Abstract
Long-term evaluations of hazard and risk related to volcanoes rely on extrapolations from volcano histories, including the uniformity of their eruption rates. We calculated volumetric magma eruption rates, compiled from quantitative eruption histories of 29 Japanese Quaternary volcanoes, and analyzed them with respect to durations spanning 101–105 years. Calculated eruption rates vary greatly (101–10−4 km3 dense-rock equivalent/1000 years) between individual volcanoes. Although large basaltic stratovolcanoes tend to have high eruption rates and relatively constant repose intervals, these cases are not representative of the various types of volcanoes in Japan. At many Japanese volcanoes, eruption rates are not constant through time, but increase, decrease, or fluctuate. Therefore, it is important to predict whether eruption rates will increase or decrease for long-term risk assessment. Several temporal co-variations of eruption rate and magmatic evolution suggest that there are connections between them. In some cases, magma supply rates increased in response to changing magma-generation processes. On the other hand, stable plumbing systems without marked changes in magma composition show decreasing eruption rates through time.
Highlights
Quantitative evaluation of eruptive histories is key to our understanding of volcanism and attempts to predict volcanic activity
Nakamura (1964) showed that constant eruption rates are typical at Izu-Oshima volcano, this is an uncommon case in Japanese arcs
We examined volumetric magma eruption rates compiled from 29 datasets of well-documented Japanese Quaternary volcanoes over the past 1 01–105 years
Summary
Quantitative evaluation of eruptive histories is key to our understanding of volcanism and attempts to predict volcanic activity. The eruption rate of Sakurajima, the most active volcano in Japan, is 1–10 km DRE/1000 years, a typical value for long-term eruptions of basaltic to andesitic volcanoes in the world (White et al 2006). Nakamura (1964) showed that constant eruption rates are typical at Izu-Oshima volcano, this is an uncommon case in Japanese arcs Such changes of eruption rates are important for the evaluation of future volcanic activity, because it is necessary to forecast the change in eruption rate. 10 ka, six Vulcanian eruptions, producing pyroclastic units of 10−3–10−2 km DRE (Numanotaira tephra group), occurred at intervals of 500–2000 years, recording a decreasing eruption rate since the Dake eruption (Fig. 18). The decreasing eruption rate at Adatara is marked after the largest eruption, and the magma-plumbing system has established a longterm stability
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