Description: On December 16, 1988, after 26 years of dormancy since the last eruption in 1962, Tokachi-dake began to erupt from the 62-II crater. The eruption started with phreatic explosions. Then, on December 19, the activity changed into phreatomagmatic explosions of Vulcanian type and continued intermittently until March 5, 1989. Although the composition of the essential ejecta, mafic andesite, is similar to those of 1926 and 1962 eruptions, the mode of the present eruption is considerably diffrent The present eruption consists of a series of 23 discrete cannon-like explosions, being frequently accompanied with small-scale pyrcclastic surges and flows. The total volume of ejecta amounts to approximately 6×105 m3, of which about 20% is essential ejecta. A complete sequence of events was compiled and distribution maps of the ash-fall, ballistic blocks, and pyroclastic surges and flows were drawn for each of the larger eruptions. The pyrrolastic surges and flows of the present eruption were small scale, low temperature pyroclastic flows, rich in accessory clasts and unaccompanied by sector collapse. Therefore, the sudden melting of snow causing disastrous mudflows, as in the case of the 1926 eruption, fortunately did not occur.

Description: The structural, temporal, compositional and volcanic evolution of oceanic intraplate islands is one of the major research areas in our department. A regional focus is on the island groups and seamounts along the passive margin off Northwest Africa. The Canary Islands which are characterized by an unususally large compositional spectrum of igneous rocks and long magmatic histories, exceeding 20 Ma in some islands, are the main target area for our ongoing combined on- and offshore studies. We here report on specific events and stages in the structural and chemical evolution of the island of Gran Canaria and its sedimentary apron using a variety of methods. Detailed studies of constructive and destructive processes during island evolution have allowed to predict - and verify by deep sea drilling - the submarine and subaerial evolution of Gran Canaria and its surrounding sedimentary basins. Our aim is to develop a globally representative model explaining the evolution of volcanic islands including aspects of volcanic hazards related to explosive eruptions and tsunamis triggered by island flank collapses.

Description: Sequences and products of the Izu-Oshima 1986-1987 eruptions which started on November 15, 1986, were investigated tephrochronologically. The results are summarized as follows : 1) Summit eruptions (Crater A) During 15-20, Nov. 1986, Strombolian eruptions continued to make a lava lake from where lava flows spilt over and went down the slope of the central cone to the caldera floor (LA I～IV). Volcanic ash and scoria (TA-1～4) were dispersed to the eastern and western parts of the island. On 21 Nov., a little after the beginning of the fissure eruption (Craters B), Strombolian eruptions were reactivated and ejected large volcanic bombs and scoria (TA-5) from Crater A. On Dec. 18, 1986, small explosion occurred from the Crater A for three or four hours, ejecting a scoria fall (TA-6) and bomb. The level of the lava lake lowered about 5 meters. On Nov. 16, 1987, a phreatic explosion occurred to break the crust of the lava lake, and the lava drained back to the deep on Nov. 18. 2) Fissure eruptions in the caldera floor (Craters B) At 16 : 15, on Nov. 21, 1986, fissure eruptions (Craters B) started on the caldera floor and extended to the slope of the central cone. The eruptions became explosive one, generating lava fountains with the height of more than 1500 meters, with a high discharge rate of 8×106 ton/hour, producing pyroclastic cones and rootless (clastogenic) lava flows (LB I and III). Subplinian scoria falls were dispersed to west (TB-1) and east (TB-2). About 5 hours after the beginning, the activity waned to produce only volcanic ash (TB-3 and -6) and finer scoria falls (TB-4 and -5) and ceased on Nov. 23. A rheomorphic lava flow (LB II) occurred from the edge of the deformed cone on Nov. 23. 3) Fissure eruptions on the somma slope (Craters C) At 17 : 45, on Nov. 21, 1986, fissure eruptions occurred on the somma slope, and produced two lava flows (LC I and II), scoria cones, and vesicular scoria falls (TC-1 and -3) from the 11 craters. 4) The 1986 eruptions ejected 0.053 km3, 7.9×107 tons of lava and pyroclasts from A, B and C craters (Table 4).

Description: Processes generating block and ash flows by gravitational dome collapse (Merapi-type pyroclastic flow) were observed in detail during the 1990–1995 eruption of Unzen volcano, Japan. Two different types were identified by analysis of video records and observations during helicopter flights. Most of the block and ash flows erupted during the 1991–1993 exogenous dome growth stage initially involved crack propagation due to cooling and flowage of the dome lava lobes. The mass around the crack became unstable, locally decreasing in tensile strength. Finally, a slab separated from the lobe front, fragmented progressively from the base to the top within a few seconds, and became a block and ash flow. Rock falls immediately followed, in response to local instability of the lobe front. Clasts in these rock falls fragmented and merged with the preceding flow. In contrast, block and ash flows during the endogenous dome growth stage in 1994 were generated due to local bulge of the dome. Unstable lava blocks collapsed and subsequently fragmented to produce block and ash flows.

Description: Obsidian stone tools were discovered at a tephra outcrop in Shari district, eastern Hokkaido, Japan. This site was named Koshikawa Site. The main stone tools obtained from the outcrop were flakes. Some of them are identified morphologically as microblades. 14C dating of charcoals buried with the stone tools in burned soil, gave an age of 23, 430±820750y. B. P. (NU-056). The age indicates that Koshikawa Site is one of the oldest archaeological sites in Hokkaido, and that the Micro-blade Culture presumably developed earlier in Hokkaido than has been thought.

Description: Fifteen Lateglacial to Holocene rhyolitic, dominantly primary tephra layers piston-cored and drilled (ICDP Paleovan drilling project) in western Lake Van (eastern Anatolia, Turkey) were precisely correlated to either of the two adjacent and active large volcanoes Nemrut and Süphan based on shard textures, mineralogy and mineral and glass compositions. The young peralkaline (comenditic to pantelleritic) primary rhyolitic Nemrut tephras are characterized by anorthoclase, hedenbergitic to augitic clinopyroxene, fayalitic olivine, minor quartz, and rare accessory chevkinite and zircon. Phenocrysts in subalkaline primary rhyolitic Süphan tephras are chiefly oligoclase-labradorite, with minor K-rich sanidine in some, biotite, amphibole, hypersthene, rare augitic clinopyroxene, relatively common allanite and rare zircon. Two contrasting explosive eruptive modes are distinguished from each other: episodic (Süphan) and periodic (Nemrut). The Lateglacial Süphan tephra swarm covers a short time interval of ca. 338 years between ca. 13,078 vy BP and 12,740 vy BP, eruptions having occurred statistically every ca. 42 years with especially short intervals between V-11 (reworked) and V-14. Causes for the strongly episodic Süphan explosive behavior might include seismic triggering of a volcano–magma system unable to erupt explosively without the benefit of external triggering, as reflected in pervasive faulting preceding the Süphan tephra swarm. Seismic triggering may have caused the rise of more mafic (“trachyandesitic”) parent magma, heating near-surface pockets of highly evolved magma – that might have formed silicic domes during this stage of volcano evolution – resulting in ascent and finally explosive fragmentation of magma essentially by external factors, probably significantly enhanced by magma–water/ice interaction. Explosive eruptions of the Nemrut volcano system, interpreted to be underlain by a large fractionating magma reservoir, follow a more periodic mode of (a) long-term relatively constant supply of parent magma, (b) evolution by low pressure crystal fractionation resulting in sporadic relatively low-volume eruption of trachytic and minor rhyolitic magmas, (c) evolution of a large magma reservoir to the point of highly explosive large-volume peralkaline rhyolitic Plinian eruptions at temporal intervals of ca. 20–40 ky, some accompanied by ignimbrites and inferred caldera collapse. A striking tephra gap between ca. 14 ka and ca. 30 ka, i.e. during glacial climate conditions, is postulated to be due to climate-forcing via lithosphere unloading following deglaciation.

Description: Thirty-two new single crystal ages document 400 000 years of widespread explosive volcanism of historically active Nemrut Volcano towering over huge alkaline Lake Van (Eastern Anatolia). The dated deposits were selected to monitor the volcanic and compositional evolution of Nemrut Volcano through time and thus to provide a rigorous temporal framework for the tephra record of the PaleoVan Drilling Project. Tephra samples were taken from large-volume deposits or those that occur in medial to distal localities, well-exposed stratigraphic sections or from the initial phase of an eruptive sequence. Mainly fallout deposits were chosen because most ignimbrites show more complex and corroded feldspar populations owing to compositional zoning and magma mixing. Moreover, fallout deposits held the promise to be more clearly identifiable with-and correlatable to-〉300 tephra layers in the PaleoVan drill cores, even though commonly in amounts marginal or insufficient in thickness to allow well-supported single crystal dating. The crystals dated are dominantly anorthoclase, the main phenoctyst phase in the trachytic to rhyolitic, slightly to strongly peralkaline Nemrut magmas. Ages obtained so far range from ca. 400 ka to ca. 30 ka for Nemrut Volcano. The causes of significant changes in the frequency, volume and composition of tephra layers per unit time are discussed in terms of external (erosion, climate changes, geodynamic factors) and internal forcing (changes in magma supply and composition and incubation periods preceding large volume rhyolitic eruptions). For example, the low frequency of tephra layers deposited prior to ca. 200 ka may be due to low explosive activity, severe erosion between MIS 9 and MIS 11, or both. Nevertheless, the overall frequency of explosive eruptions appears to have increased during the past ca. 200 ka. We also recognize a slight peak in explosive eruptions during warm periods (e.g. MIS 5 and MIS 7) and speculate on lithospheric unloading triggering increased partial melting or magma reservoir unloading following massive glacier melting. The ages of 5 dated ignimbrites span ca. 250 000 years suggesting that Nemrut Volcano went through a polycyclic evolution with multiple caldera collapses and major pyroclastic flow eruptions, the oldest dated so far as 265 ka. The widely held view of the impressive Nemrut Caldera now dated to have formed at ca. 30 ka, as the main paroxysmal event during the evolution of the volcano is no longer tenable. Distinct and coherent compositional characteristics, especially in trace element concentrations, characterize several groups of trachytic tephras. We speculate that the growth of Nemrut Volcano caused the isolation of the Lake Van basin. On account of their mineralogical (anorthoclase, hedenbergite, fayalite, aenigmatite) and alkalic chemical compositions and large volume, dated Nemrut fallout tephras are likely to represent excellent markers in lakes and other sites of paleoclimatological or archeological interest in neighboring countries to the northeast of Lake Van as far as the Caspian Sea in what may be called the East Anatolian Tephra Province

Description: The historically active Nemrut Volcano (2,948 m asl) (Eastern Anatolia), rising close to the western shore of huge alkaline Lake Van, has been the source of intense Plinian eruptions for 〉530,000 years (drilled lake sediments). About 40 widespread, newly recognized trachytic and less common rhyolitic fallout tephras and ca. 12 interbedded ignimbrites, sourced in Nemrut Volcano, are documented in stratigraphic traverses throughout an area of 〉6,000 km(2) mostly west of Lake Van. Phenocrysts in the moderately peralkaline trachytes and rarer large-volume comenditic rhyolites comprise anorthoclase, hedenbergite-augite, fayalite and, especially in trachytic units, augite, minor aenigmatite, apatite and quartz, and rare chevkinite and zircon. Dacitic to rhyolitic tephras from nearby calcalkalic Suphan Volcano (4,058 m asl), locally interbedded with Nemrut tephras, are characterized by disequilibrium phenocryst assemblages (biotite, augitic clinopyroxene and hypersthene, minor olivine, common crystal clots and/or, in some deposits, amphibole). The magma volume (DRE) of the largest Nemrut tephra sheet (AP-1) described in detail may exceed 30 km(3). Extreme facies and systematic compositional changes are documented in the ca. 30 ka Nemrut Formation (NF) deposits formed from one large and complex eruption (thick rhyolitic fallout overlain by ignimbrite, welded agglutinate, overbank surge deposits, and final more mafic fallout deposits). Common evidence of magma mixing in Nemrut ignimbrites reflects eruption from compositionally zoned magma reservoirs. Several young Cekmece Formation trachytes overlying ca. 30 ka old NF deposits and the late trachytes of the NF deposits show compositional affinities to tephra from Suphan Volcano possibly due to temporary influx of Suphan magmas into the Nemrut system following the evacuation of 〉10 km(3) magma (DRE) during the caldera-forming NF eruption. Axes of large fallout fans are dominantly SW-NE but W-E in the younger sheets resembling the direction of the present dominant wind field. Growth of Nemrut volcanic edifice and its peripheral domes since before 0.5 Ma in the hinge area between the Van and Mus tectonic basins is likely to have been the major factor in isolating Lake Van basin thus initiating the origin and subsequent alkaline evolution of the lake. This alkalinity was later significantly controlled by climate forcing. Internal forcing mechanisms (volcanic and geodynamic) may also have contributed to major lake level changes in addition to climate forcing.