summit of Mount Io is higher, you will only go up to 350 meters with the trailhead already being at an elevation of 150 meters.
Generally speaking, I would say that this hike was not as challenging as other hikes I did in Hokkaido. While I have also done my fair share of solo hikes and know how to spot where to go on an unmarked trail, I was glad to be accompanied by a guide.
After all, there are fumaroles all over the area, which makes it crucial to only walk where the trained guides walk to avoid burning yourself.
Please follow the rules and book the guided trekking tour if you want to do this hike. They are in place to protect you and the environment.
Hiking Essentials
If you want to hike Mount Io, it is advised to use hiking poles and wear trekking shoes, as the ground can be slippery. In addition to that, I highly recommend wearing long pants and bringing a jacket or sweater with long sleeves even on sunny days. After all, you have to push your way through bushes on the way back down, and being able to cover your arms is the best way to avoid scratches. The mandatory helmet as well as gloves are provided for the duration of the trekking tour.
How to Book the Trekking Tour
To book the trekking tour, you can either write an email, give them a call, or fill out a Google Docs form. You can find the contact information as well as a list of what information you have to provide to book the Mount Io Atosanupuri Trekking Tour here. If you do not speak Japanese, I recommend reaching out via email.
Weather-depending, the guided hike is offered from late May to early November. The trekking tour takes around three hours. Therefore, the tour times offered are 9 AM to 12 PM and 1 PM to 4 PM.
The Mount Io trekking tour costs ¥13.000 per person, and there is a minimum of two participants (adults and children over 12). You have to reserve it at least 3 days in advance.
A part of the fee is used for environmental conservation, trail maintenance, and other local projects, making this tour a prime example of ecotourism done right.
Other Hikes near Mt. Io
While the guided trekking tour of Mount Io is a real highlight, there are also several other hikes you can do. All of them are easy trails without much elevation gain and are therefore suitable for all ages.
Aoba Tunnel Trail — An around 1 km long trail connecting Mount Io and JR Kawayu Onsen Station. It follows the old train track and the trees lining it seem to form a natural tunnel. It takes around 30 minutes. You walk a short part of this trail at the beginning of the Mount Io trekking tour.
Tsutsijigahara Nature Trail — A 2,5 km trail to Mount Io from Eco Museum Center in Kawayu Onsen. It takes around 1 hour and as you walk, you can observe the changing vegetation as you get closer to the volcano and the ground becomes more acidic. Closer to Mount Io, you will find a large area of Ezo-iso-tsutsuji, an azalea which is endemic to Hokkaido. it is in bloom from June to July, which makes it the best time to walk along this trail.
Sakhalin Spruce Forest Trails — Two loop trails of 0,8 km and 2 km respectively, that start near the Eco Museum Center. In winter, you can also go snowshoeing.
Things to Know Before Visiting Mt. Io
Best Time to Visit
You can visit Mount Io year-round, but if you want to go hiking, April to early November is the best time. This is also the time frame when the trekking tour is offered, so you have the largest possible choice of hikes.
If you want to see the marsh labrador tea in bloom, June to July is the ideal time to visit, while the winter months are ideal if you want to see the fumaroles near the viewing area surrounded by snow.
Where to Stay
While you could stay in one of the nearby hotels in Kawayu Onsen, I recommend staying in Kushiro as this city is a great base for exploring the area. I stayed at the ANA Crowne Plaza Hotel Kushiro and can only recommend the hotel.
How to get to Mount Io
By Train
The most convenient nearby airport is Kushiro Airport, with direct flights from Sapporo (Chitose and Okadama) and Tokyo (Haneda). From there, you can take the airport bus to JR Kushiro station. The bus ride costs ¥950 and the departure times correspond with the flight arrival and departure times.
If you want to travel in a more sustainable way and want to avoid flying, you can also take the train from Sapporo to Kushiro. There are six Ozora train departures a day, and it takes between 3:51 to 4:20 hours to reach Kushiro.
To get to Mount Io by train from JR Kushiro Station, you have to take the JR Senmou Line to JR Kawayu Onsen Station. The train ride takes 1:30 to 1:40 h and costs ¥2.100.
There are five trains that stop in Kawayu Onsen a day and you can look up the timetable on Navitime. Once there, you can walk to Mount Io along the Aoba Tunnel Trail or take a taxi.
By Car
There is a lot more to see in this area, so consider renting a car to make the most of your time in Akan-Mashu National Park.
If you are driving there yourself, you can park on-site. The parking fee for a car is ¥500, while the fee for vehicles longer than 5 meters (classed as microbus) is ¥1000. The parking lot is not in operation from November to April, but it is allowed to park there if you want to visit Mount Io. Just keep in mind, that the lot is not cleared of snow and can be icy.
Is it worth it to visit Mount Io (Atosanupuri)?
Whether you only want to see Earth breathe through fumaroles or are looking for a trekking adventure that takes you to restricted areas – Mt. Io is worth a visit. There are few places where you can get as close to fumaroles in a safe way, which makes visiting Mount Io a must while you are exploring the area.
While at Mount Io, you can feel the heat, hear the steam escape the ground, and smell the sulfur. But do not touch or taste anything – it is not an experience for all five senses.
More about Japan
If you are planning to hike in Japan, you might also be interested in these hiking-related Japan travel guides:
Hokkaido Northern Islands Itinerary
Hiking the Old Tokaido Highway
Which of the hiking trails will you take when you visit Mount Io?
Let me know in the comments!
Do you want to visit MT Io?
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