The Tenmei daifunka was a large eruption of Mount Asama that occurred in 1783 ( Tenmei 3).[ 天明3年浅間山噴火の経過と災害][ 1783年浅間山天明大噴火] This eruption was one of the causes of the Tenmei famine.[ 天明3年浅間山噴火] It is estimated that about 1,500–1,624 people were killed in the eruption.
Background
Japan is situated along a zone of convergence between at least four major and minor tectonic plates. The Philippine Sea Plate dives beneath the
Amurian Plate and
Okinawa Plate along the
Nankai Trough and
Ryukyu Trench in southern Japan. In northern Japan, the
Pacific Plate subducts beneath the
Okhotsk Plate, part of the larger North American Plate, along the
Japan Trench and
Kuril Trench trenches. The
subduction process is related to the production of volcanoes in Japan as the downgoing oceanic slab undergoes dehydration at depths of roughly 90 to 100 km beneath the overriding plate.
Water in the structure of hydrated minerals interact with the upper mantle, lowering its melting point. As the mantle begins to melt, its density decreases and rises through the upper crust, forming a volcanic vent.
1783 eruption of Mount Asama
Mount Asama erupted in 1783, causing widespread damage.
[Titsingh, Isaac. (1834). Annales des empereurs du japon, p. 420.] The three-month-long
Plinian eruption that began on 9 May 1783, produced
andesitic pumice falls,
Pyroclastic flow flows, lava flows, and enlarged the cone. The climactic eruption began on 4 August and lasted for 15 hours,
and contained pumice falls and pyroclastic flows. The complex features of this eruption are explained by rapid deposits of coarse pyroclastic ash near the vent and the subsequent flows of lava; and these events which were accompanied by a high
eruption plume which generated further injections of pumice into the air.
[Yasui, Maya and Takehiro Koyaguchi. Journal Bulletin of Volcanology ( Kasan). Vol. 66, No. 3 (March 2004). pp. 243–262.]
Dutch diplomat Isaac Titsingh's account of the Asama-Yama eruption was posthumously published in French in Paris in 1820;[Titsingh, Isaac. (1820). Mémoires et Anecdotes sur la Dynastie régnante des Djogouns, Souverains du Japon.] and an English translation was published in London in 1822.[Titisngh, Isaac. (1822). Illustrations of Japan: consisting of private memoirs and anecdotes of the reigning dynasty of the Djogouns, or sovereigns of Japan.] These books were based on Japanese sources, and the work represented the first of its kind to be disseminated in Europe and the West.[Screech, T. (2006), Secret Memoirs of the Shoguns: Isaac Titsingh and Japan, 1779–1822, pp. 146–148.]
The volcano's devastation exacerbated what was already known as the "Tenmei famine".[Hall, John. (1955). Tanuma Okitsugu, 1719–1788: Forerunner of Modern Japan, p. 122.] The effects of this eruption were made worse because, after years of near or actual famine, neither the authorities nor the people had any remaining reserves.[Hall, p. 170.] The 4 August eruption killed up to 1,400 people,
Due to the Tenmei eruption, a lava flow called "Onioshidashi" flowed along the northern slope of Mt. Asama.
Kanbara tragedy
The most seriously damaged area by Tenmei eruption was the (now
Tsumagoi,
Gunma Prefecture). Kanbara was destroyed by avalanche by eruption and 477 people were killed.
Because of it, Kanbara is also called "Japan's
Pompeii".
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