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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The Shoubu volcanic ash is intercalated with the middle Pleistocene Iyoki Formation, western Shikoku, Japan. The ash has been petrographically correlated with several widespread tephras, but detailed geochemical correlations have yet to be made. We therefore examine the lithology, petrography, glass geochemistry, and fission-track (FT) ages of the Shoubu ash in an attempt to establish robust, detailed correlations. The petrography and chemical composition of glass show vertical trends in the Shoubu ash. The FT age of the lowest unit indicates that eruptions began at 0.53±0.12Ma. Although the Shoubu ash has previously been interpreted as a single, homogeneous volcanic ash, the results indicate that it either comprises several volcanic ashes or records a compositional change within a single eruptive sequence.

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In strongly weathered tephras, it is commonly the case that only quartz and opaque minerals remain unaltered. For example, the K-Tz tephra is distinguished by abundant quartz crystals. The identification of strongly weathered tephras is difficult because major-element analyses of volcanic glass are affected by weathering. Here, we propose a method of identifying weathered tephras based on major-element analyses of pristine glass inclusions preserved in quartz phenocrysts, and apply the method to identifying the K-Tz, Nr-N, and Kt-1 tephras.
We used energy-dispersive X-ray (EDX) techniques to analyze samples of the K-Tz tephra collected from a proximal location (Tanegashima, near Kikai caldera) and from three distal locations. The major-element compositions of glass inclusions are similar in all the K-Tz samples, but are distinct from those of the Nr-N and Kt-1 tephras.
Major-element analysis of quartz-hosted glass inclusions is a promising method in investigations of strongly weathered Quaternary tephras in Japan, such as K-Tz.

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本研究では，侵食速度の指標として，環流丘陵を伴う旧河道（以下，環流旧河谷）に着目した．環流旧河谷は，分布が乏しい流域があるものの，日本列島の各地に分布し，様々な比高を持つことから，侵食速度を算出する際の有効な指標になると考えられる．この環流旧河谷を用いた事例の研究を，熊野川（十津川）の中流域において行った結果，旧河床堆積物を覆う角礫層は，赤色化していることから最終間氷期以前の堆積物と考えられ，旧河床堆積物の離水年代は12.5万年前かそれより古いと考えられる．角礫層に含まれるK-Tz起源の粒子は，角礫層の堆積時に降下し，希釈されたものであり，角礫層を覆う表土に含まれるK-Tz起源の粒子は角礫層の離水後に斜面から再移動したものと解釈すれば，赤色化に基づく角礫層の年代観に矛盾はない．この離水年代と旧河床堆積物の現河床からの比高から算出した下刻速度は，約0.9 m/kyかそれより遅い可能性がある．このように，環流旧河谷は，河川の上流や西南日本などの内陸部における河川の下刻などの侵食速度の指標になるとともに，隆起速度を推定する際の有効な指標になる可能性がある．より確度の高い侵食速度の算出には，環流旧河谷に分布する旧河床堆積物や斜面堆積物などを対象とした年代測定が今後の課題である．

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美浜テフラの対比を目的として，美浜テフラ模式地で採取した同テフラの角閃石について主成分および微量成分元素組成分析をおこない，九州火山起源のテフラの保存が良好な四国沖ピストンコアMD012422に挟まれる角閃石含有テフラとの対比を試みた．その結果，美浜テフラはMD012422コアの深度26.00-26.10 mに挟まれるGHo-2（26.10）テフラと角閃石の記載岩石学的特徴および層序関係が一致し，対比できることが明らかとなった．この対比により，美浜テフラは九州に分布する火山起源のテフラである可能性が高く，MIS5.5の高海面期初頭に降灰したことが明かとなった．

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栃木県，高原火山の塩原カルデラ形成噴火について編年とマグマ系を検討した．塩原カルデラ噴出物は下位からSo-KT（KT），So-TN（TN）およびSo-OT（OT）の3つの火砕流堆積物に分けられる．KTの直下とKTとTNの間の火山灰土壌中には，黒雲母の濃集で認識される外来テフラが認められる．火山ガラスや磁鉄鉱の化学組成およびジルコンのU-Pb年代により，下位および上位の外来テフラはそれぞれ貝塩上宝テフラ（KMT：620 ka）と大町APmテフラ群（410～337 ka）に対比できる．軽石の岩石学的特徴から，いずれの火砕流堆積物にもマグマ混合の証拠が認められ，それぞれ異なる珪長質端成分マグマに由来することが分かる．特にKTとTNの間には約20万年以上の時間間隙があり，この間に珪長質端成分マグマの起源である下部地殻の諸条件（起源物質や溶融条件）が大きく変化したと考えられる．

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Tephra simulation codes were originally developed to estimate tephra fall hazards; however, existence of several unknown parameters inhibits accurate calculation without elaborate parameter tunings. One of the most sensitive unknown parameters is source magnitude distribution (SMD), which describes amount of particle release as a function of distance from the vent along the plume axis. SMD can be obtained using inversion technique from real eruption products. Inversion techniques are also required to obtain other parameters; plume height of the eruption and the wind system at the time of the eruption are the most important ones among them. Although plume height and wind system can be observable for the recent eruptions, they could have some uncertainties and require further refinements. Additionally, they are totally unknown for unobserved ancient eruptions; however, they are essential parameters to describe eruptions. There are two types of relationship between amounts of tephra deposition and eruptive parameters; linear and non-linear. Inversions for linear and non-linear parameters need different approaches and they are briefly reviewed here. Since SMD (linear) and other parameters (non-linear) are often needed to be obtained at a time, combined inversion approach, which is a hybrid of linear and non-linear inversions, was proposed and discussed in this review. The results of inversion can be evaluated using satellite data and other plume models including 3D simulations, and help to understand structure of eruption plumes. Since accurate inversions highly rely on granulometric data of the surface deposit, further developments of techniques to obtain granulometric data with lesser time and effort are also required. The SMDs obtained by recent studies show logarithmic decay and a classic theory of particle segregation from turbulent plume can be applicable; however, more case studies are needed, especially to evaluate effect of particle aggregation and in-situ observation of falling particle is critically important.

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中部更新世前期のテフラが筑紫平野とその周辺の堆積物コアと露頭から発見された．鉱物の種類組成，屈折率，化学組成，フィッショントラック年代に基づき，このテフラは約0.6 Maに東九州から噴出した由布川火砕流堆積物（Yfg-pfd）に対比される．

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