Mount Asama

Geology

Mount Asama sits at the conjunction of the Izu-Bonin-Mariana Arc and the Northeastern Japan Arc. The mountain is built up from non-alkali mafic and pyroclastic volcanic rocks dating from the Late Pleistocene to the Holocene. The main rock type is andesite and dacite.

Scientists from University of Tokyo and Nagoya University completed their first successful imaging experiment of the interior of the volcano in April 2007. By detecting sub-atomic particles called muons as they passed through the volcano after arriving from space, the scientists were able gradually to build up a picture of the interior, creating images of cavities through which lava was passing deep inside the volcano.

A University of Tokyo volcano observatory is located on the mountain's east slope. Volcanic gas emissions from this volcano are measured by a Multi-Component Gas Analyzer System, which detects pre-eruptive degassing of rising magmas, improving prediction of volcanic activity.

Eruptive history

The geologic features of this active volcano are closely monitored with seismographs and strategically positioned video cameras. Scientists have noted a range of textural variety in the ash which has been deposited in the region during the serial eruptions since the Tennin eruption of 1108.

2009 eruptions

Mount Asama erupted in early February 2009, sending ash to a height of 2 km (6,600 ft), and throwing rocks up to 1 km (⁵⁄₈ mi) from the crater. Ash fall was reported in Tokyo, 145 km (90 mi) southeast of the volcano crater. On 16 February there were 13 recorded volcanic earthquakes and an eruption emitting smoke and ash in a cloud 400 m (1,300 ft) high.

Mount Asama continued to have small eruptions, tremors and earthquakes in February and remained on level-3 alert (with a danger zone within 4 km (2 ¹⁄₂ mi) of the crater).

2008 eruptions

Three small ash eruptions occurred at Asama volcano in August 2008. This was the first activity at the volcano since 2004.

2004 eruption

A single vulcanian eruption occurred at Asama volcano at 11:02 UT on 1 September 2004. Incandescent blocks were ejected from the summit and caused many fires. The eruption sent ash and rock as far away as 200 km (120 mi).

1995 earthquakes

In April 1995, more than 1000 earthquakes were detected at the volcanic mountain.

1983 eruptions

An explosive eruption occurred on 8 April. Incandescent tephra was ejected, and ash fell 250 km (160 mi) from the volcano.

1982 eruption

Explosive eruptions occurred at the summit of Asama volcano on 26 April. Fine ash fell in Tokyo, 130 km (80 mi) to the SE, for the first time in 23 years.

Tenmei eruption (1783)

Mount Asama erupted in 1783 (Tenmei 3), causing widespread damage. The three-month-long plinian eruption that began on 9 May 1783, produced andesitic pumice falls, pyroclastic 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.

Isaac Titsingh's account of the Asama-yama eruption was posthumously published in French in Paris in 1820; and an English translation was published in London in 1822. These books were based on Japanese sources; and the work represented first of its kind to be disseminated in Europe and the West.

The volcano's devastation exacerbated what was already known as the "Great Tenmei Famine". Much of the agriculturally productive land in Shinano and Kōzuke provinces would remain fallow or under-producing for the next four or five years. 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. The 4 August eruption killed up to 1,400 people, with an additional 20,000 more deaths caused by the famine.

Tennin eruption (1108)

The eruption of Mount Asama in 1108 (Tennin 1) has been the subject of studies by modern science. Records suggest that the magnitude of this plinian eruption was twice as large as that of the Tenmei catastrophe in 1783.

Marking the span of Japan's history

The eruptions of Mount Asama mark the span of Japan's recorded history, including: 2009, 2008, 2004, 2003, 1995, 1990, 1983, 1982, 1973, 1965, 1961, 1958–59, 1953–55, 1952, 1952, 1950–51, 1949, 1947, 1946, 1944–45, 1938–42, 1935–37, 1934, 1934, 1933, 1931–32, 1930, 1929, 1929, 1927–28, 1924, 1922, 1920–21, 1919, 1918?, 1917, 1916, 1915, 1914, 1909–14, 1908, 1908, 1907, 1907, 1906, 1905?, 1904, 1903, 1902, 1902, 1900–01, 1899, 1899, 1894, 1889, 1879, 1878?, 1875, 1869, 1815, 1803, 1803, 1783, 1779?, 1777, 1776, 1769, 1762, 1755, 1754, 1733, 1732, 1731, 1729, 1729, 1728, 1723, 1723, 1722, 1721, 1720, 1719, 1718, 1717, 1711, 1710, 1708–09, 1706, 1704, 1703, 1669, 1661, 1661, 1660, 1659, 1658, 1657, 1656, 1655, 1653, 1652, 1651, 1650?, 1649, 1648, 1648, 1647, 1645, 1644, 1609, 1605, 1604, 1600, 1598, 1597, 1596, 1596, 1595?, 1591, 1590, 1532, 1528, 1527, 1518, 1427?, 1281, 1108, 887, 685.

Note: The dates of eruptions featured in this article appear in bold italics.

In Popular Culture

Mount Asama served as the backdrop to Japan's first color film, Carmen Comes Home. Several references are made to Mount Asama throughout the film, including a song composed by a blind composer, Mr. Taguchi.