Mt. Asama is an active volcano (2568 m above sea level) located on the Kamishin border, providing a magnificent landscape that can be called the symbol of Karuizawa.
Asama 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 mountaineering.
The song “Shinano no Kuni” was composed in 1899 and is now sung as the prefectural song,
The mountains rising in the four directions are Ontake, Norikura, Komagatake, and Asama, which are especially active volcanoes,” he wrote.
With the exception of Komagatake (Kisokomagatake), they are all volcanoes. These mountains have been known for religious mountaineering since ancient times. Yarigatake, Hotaka-dake, Akaishi-dake, and other high mountains over 3,000 m are rarely climbed due to their steep terrain and are not mentioned.
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 posthistoric activity.
Mt. Asama has frequently spewed lava since the beginning of the historical period. It has also frequently erupted in volcanic activity, spewing plumes of smoke hundreds of meters high, sometimes more than 1,000 meters, and causing cinders, ashfall, and blasts.
The earliest written history of the eruption of Mt.
Many records have been kept of the eruption, including the 14th year of Emperor Temmu (686), followed by the first year of Tennin (1108). Among them, the great eruption of 1783 is known to have triggered the Great Famine of Tenmei, as the volcanic ash caused a drop in temperature.
Most 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.
Its southern edge reaches as far as Nakagomehara in Saku City. It has the same physico-chemical characteristics as the Shirasu Plateau in southern Kyushu. Its geology is soft and easily eroded, resulting in the carving of U-shaped river valleys.
The local people call this U-shaped juvenile river valley “Tagiri landform” because many of the valleys are used as rice paddies. 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 from May to August 1783.
At the end of this great eruption, it spewed red-hot lava. The lava flow, 12 km long and up to 4 km wide, extends northward from the crater. The lava flow, which is made up of a series of huge andesite rocks, is called “Oni-Oshidashi” by modern people.
As a result of the Tenmei Eruption, Mt. Asama produced 150 million tons of volcanic ejecta, the largest of which was Oni-Oshidashi. Onioshidashi is now a natural park and a tourist attraction in Kita-Karuizawa.
Although it has been more than 220 years since the great explosion, the lava of Oni-Oshidashi has not weathered, and not much vegetation has grown on its rocks.
The view of the black andesite rock formations is mesmerizing.
Snow form on Mt. Asama
Because Mt. Asama is an independent peak, it 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 shape called a “climbing carp,” “carp climbing waterfall,” or “leaping carp” can be seen on the left side of the mid-slope of Mt. Asama is the only mountain in the Saku area where snow patterns can be seen.
Here, the thick snow cover has melted, and the remaining snow creates white patterns on the black mountain surface. The name “Nobori-Koi” (climbing carp) was given to this area because of the resemblance of its patches to carp, a specialty of Saku.
By the shape of the snow, farmers knew the progress of the weather and predicted the best time to do their farming. This was used to determine the dates for sowing paddy rice seedlings (sowing in strips) and planting rice.