Monitoring Quiescent Volcanoes by Diffuse CO2 Degassing: Case Study of Mt. Fuji, Japan

Since the 8th century, more than seventeen eruptions have been recorded for the Mt. Fuji volcano, with the most recent eruption occurring in 1707 (Hoei eruption). For the past 300 years the volcano has been in a quiescent stage and, since the early 1960s, has exhibited neither fumarolic nor thermal activity. However, the number of low-frequency earthquakes with a hypocentral depth of 10–20 km increased significantly beneath the northeastern flank of Mt. Fuji in 2000–2001, suggesting a possible resumption of magmatic activity. In this study, diffuse CO₂ efflux and thermal surveys were carried out in four areas of the volcano in 2001–2002 in order to detect possible signs of the upward movement of deep magma. At all survey points, the CO₂ efflux was below the detection limit with the exception of a few points with biological CO₂ emission, and ground temperatures at a depth of 20–30 cm were below ambient, indicating no surface manifestations of gas or heat emission. Should magma rise into the subsurface, the diffuse CO₂ efflux would be expected to increase, particularly along the tectonically weakened lineation on the Mt. Fuji volcano, allowing for the early detection of pre-eruptive degassing.     

Geochemistry of gases and waters discharged by the mud volcanoes at Paternò, Mt. Etna (Italy)

 Approximately 20 km south of Mt. Etna craters, at the contact between volcanic and sedimentary formations, three mud volcanoes discharge CO₂-rich gases and Na–Cl brines. The compositions of gas and liquid phases indicate that they are fed by a hydrothermal system for which temperatures of 100–150  °C were estimated by means of both gas and solute geothermometry. The hydrothermal system may be associated with CO₂-rich groundwaters over a large area extending from the central part of Etna to the mud volcanoes. Numerous data on the He, CH₄, CO₂ composition of the gases of the three manifestations, sampled over the past 5 years, indicate clearly that variations are due to separation processes of a CO₂-rich gas phase from the liquid. The effects of these processes have to be taken into account in the interpretation of the monitoring data collected for the geochemical surveillance of Etna volcano. Received: 4 September 1995 / Accepted: 14 February 1996     

Deep low-frequency earthquake swarm in the mid crust beneath Mount Fuji (Japan) in 2000 and 2001

Beneath Mount Fuji, the highest active volcano in Japan, deep low-frequency (DLF) earthquake activity has been monitored since the early 1980s. The DLF earthquakes occurred in the mid-crustal depth range, and burst-type activity lasting from several minutes to 30 min was detected 10 to 20 times in an ordinary year. The DLF earthquake activity increased sharply in the period from October 2000 to May 2001, showing swarm-like activity. The occurrence rate during the DLF earthquake swarm was approximately 20 times higher than the usual activity, and the wave energy released during the swarm period was twice as high as the total wave energy during the past 20 years. The DLF earthquakes in the period from 1987 to 2001 were relocated by estimating station corrections in order to reduce the effect of the change of seismic station distribution. The epicenters of most DLF earthquakes occurred in an elongated region with a long axis of about 5 km, whose center is located 2–3 km NE from the summit. A few percent of the DLF earthquakes, however, occurred around the summit area, significantly apart from the main epicenter region. The focal depths of well-located DLF events range from 10 to 20 km. During the high activity period in 2000 and 2001, most DLF events occurred within this main hypocenter area. The sharp increase of DLF earthquake activity at Mount Fuji started immediately after magma discharge and intrusion events in the Miyake-jima and Kozu-shima regions in July and August 2000. The tectonic and volcanic activity changes around the area suggest that the DLF earthquake swarm at Mount Fuji was triggered by the change of state of the deep magmatic system around Mount Fuji.Editorial responsibility: J Stix     

Ra or Ra/Ba dating of Holocene volcanic rocks: application to Mt. Etna and Merapi volcanoes

This paper shows how ²²⁶Ra–²³⁰Th disequilibria can be used to date Holocene volcanic rocks from some well selected volcanoes. A systematic study of these disequilibria on historical or well-dated volcanic samples is indeed first required to test the applicability of this method. Two examples are described here to illustrate its potential. In the case of Mt. Etna, the good correlation observed between (²²⁶Ra)₀ activities at the time of eruption and Th contents in lava flows from the last two millennia [M. Condomines, J.C. Tanguy, V. Michaud, Magma dynamics at Mt. Etna: constraints from U–Th–Ra–Pb radioactive disequilibria and Sr isotopes in historical lavas, Earth Planet. Sci. Lett. 132 (1995) 25–41] is used to infer the ages of several newly analysed lava flows. The calculated ages are in good agreement with those deduced from the archaeomagnetic curve describing the variation of the geomagnetic field direction in southern Italy [J.C. Tanguy, I. Bucur, J.F.C. Thompson, Geomagnetic secular variation in Sicily and revised ages of historic lavas from Mt. Etna, Nature 318 (1985) 453–455, J.C. Tanguy, M. Le Goff, V. Chillemi, A. Paiotti, C. Principe, S. La Delfa, G. Patane, Variation séculaire de la direction du champ géomagnétique enregistrée par les laves de l'Etna et du Vésuve pendant les deux derniers millénaires, C. R. Acad. Sci. Paris 329 (1999) 557–564, J.C. Tanguy, M. Le Goff, C. Principe, S. Arrighi, V. Chillemi, A. Paiotti, S. La Delfa, G. Patane, Archaeomagnetic dating of Mediterranean volcanics of the last 2100 years: validity and limits. Earth Planet. Sci. Lett. 211 (2003) 111–124]. We also present a whole set of new U-series data on historical, recent, and older samples from Merapi (Indonesia), and show that the (²²⁶Ra)/Ba ratio has probably maintained a quasi-steady state value during at least the past four millennia, and can be used to infer the (²²⁶Ra)₀/Ba ratio of old volcanics at the time of eruption, and thus their ages. Comparison with ¹⁴C ages available on three samples [R. Gertisser, J. Keller, Temporal variations in magma composition at Merapi volcano (Central Java, Indonesia): magmatic cycles during the past 2000 years of explosive activity, J. Volcanol. Geotherm. Res. 123 (2003) 1–23] shows an excellent agreement. These dating methods, based on the post-eruptive decrease of ²²⁶Ra excesses can be confidently used to date young rocks on both volcanoes, an important step to infer their recent eruptive history and magmatic evolution. It also opens the possibility to extend the geomagnetic field variation curve back into the past few millennia. The promising results obtained in this work should encourage new systematic U-series studies to test the applicability of such methods to other permanently active volcanoes showing ²²⁶Ra excesses.     

On crustal movement in Mt. Qomolangma area

Mt. Qomolangma lies in the collision zone between the fringe of Eurasia plate and Indian plate. The crustal movement there is still very active so far. In the past three decades China carried out five geodetic campaigns in Mt. Qomolangma and its north vicinal area, independently or cooperatively with other countries, including triangulation, leveling, GPS positioning, atmospheric, astronomical and gravity measurements. On the basis of the observation results achieved in the campaigns the crustal movements in the area were studied and explored. A non-stationary phenomenon both in time and space of the crustal vertical movement in the area is found. There seems to be some relevance between the phenomenon of non-stationary in time and seismic episode in China. The phenomenon of non-stationary in space is possibly relevant to the no-homo- geneity of crustal medium and non-uniform absorption of terrestrial stress. The horizontal crustal movement in the area is in the direction of NEE at a speed of 6–7 cm per year, and the trend of strike slip movement is manifested evidently in the collision fringe of Indian plate and Qinghai-Xizang block.     

日本1995年阪神大地震及火山考察与启示

简述了１９９５年１月１７日日本７．２级阪神大地震的震害,地震断层以及１８９１年浓尾级地震根尾谷地震断裂、北伊豆地震旦那断层和大室火山、伊豆大岛火山的一些特征,最后论述了这次考察的启示。     

Evaluation methods of heat discharge and their applications to the major active volcanoes in Japan

The rates at which thermal energy is released by non-eruptive mechanisms associated with active volcanoes in Japan have been estimated from surface temperature distributions or from shapes of the fumarolic plume rise. Values of 5.3 x 10⁷ W and 1.2 x 10⁸ W have been calculated for non-eruptive release rates in 100-km segments of the Northeast and the Southwest Japan Arc, respectively. It appears that non-eruptive heat discharge is of the same order as that caused by eruptions.     

Anhysteretic remanent magnetization (ARM) in magnetite grains

Summary ARM has been measured in a range of inducing, steady fields up to 50 oersteds and for 6 sizes of magnetite grains with average diameters 5 m to 174 m. For all sizes a slight non-linearity of ARM with inducing field was found, apparently comprising a non-linear contribution independent of grain size plus a linear contribution which increased with decreasing grain size. In the largest grains induced ARM agreed well with multidomain grain theory. Relative enhancement of ARM in smaller grains is comparable to the enhancement of thermoremanence and therefore appears to indicate a pseudosingle domain contribution to ARM in small grains. However the observations allow an alternative explanation in terms of more extreme dimension ratios in the smaller grains. Presentation of the equations for multidomain ARM and TRM using observed instead of intrinsic susceptibilities makes it appear that the inadequacy of multidomain theory (and consequent necessity for pseudo-single domain theory) are less serious than has been supposed.     

珠峰地区似大地水准面精化与珠峰顶正高的确定

本文使用珠峰及其周边地区的重力数据与SRTM3、1∶50000 DEM、GTOPO30地形数据,以该地区的44个GPS水准点为控制,选择国内外的EGM96、WDM94、IGG05B、DQM2000D和CG03C作为参考重力场模型,采用移去-恢复技术,首次完成了珠峰地区分辨率为2.5′×2.5′高精度似大地水准面,其精度达到±9 cm,并据此推算了珠峰顶高程异常值. 再利用登山线路上的新测重力点与珠峰地形数据,依据严格的重力归算理论及移去-恢复技术,完成了珠峰顶似大地水准面与大地水准面差值计算,即珠峰正常高与正高的换算.     

Hazards from pyroclastic density currents at Mt. Etna (Italy)

Despite the recent recognition of Mount Etna as a periodically violently explosive volcano, the hazards from various types of pyroclastic density currents (PDCs) have until now received virtually no attention at this volcano. Large-scale pyroclastic flows last occurred during the caldera-forming Ellittico eruptions, 15–16 ka ago, and the risk of them occurring in the near future is negligible. However, minor PDCs can affect much of the summit area and portions of the upper flanks of the volcano. During the past ~ 20 years, small pyroclastic flows or base-surge-like vapor and ash clouds have occurred in at least 8 cases during summit eruptions of Etna. Four different mechanisms of PDC generation have been identified during these events: (1) collapse of pyroclastic fountains (as in 2000 and possibly in 1986); (2) phreatomagmatic explosions resulting from mixing of lava with wet rock (2006); (3) phreatomagmatic explosions resulting from mixing of lava with thick snow (2007); (4) disintegration of the unstable flanks of a lava dome-like structure growing over the rim of one of the summit craters (1999). All of these recent PDCs were of a rather minor extent (maximum runout lengths were about 1.5 km in November 2006 and March 2007) and thus they represented no threat for populated areas and human property around the volcano. Yet, events of this type pose a significant threat to the lives of people visiting the summit area of Etna, and areas in a radius of 2 km from the summit craters should be off-limits anytime an event capable of producing similar PDCs occurs. The most likely source of further PDCs in the near future is the Southeast Crater, the youngest, most active and most unstable of the four summit craters of Etna, where 6 of the 8 documented recent PDCs originated. It is likely that similar hazards exist in a number of volcanic settings elsewhere, especially at snow- or glacier-covered volcanoes and on volcano slopes strongly affected by hydrothermal alteration.     

3-D density model of Mt. Etna Volcano (Southern Italy)

A detailed density model of Mt. Etna and its surrounding areas has been evaluated using a 3-D inversion of the gravimetric data acquired in the 1980's. Several high-density and low-density bodies are found, penetrating from shallow depths as far down as 12 km bsl. A positive correlation (in terms of location, extent, density, and velocity) is established between several anomalies of the density model and features identified in previously published seismic tomographies. A prominent high-density body extending down to 7 km bsl is recognized in the southern part of the Valle del Bove, and interpreted as a solidified magmatic intrusion. On the western boundary of this anomaly, a low-density body is interpreted as a bubble and liquid magma mixture. Outside the central area, three other high-density anomalies are imaged and attributed to the earliest phases of volcanic activity in the area. Several interesting low-density anomalies are also identified and correlated with known fault lines and other structural features of the region.     

Crystal size distributions and other quantitative textural measurements in lavas and tuff from Egmont volcano (Mt. Taranaki), New Zealand

 The size, shape and orientation of plagioclase crystals have been quantified in a tuff and series of andesite lavas from the active Egmont volcano (Mt. Taranaki), New Zealand. Linear crystal size distributions (CSDs) show that if the magma had several components, then only one provided the crystals. The slope of the CSD indicates that the earliest lavas measured had a residence time of ∼50 years in the magma chamber for a growth rate of 10^–11 cm/s. Subsequent lavas had slightly longer residence times (50–75 years), but the following series returned to 50-year residence times. The youngest magmas, from both Egmont summit and the parasitic Fantham's Peak, have the shortest residence times of ∼30 years. Variations in residence time may reflect changes in the magma chamber shape or depth, or the temperature of the surrounding rocks. Crystal shapes and zonation suggest that crystallization occurred in a bottle-shape magma chamber, and not in a narrow conduit. If future eruptions use the same magma chamber as the most recent eruptions, then a delay of approximately 30 years can be expected between refilling and eruption. Received: 25 October 1995 / Accepted: 19 April 1996     

Rock pillars shaped by columnar joints in granite at Mt. Mizugaki,Central Japan

Rock pillars of granite form a special type of characteristic topography in granite, but their origin is not well understood, partly because their 3D morphology has never been well characterized. Rock pillars were investigated at Mt. Mizugaki, which is underlain by Neogene granite that intruded into the Cretaceous accretionary complex in central Japan. Three rock pillars and their surrounding areas were investigated in detail using unmanned aerial vehicle (UAV) images and structure from motion (SfM). The rock pillars were up to 70 m high and were shaped by columnar joints, which has hardly been reported before in granitic rocks. Columnar joints in granite are much larger than columnar joints in volcanic rocks. The columnar joints curved vertically, and some of them showed dipyramid shapes. The large size and curved morphology of the columnar joints may be the result of the slow cooling of the granite, compared to that of volcanic rocks. Thus, the columnar joints at Mt. Mizugaki made large, high rock pillars, which are not common in volcanic rocks.     

The future danger of Mt. Kelut (Eastern Java — Indonesia)

The tunnel system of Hettinga Tromp proved that the Kelut dangers can be controlled to such an extend that no great lahars were formed during the eruption of 1951. This eruption, however, destroyed these tunnels. In 1954, a drainage tunnel system was built based on the seepage principle. But till now it has failed to drain the lake completely. The 23.5 million cb.m of water still stored up in its crater lake will form a potential danger during an eventual eruption.     

Impacts of sediment transported downstream from the 2015 deep-seated landslide in Mt. Hakusan,Japan

A massive landslide occurred in May 2015 in the Mt. Hakusan Sennindani area, leading to the discharge of a substantial amount of sediment into the Tedori River. We conducted a cross-sectional analysis of secondary data to assess the potential effects of discharged sediments on the downstream environment, including long-term turbidity in rivers, alterations in fish habitats, and groundwater depletion. To analyse the spatio-temporal changes in the river floodplain elevation and paddy fields, aerial photographs and airborne light detection and ranging data were assessed using the ArcGIS software. After the landslide, the turbidity of the Tedori River increased and continued flowing turbid for approximately 6 months. Turbid water spread in the alluvial fan through the irrigation canal network and sediment was deposited in the paddy fields, leading to a reduction in infiltration rates. The groundwater level in the alluvial fan area decreased by more than 2.0 m following the 2015 Sennindani landslide. The sediment deposition in the river floodplain increased by 0.58 m from 2013 to 2015 (pre- and post-landslide). The sediment from upstream destroyed the spawning sites of the Ayu fish along the Tedori River, leading to a decrease in the number of eggs laid in 2015 and 2016 to the lowest levels. The Tomiyo fish disappeared in 2016 and 2017, downstream of the alluvial fan, which received water recharge from the Tedori River. Moreover, Chum salmon showed an exceptionally high anadromous movement towards the Tedori River from coastal areas during 2015 and 2016. In conclusion, discharged sediment from deep upstream landslides can have various adverse impacts on downstream ecosystems, and recovery to their original state may require a considerable amount of time.     

Preliminary report on the 1963 eruption of Mt.Agung in Bali (Indonesia)

Mt. Agung in Bali which has been dormant for about hundred and twenty years showed increased activity on February 18 this year culminating with a paroxysmal eruption early in the morning on March 17; the second paroxysmal eruption occurred on May 16. The activity started with minor explosions in the main crater with the production of pyroclastics followed by the effusion of lavas which flowed over the lowest northern crater rim and the formation of nuées ardentes d’explosion which came down into the northwestern sector of the volcano. Successive nuées ardentes d’explosion which accompanied the paroxysmal cruption on March 17 and on May 16, came down along the southern, southeastern and northern slopes, devastating many villages. The first cycle of activity killed about 1700 people of which 1500 died from the nuées ardentes. Cold lahars, caused by heavy rainfall immediately after the eruption destroyed villages and constructions on the southern slope and killed about 200 more people. The nuées ardentes from the second paroxysmal eruption killed also about 200 more people who were all caught in the « Closed Zone ». A map showing the devastated area is presented.