9:15 AM - 9:30 AM
[SVC31-02] Examples of eruptions around 1960 at Mt. Asama from eruption experiences
Keywords:Asama Volcano, eruption experiences
In the activity of Lewotvi Lakilaki volcano (Indonesia) in November 2024, eruption cloud reached a maximum height of 16 km, pyroclastic flows flowed down the frank slope in all directions, and ash fell in the downwind areas. According to the Global Volcanism Program website, more than 18,000 people live within a 5 km radius. During the large-scale eruption, explosions were heard, 10 people were killed by pyroclastic flows, and many villages were affected, which became a hot topic. On the other hand, the eruption of Asama Volcano around 1960 has similarities to the above cases. Here, the purpose is mainly to understand the actual phenomenon and the extent of the impact of the eruptions on November 10, 1958 (581110 eruption, hereafter) and August 18, 1961 (610818). Monitoring of Asama Volcano began in 1911, and in the 1930s, eruption types were classified from A (violent explosion) to D (no detonation) (Minakami, 1935). According to Miyazaki (2003), in the eruptions from 1935 to 1990, A and B were less frequent, and D was the most common. The last Type A eruption was on 581110, which was the largest since the Meiji era, and its pyroclastic flows are used in numerical simulations for volcanic disaster prevention maps. According to records, the 581110 eruption occurred after a long period of precursory activity, followed by small-scale eruptions, while the 610818 eruption (Type B) was a sudden eruption. The height of the plume from both eruptions reached 7,000 m, and pyroclastic flows flowed down around the crater. Explosions and air vibrations were observed over a wide area on 581110. One climber died during the 610818 eruption, and agricultural damage in the midsummer was also significant.
Since 1961, the activity of Asama Volcano has been low for over 60 years, and magma has only risen to the bottom of the crater in 1973 and 2004. The author is conducting a survey of residents at the foot of the volcano from autumn 2023 with the aim of passing on the information on eruption to younger generations who do not know about it. In this study, in addition to the records such as Miyazaki (2003) and Murai and Hosoya (1964), the residents' personal experiences and newspaper articles were mapped to examine the phenomenon and the extent of the damage from various angles.
The 581110 eruption occurred at 22:55, and a fire column was witnessed from Karuizawa Station, more than 28,000 pieces of glass were broken at the foot of the volcano, and changes in microbarometers were observed in Kagoshima. Hot volcanic bombs fell on Asama Livestock Raising Ranch, and ash fell from the eruption cloud that dispersed northeastward as far as Onahama. At Onioshidashien, five store employees who were hit by sparks were really scary. Volcanic rocks up to 6 meters in size fell on the crater rim, and forest fires broke out on the southern slope of the volcano, and fire brigades were dispatched. Ash continued to fall, and four and a half hours later another explosion occurred and pumice fell. The 610818 eruption occurred at 14:44, and loud detonations were heard in Nagano, Maebashi, Takasaki, and other areas. In the midst of a thunderstorm, the smoke was carried by the north-northwesterly wind, causing ash to fall on the southern foot of the volcano, and muddy rain fell as far as Shimoda on the Izu Peninsula. Iwamurata was outside the western edge of the eruption cloud, and only the detonation was confirmed. Fist-sized lava fragments fell on the southern foot of the volcano, and thumb-sized pumice was also included around Karuizawa Station. Meanwhile, rocks up to 50cm in size were seen falling on the northern foot of the volcano, and there are records of a bus fleeing at high speed on the toll road along the northeastern flank slope. Hot ash and pebbles peeled off the paint of cars near Onioshidashi Park, and there are reports of strong blasts being felt at Asama Livestock Raising Ranch. In both eruptions, the pyroclastic flow itself stopped probably within several kilometers from the crater, but it is believed that the effects extended several kilometers in the direction of the crater. Additionally, in the 581110 eruption, a small pumice eruption apparently occurred 4.5 hours later due to decompression and foaming of magma that caused by removal of a “plug” in the conduit the initial large explosion.
Since 1961, the activity of Asama Volcano has been low for over 60 years, and magma has only risen to the bottom of the crater in 1973 and 2004. The author is conducting a survey of residents at the foot of the volcano from autumn 2023 with the aim of passing on the information on eruption to younger generations who do not know about it. In this study, in addition to the records such as Miyazaki (2003) and Murai and Hosoya (1964), the residents' personal experiences and newspaper articles were mapped to examine the phenomenon and the extent of the damage from various angles.
The 581110 eruption occurred at 22:55, and a fire column was witnessed from Karuizawa Station, more than 28,000 pieces of glass were broken at the foot of the volcano, and changes in microbarometers were observed in Kagoshima. Hot volcanic bombs fell on Asama Livestock Raising Ranch, and ash fell from the eruption cloud that dispersed northeastward as far as Onahama. At Onioshidashien, five store employees who were hit by sparks were really scary. Volcanic rocks up to 6 meters in size fell on the crater rim, and forest fires broke out on the southern slope of the volcano, and fire brigades were dispatched. Ash continued to fall, and four and a half hours later another explosion occurred and pumice fell. The 610818 eruption occurred at 14:44, and loud detonations were heard in Nagano, Maebashi, Takasaki, and other areas. In the midst of a thunderstorm, the smoke was carried by the north-northwesterly wind, causing ash to fall on the southern foot of the volcano, and muddy rain fell as far as Shimoda on the Izu Peninsula. Iwamurata was outside the western edge of the eruption cloud, and only the detonation was confirmed. Fist-sized lava fragments fell on the southern foot of the volcano, and thumb-sized pumice was also included around Karuizawa Station. Meanwhile, rocks up to 50cm in size were seen falling on the northern foot of the volcano, and there are records of a bus fleeing at high speed on the toll road along the northeastern flank slope. Hot ash and pebbles peeled off the paint of cars near Onioshidashi Park, and there are reports of strong blasts being felt at Asama Livestock Raising Ranch. In both eruptions, the pyroclastic flow itself stopped probably within several kilometers from the crater, but it is believed that the effects extended several kilometers in the direction of the crater. Additionally, in the 581110 eruption, a small pumice eruption apparently occurred 4.5 hours later due to decompression and foaming of magma that caused by removal of a “plug” in the conduit the initial large explosion.