This closeup view on May 20, 1991, shows the first lava extrusion of the 1990-95 eruption of Unzen volcano in Japan. The dome was extruded in the Jigoku-ato crater, which was formed by an explosion on the first day of the eruption, November 17, 1990. By May 23 the dome reached a height of 44 m and had a diameter of 110 m. It then began spilling over the east crater rim (upper right). Periodic collapse of the oversteepend front of the dome produced pyroclastic flows that traveled progressively farther down the Mizunashi valley.
The 1990-95 eruption of Unzen volcano, on the southern Japanese island of Kyushu, produced a lava dome at the summit of Fugen-dake. The rising sun colors the dome, seen here from the NE on February 2, 1995, near the end of the eruption. By this time the dome had grown to a height of 1500 m, about 200 m above the pre-eruption surface. Periodic collapse of the growing lava dome had produced pyroclastic flows that devastated areas on the SE and NE flanks. Thousands of persons living below the dome faced long-term evacuation.
A house on the SW flank of Unzen volcano is buried to its eaves by deposits from lahars (volcanic mudflows). Redistribution of material shed off of Fugen-dake lava dome (background) produced lahars that devastated populated areas near the volcano. The lahars had low temperatures, unlike pyroclastic flows, and did not ignite the houses. Dome growth, which had begun in May 1991, ceased at about the time of this February 3, 1995 photo.
This 18th century water-color map of Unzen volcano on the Shimabara Peninsula shows the extent of the catastrophic landslide from Mayu-yama (lower center) in 1792 that swept into the Ariake Sea at the bottom of the map. The irregular, orange-colored area along the coast delineates the extent of runup of the tsunami that was created when the avalanche entered the sea. The tsunami swept a 77-km length of the peninsula and caused nearly 15,000 fatalities here and along coastlines across the Ariake Sea. Map from Shimabara City Honko temple (published in Miyachi et al., 1987).