The Hirano volcanic ash in Nomura Town, southwestern Shikoku, Japan, has been characterized by petrography, refractive index and geochemical composition of volcanic glass (major and trace elements), and fission-track age of zircon. The Hirano volcanic ash has abundant vesicular glass shards and phenocrysts of biotite, hornblende and orthopyroxene. The volcanic glass has a rhyolitic composition. LREE (Light Rare Earth Element) profiles of the volcanic glass are steep with La/Sm_N=5.0-5.3 and those of HREE (Heavy Rare Earth Element) are flat with Gd/Yb_N=1.2-1.3. They have a weakly developed Eu anomaly. The Hirano volcanic ash has similar values of some incompatible trace element ratios, such as La/Y, Ba/La and Nb/Zr, with the Yufugawa pyroclastic flow deposit in the Ooita Prefecture. The fission-track age of 0.46±0.09Ma (1σ) was obtained for zircons from the Hirano volcanic ash. The Hirano volcanic ash can be correlated to the Yufugawa pyroclastic flow deposit based on petrographical, geochemical and geochronological data.

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Tokachi-dake volcano restarted eruptive activity at the Ground crater in middle Holocene after long dormancy of nearly 10ky. The activity at the crater (Stage 1) was the most explosive and voluminous one in the volcano during Holocene. We newly found a pyroclastic flow deposit beneath already recognized pyroclastic flow deposit (Gfl-1: Ground Crater pyroclastic flow deposit 1) of the Stage-I, intercalated with lahar deposits and thin soils. The deposit is composed of gravel-sized blackish blocks, pumices, banded pumices and altered blocks with yellowish to reddish brown colored fine sand matrix. Progressive thermal demagnetization experiments for the blackish blocks and the pumices show that the direction of the remnant magnetization of the deposits is close to that of the geocentric axial dipole and did not change up to blocking temperature of about 580℃, indicating that these blocks and pumices are essential magmatic materials. Thus, the deposit can be considered as pyroclastic flow one. However, this is characterized not only by the heterogeneous distribution of these essential materials in the deposit but also by heterogeneous matrix. These features and abundant accidental altered blocks suggest that generation of the pyroclastic flow might be related with sector collapse of the volcanic edifice. This is consistent with the topographic feature of the Ground crater. The petrography and the whole-rock chemical compositions of these essential materials are similar to those of the Stage I. This suggests that the newly found pyroclastic flow must be related to the initial eruptive activity of the Stage I. New ¹⁴C ages for the deposit are in 4.7ka, indicating that the activity of the Stage I began much earlier than previously recognized age (3.3ka). Finding of the pyroclstic flow deposit, named as Gfl-0, suggests that the Stage I had continued and been derived from the same magma system for more than 1400 years. However, considering a long interval between Gfl-0 and Gfl-1, the Stage I might be divided into two sub-stages, Stage I-0 and Stage I-1.

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Five Holocene tephras originating from Hokkaido volcanoes underlie coastal lowlands on Kunashiri and Shikotan islands, Southern Kuril Islands. These Hokkaido tephras were identified based on the refractive index and major element composition of glass shards in the tephra. They are: Tarumae-a (Ta-a, AD 1739), Komagatake-c2 (Ko-c2, AD 1694), Mashu-b (Ma-b, 774-976 cal BP), Tarumae-c (Ta-c, 2500-2800 cal BP), and Mashu-d1 (Ma-d1, 3267-3368 cal BP). Ko-c2 and Ta-c are the most widely distributed ash fall deposits, and provide valuable time markers for examining the stratigraphy of these islands, including possible paleotsunami deposits. On Kunashiri Island, 12 tephras that probably originated from at least three volcanoes located on Kunashiri Island are interspersed with the five Hokkaido tephras. These tephras are classified into three groups according to the combination of TiO₂ and K₂O abundance in glass shards. Many of them contain glass shards showing relatively low refractive index (n=1.480-1.490) and high SiO₂ content (77-79%) in comparison with the widespread tephras from Hokkaido Island.

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