Tephra Analysis Research Articles

Recovery of DNA and pollen from New Zealand lake sediments

An undisturbed sediment core taken from Round Lake, Hawke's Bay, New Zealand, using a specially designed sterile sampler, has been dated by tephra analysis and radiocarbon and analysed for pollen, charcoal and DNA. It appears to cover the last ca. 3600 years. There are clear indications of Māori effects on vegetation from ca. 800 BP. DNA was extracted from the core and amplified using bacterial and a range of other PCR primers targeting human and other animal mtDNA sequences. Cloned bacterial DNA sequences from just above the Taupo tephra (dated to AD 217–247) produced 98% and 99% similarity matches with human faecal bacteria. The 98% match was to the human gut bacterial genus Prevotella. This genus can, however, be found in a range of animal (including insect) guts. Extracted DNA was matched closely to the New Zealand native fish species Gobiomorphus cotidianus. Further work is needed to establish unequivocally that no DNA movement through the profile is occurring, but these results suggest a new technique of potentially revolutionary importance for Quaternary research.

Volcanic Ash Deposition and Long-Term Vegetation Change on Subantarctic Marion Island

ABSTRACTA c. 5500 year record of peatland development and vegetation change was generated from a core recovered from an Agrostis magellanica peat bog on subantarctic Marion Island, using palynomorph, plant macrofossil, and tephra analyses. Two tephra horizons (both 17 cm thick) were identified and dated to ca. 2900 cal. BP and ca. 1700 cal. BP. Succession of the vegetation as a consequence of tephra deposition, particularly by the pioneer Azorella selago, appears to have been very slow, lasting as long as c. 700 yr. The slow pace of vegetation succession highlights the sensitivity of the indigenous Marion Island flora to environmental change, and the vulnerability to the spread of alien invasive species.

立川断層の最新活動時期―東京都西多摩郡瑞穂町箱根ケ崎におけるトレンチ調査結果―

The Tachikawa fault, which is the only active fault in the Tokyo Metropolis, is expected to be the source of shallow intra-plate earthquakes in the future. We performed additional trenching surveys at the northwestern part of the fault to obtain the paleoseismological parameters for evaluating earthquake potential caused by the fault. Trench wall observation, radiocarbon dating, and tephra analyses constrained the last surface-rupturing event at the Tachikawa fault between about 13, 700 cal yBP and 12, 800 cal yBP. The vertical separation of the event is estimated to be more than 2.6 meters.

Using geochemistry as a tool for correlating proximal andesitic tephra: case studies from Mt Rainier (USA) and Mt Ruapehu (New Zealand)

AbstractVolcanic hazards assessments at andesite stratovolcanoes rely on the assessment of frequency and magnitude of past events. The identification and correlation of proximal and distal andesitic tephra, which record the explosive eruptive history, are integral to such assessments. These tephra are potentially valuable stratigraphic marker beds useful to the temporal correlation and age dating of Quaternary volcanic, volcaniclastic and epiclastic sedimentary deposits with which they are interbedded. At Mt Ruapehu (New Zealand) and Mt Rainier (USA), much of the detail of the recent volcanic record remains unresolved because of the difficulty in identifying proximal tephra. This study investigates the value of geochemical methods in discriminating andesitic tephra. Our dataset comprises petrological and geochemical analyses of tephra that span the late Quaternary eruptive record of each volcano. Our data illustrate that andesitic tephra are remarkably heterogeneous in composition. Tephra compositions fluctuate widely over short time intervals, and there are no simple or systematic temporal trends in geochemistry within either eruptive record. This complexity in tephra geochemistry limits the application of geochemical approaches to tephrostratigraphic studies, beyond a general characterisation useful to provenance assignation. Petrological and geochemical data suggest that the products of andesite systems are inherently variable and therefore intractable to discrimination by simple geochemical methods alone. Copyright © 2006 John Wiley & Sons, Ltd.

An 18 m thick volcaniclastic interval in Pantelleria Trough, Sicily Channel, deposited from a large gravitative flow during the Green Tuff eruption

A 30-m long piston core from the floor of Pantelleria Trough penetrated an 18 m thick volcaniclastic interval under- and overlain by hemipelagic sediments. The distribution and thickness of the interval is mapped in 3.5 kHz profiles across the trough. Core sediments have been analysed for grain size, carbonate content, detrital petrology, and physical properties such as bulk density and magnetic susceptibility. Chemical analyses of tephra and included minerals have been made by electron microprobe. The volcaniclastic interval is correlated with the youngest large explosive eruption on Pantelleria, the 50 ka Green Tuff ignimbrite eruption, on the basis of the sedimentation rate of overlying sediment, calcareous nannofossil and foraminiferal biostratigraphy, a calibrated radiocarbon age of 43–47 ± 2 ka (possibly infinite) in the underlying marls, and many similarities in tephra and mineral chemistry and abundance. The lower 8 m of the volcaniclastic interval consists of poorly sorted massive units of lapilli tuff, interpreted as resulting from the direct flow of a pyroclastic flow into the sea, with the energetic hyperconcentrated flows crossing the length of Pantelleria Trough and eventually “freezing” on the low gradients. The overlying 10 m thick turbidite probably developed from the dilute turbulent pyroclastic flow of the co-ignimbrite cloud and the resulting turbulent subaqueous flow eroded bioclastic material from the shelf and deposited a well-graded bed from sand through silt to mud. The poorer sorting of the volcaniclastic interval compared with the Green Tuff ignimbrite on land supports the concept that ignimbrite deposits are sorted by aggrading bed processes.

Interpretation of charcoal and pollen data relating to a late Iron Age ritual site in eastern Ireland: a holistic approach

The study of charcoal produced by five burning episodes that occurred in a rapid succession within a ritual pit dating to the late Iron Age at Raffin Fort, Co. Meath, Ireland, reveals considerable variation in the charcoal assemblages resulting from each burning episode. Wood selection processes are considered against the background of information on woodland composition and land-use history provided by a detailed pollen diagram from nearby Emlagh Bog, the chronology of which is based on both AMS 14C dates and tephra analysis. A human skull fragment lay on top of the charcoal layers but the radiocarbon evidence indicates that the skull predated the burnings by at least a century. This and other evidence indicate a ritual pit with the skull as a human relic. It is suggested that, in this instance, wood selection was neither random nor determined solely by availability or combustibility, but instead may have been informed by socio-religious belief systems pertaining to trees and wood. Early Irish documentary sources, which reveal a complex ethnography of wood and trees in later prehistoric and early historic Ireland, are reviewed. The results shed fresh light on aspects of late Iron Age archaeology in a part of Europe that was outside the direct influence of the Roman world. New information is provided on a distinctive feature in late Holocene Irish pollen records namely the Late Iron Age Lull (ca. a.d. 1–500). During this time, widespread regeneration of woody vegetation took place. In the subsequent early Medieval period renewed farming activity resulted in substantial decline in woodland, a pattern also seen at many other locations in Ireland.

The age and origin of the Labyrinth, western Dry Valleys, Antarctica: Evidence for extensive middle Miocene subglacial floods and freshwater discharge to the Southern Ocean

A 50! -km-long network of bedrock channels and scoured terrain occupies the ice-free portion of a major trough that crosses the Transantarctic Mountains in southern Victoria Land. The channels, collectively termed the Labyrinth, emerge from beneath the margin of the East Antarctic Ice Sheet (Wright Upper Glacier) and are incised into a 300-m-thick sill of Ferrar Dolerite at the head of Wright Valley. Upper- and intermediate-elevation erosion surfaces of the Labyrinth exhibit striations and molding characteristic of glacial erosion. Channels and canyons on the lower surface are as much as 600 m wide and 250 m deep, have longitudinal profiles with many reverse gradients, and contain potholes ! 35 m deep at tributary junctions. These characteristics are most consistent with incision from fast-flowing subglacial meltwater; estimated discharge is on the order of 1.6-2.2 10 6 m 3 s # 1 . Our 40 Ar/ 39 Ar analyses of volcanic tephra from the Labyrinth show that the chan- nels are relict, that major channel incision predates 12.4 Ma, and that the last major subglacial flood occurred sometime between 14.4 Ma and 12.4 Ma. The most plausible origin for the Labyrinth is erosion associated with episodic drainage of subglacial lakes in East Antarctica. One compelling possibility is that discharge of large volumes of sub- glacial meltwater to the Southern Ocean, and to the Ross Sea in particular, may have coincided with, and contributed to, oscillations in regional and/or global climate during the middle Miocene.

Identification of Aniakchak (Alaska) tephra in Greenland ice core challenges the 1645 BC date for Minoan eruption of Santorini

Minute shards of volcanic glass recovered from the 1645 ± 4 BC layer in the Greenland GRIP ice core have recently been claimed to originate from the Minoan eruption of Santorini [Hammer et al., 2003]. This is a significant claim because a precise age for the Minoan eruption provides an important time constraint on the evolution of civilizations in the Eastern Mediterranean. There are however significant differences between the concentrations of SiO2, TiO2, MgO, Ba, Sr, Nb and LREE between the ice core glass and the Minoan eruption, such that they cannot be correlatives. New chemical analyses of tephra from the Late Holocene eruption of the Aniakchak Volcano in Alaska, however, show a remarkable similarity to the ice core glass for all elements, and this eruption is proposed as the most likely source of the glass in the GRIP ice core. This provides a precise date of 1645 BC for the eruption of Aniakchak and is the first firm identification of Alaskan tephra in the Greenland ice cores. The age of the Minoan eruption of Santorini, however, remains unresolved.

High‐resolution study of Icelandic tephras in the Kangerlussuaq Trough, southeast Greenland, during the last deglaciation

AbstractTephra abundance data and geochemistry in Late‐glacial and Holocene sediments on the East Greenland shelf are presented. Two well‐known tephras were identified from electron microprobe analysis of tephra shards picked from ash peaks in the cores. These are the Vedde Ash and Saksunarvatn Ash, which probably were deposited on the shelf after transport on drifting ice. The radiocarbon dates (marine reservoir corrected by −550 yr) that constrain the timing of deposition of the tephra layers compare well with the terrestrial and ice‐core ages of the tephras without requiring additional reservoir correction to align them with the known tephra ages. Several prominent tephra layers with a composition of Ash Zone 2 tephra punctuate the deglacial sediments. These tephra peaks coincide with significant light stable isotope events (signifying glacial meltwater) and fine‐grained sediments poor in ice‐rafted detritus. We interpret the Ash Zone 2 tephra peaks as sediment released from the Greenland Ice Sheet during strong melting pulses of the deglaciation. Copyright © 2002 John Wiley & Sons, Ltd.

A 28 000–6600 cal yr record of local and distal volcanism preserved in a paleolake, Auckland, New Zealand

A 52.5 m core was extracted from Pukaki Crater, an infilled basaltic explosion crater in the Auckland Volcanic Field, for detailed tephra and palynological analysis. The core consists of a lower 6 m of finely laminated lacustrine sediments representing the interval c. 28 000–6600 cal yr overlain by 46.5 m of homogeneous marine silts deposited between c. 7600 and 6600 cal yr. Favourable conditions have preserved at least 40 tephra layers in the sediments. These have been derived from one local and five distal sources and were deposited within the crater lake between c. 28 000 and c. 7600 cal yr. The tephra beds were identified by stratigraphic position, geochemical analyses, and ferro‐magnesian mineral assemblage. This tephrostratigraphic framework is underpinned by three distinctive tephra beds, namely Tuhua (c. 6950 cal yr), Rotoma (c. 9500 cal yr), and Kawakawa (c. 26 500 cal yr). Of the 40 tephra beds, 7 are sourced from the rhyolitic Okataina Volcanic Centre (Mamaku c. 8200 cal yr; Rotoma c. 9500 cal yr; Waiohau c. 13 800 cal yr; Rotorua c. 15 800 cal yr; Rerewhakaaitu c. 17 700 cal yr; Okareka c. 21 400 cal yr; Te Rere c. 25 000 cal yr), 3 from the rhyolitic Taupo Volcanic Centre (Opepe c. 10 200 cal yr; Kawakawa c. 26 500 cal yr; Poihipi c. 27 500 cal yr), 5 from the andesitic Tongariro Volcanic Centre, 14 from the andesitic Taranaki Volcano, 1 from Mayor Island (Tuhua c. 6950 cal yr), and 8 from the basaltic Auckland Volcanic Field. In addition, two previously unidentified rhyolitic tephra (c. 17 100 cal yr and c. 20 720 cal yr) are recorded. The occurrence of numerous andesitic and rhyolitic tephra beds in the Auckland region extends the known dispersal of the units and has implications for the assessment of volcanic hazards from distal sources. Many of the Taranaki‐derived tephra beds do not stratigraphically match those recorded in the Waikato lakes region and this suggests that Taranaki Volcano produced more ash than previously estimated. The distal tephra record preserved at Pukaki provides age constraints for Auckland Volcanic Field basaltic tephra that are otherwise poorly dated. Basaltic fall events are recorded at c. 14 450 cal yr, 15 750 cal yr, 19 380 cal yr, 19 420 cal yr, 23 825 cal yr, 24 175 cal yr, 25 200 cal yr, and 25 700 cal yr. Fresh glass in the basaltic tephra allows them to be chemically fingerprinted and discriminated, and this will open a new avenue to development of a regional basaltic tephrostratigraphy.

Palaeoenvironmental and palaeoclimatic implications of the Late‐Quaternary sediment record of Vico volcanic lake (central Italy)

AbstractA 15‐m‐long sediment core recovered from the Lago di Vico caldera lake in central Italy has been the subject of macrofacies description and sedimentological (organic carbon content, grain size and mineralogy) investigation. The results have been integrated with the pollen data from the same core in order to provide a regional climatic and environmental history, with inferences on past lake levels and on moisture and temperature regimes. Radiometric (14C and 40Ar/39Ar) dating, biostratigraphical considerations and tephra analyses provide a chronological framework and indicate that the sequence spans the last 90 000 yr. Several moist periods have been identified that were characterised by enhanced weathering by hydrolysis of the catchment rocks. These alternated with relatively dry phases associated with lowering of lake‐levels. The lowest hydrolysis efficiency of the whole record, accompanied by notable aeolian deposition, was attained during the last glacial phase but moisture conditions were such that the lake‐level did not decrease, probably owing to reduced temperatures. Evidence for cool climate also emerges for the early Pleniglacial. The highest available moisture was achieved within the Holocene at 5 kyr BP. The Late Holocene does not show either increase of aridity or degradation of the vegetation cover, until at least Roman times. Copyright © 2001 John Wiley & Sons, Ltd.

Late Quaternary Eolian Deposition in Central Italy

Records of eolian quartz from two continuous sediment sequences drilled in Lagaccione and Lago di Vico volcanic lakes in central Italy contribute to the knowledge of eolian deposition in the central Mediterranean during the last 100,000 years. The chronology is based on 14C and 40Ar/39Ar dating and tephra analysis. Pollen data provide the paleoenvironmental framework and enable correlation between the cores. Eolian inputs were high during the steppe phases corresponding to oxygen isotope stages 4 and 2. Low inputs correspond to the forest phases of the last interglacial and the middle Holocene. Eolian inputs have increased in the late Holocene. Patterns of eolian deposition in central Italy resemble the Antarctic dust record from the Vostok ice core. The Italian patterns may also correspond with hydrological changes registered in North Africa. The main source of dust loading over the Mediterranean now, North Africa, may have played an important role in dust supply throughout the last climatic cycle.

Fernandina Volcano's evolved, well‐mixed basalts: Mineralogical and petrological constraints on the nature of the Galapagos plume

Fernandina Volcano, the most active of Galapagos volcanoes and the one most directly overlying the Galapagos hotspot, is one of a small number of active, plume‐related oceanic island volcanoes with a well‐documented recent eruptive record. Whole rock and glass analyses of lava and tephra from all 12 known eruptions from 1958 to the present show them to be evolved (Mg # (= Mg/Mg + Fe2+) of 0.47–0.56), plagioclase‐phyric, clinopyroxene‐ and olivine‐bearing tholeiites. Thermodynamic modeling indicates that this phase assemblage erupted at 1100–1130°C and is stable only at low pressures (<0.1–0.2 GPa), thereby representing crystallization within a shallow magma chamber underlying the well‐defined, 850‐m‐deep, 5 by 6.5 km caldera. These tholeiites are remarkably homogenous, as is shown by narrow ranges in Zr/Y (5.7–6.3), (La/Sm)N (1.4–1.7), and (La/Yb)N (3.8–4.3). Prehistoric Fernandina lavas, selected for petrographic and geographic variation over the entire subaerial volcano, are of remarkably similar composition (e.g., Zr/Y is 5.2–6.1, (La/Sm)N is 1.5–1.6, and (La/Yb)N is 3.4–4.1), with a single example of a more primitive lava having an Mg # of 0.63, with 8.5% FeO at 8% MgO. Cr‐spinel and glass melt inclusions in plagioclase, together with zoned olivine, give evidence for a range of parental melts in the recent shallow magmatic system, with Mg # as high as 0.62. Extensive, shallow magma mixing is required to explain these variations in mineral and inclusion chemistry, indicating more thermal variation within the shallow magmatic system than is implied by the relatively monotonous whole rock compositions. Apparently, Fernandina's shallow magma chamber has physically blocked passage of more primitive magmas to the surface and homogenized the erupted lavas by extensive mixing. Small variations in lava isotopic and compatible element composition, combined with the need to resupply melt to maintain thermal balance, indicate that replenishment of the magma chamber is semicontinuous, with resupply occurring of the order of a decade or less. Plagioclase‐dominated, evolved Fernandina lavas are in sharp contrast to more primitive, olivine‐dominated Hawaiian lavas; the total lack of primitive melts in the shallow Fernandina magmatic system implies that substantial fractionation and heat loss occurred during melt transportation from the mantle source to the edifice magma chamber, despite the fact that these melts were transported through relatively warm, young, and thin lithosphere adjacent to the Cocos‐Nazca ridge. The diffuse nature of Galapagos volcanism, with 20th century eruptions from eight distinct volcanoes over a 20,000 km2 area, further supports this interpretation and suggests that the Galapagos plume is relatively diffuse, weak, and significantly less thermally intense than the vigorous Hawaiian plume. It may in fact be waning.

Late Pleistocene and Holocene pollen stratigraphy at Lago di Vico, central Italy

A new pollen record from Lago di Vico (core V1) provides fundamental new information towards reconstruction of flora and vegetation history in central Italy during the last 90 000 years. The chronological framework is secured by seventeen AMS14C dates, one40Ar/39Ar date and tephra analyses. At the base of the pollen record, i.e. shortly after the40Ar/39Ar date 87 000±7000 B.P., three phases with significant expansion of trees are recorded in close succession. These forest phases, which stratigraphically correspond to St Germain II (and Ognon?) and precede pleniglacial steppe vegetation, are designated by the local names Etruria I, Etruria II and Etruria III. During the pleniglacial, a number of fluctuations of angiosperm mesophilous trees suggest the presence of tree refugia in the area. The lowest pollen concentration values are recorded at ca. 22 000 B.P. which corresponds with other pollen records from the region. The late-glacial is characterized by an expansion in the arboreal pollen curves that is less pronounced, however, than in other pollen profiles from Italy. The Holocene part of the profile is consistently dominated by deciduous oak pollen. No major changes in arboreal pollen composition are recorded but several marked and sudden declines of the tree pollen concentration suggest that the forest cover underwent dramatic changes. Clear evidence for human impact is recorded only when cultivated crops became important which dates to ca. 2630±95 B.P.

Late Holocene forest disturbance in Gisborne, New Zealand: A comparison of terrestrial and marine pollen records

A late Holocene (from c. 5500 yr B.P.) record of vegetation change is presented for the Gisborne region, based on pollen, charcoal, and tephra analyses of a terrestrial and a marine core. Up until the time of anthropogenic deforestation about 650 yr B.P., well drained lowland areas were covered with a Prumnopitys taxifolia, and Dacrydium cupressinum‐dominated podocarp/hardwood forest. The poorly drained Dacrycarpus dacrydioides‐dominated alluvial swamp forests were not as vulnerable to fire, and remained on the Gisborne Plains until European drainage and clearance began in the 19th century. In the last 5500 yr B.P., the lowland forests have been disturbed by at least five ashfalls originating from volcanic eruptions in the Central Volcanic Region. Where the terrestrial and marine cores overlap, comparisons of the pollen records show the vegetation changes and taxa present to be comparable. The fire record was not clear in the marine record, as the charcoal curve was diluted with high background levels of reworked charcoal. Sedimentation rates from the marine core indicate tha erosion in the Waipaoa catchment has increased significantly since European clearance of soil‐protecting remnant forest and fern/scrubland and its replacement with pasture.

Distinguishing subglacial till and glacial marine diamictons in the western Ross Sea, Antarctica: Implications for a last glacial maximum grounding line

Analyses of lithology, stratigraphy, and tephra from marine sediment cores collected from the western Ross Sea during cruises Eltanin 32 and 52 and Deep Freeze 80 and 87 indicate that subglacial till does not extend to the continental shelf edge. Subglacial till occurs as the lowest unit in most cores landward (south) of approximately 74°S, while seaward of approximately 74°S, the lowest diamicton units are glacial marine diamictons. Glacial marine diamictons are distinguished from subglacial tills by the presence of higher and more variable total organic carbon content downcore, distinct tephra layers, stratification, higher diatom and foraminifera abundances, higher sand content, and radiocarbon dates in chronological order downcore. Sand-sized tephra layers from two cores on the outer continental shelf are interpreted as single eruptive events, one likely to have been derived from the Mount Melbourne volcano and the other from the Pleiades volcano. Radiocarbon dates from sediment above and below the tephra layer in one of these cores (Df87-32) show that deposition indicative of open-water conditions occurred between 22 and 26 ka in the western Ross Sea.

Tephra analysis of sediments from Midge Lake (South Shetland Islands) and Sombre Lake (South Orkney Islands), Antarctica

Lake sediment cores from Midge Lake, Livingston Island, South Shetland Islands and Sombre Lake, Signy Island, South Orkney Islands were analysed for volcanic tephra using light microscopy and magnetic susceptibility. Cores were dated using published 14C and 210Pb chronologies. Electron probe microanalyses of discrete tephra glass shards were undertaken to characterise the tephra geochemically in order to identify possible source volcanoes and refine tephrochronological data for the region. Results identified five tephra horizons in a core from Midge Lake. Four of these tephra at 3–4 cm, 8–9 cm (c. 450 yr BP), 15–16 cm (c. 755 ± 105 yr BP) and 21–22 cm (c. 1340 ± 100 yr BP) consisted of sodic basaltic to basalticandesitic glasses, containing abundant labradoritic feldspar inclusions, and a single ‘acidic’ tephra was found at 2–3 cm. Seven tephra horizons were identified in the Sombre Lake core including three basaltic tephra at 3–9 cm (30 ± 4 yr BP to 125 ± 25 yr BP), 31–32 cm and 44–46 cm (1325 ± 50 14C yr BP) and four acidic tephra at 21–22 cm and 24–25 cm, 33–36 cm (c. 1021 14C yr BP) and 54–56 cm (c. 1450 14C yr BP). These are the first tephra to be identified from the South Orkney Islands. Geochemical and grain size analysis indicated that the analysed Midge Lake tephra were derived from the Quaternary Deception Island volcano. Smaller grain sizes, congruent geochemical data and prevailing wind directions also indicate this volcano as the likely source of Sombre Lake tephra. Results highlight the importance of establishing geochemical consistency between tephra deposited across wide geographical areas, during apparently synchronous time periods, if they are to be used in a regional tephrochronology.

Assessing the impact of volcanic activity on mid-Holocene climate in Ireland: the need for replicate data

Analyses of pollen, tephra, mineral input and degree of peat humification from three neighbouring raised peat profiles at Corlea, central Ireland, covering the period of the deposition of a tephra layer dated to just before 2290 cal. BC, and thought to represent Hekla-4 (2310±20 BC), are used to show the problems of relying on data from a single profile when invoking relationships between volcanic activity, climate and ecosys-tem response. While there appears to be a strong correlation between tephra deposition and flooding of the bog surface in one profile, with a short-lived increase in the rate of peat accumulation, comparison with the other two records suggests that peat had already begun a trend to a less humified condition before tephra deposition, and that evidence of local bog surface flooding was neither consistent nor synchronous.

Sulfur diffusion in rhyolite melts

Diffusion rates for sulfur in rhyolite melt have been measured at temperatures of 800–1100° C, water contents of 0–7.3 wt%, and oxygen fugacities from the quartz-fayalite-magnetite buffer to air. Experiments involved dissolution of anhydrite or pyrrhotite into rhyolite melt over time scales of hours to days. Electron microprobe analysis was used to measure sulfur concentration profiles in the quenched glasses. Regression of the diffusion data in dry rhyolite melt gives Dsulfur=0.05·exp{−221±80RT}, which is one to two orders of magnitude slower than diffusion of other common magmatic volatiles such as H2O, CO2 and Cl-. Diffusion of sulfur in melt with 7 wt% dissolved water is 1.5 to 2 orders of magnitude faster than diffusion in the anhydrous melt, depending on temperature. Sulfur is known to dissolve in silicate melts as at least two different species, S2− and S6+, the proportions of which vary with oxygen fugacity; despite this, oxygen fugacity does not appear to affect sulfur diffusivity except under extremely oxidizing conditions. This result suggests that diffusion of sulfur is controlled by one species over a large range in oxygen fugacity. The most likely candidate for the diffusing species is the sulfide ion, S2−. Re-equilibration between S2− and S6+ in oxidized melts must generally be slow compared to S2− diffusion in order to explain the observed results. In a silicic melt undergoing degassing, sulfur will tend to be fractionated from other volatile species which diffuse more rapidly. This is consistent with analyses of tephra from the 1991 eruption of Mount Pinatubo, Philippines, and from other high-silica volcanic eruptions.

兵庫県氷上盆地における地下地質構造調査

Seismic reflection survey and boring were performed in Hikami Drainage Basin in Hyogo Prefecture.Surveyed area is located near Iso where the lowest watershed in the main devide of the Honshu Island is located.Seismic profiles of the reflection survey show that unconsolidated sediments is 80 to 90 meters thick. The cored boring was drilled to depth of 100 meters on the profile line of the survey. This boring reached green rock of Tanba group at the depth of 96.6 meters (TP-5.92m).Cored samples contain a volcanic ash layer in depths ranging from 4.10 meters to 4.30 meters. As a result of Tephra analysis, it became clear that this volcanic ash was Aira-Tn (AT) tuff having ages of 22, 000 year. Therefore Holocene sediments are less than 4.1 meters in thick in this boring point. It is considered that almost unconsolidated sediments are Pleistocene.Sedimennts in depth from 0.6 meters to 6.5 meters contains rich silt and clays. Almost sediments under depth 6.5 meters are gravel and sand. The value of coefficient of permeability of these gravel and sand is 10-2-10-3cm/s which was obtained by the permeability test.This stratum of gravel is aquifer which provide much ground water in this area.