Asama Volcano Research Articles

Cryptotephra preserved in Lake Suigetsu (SG14 core) reveals the eruption timing and distribution of ash fall from Japanese volcanoes during the Late-glacial to early Holocene

Long sedimentary successions extracted for palaeoclimate research regularly preserve volcanic ash (tephra) fall from explosive eruptions and are increasingly used to elucidate the timing and scale of past events. This study investigates the non-visible tephra (cryptotephra) layers preserved in the annually laminated and intensively 14C dated sediments of Lake Suigetsu (SG14 core), Japan. The cryptotephra investigations reported here focus on the Late-glacial to early Holocene sediments that were deposited between two visible tephra layers, the Ulleungdo (U)-Oki (10.2 ka) and the Sambe ‘Sakate’ (19.6 ka), and consequently span an interval of abrupt climate change making any newly identified cryptotephra layers invaluable chrono-stratigraphic markers. Using major and trace element volcanic glass compositions the cryptotephra are used to assign provenance to chrono-stratigraphically relevant eruption units. Five new cryptotephra layers are identified within this time interval. Three cryptotephra layers are from Kyushu volcanoes (SG14-1337 and SG14-1554 [Sakurajima]; and SG14-1806 [Kirishima]), all of which offer important chronological constraints on archaeological (Jomon) cultural transitions in southern Japan during the last termination. Another cryptotephra (SG14-1579), is assigned to activity on Niijima Island providing the first known distal occurrence and age of the eruption. Finally, the SG14-1798 cryptotephra precisely dated at 16,619 ± 74 IntCal20 yrs BP (2σ) is linked to Asama (As) volcano and more precisely the later phases of the As-YKU eruption. This discovery greatly expands the distribution of ash fall from this multi-phased eruption at Asama volcano, which affected an area in the region of 120,000 km2. Refining the timing of the eruption and the distribution of As-YKU ash fall is important as it offers an excellent chrono- and climato-stratigraphic marker suitable for assessing spatial variability in environmental response to past climate change during the termination of the last glacial.

Sulfur‐rich mafic magma injection into the felsic magma chamber beneath Asama volcano, central Japan: Records in olivine‐hosted melt inclusions from the Itabana and Tenmei eruptions

AbstractEven though no basalts have erupted at Asama volcano, its large, felsic magma chamber standing beneath the summit is frequently replenished by cryptic injections of mafic magma of basalt‐basaltic andesite composition. This mafic magma is preserved within melt inclusions trapped in olivine phenocrysts collected from the old Itabana pumice of the Kurofu stage and the Tenmei pumice of the current Maekake stage. The trapped mafic melts provide a detailed and vivid record of cryptic mafic magma injection into the felsic chamber where they admix to erupt andesite magma. The main phenocrysts of plagioclase, orthopyroxene, and clinopyroxene, commonly seen in the erupted products, are derived from the felsic magmas and trapped felsic melts of dacite‐rhyolite compositions, containing low sulfur contents (0.3 wt% of SO3 or less; most are lower than 0.10 wt%). In contrast, the mafic melts, entrapped by olivine phenocrysts, show high concentrations of SO3, up to 1.06 wt% for Itabana and SO3 0.65 wt% for Tenmei. In addition, the olivine phenocryst commonly encloses early crystalline phases precipitated from the sulfur‐rich mafic magma, such as Cr‐spinel, Mg‐rich orthopyroxene, Fe, Cu, and Ni‐bearing sulfides, and often Al‐rich clinopyroxene. The olivine‐hosted mafic melt inclusions always contain numerous vesicles. Furthermore, they are often included as hourglass‐shaped trapped melts, exhibiting snapshots of intense foaming and gas phase exsolution during the olivine growth and probably in the process of the cryptic injection into the felsic magma beneath the Asama summit. Our new data contributes to a better understanding of the magmatic system of the Asama volcano but also highlight the importance of the “Excess sulfur problem”, especially concerning the 1783 Tenmai eruption, which was contemporary to the Laki Fires.

Recent volcanic activity at the Asama volcano and long-period seismic signals.

Modern observation systems composed of seismic, geodetic, other geophysical, and geochemical networks developed in and around volcanic areas provide a mass of knowledge about volcanic activities. This paper summarizes the magma pathway and recent volcanic activity of the Asama volcano. The seismic velocity structure beneath the Asama volcano was investigated via seismic ambient noise tomography and active source seismic tomography. The magma pathway in the upper crust beneath the Asama volcano was synthesized by combining the velocity structure with a hypocenter distribution of volcanic earthquakes and ground deformations before and after eruptions. Temporal evolutions of multidiscipline data regarding the volcanic activity from October 2003 to January 2018 revealed that the supplied amount of magma from the magma chamber and the internal condition in the shallow regions of the conduit controlled the recent eruptions.

Amorphous silica coating on flank deposits of the 1783 CE eruption at Asama volcano

Silica-rich coatings of up to 660 μm thickness were found on the juvenile volcanic lapilli and blocks of the 1783 CE pyroclastic flow deposits 1.9–3.6 km northeast of the Maekake crater of Asama volcano in Central Japan. These coatings are composed of fine-grained volcanic ash particles with silica-rich cement. Raman spectroscopic measurements revealed that the interstitial silica-rich phase is hydrous amorphous silica and is considered to be a reaction product of ash particles with acidic volcanic rain and fog like volcanic smog (vog) as it has been recorded in Hawaii. The formation of amorphous silica without jarosite and the preferential alteration of plagioclase compared with pyroxene indicate that the reaction occurred with a sulfuric acid solution of pH < ~3. The porous structure and large surface area of the ash layer would have been favorable for the dissolution of sintered volcanic ash and the precipitation of amorphous silica. The thickness of the coating and degree of alteration in the plagioclase phenocrysts adjacent to the coating tend to decrease with increasing distance from the volcanic crater, which is consistent with the absence of fumarolic areas in the flank. The Asama-Maekake volcano has repeated Vulcanian and phreatic eruptions since 1783 CE, especially in the first half of the 20th century. The amorphous silica coating recognized in this study is assumed to have formed mainly during this period, which can thus be an indicator of the acidity and distribution of past acidic volcanic rain and fog.

Fluorine and Chlorine Contents of Volcanic Ash from the 2004 Eruption of Asama Volcano, Japan

Fluorine and Chlorine Contents of Volcanic Ash from the 2004 Eruption of Asama Volcano, Japan

Advances in gravity analyses for studying volcanoes and earthquakes

This report highlights the usefulness and applicability of various gravimetric methods for studying earthquakes and volcanic activities. A high-resolution gravity anomaly map of Japan reveals areas with very steep horizontal gradients, where potential seismic faults are likely to be buried. Such traditional geoprospecting is coupled with novel cosmic-ray radiography to produce a fine-resolution (<100 m) three-dimensional density structure of a volcano. On the other hand, temporal gravity changes provide invaluable information about the process of earthquake faulting, volcanic eruptions, caldera formation, etc. Specifically, in this report we present our previous work on gravity research for solid earth science: (1) the first detection of coseismic gravity changes, (2) the virtual visualization of the rising and falling of magma in a conduit of Asama volcano, and (3) the large-scale lateral movement of magma during the Miyake-jima eruption in 2000.

Air-Fall Ash from the Main Crater of Asama Volcano on August 7, 2019, and its Water-Soluble Components

We collected volcanic ash immediately following the eruption of Mt. Asama on August 7, 2019, observed the characteristics of ash particles, and analyzed the water-soluble components. The volcanic ash consisted mostly of altered fragments, and no clear evidence of essential materials was found. The volcanic ash contained large amounts of water-soluble components, Cl and SO4 at concentrations of 8,710 mg/kg and 49,100 mg/kg, respectively. These results indicate that this eruption was caused by the phreatic explosion and that part of the volcanic edifice of Mt. Asama was fractured and emitted.

Surface deformation of Asama volcano, Japan, detected by time series InSAR combining persistent and distributed scatterers, 2014\u20122018

Asama volcano is one of the most active volcanoes in Japan. Spatially dense surface deformation at Asama volcano has rarely been documented because of its high topography and snow cover around the summit. This study presents the first interferometric synthetic aperture radar (InSAR) observation of ground deformation at Asama volcano with 120 Sentinel-1 SAR images from both ascending and descending tracks and 20 descending ALOS-2 images acquired between 2014 and 2018. We exploited both persistent and distributed scatterers to overcome decorrelation of SAR signals and applied a three-dimensional unwrapping method to retrieve the displacement time series efficiently. Our observations reveal an asymmetric deformation around the volcano with two main deformation regions on the northeast and southeast flanks, respectively. The northeast flank (NEF) exhibits line-of-sight (LOS) extensions in all the three SAR datasets with maximum velocities of − 14, − 10, and − 12 mm/year for the descending ALOS-2, ascending, and descending Sentinel-1 measurements, respectively. The southeast flank (SEF) shows LOS extensions in the ascending observations and LOS shortening in the descending observations with velocities between − 12 and 9 mm/year. Decomposition of the LOS displacements reveals nearly pure subsidence at the NEF, while the SEF exhibits a substantial eastward component as well as subsidence. Comparisons of the vertical subsidence at two continuous GNSS stations near the summit crater with our InSAR observations indicate small discrepancies smaller than 4 mm/year. We interpreted that the subsidence at the NEF of Asama is primarily due to the hydrothermal activity, while the deformation at SEF is plausibly due to flank instability. We highlight that efforts should be taken to monitor the slope instability at Asama volcano in the future.

Database of Crustal Deformation Observed by SAR: Improving Atmospheric Delay Mitigation for Satellite SAR Interferometry and Developing L-Band Multi-Type Portable SAR

Spaceborne synthetic aperture radar (SAR) and ground-based radar interferometers (GBRIs) can be used to detect spatially detailed crustal deformations that are difficult to detect by on-site observations, the Global Navigation Satellite System, tiltmeters, and so on. To make such crustal deformation information readily available to those engaged in evaluating volcanic activities and researching the mechanisms, we are preparing a database within the Japan Volcanological Data Network data sharing system to store crustal deformation detected by spaceborne SAR and GBRIs (Subtheme 2-1, Project B, the Integrated Program for Next Generation Volcano Research and Human Resource Development). In this study, we examined methods to reduce atmospheric delay noise in SAR interferometry using the numerical weather model and determined the methods for resampling the analytical values of the numerical weather model and estimating atmospheric delay to efficiently determine atmospheric delay. We show that the atmospheric delay can be estimated with higher accuracy by properly combining the isobaric surface and ground surface data of the mesoscale model (MSM) provided by the Japan Meteorological Agency. We are developing a multi-type portable SAR system as a GBRI system such that it would allow campaign observations whenever increased volcanic activities are observed and acquire crustal deformation with a higher temporal resolution than spaceborne SAR for storage in the database. This system employs L-band radar, which has a higher penetrability against vegetation. Two modes of observations are possible: ground-based SAR and car-borne SAR. The prototype was fabricated to conduct experiments necessary to develop a working model. The experimental observations was carried out around Asama volcano, and we confirmed that clear fringe was obtained.

Feasibility Study on a Multi-Channeled Seismometer System with Phase-Shifted Optical Interferometry for Volcanological Observations

A new Phase-Shifted Optical Interferometry seismometer system was tested in terms of its feasibility for multi-channeled volcanological observations in two volcanos in Japan. The system is capable of both sensing ground motions and transferring its signals through optical means. The prototype of this system comprises three optical-wired stations and optical components, and was deployed in Sakurajima Volcano in 2016 and in Asama Volcano in 2017. The system successfully operated for 134 days in total and provided seismograms that are in good agreement with those obtained using conventional systems. Several obstacles for putting this system to practical use that need to be solved were found through tests. Their solutions will be explored in subsequent research.

Comparison of high- and low-frequency signal sources for very-long-period seismic events at Asama volcano, Japan

Very-long-period (VLP) seismic events at Asama volcano in central Japan are characterized by a transient signal of 10–20 s duration. Associated with the transient motion, a high-frequency (HF) oscillation within the 5–10 Hz band is observed. We investigated the location and size of the oscillation source in the HF band (HF source) using an amplitude source location method and compared our results with those for the VLP band (VLP source) deduced in our previous waveform inversion study. We analysed 1437 VLP events recorded during an intense observation campaign during 2008–2009, and additional 571 events surrounding an eruptive activity in 2015 (including a VLP event that immediately preceded an eruption). The HF source locations of most events were deeper than the VLP source locations by ∼150 m, although there was almost no time lag between the signals. This suggests a strong connection between the two sources, with one source immediately responding to the other. The eruptive VLP event had an HF source location close to normal VLP events but had a greater event size. We surmise that the HF signal is caused by an inflow of volcanic gas from depth into a semi-vertical crack-like cavity (as imaged in our previous waveform inversion study), and the VLP signal is caused by resultant inflation of the same cavity. The centroid of inflation (VLP source) is near the roof of the cavity, where gas accumulates, whereas the HF oscillation is emitted more intensely from lower and narrower portions of the cavity. This results in source depth differences between the two signal bands. In this model, the inflation rate of the cavity is controlled by the volume flux of the gas inflow, producing similar temporal variations between the VLP and HF signals. According to this model, the eruptive VLP is associated with a greater amount of gas inflow and accumulation, which likely played a key role in the eruption.

Interannual changes in radiocesium concentrations in annually laminated tufa following the Fukushima Daiichi Nuclear Power Plant accident

Chemical and radiocesium concentrations in water and riverbed tufa of the Nigori River, flowing out of the southern foot of Mt. Asama volcano in central Japan, were investigated following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. This tufa is characterized by porous and dense laminae. Its annual lamination (varve) is formed by seasonal changes in dissolved CO2 concentration in water with temperature, and the tufa calcite is mostly precipitated during summer. We analyzed radiocesium concentrations in ∼4-mm-thick tufa samples that included four or five varves collected after the fall in 2011–2014. The activity ratio of 134Cs/137Cs in tufa collected in 2011 and 2014 was 0.96 ± 0.01 and 0.99 ± 0.01, respectively, which implies radiocesium generated as a result of the FDNPP. Sequential extractions indicate that 137Cs in tufa collected in 2011 is occupied in exchangeable and carbonate phases (55.2% and 44.8%, respectively). The 137Cs concentrations equivalent to tufa calcite that were precipitated after 2011 showed variations similar to the amount of summer rainfall during 2011–2014, which may be attributed to increases in dissolved 137Cs concentrations in river water associated with intensified rainfall and microbial action over the summer. In contrast, the 137Cs sorbed to tufa calcite was not retained in the riverbed, and its migration may be attributed to the porous texture of tufa and the high flow rate of the river. Therefore, tufa calcite is easier to dissolve even though it adsorbs compared with other minerals (mica, andosol etc.).

浅間火山1783年(天明3年)噴出物の元素組成

浅間火山1783年(天明3年)噴出物の元素組成

17．浅間山に発生する地震の研究(2) : 連続的微噴火にともなう地震について : 日本火山学会1974年度春季大会

17．浅間山に発生する地震の研究(2) : 連続的微噴火にともなう地震について : 日本火山学会1974年度春季大会

浅間火山 1973 年 2～3 月の噴火の際に発生した小型火砕流

浅間火山 1973 年 2～3 月の噴火の際に発生した小型火砕流

Mullite in a buchite from Asama volcano and its sub–micrometric core–rim texture with sillimanite

Mullite in a buchite from Asama volcano and its sub–micrometric core–rim texture with sillimanite

浅間山2004年噴火と過去の噴火との比較による活動評価(＜特集＞2004年浅間山噴火(1))

浅間山2004年噴火と過去の噴火との比較による活動評価(＜特集＞2004年浅間山噴火(1))

浅間火山で頻発した小噴火の噴煙運動の特徴 : 2004年9月15-18日噴火(＜特集＞2004年浅間山噴火(2))

浅間火山で頻発した小噴火の噴煙運動の特徴 : 2004年9月15-18日噴火(＜特集＞2004年浅間山噴火(2))

2004年浅間山噴火に先行する特異な長周期地震活動(＜特集＞2004年浅間山噴火(1))

2004年浅間山噴火に先行する特異な長周期地震活動(＜特集＞2004年浅間山噴火(1))

凝集粒子を用いた噴煙高度の推定 : 浅間火山2004年9月23日噴火に伴う降下火砕物の堆積様式(＜特集＞2004年浅間山噴火(2))

凝集粒子を用いた噴煙高度の推定 : 浅間火山2004年9月23日噴火に伴う降下火砕物の堆積様式(＜特集＞2004年浅間山噴火(2))