Tateyama Volcano Research Articles

Variations in thermal state revealed by the geochemistry of fumarolic gases and hot-spring waters of the Tateyama volcanic hydrothermal system, Japan

This study reports the chemical and isotopic compositions of hot-spring waters and fumarolic gases sampled in the Jigokudani Valley of Tateyama Volcano (central Japan) in 2015 and 2016 to reveal the state of the underlying hydrothermal system. We discuss the cause of temporal variations in geochemical data in terms of temperature change in the hydrothermal system and clarify the relationship between hot-spring waters and fumarolic gases. The volcanic gas supplied from deep-seated magma was separated into liquid and vapor phases when it reached a shallow depth. Each phase formed the following three types of hot-spring water: (1) high anion concentrations and isotopic compositions similar to magmatic water, (2) lower isotopic compositions compared to type-1 waters and large variations in Cl−/SO42−, and (3) low Cl− and total anion concentrations. The formation of type-1 and type-2 hot springs was influenced by magmatic components such as HCl and SO2. We consider that type-1 hot springs are derived from the liquid phase while type-2 hot springs are derived from the vapor phase of the two-phase zone. The temporal variations in Cl−/SO42− are considered to result from temperature changes in the reservoir where liquid and vapor separated, as the HCl partitioning coefficient between the vapor and liquid phases is strongly dependent on temperature. Type-3 hot springs are derived from the vapor phase, which is depleted in HCl and SO2. We propose that the Cl− concentration of type-2 hot springs could be a measure of volcanic activity because it reflects the thermal state of the shallow two-phase zone where phreatic eruptions occur.

P54 立山地獄谷で2010年5月に形成された硫黄溶岩の産状と岩石学的特徴(ポスターセッション)

P54 立山地獄谷で2010年5月に形成された硫黄溶岩の産状と岩石学的特徴(ポスターセッション)

G47 立山火山五色ヶ原周辺の地質といわゆる「立山カルデラ」の成因

G47 立山火山五色ヶ原周辺の地質といわゆる「立山カルデラ」の成因

Resistivity structure and geochemistry of the Jigokudani Valley hydrothermal system, Mt. Tateyama, Japan

This study clarifies the hydrothermal system of Jigokudani Valley near Mt. Tateyama volcano in Japan by using a combination of audio-frequency magnetotelluric (AMT) survey and hot-spring water analysis in order to assess the potential of future phreatic eruptions in the area. Repeated phreatic eruptions in the area about 40,000years ago produced the current valley morphology, which is now an active solfatara field dotted with hot springs and fumaroles indicative of a well-developed hydrothermal system. The three-dimensional (3D) resistivity structure of the hydrothermal system was modeled by using the results of an AMT survey conducted at 25 locations across the valley in 2013–2014. The model suggests the presence of a near-surface highly conductive layer of <50m in thickness across the entire valley, which is interpreted as a cap rock layer. Immediately below the cap rock is a relatively resistive body interpreted as a gas reservoir. Field measurements of temperature, pH, and electrical conductivity (EC) were taken at various hot springs across the valley, and 12 samples of hot-spring waters were analyzed for major ion chemistry and H2O isotopic ratios. All hot-spring waters had low pH and could be categorized into three types on the basis of the Cl−/SO42− concentration ratio, with all falling largely on a mixing line between magmatic fluids and local meteoric water (LMW). The geochemical analysis suggests that the hydrothermal system includes a two-phase zone of vapor–liquid. A comparison of the resistivity structure and the geochemically inferred structure suggests that a hydrothermal reservoir is present at a depth of approximately 500m, from which hot-spring water differentiates into the three observed types. The two-phase zone appears to be located immediately beneath the cap rock structure. These findings suggest that the hydrothermal system of Jigokudani Valley exhibits a number of factors that could trigger a future phreatic eruption.

Imaging the hydrothermal system beneath the Jigokudani valley, Tateyama volcano, Japan: implications for structures controlling repeated phreatic eruptions from an audio-frequency magnetotelluric survey

This study focuses on the results of an audio-frequency magnetotelluric (AMT) survey across the Jigokudani valley, Tateyama volcano, Japan, to investigate the spatial relationship between the distribution of electrical resistivity and geothermal activity and to elucidate the geologic controls on both its phreatic eruption history and recent increase in phreatic activity. The AMT data were collected at eight locations across the Jigokudani valley in September 2013, with high quality data obtained from most sites, enabling the identification of an underground 2D resistivity structure from the transverse magnetic (TM) mode data. The data obtained during this study provided evidence of a large conductive region beneath the surface of the Jigokudani valley that is underlain by a resistive layer at depths below 500 m. The resistive layer is cut by a relatively conductive region that extends subvertically toward the shallow conductor. The shallow conductive region is divided into an uppermost slightly conductive section that is thought to be a lacustrine sediment layer of an extinct crater lake containing hydrothermal fluids and a lower section containing a mix of volcanic gases and hydrothermal fluids. The low permeability of the clay zone means that the uppermost clayey sediments allow the accumulation of gases in the lower section of the conductive region, suggesting the existence of a cap structure. The deep resistive layer likely consists of units similar to the granitic rocks that are widely exposed throughout the Jigokudani valley. We suggest that the relatively conductive zone that separates these granitic rocks represents a high-temperature volcanic gas conduit, given that the most active fumarole in the Jigokudani valley lies directly along the trajectory of this path.

The Catastrophic Tombi Landslide and Accompanying Landslide Dams Induced by the 1858 Hietsu Earthquake

In the Joganji River basin, huge volume of sediment has been carried downstream and has formed the alluvial fan. The sediment runoff (erosion) volume is assumed to be 1.2 × 1011 m3, accounting by the hypsometric curve of the Joganji River, which indicates the amount corresponding to rise in the mountains of the upstream, 1 mm/year at average, since the start of the quaternary period. The fast-flowing Joganji River originating on the Tateyama Volcano slope was, until the end of the Edo Period (1607-1867), relatively stable as indicated by boat services operating from the river mouth to the fan apex. The Hietsu earthquake on April 9, 1858, caused numerous sediment disasters along the Atotsugawa fault system, some of the sediment movements built up landslide dams. Especially the catastrophic Tombi Landslide (Tombi-Kuzure) in the Tateyama Caldera, the upstream of the Joganji River, was the largest in the earthquake. The volume of the Tombi Landslide is estimated 103-127 million m3, one of the largest movements in the world calculated the volume difference of the configuration and the landform before the landslide based on wide-ranging historical data. The landslide dam broke twice – on April 23, 14 days after the quake and June 7, 59 days after it –, generating a large-scale outburst flood and sediment deposition on the Joganji River’s alluvial fan. Considering the carbon (14C) dating for the years 220-320 of pieces of wood sample at some deposits along the upstream of the Joganji River, it suggests that major sediment movement may have occurred in the Hietsu earthquake. But the years 720-940 suggest that major sediment movement may have occurred previously. Topographicaly, such a huge landslide is part of the mountain range erosion and disintegration process, making it important to be able to predict potential sediment movement’s scale and form accurately enough to minimize disaster and to better understand the overall landslide occurrence topographical changes.

Glacial Fluctuations Controlled by Volcanic Events on the Tateyama Volcano, Hida Range, Central Japan, during the Last Glacial Period

Glacial fluctuations controlled by volcanic events on the Tateyama Volcano (about 2, 670m a. s. l.) in the Hida Range, central Japan, during the last glacial period were reconstructed on the basis of glacial sediments, landforms, volcanic ejecta and their stratigraphic relationships. On Mt. Tateyama (3, 015m a. s. l.) comprising granitic bedrock, glaciers became less extensive depending on the climate change from Murodo Stades I (just before 70ka) and II (just after 70ka) through Tateyama Stades I (just before 29 cal ka), II (18-20ka) and III (10-11ka). In contrast, glaciers on the Tateyama Volcano adjacent to Mt. Tateyama became more expansive from Murodo Stades I and II through Tateyama Stade I, because the successive emergence of lava peaks progressively widened the accumulation area. In addition, a glacier rich in basal water may have surged from a lava peak in Murodo Stade II, due to high geothermal flow. However, it has not been confirmed whether or not the glacier snout descended most in Tateyama Stade I. In Tateyama Stade I, the repeated collapse of caldera walls decreased the accumulation area on the lava peaks, which resulted in intermittent glacial retreat on the volcano. In Tateyama Stades II and III, the glaciers on the volcano advanced to lesser extent depending on the climate change, because the Tateyama Volcano maintained its height and size.

Timing of Glacial Advances and Volcanic Activities on Mt. Tateyama, Hida Range, Central Japan during the Late Stade of the Last Glacial Period

The timing of the glacial advances and volcanic activities on Mt. Tateyama (3,015m) and Tateyama Volcano in the Hida Range in central Japan during the late stade of the last glacial period were clarified based on three moraines and their stratigraphic relationships with volcanic ejecta. The late stade was subdivided into Tateyama Stades I (just before 29cal ka), II (18-20 10Be ka) and III (10-11 10Be ka). The glaciers during the late stade attained their maximum advances in Tateyama Stade I and retreated with time. The maximum glacial advances during the late stade were caused just before 29cal ka in MIS 3 on the high mountains in the Hida Range simultaneously. Between Tateyama Stades I and II, the Tateyama Volcano gave rise to phreatic explosions that fragmented a lava layer overlying explosion crater. The fall of the lava fragments, however, did not trigger off the start of the glacial retreat and advance on Mt. Tateyama.

Glacial Expansion during the Early Stade of the Last Glacial Period on Mt. Tateyama, Central Japan

This paper reconstructs the flow directions and extent of glaciers on the western slopes of Mt. Tateyama (3, 015m asl) in central Japan from distribution, materials, and facies of two glacial sediments and related deposits. The timing of the larger glacial expansion during the Last Glacial period is then discussed on the basis of their stratigraphic relationships with dated tephras such as K-Tz (95 to 90 ka), Tt-E (ca. 70 ka), and DKP (52 to 50 ka), The wider glacial extension occurred and deposited the Jodosawa Gravel during Murodo Stade I (95 to 70 ka) in MIS 5b to 4 (marine oxygen isotope stage 5b to 4). In this substade, the glaciers extended from the non-volcanic Tateyama Main Ridge onto the flat surface of the pyroclastic flow deposits erupted from the Tateyama Volcano, and overflowed to the north from the basin. The glaciers eroded the pyroclastic flow deposits during Murodo Stade I, and extended to at least 2, 300m asl. Between Murodo Stades I and II, the glaciers were forcefully melted by the pumice fall erupted from the Tateyama Volcano, and temporarily retreated upstream. During Murodo Stade II (70 to 50 ka) in MIS 4 to early MIS 3, the snout of glaciers readvanced to about 2, 350m asl, and deposited the Murodo Gravel. The glacial readvance was restored in size soon after the pumice fall had finished.

Resistivity structure across Itoigawa-Shizuoka tectonic line and its implications for concentrated deformation

We investigated the deep crustal resistivity structure across Itoigawa-Shizuoka Tectonic Line (ISTL), one of the most dangerous active intraplate faults in Japan, by use of wide-band magnetotelluric (MT) method. The 28 MT stations were aligned perpendicular to the ISTL. A two-dimensional model was created in transverse magnetic (TM) mode where electric currents flow in N60°W-N120°E directions. The model showed good correlations with the surface geology. In particular, we found a thick (∼6 km) surface conductor to the east of ISTL which corresponds to the heavily folded sedimentary layer. The Japan Alps to the west of the ISTL is characterized by the resistive upper crust, where the pre-Tertiary rocks crop out. The Japan Alps is underlain by a conductor below 15–20 km depth, which is consistent with the low seismic velocity anomaly. We also found a localized shallow conductor corresponding to the Mt. Tateyama volcano. The most important feature is the conductor in the mid-crust directly under the area of active folding to the east of the ISTL. This may imply a localized zone of fluids because of the enhanced porosity in a shear zone. The recent seismicity clusters in the resistive crust underlain by the conductor, and this suggests the fluid involvement in earthquake generation processes.

北アルプス，立山火山のK-Ar年代

北アルプス，立山火山のK-Ar年代

立山火山のＫ‐Ａｒ年代

K-Ar age determination based on the Peak Height Comparison Method has been made on four lavas from Tateyama Volcano, which is located in the northern margin of the Norikura Volcanic Chain in Central Japan. Two lavas that erupted in the First and Third Stages gave significant K-Ar ages as 133 ± 22 and 47 ± 9 ka, respectively. K-Ar age of the First Stage Lava in Tateyama Volcano, incorporated with some ages already reported on Norikura and Yakedake Volcanoes also belonging to the Norikura Volcanic Chain, clarified that the activity of this Volcanic Chain commenced in the order of Norikura, Tateyama and Yakedake Volcanoes. K-Ar age of the Third Stage Lava is consistent with that of the Daisen-Kurayoshi Pumice (DKP: ca. 48 ka) covering the Third Stage Lava.

38B. Genetic relation between phreatic explosions of the 4th volcanic period and fault movements of Midagahara Fault on Tateyama volcano, central Honshu.(Abstracts of Papers Presented at the Fall Meeting of the Society)

38B. Genetic relation between phreatic explosions of the 4th volcanic period and fault movements of Midagahara Fault on Tateyama volcano, central Honshu.(Abstracts of Papers Presented at the Fall Meeting of the Society)

長野県における後期更新世の降下火山砕屑物層序

In this paper, the results of a detailed stratigraphical study on air-fall pyroclastics (the Osakada Loam Formation, the Hata Loam Formation and the Omachi Loam Formation) are outlined. Especially valuable as marker beds are nine Ontake volcano pumice falls in the Osakada Loam Formation, six Ontake scoria falls in the Hata Loam Formation and two pumice falls that are inferred to originate from the Tateyama volcano which is intercalated in the Omachi Loam Formation. The Ontake Pm-1', Pm-1A, Pm-2A, Pm-2B and Pm-3D beds and the Tateyama Dpm and Epm beds are each subdivided into several sedimentary units which are widely recognized by their grading structure or lithofacies.The stratigraphic positions of fine-grained ash beds are determined by stratigraphical survey of subaquatic sediments that intercalate the upper Pleistocene air-fall pyroclastics. KIGOMA ash and vitric N-Tf, K-Tf, O-Tf, and T-Tf ashes are well sorted, and the thickness of these beds are constant. It is assumed that these ashes were supplied by anomalous volcanoes.Tracing these wide-spreading pumice or scoria beds together with the ashes as sets of marker beds made it possible to correlate stratigraphic successions of separated areas. It appears that the Osakada Loam Formation, the Upper Omachi Loam Formation II, the Middle and Upper Saku Loam Formation (originating from the Yatsugatake volcano) and the Nojiri and Kaisaka Loam Formations (originating from the Kurohime and Myoko volcanoes) have accumulated during the 50, 000-10, 000 years before the present.

Genetic environments of the banded sulfur sediments at the Tateyama Volcano, Japan

Banded sulfur sediments, characterized by alternate layers of yellowish, fine‐grained sulfur and dark gray clays, occur in a now‐extinct crater lake of the Tateyama volcano, central Japan. Stratigraphic variations in the sulfur content, sulfur isotopic ratio, mineralogy, and content of diatom fossils suggest that the lamination represents seasonal repetition of environmental conditions of the lake water; colloidal sulfur, formed by oxidation of volcanic H2S in the presence of dissolved oxygen, and freshwater benthonic diatoms (Pinnularia braunii (Grun.) Cl. var. amphicephala (A. Mayer) Hust.), flourished during oxidative‐convective periods, whereas detrital materials rich in clays were deposited onto the lake bottom during reducing‐stagnant periods. A sedimentation period of 3000 to 4000 years is calculated from the total thickness of the banded sulfur sediments coupled with the sedimentation rates of 1 to 2 mm/yr deduced from the above model. The estimated period is in good agreement with the age of phreatic explosion (3000 to 6300 years ago based on tephra chronology), which created the crater lake.

Genesis of Banded Sulfur Sediments at the Jigokudani Valley, Tateyama Volcano, Japan

Genesis of Banded Sulfur Sediments at the Jigokudani Valley, Tateyama Volcano, Japan

GLACIAL LANDFORMS AND ACCUMULATION TERRACES AROUND MT. CHOGATAKE, THE NORTHERN JAPANESE ALPS, CENTRAL JAPAN

The Pleistocene glacial landforms in the Northern Japanese Alps have been studied by many researchers, and the existence of several glacial stades, ranging from 60, 000 to 10, 000 years B. P., has been proposed by Kobayashi (1958), Iozawa (1962, 1972), Koaze et al. (1974), Fukai (1975) and Ono (1980). The glacial extent and the valley filling before 60, 000 years B. P. have been little recognized. This paper describes the glacial landforms and the accumulation terraces before 60, 000 years B. P., located along the River Karasu, at the eastern part of Mt. Chogatake in the Northern Japanese Alps. At Chogatake Cirque, a rather dissected old cirque at the eastern side of Mt. Chogatake (2, 664 m), the cirque bottom, situated about 2, 000 m in altitude, is partly eroded away by the dissection of the River Chozawa. In this area, the present writer found out two sets of terminal moraines: the Honzawa and the Mameuchi Moraines (Fig. 5). The former, located 1, 600 m high, indicates the Pleistocene maximum glacial extension along the Hon-zawa Valley, and the latter, located at a height of 1, 900 m on the frontal edge of the Chogatake Cirque, shows a recessional feature. Along the downstream of the River Karasu, five accumulation terraces develop which are classified into Terraces I to V in this paper (Fig. 8). Terrace II which extends to the Honzawa Moraine on the terrace profile (Fig. 9), consists of fluvioglacial deposits judging from the sedimentary facies. The pumice fall deposits of Tateyama Volcano (DPm) are intercalated in the periglacial deposits covering the gravel of Terrace II. The pumice fall deposits of the EPm or OPm are intercalated in the periglacial deposits cover-ing Terrace III (Fig. 7). In view of the presumed age of the DPm fall, a stage of glacial extension and accumu-lation terracing (Tarrace II) in this area should be one of the cold periods before 100, 000 years B. P.. This glacial stage is named here the Chogatake Glacial, which can be divided into two stades, judging from the existence and location of the two terminal moraines. After the Chogatake Glacial, a periglacial environment seems to have governed this area during the period between 60, 000 and 35, 000 years B. P., on the basis of the presumed age of the EPm and OPm. Almost no glaciation occurred around the Chogatake Cirque, although the existence of a glacial stade of this period is widely recognized in other parts of the Northern Japanese Alps by many researchers (Fig. 10).

The recent deposits of phreatic explosions in Tateyama volcano.

The recent deposits of phreatic explosions in Tateyama volcano.

The Omachi Tephra Formations and Tephrochronology

The tephras supplied from Late Quaternary volcanoes in Central Japan have been distinguished into some tephra regions. In this paper, the author has made the characterization, classification and tephrochronologic consideration of the Omachi Tephra formations, which are developed in the Omachi Tephra region. The Omachi Tephra formations consist of pumices, scoriae and fine volcanic ash, of which lithologic and petrographic characterization have been made.(1) Studies were especially made on pumices and scoriae by means of (a) field observations, (b) analysis of heavy mineral assemblage, (c) thermomagnetic and X-ray analysis of Fe-Ti oxides, (d) chemical analysis of pyroxene by electron micro-probe technique. Throughout the whole sequence of petrographic features of the Omachi Tephra formations two cycles were found. If the biotite and/or hornblende phenocrysts are typical of acid liquids, the followings may be concluded; (i) From the Lower to Middle Tephra units, the composition of magma changed from salic one (biotite-hornblende-dacite) to mafic (two pyroxene andesite). (ii) After an interval of ash shower, the Upper Tephra unit shows a change from slightly salic (hornblende-two pyroxene-dacitic andesite) to mafic activity (hornblende-two pyroxene andesite). And the ash fall activity of the source volcano finished.(2) Based on the distribution of the Omachi Tephra, it is inferred that the source vent should be at Mt. Tateyama.(3) If the assumption mentioned above could be correct, two cycles recognized from the section of the Omachi Tephra formations seem to correspond with the already known two cycles in chemical composition of volcanic products from Tateyama volcano (after Yamasaki et al., 1966).(4) The Omachi Tephras have been traced to the East Shinshu district and show the relationships with the tephras of other tephra regions. The pumice layer DPm of the Omachi tephra stratigraphically lies above the pumice layer Kwp from Mt. Yatsugatake, and also a little lower horizon of the Pm-I from Mt. Ontake. On the one hand, as the latter is embedded within the middle part of the Shimosueyoshi “Loam” tephra unit in the South Kanto districts, the Upper unit of the Omachi Tephra formation should naturally be correlated with the Shimosueyoshi stage.(5) As the DPm layer is thought to be correlated with the pumice flow activity of the third period in volcanic history, so the activity of Mt. Tateyama must at least have continued down to the Shimosueyoshi “Loam” age.(6) Many pumice grains which are identical with those of the IIIrd period pumice flow are contained within the gravel bed of the highest terrace on the right side of the Joganji river. So this terrace could be correlated to the Narimasu or Musashino terraces.

26. Tateyama Volcano(Abstracts of Papers submitted for the Meetings of the Society)

26. Tateyama Volcano(Abstracts of Papers submitted for the Meetings of the Society)