Fig 3 - uploaded by Alexandros Panagiotis Poulidis
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Comparison of monthly volcanic ash sums estimated via Eq. (1). Values derived from site measurements at 62 sampling points during periods of eruptivity at Showa crater from January 2009 to October 2017 (grey circles), and values recorded at Minamidake summit crater from November 2017 to December 2020 (dots).
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At Sakurajima volcano, frequent Vulcanian eruptions have been seen at the summit crater of Minamidake since 1955. In addition to this eruption style, the eruptive activities of Strombolian type and prolonged ash emission also occur frequently. We studied the design of a simulator of advection-diffusion-fallout of volcanic ash emitted continuously....
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Context 1
... monthly volcanic ash emissions obtained by applying this empirical equation were compared with the monthly mass eruptions of volcanic ash from 2009 to 2020 (January 2009-October 2017: eruption at Showa crater, November 2017-December 2020: Minamidake), as shown in Fig. 3. It is possible to estimate volcanic ash emissions with an accuracy of 0.5 to 2 times for eruptions at the Showa and Minamidake craters of Sakurajima. This equation has been applied to the monthly mass eruption of volcanic ash but has also been shown to be applicable to individual Vulcanian eruptions [9]. Here, this equation is applied ...
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Citations
The 1914 eruption with VEI 4 Plinian pumice falls and the lava flow at Sakurajima Volcano is the largest-scale eruption in Japan after the 20th century. From the uplift of the ground of Aira Caldera where the main magma reservoir of Sakurajima is located and long-term recurrence interval of VEI 4 eruption, a large-scale eruption is expected to occur on the volcano in the near future. For such a large-scale eruption, it is important to (1) understand the precursory activity, (2) forecast eruption, (3) evaluate hazards, and (4) improve disaster prevention literacy. Respectively, (1) the intrusion of magma induces elastic deformation and fracture of rock (volcano-tectonic (VT) earthquake). This may be followed by an opening tensile crack. Evolution of magma intrusion may appear as a conjugate crack. (2) Magma intrusion rate is a key factor to forecast scale and type of eruption. Magma intrusion rate increased up to >10 ⁸ m ³ /day before the Plinian eruption. Very high seismicity of low-frequency earthquake follows VT earthquake swarm. (3) Simulation tools have been developed for various kinds of volcanic hazards. A key parameter is allocation of intrusive magma to tephra, pyroclastic flow, and lava flows. (4) Evacuation from volcanoes is an essential countermeasure against volcanic disaster risk. A large eruption, especially pumice fall, requires a wide alert zone. Since awareness of evacuation from the massive tephra fall is low in areas far from the volcano, workshops for residents were repeated to enhance awareness of evacuation from the massive tephra.
Volcanic ash hazards present life‐threatening dangers to populations near volcanoes during large explosive eruptions. Vulnerable infrastructures demand a comprehensive disaster risk reduction strategy to protect residents from enormous ashfall accumulations. To prepare for the next large eruption of Sakurajima volcano, authorities in Kagoshima City are developing a countermeasure plan utilizing ash dispersal prediction 24 hr before an eruption. However, the absence of large eruptions in the last century makes it challenging to confirm the accuracy of predictions for hazard area designation. To ensure established protocols are effective, uncertainties in ashfall predictions must be addressed, enabling authorities to make appropriate responses. We simulated the previous large eruption of Sakurajima volcano using multiple wind forecast lead times as historical predictions from July 2018 to December 2022. The uncertainty in prediction results was evaluated by comparing simulation outputs with validation data from the ash dispersal data set. We examined uncertainty in hazard area assignment and its variation depending on risk items, wind field states, and the influences of seasonal patterns and events. Updating ashfall predictions with improved wind forecasts reduces uncertainty for all risk items and increases the precision of identified hazard zones. Furthermore, uncertainty levels are influenced by seasonality and can shift significantly with varying wind strengths controlling ash dispersal process. Providing uncertainty information is vital for decision‐making during ash fallout events, and it is recommended to update response decisions 12 hr after the initial prediction. This study's outcomes will aid in developing better disaster risk management strategies, focusing on volcanic ash hazards.
