Aso volcano eruption on October 8, 2016, observed by weather radars

Abstract

An explosive eruption occurred at the Naka-dake first crater of Aso volcano at 1:46 on October 8, 2016 (JST). According to the field survey conducted by Kumamoto University, Kyoto University, the National Institute of Advanced Industrial Science and Technology, and the Japan Meteorological Agency (JMA), a large amount of ash fell in the northeast direction of Mt. Aso; in addition, ash falls were confirmed in Kumamoto, Oita, Ehime Kagawa and Okayama Prefectures. Although the eruption was not observed using a distant camera, the eruption cloud echoes were captured by five JMA operational weather radars (Fukuoka, Hiroshima, Tanegashima, Muroto-misaki and Matsue). Using these radars, we found that the eruption cloud echo moved in the northeast direction at the lower troposphere, and in the east-northeast direction at the middle troposphere. This result is consistent with the vertical wind shear observed by the JMA wind profiler. After that, the echo of the volcanic ash cloud in the middle troposphere flowed more than 200 km from Mt. Aso and became ambiguous near Tosa Bay in Kochi Prefecture. In this study, we introduce a new probabilistic plume height estimation method. This method probabilistically evaluates errors due to radar beam width and refractivity of the atmosphere. Using this method, the eruption cloud height is estimated at 12,000 ± 687 m (1σ) above sea level (ASL). This height is lower than 13-14 km, the SO 2 cloud altitude estimated by Himawari-8 Ash RGB and the JMA Global Atmospheric Transport Model and is also lower than the radar echo height indicated by JMA (15 km). However, the plume height derived using this method is consistent with 39,000 feet (11.9 km) ASL and the volcanic eruption cloud height analyzed by the Tokyo Volcanic Ash Advisory Center using Himawari-8 infrared bands. Based on the result of the probabilistic estimation method and the duration of the volcanic earthquake due to the eruption (160-220 s), the total emission mass was estimated to be 3.2-7.5 × 10 8 kg, which is almost consistent with the field survey (6.0-6.5 × 10 8 kg).

The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu–Shirane volcano, Japan: Eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

“…The total mass of ash (3.2-7.5 × 10 8 kg), as estimated from the cloud height by the echoes (12,000 m) and duration of ash emission (160-220 s), is consistent with field observations (6.0-6.5 × 10 8 kg; Sato et al 2018).…”

“…In such a situation, radar observations (Syarifuddin et al 2019;Marzano et al 2020) can track an ash cloud. Sato et al (2018) presented a time-series of the ash cloud echo of the phreatic eruption at Aso volcano on 8 October 2016. The echo obtained from weather radar with a wavelength of 5.6 cm (C-Band), operated by the Japan Meteorological Agency (JMA), is consistent with the distribution of the tephra deposit.…”

Influence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcano

“…In general, secondary accumulation maxima are documented in distal regions, typically hundreds of kilometers from the volcano (e.g., the 1980 eruption of Mt. St. Helens; Sarna-Wojcicki et al 1981, June 15, 1991Weisner et al 2003, andthe August 18 andSeptember 16-17, 1992 eruptions of Mt Spurr;McGimsey RG Neal and Riley 2001). Wet aggregation could have enhanced the effective removal of airborne fine particles from the plume.…”

Special issue “Advancement of our knowledge on Aso volcano: current activity and background”

“…Weather radars of JMA also captured the volcanic ash cloud from the explosive eruption of Aso on October 8, 2016 (JST). Sato et al (2018) used five radars' data and found that the ash cloud travel more than 200 km away from the crater. The eruption altitude was estimated to be 12,000 m ASL ± 687 m (1σ).…”