Active Stratovolcano Research Articles

Archaeal diversity from hydrothermal systems of Deception Island, Antarctica

Antarctica is an extreme continent composed of cold environments but also of several geothermal sites, among them is Deception Island, an active stratovolcano located in the South Shetland archipelago. From this island, few microbiological studies have been performed, and the presence of archaea has not been reported. In order to investigate the archaeal diversity in hydrothermalism from Deception Island, different submarine samples were taken from the flooded caldera. Samples were analyzed by denaturing gradient gel electrophoresis (DGGE) of the 16S rRNA gene in conjunction with culture-dependent methods at hyperthermophilic temperatures. Analysis from DGGE band sequencing showed the presence of archaea belonging to the hyperthermophilic genus Thermococcus and different uncultured archaea closely related to environmental clones from hydrothermal vents. Archaea from the psychrotolerant genus Methanococcoides were also detected. Additionally, we have successfully isolated an anaerobic hyperthermophilic archaeon closely related to Thermococcuscelericrescens. Cells were irregular cocci with a diameter between 0.6 and 2 μm and grew at 50–90 °C and at a NaCl concentration of 1–5 %. Here, we present, based on culture-dependent and culture-independent approaches, the first report on archaea from marine hydrothermal sites of Antarctica.

Long-and Short-Term Deformation Monitoring of Santorini Volcano: Unrest Evidence by DInSAR Analysis

Santorini Volcano is an active strato volcano, located at the central part of the Hellenic Volcanic Arc, developing ad retro of the Hellenic Arc and Trench. The explosive history of the volcano dates back to 1645 BC with the Minoan eruption, while it is documented to have produced at least ten eruptions until 1950 AD. The most recent volcanic unrest began in early 2011. Multi-reference Synthetic Aperture Radar (SAR) Interferometric techniques were applied to study the evolution of ground deformation during 1992-2011, with the use of ERS-1 and -2 and ENVISAT radar imagery. Datasets of common acquisition geometry were added into a single stack so as to obtain the linear deformation rates by means of phase averaging. However, to reveal the deformation history of the volcano, Singular Value Decomposition (SVD) method was implemented. This allowed retrieving ground deformation time-series on a pixel basis over regions with high temporal coherence levels. Results from independent tracks, agreeing with each other, suggest a deformation rate of approximately 5 mm/yr of subsidence at the southern part of Nea Kammeni Volcano, for the period 1992-2010. For the unrest period of 2011, intense uplift of 4.8 cm was observed throughout Nea Kammeni. Global Positioning System (GPS) observations from a local geodetic network confirm the DInSAR findings.

A fast GIS-based risk assessment for tephra fallout: the example of Cotopaxi volcano, Ecuador

We present a comprehensive probabilistic hazard assessment for tephra fallout of Cotopaxi volcano (Ecuador), a quiescent but active stratovolcano known for its highly explosive behaviour. First, we developed a set of possible eruptive scenarios based on thorough field investigations, literature studies and using the Global Volcanism Program (GVP) database. Five eruption scenarios were identified, including two based on large pre-historical sub-Plinian/Plinian eruptions with eruptive parameters constrained from field investigations (One Eruption Scenario; OES) and three Eruption Range Scenarios (ERS) based on the Volcanic Explosivity Index (VEI) classification, for which eruptive parameters (i.e. erupted volume, plume height and median grainsize) were stochastically sampled within boundaries defined by VEI 3, 4 and 5. Second, the modelling was performed using the advection-diffusion model TEPHRA2 in combination with wind profiles from the NOAA NCEP/NCAR Reanalysis 1 database. We performed 1,000 runs for each eruption scenario, stochastically sampling a wind profile (OES and ERS) and a set of eruptive parameters (ERS only) at each run. Using the conditional probabilities of occurrence of eruption of VEI 3, 4 and 5 calculated from the GVP catalogue, we assessed the probability of tephra accumulation in a given time window. Based on the GVP database, a simple Poisson model shows that an eruption of VEI ≥3 has a 36 % probability of occurrence in the next 10 years. Finally, the hazard assessment was compiled based on three different outputs, including (i) probability maps for a given tephra accumulation, (ii) isomass maps for a given probability value and (iii) hazard curves for a given location. We conclude that the area west of Cotopaxi is exposed to light to severe tephra fallout for the smallest eruption magnitude considered (i.e. VEI 3). This area comprises a main communication axis (Panamerican Highway) topographically constrained at the bottom of the Interandean Valley, as well as the capital Quito and the town of Latacunga. In a companion paper, Biass et al. (this volume) propose a method for a rapid risk assessment for tephra fallout using global and easily accessible data and the hazard assessment described here.

Latest Pleistocene and Holocene glacier fluctuations on Mount Baker, Washington

Glaciers on stratovolcanoes of the Pacific Northwest of North America offer opportunities for dating late Pleistocene and Holocene glacier advances because tephra and fossil wood are common in lateral moraines and in glacier forefields. We capitalize on this opportunity by examining the Holocene glacial record at Mount Baker, an active stratovolcano in northwest Washington. Earlier workers concluded that glaciers on Mount Baker during the early Holocene were more extensive than during the Little Ice Age and hypothesized that the explanation lay in unusual climatic or hypsometric effects peculiar to large volcanoes. We show that the main argument for an early Holocene glacier advance on Mount Baker, namely the absence of ca 10,000-year-old tephra on part of the south flank of the mountain, is incorrect. Moreover, a lake-sediment core indicates that a small cirque moraine previously thought be of early Holocene age is also likely older than the tephra and consequently of late Pleistocene age.Lateral and end moraines and wood mats ca 2 km downvalley of the present snout of Deming Glacier indicate that an advance during the Younger Dryas interval was little more extensive than the climactic Little Ice Age advance. Tephra and wood between tills in the left lateral moraine of Easton Glacier suggest that ice on Mount Baker was restricted in the early Holocene and that Neoglaciation began ca 6 ka. A series of progressively more extensive Neoglacial advances, dated to about 2.2, 1.6, 0.9, and 0.4 ka, are recorded by stacked tills in the right lateral moraine of Deming Glacier. Intervening retreats were long enough to allow establishment of forests on the moraine. Wood mats in moraines of Coleman and Easton glaciers indicate that Little Ice Age expansion began before 0.7 ka and was followed by retreat and a readvance ca 0.5 ka. Tree-ring and lichen data indicate glaciers on the south side of the mountain reached their maximum extents in the mid-1800s.The similarity between glacier fluctuations at Mount Baker and those elsewhere in the Cascades and in British Columbia suggests a coherent history of Holocene climate change over a broad area of the western Cordillera. We found no evidence that glaciers on stratovolcanoes behave differently than glaciers elsewhere.

Mineralogical and numerical approaches to establish the pre-eruptive conditions of the mafic Licán Ignimbrite, Villarrica Volcano (Chilean Southern Andes)

The Licán Ignimbrite represents a large explosive basaltic andesite event in the eruptive history of the Villarrica Volcano, an active stratovolcano of the Southern Andean Volcanic Zone. A mineralogical study of this ignimbrite indicates important disequilibrium features. Resoption textures were observed around Ca-rich (An74–92; Group 1) and more sodic (An35–44; Group 2) plagioclase phenocryst cores. Rims on these phenocrysts as well as microlites grew with an intermediate composition (An47–63; Group 3). Low- and high-Mg clinopyroxene and orthopyroxene phenocrysts were also identified; most of them showing reverse Mg zoning. Based on these mineralogical data and thermodynamic modeling, an increase of about 200°C in temperature (from ~900–1000° to ~1100–1150°C), a decompression of ~400bar (equivalent to ~1.5km) and a decrease in H2O content in the melt of ~1.6wt.% are identified during crystallization. Addition of hot magma from below would have caused heating of the reservoir with the consecutive ascent of magma pulses, H2O exsolution and convective mixing (compositional and/or thermal mixing). A numerical model using the Finite Element Method was developed to assess the response of the Licán Ignimbrite reservoir upon conductive heating by 200°C by mafic underplating; this model indicates a rapid (tens of years) temperature homogenization of this system, with ascending magma plumes with velocities as high as 6m/h. Because the Licán Ignimbrite erupted at the end of the Pleistocene glaciation, glacial unloading could have also contributed to depressurization of the reservoir.

Geochemical evolution of Monowai volcanic center: New insights into the northern Kermadec arc subduction system, SW Pacific

We present trace element and Sr-Nd-Pb isotope data on volcanic rocks recovered from the submarine Monowai volcanic center, which marks the midpoint of the ∼2500 km long Tonga-Kermadec arc. The center consists of a large (12 × 9 km) partly hydrothermally active caldera and a 12 km diameter ∼1500 m high volcanically and hydrothermally active stratovolcano. The stratovolcano lavas are tholeiitic basalts, which show variable evidence for plagioclase (±pyroxene) accumulation. The caldera lavas range from basalt to andesite, with the compositional variation being consistent with fractional crystallization as the dominant process. The mafic Monowai magmas were generated by relatively high degrees (12%–20%) of partial melting of a previously depleted MORB-type spinel-peridotitic mantle, metasomatized by slab-derived fluids. Strongly fluid mobile 87Sr/86Sr and 207Pb/204Pb ratios of the Monowai basaltic lavas are similar to those from the Putoto, Raoul, and Macauley volcanic centers 200–400 km to the south, suggesting derivation largely from subducted sediment. In contrast, variably fluid immobile 143Nd/144Nd ratios suggest an isotopically heterogeneous mantle along this segment of the arc. Higher 206Pb/204Pb in Monowai lavas imply some influence from the nearby subducting Louisville seamounts in melt generation. The formation of one of the Earth's largest submarine mafic calderas can best be explained through drainage of a single magma reservoir and subsequent collapse caused by trench-perpendicular extension, probably via southward progressive rifting of the northern Havre Trough.

Thermophilic bacteria present in a sample from Fumarole Bay, Deception Island

AbstractDeception Island, an active stratovolcano located in the South Shetland Islands, Antarctica, provides excellent conditions for the thermophilic bacteria growth because of high ground temperatures in specific areas, such as Fumarole Bay where the temperatures are above the mesophilic range. Denaturing Gradient Gel Electrophoresis (DGGE) was used with the 16S ribosomal gene to analyse cultures of thermophilic bacteria from a soil sample taken from Fumarole Bay. Nine bands were sequenced and analysed from DGGE and they indicated the presence of bacteria from the generaGeobacillus,Bacillus,Brevibacillus,Thermusand uncultured sulphate reducing bacteria. Some of which have been reported in other Antarctic geothermal sites.Geobacillus,BacillusandBrevibacillusgenera were successfully cultivated in an enriched medium. A pure culture of one thermophilicGeobacillusbacterium was obtained closely related toGeobacillus jurassicus.

活火山のマグマ供給系進化に関する岩石学的研究の進展

精度の高い噴火史を基にした岩石学的研究により，沈み込み帯活火山のマグマ供給系進化の解明が格段に進展し，その成果は噴火予知にも利用されつつある．玄武岩主体の活動的な火山の場合は供給系の構成が明らかにされると共に，浅部マグマ溜りが深部から注入を受けて進化する経過や，より深部の組成変化とその要因が解明されつつある．一方，安山岩～デイサイト質の火山では噴出物の特徴の時間変化に多様性があり，一噴火で急変するもの，100～800年程度で周期的に変化するもの，あるいは時間変化が見られないものがある。各々について供給系の構成や特に浅部マグマ溜りの進化を精度良く解明する研究が活発に行われている．また，噴出率の急上昇など特徴的な変化が認められる時期には浅部－深部マグマ溜りあるいは初生マグマ発生領域に大きな転換が起こっていることが判明してきている．この場合マグマ溜りの寿命について制約条件が得られる．

Phreatomagmatic deposits and stratigraphic reconstruction at Debunscha Maar (Mt Cameroon volcano)

The Debunscha Maar (DM) is located on the southwest flank of Mount Cameroon, an active stratovolcano on the Cameroon volcanic line (CVL). Here, we present the physical characteristics of the pyroclastic deposits at DM with the aim of deciphering tephra emplacement mechanisms, evolution of water–magma interaction and reconstructing the stratigraphy beneath the maar. From GPS measurements, the crater has long and short axes of 500 m and 320 m, respectively. Generally, the pyroclastic deposits are well stratified and present a variety of depositional bed forms including structureless/massive beds, massive beds with faint internal stratifications, inversely graded beds, lens- shaped units, impact sags, cross lamination, planar beds as well as dune-like beds. Clast sizes include ash, lapilli-tuff, bombs and blocks (pyroclastic breccia), with clast lithologies consisting of entrained lithics of porous ankaramite pillow lavas, lithified sediments (sandstone and shale) and juvenile material. The porous ankaramite pillow lavas have glassy margins and vesicle zonations typical of pillow lavas formed by subaqueous eruption. The pillow fragments are more common in early-formed eruption products at the base of the deposit. The lithified sandstones show planar laminations and together with the shales occur predominantly in stratigraphic positions above the ankaramite pillow lavas. The juvenile materials include basaltic bombs with low vesicularity (< 15%) and moderate vesicularity (15–50%). The bombs have chilled surfaces and their abundance increases towards the top of the deposit. The presence of accretionary lapilli, fragments of country-rock and juvenile clasts with ragged surfaces as well as curved and chilled margins, is unambiguous evidence in support of phreatomagmatic activity. Of the observed lithic clasts, only the pillow lavas would appear to have the porosity necessary to furnish the required amount of water to feed the phreatomagmatic maar eruption. The clast stratigraphy suggests that the maar is underlain by ankaramite pillow lava that erupted on a consolidated sedimentary substratum. Studying deposits resulting from maar eruptions has a direct implication for hazards assessment at areas of active maar volcanism because many surface processes occur around such volcanoes well after the eruptive activities have stopped.

ASTER- and field-based observations at Bezymianny Volcano: Focus on the 11 May 2007 pyroclastic flow deposit

Bezymianny (Kamchatka Peninsula, Russia) is an active stratovolcano, characterized by a summit lava dome and overlapping pyroclastic flow (PF) deposits to the southeast. Three explosive eruptions (24 December 2006, 11 May 2007, and 14 October 2007) generated PFs that were dominated by juvenile material and were emplaced primarily due to column collapse. Following this, a gravitational lava flow front collapse event generated block and ash flow on 5 November 2007. Moderate spatial resolution data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument were collected between October 2006 and December 2007 to assist in post-eruption monitoring and interpretation of the volcanological processes that produced the PF deposits. Using multitemporal ASTER thermal infrared (TIR) data, three periods of increased activity were observed that coincided with each eruption and subsequent activity. During a field campaign in August 2007, the May 2007 PF deposit was investigated in detail. Eight ASTER TIR pixels (90 m spatial resolution) were selected from the 30 June 2007 ASTER TIR image, seven of which were accessible in the field. Forward-Looking Infrared (FLIR) image and thermocouple data over these areas were collected to observe thermal heterogeneities with distance along the PF deposit. Although synchronous ASTER data were not possible at the time of fieldwork due to cloud cover, a field survey of blocks versus ash in each pixel was carried out to investigate thermal and textural variation with distance from the vent and to provide preliminary field results. Based on the field-derived temperature data and surface block percentages, the May 2007 PF deposit was more block-rich in the medial portion of the flow surface, but more ash-dominated at the PF terminus region, which promoted more rapid cooling. We present multitemporal ASTER data spanning a 14 month period and highlight ground-based observations acquired within the same period of eruptive and dome-growth activity. These data collectively provide thermal radiative and emissivity information on an actively changing explosive volcanic system and specifically documents changes over recently-emplaced and cooling PF deposits.

Lahar flow simulations using LAHARZ program: Application for the Popocatépetl volcano, Mexico

Lahars are a type of catastrophic event that is generated in volcanic environments. Due to the recent technological advances computer simulated models have become widely used by the scientific community to predict the distribution of catastrophic events, such as floods, debris avalanches, earth landslides or lahars, and to mitigate possible damage to populations located in a risk area. Our study risk area is located in the Popocatépetl volcano, a large and active stratovolcano in the Trans Mexican Volcanic Belt. Here, lahars have been occurring during the last century, and some of them have seriously affected nearby towns. Since one of the main input parameters into a lahar simulation is the Digital Elevation Model (DEM), this paper focuses on studying lahar simulations on Popocatépetl using DEMs obtained from various sources with the aid of a popular package known as LAHARZ. The first simulations were performed using a 1:50,000 topographic map with 20-m contours interval. The second set of tests used an enhanced DEM with profiles measured during fieldwork in the lahar channel. In the last set of tests, we added lateral artificial barriers to the channel profiles used in the previous enhanced DEM. Our results show that the use of high resolution and detailed DEMs does not necessarily guarantee a realistic lahar simulation as was previously thought, and a detailed explanation as to why the LAHARZ code computation creates ragged edges is offered. Our results also offer useful information on the level of detail necessary for an input DEM into LAHARZ in order to obtain lahar simulations closer to real lahars. The minimum resolution for the DEM used in simulations must be less than the width of the narrowest cross-section of the channel to realistically reproduce the lahars. For DEMs with lower resolution, sometimes the modeled lahars are shorter in length, and therefore underestimate real hazards to populations. Also, the results show that lateral barriers are sometimes needed to obtain more realistic inundation areas.

Closed Basin Brine Evolution and the Influence of Ca–Cl Inflow Waters: Death Valley and Bristol Dry Lake California, Qaidam Basin, China, and Salar de Atacama, Chile

Diagenetic-hydrothermal brines, here called “hydrothermal Ca–Cl brines,” have compositions that reflect interactions between groundwaters and rocks or sediments at elevated temperatures. Hydrothermal Ca–Cl brines reach the surface by convection-driven or topographically driven circulation, and discharge as springs or seeps along fault zones to become important inflow waters in many tectonically active closed basins. Case studies from (1) Qaidam Basin, China, (2) Death Valley, California, (3) Salar de Atacama, Chile, and (4) Bristol Dry Lake, California illustrate that hydrothermal Ca–Cl inflow waters have influenced brine evolution in terms of major ion chemistries and mineral precipitation sequences. All four basins are tectonically active; three (Death Valley, Salar de Atacama, and Qaidam Basin) have well-documented Ca–Cl spring inflow and Holocene faulting. Bristol Dry Lake has young volcanic deposits and Salar de Atacama has an active stratovolcano on its eastern margin, indicating subsurface magma bodies. A midcrustal magma chamber has been identified in southern Death Valley. Volcanism and faulting in these closed basins provides the heat source for hydrothermal-diagenetic processes and the energy and pathways to deliver these waters to the surface.

Inner structure of La Fossa di Vulcano (Vulcano Island, southern Tyrrhenian Sea, Italy) revealed by high‐resolution electric resistivity tomography coupled with self‐potential, temperature, and CO2 diffuse degassing measurements

La Fossa cone is an active stratovolcano located on Vulcano Island in the Aeolian Archipelago (southern Italy). Its activity is characterized by explosive phreatic and phreatomagmatic eruptions producing wet and dry pyroclastic surges, pumice fall deposits, and highly viscous lava flows. Nine 2‐D electrical resistivity tomograms (ERTs; electrode spacing 20 m, with a depth of investigation &gt;200 m) were obtained to image the edifice. In addition, we also measured the self‐potential, the CO2 flux from the soil, and the temperature along these profiles at the same locations. These data provide complementary information to interpret the ERT profiles. The ERT profiles allow us to identify the main structural boundaries (and their associated fluid circulations) defining the shallow architecture of the Fossa cone. The hydrothermal system is identified by very low values of the electrical resistivity (&lt;20 Ω m). Its lateral extension is clearly limited by the crater boundaries, which are relatively resistive (&gt;400 Ω m). Inside the crater it is possible to follow the plumbing system of the main fumarolic areas. On the flank of the edifice a thick layer of tuff is also marked by very low resistivity values (in the range 1–20 Ω m) because of its composition in clays and zeolites. The ashes and pyroclastic materials ejected during the nineteenth‐century eruptions and partially covering the flank of the volcano correspond to relatively resistive materials (several hundreds to several thousands Ω m). We carried out laboratory measurements of the electrical resistivity and the streaming potential coupling coefficient of the main materials forming the volcanic edifice. A 2‐D simulation of the groundwater flow is performed over the edifice using a commercial finite element code. Input parameters are the topography, the ERT cross section, and the value of the measured streaming current coupling coefficient. From this simulation we computed the self‐potential field, and we found good agreement with the measured self‐potential data by adjusting the boundary conditions for the flux of water. Inverse modeling shows that self‐potential data can be used to determine the pattern of groundwater flow and potentially to assess water budget at the scale of the volcanic edifice.

Deformation of the Augustine Volcano, Alaska, 1992–2005, measured by ERS and ENVISAT SAR interferometry

Abstract The Augustine Volcano is a conical-shaped, active stratovolcano located on an island of the same name in Cook Inlet, about 290 km southwest of Anchorage, Alaska. Augustine has experienced seven significant explosive eruptions—in 1812, 1883, 1908, 1935, 1963, 1976, 1986, and in January 2006. To measure the ground surface deformation of the Augustine Volcano before the 2006 eruption, we applied satellite radar interferometry using Synthetic Aperture Radar (SAR) images from three descending and three ascending satellite tracks acquired by European Remote Sensing Satellite (ERS) 1 and 2 and the Environment Satellite (ENVISAT). Multiple interferograms were stacked to reduce artifacts caused by atmospheric conditions, and we used a singular value decomposition method to retrieve the temporal deformation history from several points on the island. Interferograms during 1992 and 2005 show a subsidence of about 1–3 cm/year, caused by the contraction of pyroclastic flow deposits from the 1986 eruption. Subsidence has decreased exponentially with time. Multiple interferograms between 1992 and 2005 show no significant inflation around the volcano before the 2006 eruption. The lack of a pre-eruption deformation signal suggests that the deformation signal from 1992 to August 2005 must have been very small and may have been obscured by atmospheric delay artifacts.

Geophysical survey of the intra-caldera icefield of Mt Veniaminof, Alaska

AbstractMt Veniaminof is a large active stratovolcano located on the Alaska Peninsula (56.2° N, 159° W). We present results of the first geophysical survey of the icefield that fills much of the 10 km×8 km caldera that was most recently modified during the last major eruption roughly 3700 BP. The subglacial topography and ice volume are derived from an 8MHz radio-echo sounding survey conducted in July 2005. Prominent internal reflectors are assumed to be isochronal ash/acid deposits related to local eruptions. Accumulation rates and basal melt rates are calculated using a Nye one-dimensional steady-state accumulation model applied at a location that approximates an ice divide and calibrated by matching internal reflectors with published records of recent local volcanic eruptions. The model yields order of magnitude estimates of the accumulation rate of 4ma–1 water equivalent and 2 ma–1 of basal melt. The subsequent geothermal flux of ∽19Wm–2 is similar to active hydrothermal vents in volcanic lakes. We suggest that these values represent an upper limit for the geothermal flux within the ice-covered regions of the main caldera. We also analyze likely subglacial meltwater flow paths to examine the implications of recent eruption activity at an active intra-caldera cinder cone. Two lava-producing eruptions from the cinder cone in 1983–84 and 1993–94 melted roughly 0.17km3 of ice. The lack of significant deformation of the internal stratigraphy to the south and east of the melt hole suggests that any subglacial drainage in those directions was entirely within subglacial deposits. We suggest that the more likely drainage route was northwest into a large outlet glacier.

Glacier retreat during the recent eruptive period of Popocaté petl volcano, Mexico

AbstractPopocatépetl (19°02’ N, 98°62’W; 5424 m) is one of the largest active stratovolcanoes in the Transmexican Volcanic Belt. A glacier located on the north side has undergone severe ablation since the volcano reinitiated eruptive activity in December 1994. In our study, we calculate the extent of the glacier recession and the loss in glacial mass balance during the period of greatest laharic activity (1994–2002), using photogrammetric treatment of 20 pairs of aerial photographs. The results indicate that from November 1997 to December 2002, the glacier released approximately 3 967 000 m3 of water. A period of intense glacier melting occurred from 4 November 2000 to 15 March 2001 during which time 717 000 m3 of water was released. Much of the melting was attributed to the pyroclastic flow that took place on 22 January 2001 and produced a 14.2 km lahar with 68 000 m3 of water. Among the many types of volcanic events, pyroclastic flows were the most effective in causing sudden snowmelt, although small explosions were also effective since they deposited incandescent material on the glacier. The collapse of the plinian columns covered the glacier with pyroclasts and increased its volume. The existence of control points for georeferencing and a knowledge of the topography underlying the glacier previous to the eruption would have provided more accurate and useful results for hazard prevention.

Peningkatan kegiatan Gunung Api Tangkubanparahu Jawa Barat pada bulan April 2005

http://dx.doi.org/10.17014/ijog.vol1no4.20063Tangkubanparahu is an active strato volcano located in West Java lying about 30 km to the north of Bandung City. Its crest is 2084 m above the sea level. In order to gain a better understanding on volcanism and magmatism of this volcano, various research and monitoring have been carried out, such as geochemistry and geophysics. Chemical composition of volcanic gases collected from the Ratu Crater (950 C in 1994, 1997, 1998 ratio of CO /H S, CO /H , and H /Ar, is suggested to indicate the presence of a fast fl uid movement and 2005, shows that the gas is hydrous with the main component of H O, CO , H S and small amount SO ; where CO content is higher than (SO + H S). The gas composition showing high of value from the depth before condensed at the shallow surface water area. Hotspring from the Domas Crater contains a high concentration of SO , low of Cl and absence of H CO . The high sulphate content is suggested to be originated from the volcanic gases, especially hydrogen sulphide oxydated near the surface, that then the gas infl uenced chemical composition due to shallow water.Continuous seismic monitoring uses one permanent station, while the other methods like Electric Distance Measurement (EDM), Global Positioning System (GPS) and Seismometer have been installed temporary. From geophysical evidence on April 2005 activity, some valuable information can be obtained. Hypocenter is located at the depth less than 2 km beneath an area between the Ratu and Domas Craters, while pressure source of deformation is below Domas Crater. Some low frequency volcanoquakes is possibly caused by volcanic gases released from the reservoir.

Quantifying recent pyroclastic and lava flows at Arenal Volcano, Costa Rica, using medium‐footprint lidar

Arenal volcano is a small, active stratovolcano in Costa Rica. In 1998 and 2005, NASA's Laser Vegetation Imaging Sensor (LVIS) was used to collect wide‐swath 3‐dimensional topographic images of the volcano. The LVIS is a full‐waveform, scanning, medium‐sized footprint, airborne laser altimeter system. By digitally recording the shape of the returning laser pulse (waveform), the LVIS provides a precise and accurate view of both the sub‐canopy and canopy‐top topographies as well as the vertical and horizontal structure of vegetation at 15–25 m horizontal resolution. By comparing georeferenced waveform data collected in 1998 and 2005, we mapped lava and pyroclastic flows deposited during this period. The active crater grew by 3.82 m yr−1. A flow volume estimate of 2.19 × 107 m3 (Dense Rock Equivalent of 1.89 × 107 m3 or 0.085 m3s−1) was obtained for the period 1998 to 2005. Precise elevation and elevation change data such as those provided by the LVIS are essential to calculate eruption volume and to study magma‐supply dynamics, as well as assess the danger posed by the volcano to the local population from hazards such as pyroclastic flows.

Devastating landslides related to the 2002 Papandayan eruption

http://dx.doi.org/10.17014/ijog.vol1no2.20063Papandayan is an A-type active strato volcano located at some 20 km SW of Garut or about 70 km SE of Bandung the capital city of West Java Province. Geographically, the summit of this volcano lies at the intersection between 07º 19’ 42” S and 107º 44” E. The 2002 Papandayan eruption was preceded by two felt earthquakes, 8 times of A-type volcanic earthquakes and 150 times of B- type volcanic earthquake. These events were followed by a phreatic eruption that took place on 11 November at 16.02 local time. Field observation shows that the summit region, mainly around the craters consists of rocks that have hydrothermally altered to yield clay rich material. This clay rich material covers most of the crater fl oors and the crater rim. Mount Nangklak that forms part of the rim also contains a lava plug from the Old Papandayan volcano. This mountain is covered by fi ne grained, unconsolidated material, and altered rocks. Much of this altered rocks coincides with solfataric and fumarolic activities of 80 to &gt; 300°C. The summit area also contains high discharge of water either originating from the springs or surface water. The increase in seismicity, the fi ne-grained hydrothermal altered rocks, and the existence of some faults that pass through the summit region might have weaken the stability of the summit area. As the result, a landslide occurred on the north fl ank of Mount Nangklak where the landslide material blocked the upper course of Cibeureum Gede River. This landslide material had formed big mudfl ows that caused several houses of fi ve villages were partly burried, some bridges were devastated and several hectares of cultivated land were damaged.

Properties of sector-collapse and debris avalanches on Quaternary volcanoes in Japan

Many types of mass movements frequently occur on volcanic edifices. The most dangerous is a gigantic sector-collapse with its following debris avalanche, as in the Mount St. Helens and Mt. Bandai cases. A total of 128 debris avalanches are described for 67 Quaternary volcanoes in Japan. Two-fifths of Japanese volcanoes show evidence of debris avalanches. Debris avalanches have occurred at the rate of one every 60 years during the last 500 years in Japan. Most are larger than 0.2km3. Deposits usually spread widely around the foot of volcanoes. One-third of debris avalanche deposits are accompanied by hummocky hills, which provide a good index of debris avalanches. Only 48 debris avalanches have obvious amphitheaters. Geological or geomorphological evidence indicates source positions of 65 debris avalanches. Gigantic sector-collapses tend to occur on the upper part and crest of volcanoes. Two-thirds of debris avalanches did not have a clear source area. Topographic features of amphitheaters are easily eroded or buried. The causes of destruction of volcanic bodies are not well known. Most height-to-length ratios (H/L) of debris avalanches range from 0.2 to 0.08 and indicate high mobility. Gigantic sector-collapses and debris avalanches are usual processes of destruction of volcanic edifices. Debris avalanches tend to occur repeatedly on active stratovolcanoes, which have the cone shape characteristic of Mt. Fuji. Debris avalanches on Quaternary volcanoes are usually larger than those in other geologic regions.