Explosive activity of Zavaritsky volcano (Simushir Island, Central Kuriles) during the Holocene

In our paper we represent the first data on the Holocene explosive activity of Zavaritsky volcano, the largest caldera center on Simushir Island (Central Kuriles). For the first time, we reconstructed the chronology of explosive eruptions of this volcanic center for the past 10 000 years, as well as estimate the parameters of its largest eruptions. In total, more than 40 tephra horizons have been identified, which allows us to estimate the frequency of eruptions: 1 event in 250 years. Constructed age model allowed us to determine the age of most eruptions. Volcanic glasses of Holocene tephras correspond in composition to low-potassium basaltic andesite-rhyolites, while the very low K2O content makes it possible to fairly confidently distinguish Zavaritsky tephra not only from the tephra of neighboring moderate-potassium volcanoes, but also from the tephra of other low-potassium volcanoes of the Kuril-Kamchatka Island arc. Holocene activity of Zavaritsky volcano started with two powerful eruptions with a conservatively estimated magnitude (M) of 6.4 and 5.6, which occurred about 9.5 and 9.2 thousand years ago (ka BP). Tephra from the first eruption (ZV-1) spread to the northeast and was found as far as northwestern North America. Tephra from the second powerful eruption (ZV-3) spread north and was found in sediments of the Sea of Okhotsk. Volcanic glass of ZV-1 tephra is characterized by rhyolitic composition with the highest SiO2 content (72.5‒74 wt. %). Glasses of the ZV-3 tephra varied in composition from dacites to rhyodacites (65‒71.9 wt. % SiO2). The products of subsequent eruptions were represented by scoria with glasses of dacite — andesite and basaltic andesite composition. Dacitic glasses reappeared only in the tephra of the last large explosive eruption that occurred early before the middle of the 19th century. Our studies revealed the catastrophic explosive eruptions of Zavaritsky volcano during the Early Holocene and sustained activity of this eruptive center throughout the Holocene. The appearance of high-silica glasses in the tephra of the last powerful eruption (ZV-40) indicates a possible strong eruption in the near future.