The author reviews the literatures published in the 1980's, on the subaqueous volcanic rocks consisting of coherent lavas and volcaniclastic rocks. The literatures on subaqueous lavas are dealing with formation of pillow lavas, lava lobes and pseduo-pillow lavas, and those on subaqueous volcaniclastic rocks are concerning about mechanism and physical condition of the fragmental rocks, such as pyroclastic rocks, hyaloclastites and peperites. Finally, he reviews several papers on reconstruction of submarine volcanoes. In addition, he introduces several actual examples of subaqueous lavas of geologic time by photographs.

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In the Shimane Peninsula, lower (Koura Formation) to middle (Josoji and Ushikiri Formations) Miocene strata, consisting mainly of shale and volcanigenic materials are distributed. The middle Miocene magmatism can be divided into three stages based on the type of activity. The Sanami volcanic rocks lie stratigraphically in the middle of the Ushikiri Formation, approximately at the boundary between the effusives of Stage II (the formation of isolated submarine volcanoes) and Stage III (eruption of sheet flows). The Sanami volcanic rocks comprises, in stratigraphic order, basalt pillow lavas, andesite sheet flows, basalt volcaniclastic rocks, basalt sheet flows and dacite pyroclastic rocks. The succession is cut by northwest trending faults, along which basaltic dikes have been intruded. These faults and dikes are particularly abundant in a narrow zone around Sanami Bay, which includes much evidences of nearvent activity such as; feeders to pillow lava, high velocity pyroclastic flows containing many bombs, a crater and neck breccias. The explosive activities in Sanami district took place alternately with effusions of sheet flows in a shallow marine environment, which is corroborated by the marine shell fossils.

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Neogene siliceous shales are widely distributed in the southwestern part of the Shiretoko Peninsula, Northeast Hokkaido, Japan. These shales have been intruded by many basaltic dykes and sills, and some of these intrusive rocks erupted in submarine environments. In this paper, I describe the dykes, subaqueous flow deposits, massive lavas, lava lobes, and hyaloclastites in the Onnebetsu River in this district, to reconstruct a submarine volcano which intruded and erupted on the wet sediments. The dyke which intruded into the wet sediments formed peperites, and deformed the sediments. The magma exploded in the wet sediments and produced subaqueous pyroclastric flow deposits. It was probably due to phreatomagmatic explosion by contact-surface steam explosivity. Finally, several lavas grading into lava lobes and hyaloclastites flowed on the deposits. These volcanic rocks made up a monogenetic submarine volcano.

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The Upper Donzurubo Member of Nijyo Group consists of pyroclastic flow deposits and epiclastic tuffaceous sediments. The total thickness of the Member is about 150m. This Member is subdivided into three units; lower tuff dominant unit, middle pyroclastic flow deposits unit and upper volcanic breccia dominant unit. Lower and upper units contains some accrretionary lappilli. Pyroclastic flow deposits, ranging in thickness from 1 to 8m, are poorly sorted and made up of rhyolite fragments, pumice and tuff. They shows inverse-normal grading of density fragments, and pumice fragments concentrated in the uppermost part of a flow unit. Pyroclastic flow deposits are covered with parallel laminated tuff bed and lappilli tuff bed. Some pumices, protrude from pyroclastic flow deposits, are infilled by the tuff bed. Tuff beds are considered to be deposited following the volcanic eruption of the pyroclastic flow. The tuff beds are deposits in relatively shallow water or in ash surge.

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Middle Miocene subaqueous rhyolitic lavas and volcaniclastic rocks are dominated over the southern part of the Inner Zone of Northeast Japan. Managawa rhyolite lavas and Yatagashima.volcaniclastic rocks are one of these rocks. The former occur as discrete domes in the latter. The domes generally consist outwards of a massive lithic rhyolite core, a flowed lithic rhyolite, a flowed spherulitic rhyolite, and a perlite rim. Yatagashima volcaniclastic rocks are composed mainly of pumice lapilli, and contain some lithic or glassy fragments. A inferred eruptive cycle began with eruption of vesicular lava, Yatagashima volcaniclastic rocks were formed during initial stage of this cycle, and lithic or glassy fragments were derived from disintegration of domes which were extruded during later stage. This cycle was repeated until the total lava domes and volcaniclastic rocks were formed.

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The Neogene system composed of thick volcanics and normal sediments is distributed in the Ikarashi River area situated in the eastern part of Niigata plain. This paper described petrography and the mode of occurrence of dacite lava and volcaniclastic rocks in the upper Miocene Shigekurayama Formation. Their typical occurrence is pumiceous hyaloclastites which contain many lava domes. The lava domes have glassy perlitic rim. The dacitic volcanic activity is considered to have begun by formation of the pumiceoucs hyaloclastites, followed by intrusion of lava dome of non-vesiculated magma.

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Facies models for silicic subaqueous tephras in the Niigata region, central Japan are presented. These tephras are intercalated in the upper Miocene to lower Pleistocene of deep to shallow marine, lacustrine and fluvial environments. Lithofacies of these tephras are diverse, though mostly medial to distal facies, and possible origin of each lithotype is discussed in terms of subaqueous fallout, ash cloud, subaqueous flow and epiclastic ones. Origin of ash flow turbidites, some subaqueous tephra sequences and the possible origin of tephras by subaqueous eruption are also discussed. To establish facies models, tephras were firstly grouped into three grain-size populations; that is (A) silt to fine sand-sized, (B) fine sand-sized to granule-sized, (C) containing 5% or more pumice clasts larger than granule size. TypeA1 (massive or partly laminated), TypeA2 (normally graded, gradational to mud upwards) and TypeBl and TypeC1 (sorted pumice clasts making laminations in sediments) are variations of fallouts. TypeA3, TypeB4 (inverse-to-normally graded turbidites with crude laminations) and TypeC3 (inverse-to-normally graded pumiceous turbidite with pebbly base) are referred to ash flow turbidites possibly as well as TypeB3 (inverse-to-normally graded pumice clasts in ashes). TypeA5 (crudely laminated fine ashes with some pumice clasts) is representative of ash clouds as well as TypeB2 (scattered pumice clasts in ashes or sediments). TypeC2 (inversely graded pumiceous ash) is indicative of pumiceous debris flow. TypeA4 (organized to Bouma sequence) is mostly dilute ash flow turbidite. Some of TypeB5 (organized to Bouma sequence with accidental grains to some extent) are also referred to ash flow turbidites, but most of TypeB5 are epiclastic, as well as TypeC4 (normally graded pumiceous volcaniclastic sediments with rip-up clasts). It is noteworthy that most of TypeB4 as well as TypeA3 and TypeC3 are widely traceable (more than 50km) with small -ΔT/ΔD (differential aspect ratio) such as 1:20000 to 1:200000. They are turbidites directly transformed from subareal ash flows by mixing with water in subaqueous environments, or differentiated at the base of the dense ash clouds of subaqueous eruption column. The author referred them to ash flow turbidites. The model sequence inlcuding ash flow turbidite units is also presented, in which ash flow turbidite occupies the basal unit (Unit-I). In the case of subaqueous eruptions, fines and pumices are confined in water as suspension or dense ash cloud, then ash clouds of fines with some pumice clasts (TypeA5), dilute ash flow turbidites (TypeA4) and/or pumiceous debris flows (TypeC2) will be generated. Thus, the tephra sequence such as the piles of TypeA4, TypeA5 or TypeC2, and composite sequences of TypeC3-TypeA4 (double grading) implicate the possibility of subaqueous eruptions.

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Behavior of chlorine and fluorine during felsic magma crystallization is discussed based on many previous researches. Chlorine is strongly partitioned into the exsolved vapor and removed from magma during its degassing. Whereas, fluorine has a tendency to remain in magma. Halogen and some REE contents of apatite is expected to be an indicator of vapor saturation and degassing in the process of magma intrusion into the volcanic conduit, from apatite chemistry of a dome dacite of the Oetakayama volcanoes, Southwest Japan. Some problems related to the mechanisms of apatite crystallization in magma are discussed.

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