Yosomi-yama Route

From the starting point you ascend following the bank of the Ko Usu Ishi river. This river was artificially formed following the 1977-78 eruptions to help prevent mud slides from future eruptions from damaging the Toyako Onsen town area.

From the Ko Usu Ishi river bank you turn left and head up a steep staircase. You are now climbing Mt. Nishimaru-yama, which was formed during the 1910 eruption.

This pyroclastic cone was formed by a tremendous explosion of superheated underground steam which spewed forth in a geyser and created this spectacular geographical terrain.

After passing Mt. Nishimaru-yama you descend slightly and enter a paved road built for local industry. Along this road is the well for one of the sources of Toyako Onsen, and here you can find information on onsens from the Ministry of the Environment.

At this guidepost you turn left off of the paved road and back onto the footpath.

Here you come to a 3-way fork in the footpath.

If you turn right here you will enter a course which runs counter-clockwise around crater number 20.

This path runs along a ridge between crater number 20 on the left and crater number 19 on the right. Crater number 20 is the second largest crater formed during the 1910 eruption. It is also the deepest crater. According to a survey done in 1913 it has a depth of 43m and a diameter of 130m×115m.

Keep walking along crater number 20 and crater number 25 beside it following the guideposts towards the summit of Mt. Yosomi-yama. (The undergrowth in this area can be quite thick at certain times of year so the path may be difficult to follow. Please bring a map and compass with you to aid in navigation).

On the way to the summit there is a steep cliff to the southwest. This was formed by the dislocation of earth during the rise of Mt. Yosomi-yama.

The summit of Mt. Yosomi-yama. There is a viewing platform here from which you can see Lake Toyako and the summit of Mt. Yotei.

Walk for a ways down from the summit towards the old Usu volcano observatory of Hokkaido University and turn right at the guidepost down an incline. Making your way down along the cliff formed by the rise of Mt. Yosomi-yama you will cross a wooden bridge. To the left of this bridge is a fumarole.

This fumarole was formed during the 1910 eruption by rising magma. The steam rising from this fumarole is currently around 50℃. Descending from this point you return to the old Usu volcano observatory of Hokkaido University road.

Continue descending along this path for a time.

Entering out onto the old industrial road you turn left and walk down the hill.

Turning right at the guidepost you will come to a wooden staircase.

At the bottom of this staircase you will come to the old Usu volcano observatory of Hokkaido University. From the 1977-78 eruptions until the premonitions of the 2000 eruption began this observatory researched and predicted volcanic activity at not only Mt. Usu but also the 5 main volcanoes throughout Hokkaido. Descending along the path from here you will return to the lake shore. Turning left and walking along the lake shore you will return to the departure point.