* ** Casualties by the 3 June 1991 pyroclastic flow at Unzen volcano Shinichi SUGIMOTO * and Daisuke NAGAI ** Abstract The 1990-1995 eruption of Unzen volcano, Japan, was characterized by lava dome growth and pyroclastic flows triggered by dome collapse. One of the largest pyroclastic flows occurred at 4:08 p.m. on June 3, 1991. The associated pyroclastic surge killed 43 people and injured 9 persons. The event was the worst volcanic disaster within a few decades in Japan. The victims due to the pyroclastic surge included following persons: fire brigade members watching for lahars and for safety of houses in the evacuation area, local residents returning home for retrieving their property and goods, press people taking photos of the pyroclastic flow, taxi drivers hired by the press, volcanologists recording volcanic activity on video tape, and policemen [OR a policeman] calling for peoples evacuation. Only a few people who were located near the distal end of the pyroclastic surge could survive. The mortality rate was 100% at the upstream area about 4.3 km from the source. The mortality extended to 69% at the downstream area near the distal end of pyroclastic surge. The overall survival rate (18%) is very low. This fact indicates that the only way to avoid disasters due to pyroclastic flows is to evacuate before they occur. Governments must designate the warned area and/or declare an evacuation instruction for residents to keep people out unconditionally, in cooperation with the volcanologists. Key words: casualties, pyroclastic flow, Unzen Volcano, volcanic disaster 1990 11 17 4 Nakada et al., 1999 9,400 1991 6 3 4 08 Fig. 1 43 2,300
Fig. 1. Map showing the area affected by the 3 June 1991 pyroclastic flow at Unzen volcano. Data from Ministry of Construction (1994)., 1998 11,000 1995 5 2005 6 22 1991 6 3
1997 1991 4 1993 3, 2001 2001 1991 6 3 1991 5 24 6 3 5 26 275 296 3, 1998 26 2.5km 293km 6 3 15 30 15 416 8 16 08 3.2km 4km Nakada and Fujii, 1993 ash cloud Fisher. 197916 08 43 9, 1997 49 130 1991 6 3Fig.1 5 15 2 15 131 Fig. 2 16 4 08 4km Fig. 1. 16 13 3 16
. 16 40 57. 17 03 5 5 20 17 55.. 18 13 3 6 25. 6 3 15 131 10 NHK 23 4 Fig. 2 20 16 5 Fig. 15 50m 2 2 200m 3 3 3 2 1 3
Fig. 2. Distribution of casualties due to the June 3,1991 pyroclastic flow, or surge. Data from Shimabara police office. 16 08 2005 614 2005 9 17 NNN 378 15 57 16
16 01 16 06 4 6 16 07 16 08, 16 09 6 3 16 08 53 40 3 9 Table 1 Fig. 2 22 9No. 7 8 11 12 13 15 16 17 18 1No. 19 1No. 25 No. 25 No. 23,24 2No. 23 241 No. 28 No. 28 No. 29 1No. 20 4No. 5 6 10 22KTN 1 No. 9 1No. 21 1No. 322 150m 6 2No. 1 2 1No. 261No. 141No. 4
Table 1. List of casualties due to the June 3,1991 pyroclastic flow at Unzen volcano.
1No. 27 7 19 45 6 331 283 28 2 No. 7 21 21, 1992 2 1 No. 11 3 No. 12 3 4 No. 19 4 100mNo. 23 No. 24 23 4 No. 5 No. 6 No. 10 No. 22 No. 9 G No. 33 No. 1 4 3 1 No. 2 4 No. 26 131 5 29 6 2 5 26 6 2 3 H No 41 I No. 4 16 16 04 16 05 10
16 10 16 11 H 1289 I, 1998 5 154 24 2526 Fig.1 4km 200m 3 5 29 19 06 3.3km 3 22 5 30 3 31 3 JNN 6 3 3 250m 2 15 6 2 2 40%
No. 44 NTT 5% No. 45 3 No. 46 1 No. 46 2 1 2 30cm No. 48 No. 46 No. 47 No. 47 U 57
12 12, 2001 15% No. 46 13% No. 47 20% No. 48 15 No. 46 No. 47 No. 48 3 10m No. 48 No. 45No. 47 1 No. 49 80m 16 1 No. 50 15 57
2No. 50 U, 2001 No. 501 2 No. 51 No. 52 6 8 30m 1991 6 3 22 m 2 30m No. 21 m No. 17 70m 40m No. 15No. 25 KTN KTN No. 9
No. 8No. 750m 80m No. 11No. 18 3 No. 5 6 9 1022 1997 No. 15 20 25m 27 3 1 9 11 2 3 3 2 2 1 112 9 No. 1 2No. 26 No. 14 5 3 1997 No. 2 26 1 12 9 1 2 9 7 4 1 2
3 2 40% 60% 90%100% 1m,1.2m1.1m 1997 2 2 25 3 26 1869% 5343 19% 1 1997 1991 6 3 68pp Fisher, R.V. (1979) Models for pyroclastic surges and pyroclastic flows. J. Volcanol. Geotherm. Res., 6, 305-318. 1994 58pp 1992 314pp 1998 514pp Nakada, S., and Fujii, T. (1993) Preliminary report on the activity at Unzen Volcano (Japan), November 1990- November 1991: Dacite lava domes and pyroclastic flows. J. Volcanol. Geotherm. Res., 54, 319-333. Nakada, S., Shimizu, H., and Ohta, K. (1999) Overview of the 1990-1995 eruption at Unzen Volcano. J. Volcanol. Geotherm. Res., 89, 1-22. 1992 78pp 2001 204pp