The Tokachi (Tokachidake / Diesetsuzan) Volcanic Group includes multiple stratovolcanoes and dome complexes arranged generally along a SW – NE line in central Hokkaido, Japan. The volcanoes erupt primarily andesite, basalt and the occasional dacite. The highest peak in the group is Mount Tokach, at 2,077 mi. Recent activity is on the NW end of the primary line.
The Tokachi Volcanic Group is located in the SW portion of the Diesetsuzan National Park in central Hokkaido. This national park is just under 2,300 km2 in the mountainous center of Hokkaido. It is the largest national park in Japan. The name translates to “great snowy mountains” and contains 16 peaks over 2,000 m high. It has some of the most rugged scenery in Japan, back country skiing, hiking, camping, wildlife viewing, and alpine meadows. There are multiple hot spring resorts in the park associated with active and recently active volcanic systems. There are also natural hot springs accessible when hiking, though caution is recommended as these tend to heat up when volcanic activity increases in some locations.
The park contains three volcanic groups. The Daisetsuzan Volcanic Group is in in the northern part of the park. It includes Hokkaido’s tallest volcano, Mount Asahi. The Tokachi Volcanic Group is in the SW part of the park and includes Mount Tokachi. The Shitaribetsu Volcanic Group is on the eastern part of the park and includes Mount Ishikari. The Ishkari River with its headwaters on the flanks of Mount Isikari is nearly 270 km long, one of the longer rivers in Japan. Fishing, canoeing and other water sports are available on the river and on various lakes in the park.
The park is accessible from Sapporo by train and then bus. Vehicle rental is also encouraged. The local winter highlight is the Sounkyo Ice Waterfall Festival Jan – Mar each year. The area has a long winter with plenty of snow and a short summer. Autumn foliage reaches its peak mid-Sept before the first snows in Oct. Late fall visits are highly recommended. There are four hiking trails to the peak of Tokachi. Hot springs are found at its base. As the park is rugged and the weather cold and harsh, hikers and campers need to be careful of local conditions. In Jul 2009, 64-year old hiker died of exposure. 5 other members of his party had to be rescued.
There is a thriving skiing operation in the park. There is a cable car in the northern end of the park up Mount Asahi that runs year-round. Tokachi is popular for back country powder skiing, though there are no lifts or ropeways up its flanks and few if any marked trails.
Granyia covered the Daisetsuzan Volcanic Complex and Mount Tokachi in her Volcano Armchair Hiking Christmas Special post Dec 2019.
The closest towns are Kamifuran Town with just under 12,000 people, and Biei Town with nearly 11,000. The Daisetsuzan National Park surrounds the volcanic group and sees around 350,000 visitors to the Tokachi area each year. There are 15,000 mountain climbers on Tokachi yearly. Around 60,000 live within 30 km, 1.4 million within 100 km.
The volcano is well instrumented with multiple seismometers, GPS, tiltmeters, microphones, and cameras.
Recent volcanoes in this portion of central Hokkaido are grouped into the Taisetsu – Tokachi – Shikaribetsu (TTS) Volcanic Field.
Welded tuff composed by over eight silicic pyroclastic flow deposits came from the TTS. The largest of these was the caldera forming eruption a the Tokachi – Mitsumata Caldera on the NE part of the TTS. After multiple caldera-forming events, this activity created two volcanic groups – the Nipesotsu – Shiraribetsu group to the south and the Taietsu – Tokachi group to the NE.
The Shikaribetsu volcanic group was andesitic dome-forming eruptions several tens of thousands of years ago. The Nipesotsu group has an andesitic stratovolcano 400 ka, Maruyama volcano on the southern part of Nipesotsu volcano is still active. The Taisetsu volcano group is to the north and has two stratovolcanoes, Kita and Minami Taisetsu volcanoes. The most explosive eruption of these two took place 38 ka at Taisetsu volcano. The Tokachi group is located at the SW end of the Taisetsu – Tokachi volcanic chain and is still currently active.
VOGRIPA lists two caldera forming eruptions as VEI 7 eruptions in the region. The first, from Tokachi produced the Tokachi ignimbrite, the HR-6 ash. This eruption took place 1.25 Ma and was a VEI 7 that produced over 100 km3 of bulk volume. The Tokachi deposit has a wide distribution and range of ages.
The more recent caldera forming event from Tokachi-Mitsumata took place 1 Ma, ejected over 100 km3 bulk volume, and created the 8 km diameter caldera. It is bounded by the Ishkari Mountains in the north and by the Nipesotsu-Maruyama Volcanic Group to the south.
There were 5 subsequent VEI 6 eruptions 1.25 – 0.14 Ma that produced around 10 km3 apiece. Most of these took place 1.25 – 0.51 Ma. There was an extended 0.37 Ma hiatus between the last two of these. There are multiple pyroclastic flow units in the Biei and Kamikawa areas of central Hokkaido. These are the Biei, Tokachi and Sounkyo deposits. There is a significant discrepancy in the age of the Biei deposit, with one source dating it around 0.8 Ma and the other at 1.9 Ma. I tend to believe the latter, as it is overlain with the two ignimbrites from Tokachi.
The Tokachidake Volcano Group includes at least 12 volcanoes 1,400 – 2,000 m above sea level. Base diameters are 3 – 10 km. The primary string of 6 volcanoes is aligned NE – SW in a 18 km line. There are another three volcanoes oriented at right angles to this string. The volcanoes are surrounded by volcanic fans / debris fields. There are craters visible along with fresh lava flows on the NW slope near the summit of Tokachi, situated at the center of the group. There is a crater on the NW side of Kamihorokamettoku. This has been enlarged by erosion and has collapsed walls. There are also debris avalanche and landslide deposits widely distributed on the downstream side of the crater and collapsed walls.
Basement rocks of the group are Pliocene volcanic rocks including the Biei pyroclastic flow deposits, 1.9 Ma, and Tokachi pyroclastic flow deposits, 1.1 – 1.2 Ma. These are rhyolitic ignimbrites. Both flows are sourced from the NE part of the group. The Biei flow deposits are cut by faults and covered by more recent deposits from the Tokachi Volcano Group. There are no other recognizable faults, meaning that more recent faults have not been active under the group.
Activity has been divided into three stages, Older, Middle and Younger. These date respectively 1 Ma – 500 ka, 300 – 60-50 ka, and 60-50 ka – present.
The Older stage took place from the Tairoku volcano and associated with two substantial lava flows, though their actual source is unknown. This volcano is on the southern part of the group and is surrounded with significant deposits of gently sloping debris from the volcano group.
The Middle Stage saw an expansion of the number and distribution of eruptive centers. Products are generally basaltic to andesitic lavas and pyroclastics that built stratovolcanoes. There was likely a hiatus in activity of several hundred thousand years between the Older and Middle stages. Three volcanoes were active in the NE, SW and SE parts of the group 300 – 200 ka. Most of these have heavily eroded craters. A second round of activity 200 – 60-50 ka filled in the gaps between the first three volcanoes during this stage. They also built the line of volcanoes perpendicular to the main group. There were at least two small flank collapses creating western-facing amphitheaters at the summit craters of Biei and Furano. Other craters have been eroded. All volcanoes are surrounded by widely distributed debris and lahar deposits.
The Younger stage has seen eruptive centers converge to the central part of the volcano group. While there may have been a hiatus between activity of the Middle and Younger stages, it has not been defined as yet. Eruptive products are basalt and andesitic lavas and pyroclastics erupted from multiple craters. Lava flows are clearly visible from this stage.
During the early part of this stage, eruptions took place from Kamihorokamettoki, Nokogiri and the summit of Tokachi, a 3 km diameter location. There was a debris avalanche followed by a series of lava flows. The Kamihorokamettoki crater largely disappeared due to collapses and erosion.
The more recent activity created the Ground, Suribachi, Kitamuko, Central and 62 craters on the NW side of Tokachi and the Nukkakushi crater on the W side of Kamihorokamettoki. Nukkakushi activity was only phreatic while the rest of the activity was magmatic producing pyroclastic flow, air fall and lava flow deposits. There was also a small amount of debris flow deposits from this activity. Most of the activity was basaltic and andesitic with repeated explosive and effusive eruptions.
Recent eruptions have taken place on the NW flank of Tokachi, forming multiple craters. The most recent peak of activity was 4.7 – 3.3 ka, with repeated dome collapses, explosive eruptions, and pyroclastic flows. The Ground Crater was formed around this time. Near the end of this period, the crater produced lava flows and a pyroclastic flow.
Over the last 3,300 years, activity can be divided into four stages. Stage I was more recent than 10 ka, produced the most explosive and voluminous eruptions, and created the Ground Crater. This eruption started with scoria and pumice air-falls and pyroclastic flows. It ended with basaltic lava flows. Ground Crater produced at least two pyroclastic flows 4.7 and 3.3 ka. These were followed by effusive lava flows. Total Ground Crater deposits are estimated at 0.07 km3 DRE.
Stage II included three explosive eruptions to create a maar and multiple scoria cones on the NW flank of the volcano. Like Stage I, it ended with effusion of basaltic lava flows. This stage ended around 1,000 years ago. This activity took place at the Suribachi and Kitamuki craters. It also produced the Yakeyama lava, all to the N of Ground Crater. Activity here produced welded pyroclastics, built multiple scoria cones, blanketed the area with ash fall, and ended with another lava flow. Total volume of this activity is estimated at less than 0.04 km3 DRE.
Stage III began after several hundred years of dormancy with an explosive eruption that formed Central Cone. This stage also ended with an effusive lava flow. It took place 800 – 300 years ago. Activity built a small pyroclastic cone on the NW side of Ground Crater. Ejecta was basalt, small scale scoria deposit, and an a’a lava flow at the end of the activity. Total ejecta is estimated at 0.02 km3 DRE.
Stage IV began in 1926 with multiple magmatic eruptions near Central Cone. In 1962, a voluminous explosive eruption created new craters on the southern flank of the cone. Today, the 1962 eruption is considered to be the first eruption of the new stage due to the change in eruptive style at each stage. Total amount of effusive magma over the last 3,300 years is 0.1 km3. Each eruption produces less than 0.02 km3 DRE, a low discharge rate compared with other active Japanese volcanoes. However, lahars are repeatedly associated with the volcano over the last 3,300 years and should be considered a serious hazard from the volcano.
The volcano produced a pyroclastic flow in 240 BC that reached 6 km NW of the crater. An eruption in 1670 produced a a’a lava flow that reached 3 km NW of the crater. For an active volcano, Tokachi does not have an extensive history of recorded eruptions, with most records being after 1857.
There were three magmatic eruptions of Tokachi in the 20th Century. Different modes of magma ascent caused the different eruption styles.
The 1926 eruption was the most severe volcanic event in Japan during the last century. It produced a sector collapse, debris avalanche, and lahar that ran out at least 25 km, destroying forests, farms and a town, killing 146. Melted snow from the eruption created the lahar. It was a phreatomagmatic eruption from the Taisho vent and preceded by 3 years of increased solfataric activity, rumbling, tremors, and minor ash ejection.
Basaltic magma for the 1962 eruption appeared to be injected into a zoned andesitic magma chamber several months before the eruption. The mixed magma rapidly ascended without stagnating and produced a subplinian eruption. This created the 62-0 – 62-4 vents. The eruption put a plume 12 km above the volcano and killed 5 mine workers on a sulfur mine with ballistic blocks. Only the 62-2 and 62-3 craters still exist.
This also took place some six months before the 1988 – 1989 eruption. In this case, the rising magma stagnated a bit at shallower levels before the eruption, creating a series of Vulcanian eruptions. There were 23 explosions over the 3 months of the 1988 – 1989 activity. The series kicked off with a small phreatomagmatic eruption in Dec 1988. The eruptions produced small pyroclastic flow and surge deposits and ejected ballistic bombs around the 62-2 crater.
There have been no eruptions after 1988 – 1989, though vigorous fumarole activity from recent craters suggest we are at the start of the next cycle of activity.
Recent eruptive activity has followed increased fumarole and thermal activity, rising ground temperatures, and increased volcanic gasses for several years before the eruption. Increased seismic activity shows up several months before eruptions. Eruptions are immediately followed by further increases in seismic activity and deformation around craters. Explosive eruptions are preceded by inflation below the crater and increased low frequency earthquakes.
Sulfur mining on Tokachi began around 1912 at Central Crater. Production of sulfur increased for a few years before the 1926 and 1962 eruptions. However, mining was halted after the 1926 eruption due to deaths of the miners. It resumed in 1955 but was completely abandoned completely following the 1962 eruption. Hot springs exist at several locations on the NW side of the volcano group. Temperature of the springs are 30 – 45 C. Temperatures increased before and after the 1988 – 1989 activity at Fukiage Hot Spring.
There was a weak tremor episode June 1990. Increased seismicity took place July 1995, 4.3 km NNW of 62 Crater. This continued through Dec 1995. Tremor returned May 1996. The most recent episodes took place at Taisho crater June 2012. It produced hot gas but no ejecta, volcanic glow from high temperature areas on the E wall of Taisho crater. This was interpreted at a small new fumarole. Activity also included short duration of volcanic tremor on July 11, 2021 with a small area of inflation in the shallow part of 62-2 Crater.
We covered tectonics of Hokkaido in multiple Hokkaido posts – Granyia’s Miss Akan, my Toya Caldera, Mashu Caldera, Kutcharo Caldera, and Akan Caldera. In my opinion, Granyia did it first and perhaps best, so I will reproduce her analysis from 2015 below:
Hokkaido is the northernmost of Japan’s 4 main islands and lies completely on the North American/Okhotsk Plate. However, it is situated at the junction of two arc-trench systems, NE Japan and Kuril arcs, in both of which intense volcanism has continued since the late Miocene. Tectonically, it was formed by the collision of these two arcs at the central part of Hokkaido during the Middle Miocene (ca. 12 million years ago). Subduction of the Pacific Plate occurs oblique to the Kuril Trench, causing a strike-slip movement along the Kuril Arc, which results in a local collision zone within the Okhotsk Plate in central Hokkaido.
In the eastern region of Hokkaido, NE trending uplift areas with volcanoes are arranged en echelon* toward the Kuril Islands, including the Akan volcanoes, the Shiretoko Peninsula, the Kunasir Island, and the Etorofu Island. This en echelon arrangement of the uplift areas is attributed to the oblique subduction of the Pacific Plate at the Kuril Trench. The Tokachi Volcanic Group belongs to the “volcanic front” which runs parallel to the Japan and Kuril trenches, i.e. E-W from the eastern region through the central region and then turns to N-S in the western region. It is located at the SW end of the Kurile volcanic arc.
*The term ‘en echelon’ refers to closely-spaced, parallel or subparallel, overlapping or step-like minor structural features in rock (faults, tension fractures), which lie oblique to the overall structural trend.
The Tokachi Volcanic Group continues to be an active and dangerous volcanic system. Fortunately, it seems to give ample warning before major eruptions. Sadly, it is unclear whether or not current activity is a warning or not. The other bit of good news is that this is a relatively remote region, though does support an extensive tourism flow. Lahars and debris flows generally from melted snow continue to be the most immediately dangerous threat from this volcanic group.
Dense clustering of latest Cenozoic caldera-like basins of central Hokkaido, Japan, evidenced by gravimetric study, A Yammamoto, Mar 2004 Calderas and active volcanoes in central to eastern Hokkaidy, T Hasegawa, Jun 2013