| Mount Azumaya | |
| Other Name: | 四阿山 |
| Elevation M: | 2354 |
| Map: | Japan |
| Map Size: | 250 |
| Label Position: | left |
| Listing: | 100 Famous Japanese Mountains |
| Translation: | arbour mountain |
| Language: | Japanese |
| Pronunciation: | pronounced as /ja/ |
| Location: | Chubu region and Kantō region, Honshū, Japan |
| Coordinates: | 36.5417°N 138.4131°W |
| Type: | Stratovolcano |
| Easiest Route: | Hike |
is a stratovolcano in Japan. The 2354m (7,723feet) peak lies on the border of Nagano Prefecture and Gunma Prefecture. There exist alternative spellings of the mountain's name, like: 吾妻山 and 吾嬬山 which is read as "Agatsuma-yama" (Mount Agatsuma). In the village Tsumagoi, the mountain is spelled 吾妻山.
The mountain should not be confused with of which there are two, one in Nagano Prefecture and the other in Saitama Prefecture. Though the reading is the same, the name written in Kanji differs from the mountain in this article.
Mount Azumaya was formed between 900,000 and 300,000 years ago by andesite lava flowing out of a stratovolcano. An eruption 340,000 years ago formed a caldera of circa 3 kilometers in diameter. Through erosion the mountain has arrived at its present form with several peaks. is the general term for the following peaks lying roughly on a circle:, Mount Azumaya,, .
The famous Sugadaira Kōgen ski area is found on the mountain's southwest (Nagano-) side. Also on the Gunma-side there exists a ski area. In addition, north of the mountain lies which is one of Japan's Top 100 Waterfalls.
The mountain is well connected with several hiking trails:
The gondola from Palcall Tsumagoi is also operating during the summer season and can be used to climb the mountain