Mount Tenzan

Mount Tenzan (天山), commonly known as Tenzan, is an active in Nagato Province, Yamatai. It is 3,544 m tall, making it the second-highest mountain in Yamatai after Mount Aozora, and the highest mountain in the Tenzan range. Mount Tenzan holds important historical, religious, and mythical significance to the Yamataian people, considering it to be the heart of the Yamataian civilisation and a gateway to the heavens.

A large crater lake, called Tengoku Lake, is in the caldera atop the mountain. The caldera was formed by a massive eruption in 1290, which erupted about 80-100 km² of. This was one of the largest and most violent eruptions in the last 5,000 years, and caused major environmental changes across Yashima and wider Western Escar.

1290 Eruption
The mountain's caldera was created in 1290 by a colossal eruption, one of the most violent eruptions in the last 5,000 years. The eruption, whose tephra has been found in West Kuiju and as far as Meriad, destroyed much of the volcano's summit, leaving a caldera that today is filled by Tengoku Lake.

According to historical records and the Sashizuki, the eruption was preceded by several weeks of "black smoke pouring forth from the gateway to heaven and black rains". This was interpreted as an ill omen and the Empress and much of the government fled the city to Yuki at least one week before the eruption. On about 3 November, Mount Tenzan erupted, resulting in explosions heard as far as southern Chanha. The eruption released some 80 to 100 km² of tephra, causing temporary and severe climate change over the Western Escar. Yamato and many other nearby settlements were destroyed by debris, pyroclastic flows, and landslides.

In the immediate aftermath of the explosion, a relief effort was organised by the Yamataian government. It is estimated some 2,000 to 4,000 people died in the disaster. For several days following the eruption, Yamatai and other areas in the region experienced ash rain and blackened rainfall, evident in many historical records.