弘逵 津屋’s scientific contributions

We have carried out chemical analyses on springs and underground waters collected from 31 localities on and around the Volcano Asama. Their characteristic chemical features are as follows: (A) generally rich in ΣCO2; (B) mostly poor in Cl-; (C) generally poor in SO4-- with an exception of those from Zigokudani; (D) comparatively rich in H2SiO3; (E) a little rich in Ca++: (F) show a remarkable difference between RoH and pH; and (G) give the ratios K(K+Na)=5～15% and Ca(Ca+Mg)=60～70%. They are classified according to their chemical contents into three groups: type (1) containing SO4--, ΣCO2, Al+++ and Fe++; type (2) ΣCO2 and Fe++ and type (3) chiefly ΣCO2.

伊豆大島三原山は,昭和25年7月16日中央火孔南縁より噴火を開始,漸次その活動規模を増大しつゝ連続的噴火を行い,9月23日噴火を休止,翌26年2月4日噴火を再開,4月1日まで,更に大規模な熔岩流出を伴った活動を継続した.ついで,噴火は,間歇的かつ爆発的になり,6月28日活動を停止した.本編では,昭和25年の噴火経過の観察を詳細に述べ,地形変化,噴出溶岩の温度,比熱の測定,噴出物の量(大約5千万噸)などについて記載した.

南九州の"しらす"は,その粒度組成が浅間火山の軽石ときわめてよく類似している.いずれも一般の降下性火砕堆積物とは異つた粒度組成を持つている.阿蘇火山の"灰石"も前者と同様の粒度組成を持つているCrater Lake地域の"Older Pumice"と同様に,これらの堆積物はおそらく火山砕屑流の状態で噴出し,山腹を流下して堆積したものであろう. This paper presents the results of mechanical analyses of the "Shirasu" distributed in the southern part of Kyushu Island, as a part of the writer's study on the mechanical composition of pyroclastic deposits of several volcanoes in Japan. The "Shirasu", which means "white sand", is distributed widely in the volcanic district of South Kyushu, forming a vast tableland around the north part of Kagoshima Bay. It is very often accompanied with the underlying "Hai-ishi", which means "ash stone" and may be a welded part of the "Shirasu". The "Shirasu" consists mainly of volcanic ash and pumice, accompanied with some rock fragments. Its thickness varies greatly, usually being 50 to 150 meters. It shows no bedding in almost every case, (see Figs. 1 and 2)

On August 19, 1961, a local but destructive earthquake occurred in the mountains of the Kita Mino district on the borders of Gifu, Fukui and Ishikawa prefectures, Central Japan. The writers carried out a field survey on the damage and topographic changes caused by the earthquake, and at the same time made a reconnaissance on the geologic structure of the district to see its effect, if any, on the earthquake features.

小諸附近の浅間火山軽石の粗度組成は,分級の悪いこと,粗粒部及び細粒部に長く尾を引くこと,粗変の変化が分布の全範囲にわたつてほとんど認められないこと,等の点で,降下軽石の粒変組成とは全く異つている.概してCrater Lake地域の"Older Pumice"の粒変組成に見られるような特徴を示しているが,しかし"Older Pumice"ほど分級は悪くなく,又それほど多量の大粒径の軽石を含んではいない.このような粒度組成の特徴と,分布状態とから判断して,典型的な降下軽石とは堆積の機構が全く異るものと見られる.おそらくは火山砕屑流の状態で山腹を流下して堆積したものであろうと考えられる. The phenomena of nuees ardentes or burning clouds have attracted much attension by volcanologists since the eruption of Mount Pelee in 1902, inducing some of them to do a detailed study of pyroclastic deposits, especially of nuees ardentes deposits. Among those, Fenner (1923) studied the origin of the tuff deposits in the Valley of Ten Thousand Smokes, Katmai. MOORE (1934) described the recent pumice deposits of the Crater Lake region and discussed their origin. He concluded that, judged from the size characteristics and other features, one of them, the "Older Pumice", is apparently different in origin from the pumice deposits of the normal projected type, being regarded as a product of nuees ardentes. Recently, in Japan, products of nuees ardentes or of pyroclastic flows have been reported from several volcanic regions. TANEDA (1954) studied the "Shirasu" in Southern Kyushu and concluded that it may be regarded as the nuees ardentes products showing size characteristics similar to those of the "Older Pumice" of the Crater Lake region.