active volcano
Mount Asama is an active volcano (2,568 meters above sea level) located on the Kamishin border, providing a magnificent landscape that can be called the symbol of Karuizawa.
It is a large volcano that belongs to the administrative divisions of Karuizawa Town, Miyota Town, and Komoro City in Nagano Prefecture, and Naganohara Town and Tsumagoi Village in Gunma Prefecture. Among these, most of the southern foot of Mt. Asama is in the Karuizawa town registry, and many people think that most of Mt.
The Kamishin border refers to the border between the former Shinano Province (Shinshu) and Ueno Province (Ueshu) (currently the border between Gunma and Nagano Prefectures), where steep mountains several thousand meters high rise, presenting a spectacular topography.
The mountains are especially famous for mountain climbing.
In the song “Shinano no Kuni,” composed in 1899 and now sung as the prefectural song,
four mountains are mentioned: “The mountains rising in the four directions are Ontake, Norikura, Komagatake, and Asama, which are especially active volcanoes.
Except for Mount Komagatake (Kisokomagatake), all of these mountains are volcanoes. These mountains have been known since ancient times for religious mountaineering. Yarigatake, Hotaka-dake, Akaishi-dake, and other high mountains over 3,000 m are not mentioned because few climbers climb them due to their steep terrain.
From ancient times until modern times, Mt. Asama was written as Asamatake.
Most of the early modern documents in the collection of the Komoro Volcano Museum refer to “Asamadake.
It was not until the Meiji era (1868-1912) that the name “Asama-yama” came to be used.
In Ise Monogatari (Tales of Ise) written in the early Heian period (794-1185), it is sung, “In the land of Shinano, smoke rises from Asama’s peak, and the smoke that rises from Asama’s peak in Shinano is seen by people far and near.
From this poem-tale featuring Narihira Ariwara, it is clear that Mt. Asama was called Asamatake or Asama no Utaki (Mt. Asama is called Asama Mountain in ancient times).
Because the Japanese archipelago is located along the Pacific orogenic belt, there are many volcanoes, numbering more than 300. Of these, more than 40 volcanoes have been active since the beginning of time. Of these, 15 volcanoes have produced lava or pyroclastic flows during post-historic times.
Mt. Asama has frequently discharged lava since the beginning of the historical period. It has also frequently erupted, spewing plumes of smoke hundreds of meters high, sometimes more than 1,000 meters, and producing volcanic activity such as cinders, ashfall, and blasts.
The earliest written record of the eruption of Mt. Asama is found in the “Nihon Shoki” (the oldest written record of the eruption of Mt.
Many records have been left behind, including the 14th year of Emperor Temmu (686), followed by the record of the eruption in the first year of the Tennin Era (1108). Among them, the great eruption in 1783 is known to have triggered the Great Famine of Tenmei, as the volcanic ash caused a drop in temperature.
More recently, eruptive activity continued from September 1 to December 9, 2004.
Shirasu Plateau and Lava Flow Oni Oshidashi
Volcanic ejecta from Mt. Asama are thickly deposited in Oiwabara in Karuizawa Town and Kaikoen in Komoro City. These are pyroclastic flows that erupted from the Pleistocene to ancient times.
The southern edge of the volcanic eruption reaches Nakagomehara in Saku City. It has the same physico-chemical characteristics as the Shirasu Plateau in southern Kyushu. The geology is soft and easily eroded, resulting in the carving of U-shaped river valleys.
The U-shaped river valleys in their infancy are mostly covered with rice paddies, which is why they are called “takiri landforms” by the locals. The landforms known as “Tagiri landforms” can be found at the foot of Myoko Volcano in Niigata Prefecture and in the central Ina Valley, including the Ootagiri, Nakatagiri, and Yotagiri Rivers. Inadani’s Tagiri landforms were formed by the erosion of a fan-shaped landform and differ in origin from those at the foot of Mount Asama.
The most massive explosion of Mount Asama recorded historically was the great eruption of May to August 1783.
The last of these great eruptions spewed red-hot lava. A lava flow 12 km long and up to 4 km wide extends from the crater to the north. The lava flow, which is made up of a series of huge andesite rocks, is called “Oni-Oshidashi” by modern people.
The largest of the 150 million tons of volcanic ejecta produced by the Tenmei Eruption was the Oni-Oshidashi. Oni-oshidashi is now a nature park and a tourist attraction in Kita-Karuizawa.
Although more than 220 years have passed since the great explosion, the lava of Oniooshidashi has not weathered, and not much vegetation has grown on its rocks.
The scenery of rows of black andesite rocks is fascinating to behold.
Snow form on Mt. Asama
Asama is an independent peak and can be seen in its entirety from Usuda Town (now Saku City), located at the southern edge of Saku-daira (Saku Basin), 25 km to the south.
In May, a snow pattern called “climbing carp,” “carp climbing waterfalls,” or “leaping carp” can be seen on the left side of the hillside of Mt. Asama is the only mountain in the Saku region where snow patterns can be seen.
Asama is the only mountain in the Saku region where snow patterns can be seen. Here, the thick snow cover has melted, and the remaining snow creates white patterns on the black surface of the mountain. The name “Nobori-Koi” (climbing carp) is derived from the resemblance of the patches to carp, a specialty of Saku.
The farmers knew the progress of the weather and predicted the best time to farm according to the shape of the snow. This was how they determined the dates for sowing paddy rice seedlings (sowing in strips) and planting rice.
