Discover onsen and landscapes shaped by millions of years of volcanic activity
Last updated: December 21, 2020
Volcanic activity has molded Gunma, creating abundant hot springs, mountainous landscapes, and otherworldly rock formations. The prefecture’s location at a tectonic boundary makes the region extraordinarily volcanically active. Mt. Kusatsu-Shirane (2,160 m), the source of Kusatsu Onsen and Manza Onsen, is a stratovolcano that is part of the Nasu volcanic belt. This belt formed when an oceanic plate slid beneath a continental plate, creating a chain of volcanoes, clusters of hot springs, and some of Japan’s most beautiful environments.
The most relaxing way to enjoy Gunma’s volcanic activity is from the soothing water of an onsen. Most onsen are the product of geothermically warmed groundwater. There are many hot springs around Gunma, with major onsen resorts in Kusatsu, Minakami, Ikaho, and Shima.
When water bubbles up to the surface and into your bath, it brings various minerals from inside the earth, providing bathers with different purported health benefits. Kusatsu’s waters are hot and strongly acidic. They are typically rich in sulfur, aluminum sulfate, and chloride and are thought to relieve muscle aches. Ikaho’s waters are rich in iron, said to be particularly beneficial for women’s fertility issues. Shima is known for sodium chloride and calcium chloride, touted to relieve fatigue, and Minakami has lots of calcium and sodium sulfate, thought to promote healthy skin.
Mt. Myogi’s jagged peaks were sculpted by volcanic activity. The three million-year-old peak is one of Gunma’s most famous mountains and makes for some exceptionally beautiful hiking. Just to the north sits Mt. Haruna, a striking, dormant stratovolcano with a crater lake. Enjoy hiking or take a ropeway to the mountain's summit for a panoramic view of the surrounding area.
Mt. Kusatsu-Shirane is known for its crater lake, Lake Yugama. The lake was a popular hiking spot but, since an eruption in 2018, it is forbidden to enter within a 1-kilometer radius. You can still hike nearby at the Yoshigadaira Wetlands, on the northeastern side of the mountain. From this vantage point, you can sometimes see steam rising out of the volcano.
Mt. Asama is one of the most active volcanoes in Japan. Legend has it that its nearly three-month-long eruption in 1783 was so powerful that it blocked out the sun for days. The event is still considered one of Japan’s most destructive eruptions. The Mt. Asama Magma Stone Park was created due to that eruption and helps give a scale of its impact. The black rocks that define the landscape have formed into otherworldly shapes. Asamayama Kannondo Temple, located within the park, was built to remember those who died in the disaster and remains a place to pray to ward off bad luck.