Mount Gassan (月山, Gassan) is a stratovolcano in the ancient province of Dewa (modern-day Yamagata prefecture) and the highest of the Three Mountains of Dewa. The Gassan Shrine stands at the mountain's summit, 1,984 metres (6,509 ft) above sea level.

The hike from its trailhead to the summit usually requires about 4-5 hours and can be challenging. Visitors should be aware of the weather and not try to hike it on days with wind or heavy rain. The trail is not paved and in some parts requires the use of hands to navigate certain parts of the trail.

Due to heavy winter snowfall, the mountain and shrine are inaccessible for long periods of the year; however, this also means that skiing is possible on the mountain from April to mid-summer.

The mountain is interesting in that it contains elements of both shield volcanoes as well as stratovolcanoes, although it is classified as a stratovolcano.

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  Relief Map
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  Viewed from the South
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  Ridge
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  Ridge
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  Viewed from the Peak
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  Gassan Shrine at the summit

• List of volcanoes in Japan
• List of mountains in Japan

• "Gassan". Global Volcanism Program. Smithsonian Institution. Retrieved 25 June 2021.
• Mount Gassan Travel: (Japanese)
• Mt. Gassan Page: (English)
• Mount Gassan Travel: (English)