Geological Field Sketches - The Eruption of Mount Asama

The eruption of Mount Asama in Japan in the year 1783 was among the strongest in recent history. It is rarely mentioned, however there survives plenty of contemporary documentation, most hosted nowadays in the collection of the Asama Volcanological Observatory and Mount Asama is also one of the best monitored volcanoes since 1934.

Already after May 9, 1783 some smaller explosions announced the awakening of the volcano. July 26, a large eruption column above the summit crater marks the beginning of the main eruption phase, lasting until August. August 4, a pyroclastic flow destroys 18 square kilometer of forest. August 5, another pyroclastic flows destroys four villages, killing thousands. The very same day the eruption starts to lose power.

The various eruption phases of Asama, from from the collection of historian Kenichi Maruyama (photo by volcanologist Maurice Krafft).

Another drawing shows the eruption column, lapilli-ash-fall and volcanic lightning, from the collection of the Asama Volcanological Observatory (photo by Maurice Krafft).

Map showing the extent of the destruction caused by the pyroclastic flows and lahars coming from Mount Asama, from the collection of the Asama Volcanological Observatory
(photo by Maurice Krafft).