hydraulic physical and rheological characteristics of rain triggered lahars at semeru volcano indonesia lahars volcanic debris flows have been responsible for 40 of all volcanic fatalities over the past century mount semeru east java indonesia is a persistently active composite volcano that threatens approximately one million people with its lahars and pyroclastic flows despite their regularity the behaviour and the propagation of these rain triggered lahars are poorly understood in situ samples were taken from lahars in motion at two sites in the curah lengkong river on the southeast flank of semeru providing estimates of the particle concentration grain size spectrum grain density and composition this enables us to identify flow sediment from three categories of lahars a hyperconcentrated flow b non cohesive clast and matrix supported debris flow and c muddy flood to understand hyperconcentrated flow sediment transport processes it is more appropriate to sample the active flows than the post event lahar deposits because in situ sampling retains the full spectrum of the grain size distribution rheometrical tests on materials sampled from moving hyperconcentrated flows were carried out using a laboratory vane rheometer despite technical difficulties results obtained on the 63 180 and 400 m fractions of the sampled sediment suggest a purely frictional behaviour importantly and contrary to previous experiments conducted with monodisperse suspensions our results do not show any transition towards a viscous behaviour for high shear rates these data provide important constraints for future physical and numerical modelling of lahar flows copyright 2010 john wiley sons ltd

object oriented classification of a high spatial resolution spot5 image for mapping geology and landforms of active volcanoes semeru case study indonesia the present work explores the object oriented classification ooc of high spatial resolution hsr satellite panchromatic imagery for mapping the geology of the persistently active semeru volcano and its ring plain east java indonesia a panchromatic spot5 image and a digital elevation model dem have been used to identify geologic units structures landforms and deposits the panchromatic image was georeferenced and enhanced using histogram equalization the enhanced image was segmented into polygons using the envifx exelis software the polygons were delineated and classified on the basis of spectral panchromatic hues and textures topographic slope elevation information and geologic geomorphic processes the validity of classification was evaluated by interpreting google earth images aerial photographs and limited field observations the classification consists of three hierarchical levels across the volcanic area of about 745 km2 the first operational spatial level includes seven large volcano domains based on the spectral content of the volcanic tectonic and lithological structures and principal catchments the second operational level based on contextual relationships topography drainage network vegetation cover type stratigraphy and slope dynamics encompasses 20 geological units that range between 30 and 80 km2 in area among the units the third operational level distinguishes as many as 47 geomorphological sub units 0 25 25 km2 according to slope gradient deposit type mass wasting process and weathering the resulting map provides a detailed pattern of geologic and geomorphic features unlike previous geologic maps that identified only 11 stratigraphic units we show that the high spatial resolution panchromatic spot5 scene can help to safely map the geology and landforms of persistently active volcanoes such as semeru we have applied the ooc technique on one hsr geoeye panchromatic image to map another active volcano merapi in central java after considerable geomorphic changes due to the large eruption in 2010

the cooling of frontal flow ramps a calorimetric study on the rocche rosse rhyolite flow lipari aeolian islands italy relaxation geospeedometry using differential scanning calorimetry dsc has been applied to quantify the cooling history across the glass transition of flow ramps at the front of the calcalkaline rhyolite rocche rosse flow of lipari aeolian islands italy modelled cooling rates for the obsidian retrieved from two profiles range between 0 2 and 0 03 k min 1 cooling at the flow front appears to be dominated by conductive heat loss of individual flow ramps forming individual cooling units cooling rates of tens of kelvins per day appear to have controlled the last stage of viscous deformation before the entire flow came to rest it is inferred that cooling rates slower than those modelled are required to sustain flow in highly viscous rhyolitic lavas

in situ observation of the percolation threshold in multiphase magma analogues magmas vesiculate during ascent producing complex interconnected pore networks which can act as outgassing pathways and then deflate or compact to volcanic plugs similarly in conduit fragmentation events during dome forming eruptions create open systems transiently before welding causes pore sealing the percolation threshold is the first order transition between closed and open system degassing dynamics here we use time resolved synchrotron source x ray tomography to image synthetic magmas that go through cycles of opening and closing to constrain the percolation threshold c at a range of melt crystallinity viscosity and overpressure pertinent to shallow magma ascent during vesiculation we observed different percolative regimes for the same initial bulk crystallinity depending on melt viscosity and gas overpressure at high viscosity 106 pa s and high overpressure 1 4 mpa we found that a brittle viscous regime dominates in which brittle rupture allows system spanning coalescence at a low percolation threshold c 0 17 via the formation of fracture like bubble chains percolation was followed by outgassing and bubble collapse causing densification and isolation of the bubble network resulting in a hysteresis in the evolution of connectivity with porosity at low melt viscosity and overpressure we observed a viscous regime with much higher percolation threshold c 0 37 due to spherical bubble growth and lower degree of crystal connection finally our results also show that sintering of crystal free and crystal bearing magma analogues is characterised by low percolation thresholds c 0 04 0 10 we conclude that the presence of crystals lowers the percolation threshold during vesiculation and may promote outgassing in shallow crystal rich magma at initial stages of vulcanian and strombolian eruptions

structure and emplacement of a rhyolitic obsidian flow little glass mountain medicine lake highland northern california many rhyolitic obsidian flows show consistent stratigraphic relations among textural units exposed in the flow fronts of undissected flows and in cross sections of older flows the stratigraphy of the holocene little glass mountain rhyolitic obsidian flow consists of from bottom to top air fall tephra deposits basal breccia coarsely vesicular pumice obsidian finely vesicular pumice and surface breccia slightly crystalline rhyolite occurs near the vent areas a model of obsidian flow emplacement based on these textural relations is presented this stratigraphy may reflect the distribution of volatiles within the magma source region with the interlayered contact between coarsely vesicular pumice and overlying obsidian indicating stratification of volatiles in the magma body the distribution of pumiceous and glassy zones along with the orientations of flow banding can be used to map the surface structure of rhyolitic obsidian flows this complex structure as mapped on the little glass mountain flow reflects both the initial flow stratigraphy and subsequent deformational processes during emplacement of the lava three processes disrupt the initial flow configuration the rise of coarse pumice diapirs from the base of the flow the inward propagation of fractures in areas of extension and surface folding in sites of flow parallel compression subvertical flow banding in vent areas indicates that fracturing accompanies the emergence of lava most of the observed upper surface of a dome originates as a fracture plane the structure of domes that form over vent areas may reflect the orientation of dike like conduits as well as the local state of stress during extrusion

the gulf of carpentaria heated torres strait and the northern great barrier reef during the 2016 mass coral bleaching event the 2015 16 enso event increased the temperature of waters surrounding northeast australia to above 30 c with large patches of water reaching 32 c for over two months which led to severe bleaching of corals of the northern great barrier reef ngbr this study provides evidence gained from remote sensing data oceanographic data and oceanographic modeling that three factors caused this excessive heating namely 1 the shutdown of the north queensland coastal current which would otherwise have flushed and cooled the northern coral sea and the ngbr through tidal mixing 2 the advection of warm 30 c water from the gulf of carpentaria eastward through torres strait and then southward over the ngbr continental shelf and 3 presumably local solar heating the eastward flux of this warm water through torres strait was driven by a mean sea level difference on either side of the strait that in turn was controlled by the wind which also generated the southward advection of this warm water onto the ngbr shelf on the ngbr shelf the residence time of this warm water was longer inshore than offshore and this may explain the observed cross shelf gradient of coral bleaching intensity the fate of the great barrier reef is thus controlled by the oceanography of surrounding seas

mechanisms of bubble coalescence in silicic magmas bubble coalescence is an important process that strongly affects magmatic degassing without coalescence bubbles remain isolated from one another in the melt severely limiting gas release despite this fact very little has been done to identify coalescence mechanisms from textures of magmatic rocks or to quantify the dynamics of bubble coalescence in melts in this paper we present a systematic study of bubble coalescence mechanisms and dynamics in natural and experimentally produced bubbly rhyolite magma we have used a combination of natural observations aided by high resolution x ray computed tomography petrological experiments and physical models to identify different types of bubble bubble interaction that lead to coalescence on the timescales of magma ascent and eruption our observations and calculations suggest that bubbles most efficiently coalesce when inter bubble melt walls thin by stretching rather than by melt drainage from between converging bubble walls orders of magnitude are more rapid than melt drainage bubble wall stretching produces walls thin enough that inter bubble pressure gradients may cause the melt wall to dimple further enhancing coalescence to put these results into volcanogical context we have identified magma ascent conditions where each coalescence mechanism should act and discuss the physical conditions for preserving coalescence structures in natural pumice the timescales we propose could improve volcanic eruption models which currently do not account for bubble coalescence although we do not address the effect of shear strain on bubble coalescence the processes discussed here may operate in several different eruption regimes including vesiculation of lava domes post fragmentation frothing of vulcanian bombs and bubbling of pyroclasts in conduits

crystal rich lava dome extrusion during vesiculation an experimental study abstract lava dome forming eruptions represent a common eruptive style and a major hazard at numerous active volcanoes worldwide the extrusion mechanics of crystal rich lava domes and the influence of volatiles on the transition from viscous to brittle behaviour during lava dome extrusion remain unclear understanding how gas exsolution and crystallinity control effusive versus explosive eruption behaviour is essential here we present new experimental results on the rheology of synthesised crystal rich 50 to 80 vol quartz crystals hydrous 4 2 wt h2o in the glass dacite samples which vesiculate from 5 to 27 vol gas bubbles at high temperatures from glass transition temperature to 797 c during deformation conducted in a parallel plate viscometer constant stress at 0 63 0 64 mpa and variable strain rates ranging from 8 32 10 8 to 3 58 10 5 s 1 the experiments reproduce certain aspects of lava dome deformation in volcanic conduits during vesiculation of the residual melt instigated in the experiments by increasing temperature during gas exsolution i e nucleation and growth of gas pressurised bubbles and volume inflation we find that the rheological lubrication of the system during deformation is strongly dictated by the initial crystallinity at crystal contents

application of synthetic aperture radar sar imagery to volcano mapping in the humid tropics a case study in east java indonesia volcanoes in humid tropical environments are frequently cloud covered typically densely vegetated and rapidly eroded these factors complicate field and laboratory studies and even the basic identification of potentially active volcanoes numerous previous studies have highlighted the potential value of radar remote sensing for volcanology in equatorial regions here cloud and vegetation penetrating lhh band 24 cm synthetic aperture radar sar data from the japanese earth resources satellite jers 1 are used to investigate persistently active volcanoes and prehistoric calderas in east java indonesia the lhh band jers 1 sar produces high spatial resolution 18 m imagery with relatively high incidence angle that highlights structures and topographic variations at or greater than the wavelength scale while minimising geometrical distortions such as layover and foreshortening these images along with internet browse data derived from the canadian radarsat mission provide new evidence relating regional tectonics to volcanism throughout east java volcanic events such as caldera collapse at the tengger caldera appear to have been partly controlled by northwest aligned faults related to intra arc sedimentary basins similar regional controls appear important at historically active lamongan volcano which is encircled by numerous flank maars and cinder cones a previously undocumented pyroclastic sheet and debris avalanche deposit from the jambangan caldera complex is also manifested in the synoptic radar images at the currently active semeru volcano these data permit identification of recent pyroclastic flow and lahar deposits radar data therefore offer a valuable tool for mapping and hazard assessment at late quaternary volcanoes the criteria developed in the analysis here could be applied to other regions in the humid tropics

rhyolite magma degassing an experimental study of melt vesiculation the vesiculation of a peralkaline rhyolite melt initially containing 0 14 wt h2o has been investigated at temperatures above the rheological glass transition tg 530 c by a in situ optical observation of individual bubble growth or dissolution and b dilatometric measurements of the volume expansion due to vesiculation the activation energy of the timescale for bubble growth equals the activation energy of viscous flow at relatively low temperatures 650 790 c but decreases and tends towards the value for water diffusion at high temperatures 790 925 c the time dependence of volume expansion follows the avrami equation

experimental study of bubble growth in stromboli basalt melts at 1 atm abstract volcanic eruptions are characterized by intense degassing thus it is imperative to have high quality laboratory data to constrain degassing mechanisms in order to investigate bubble formation and growth at 1 atm degassing experiments using a stromboli basalt were performed on the gsecars x ray beamline at the advanced photon source volatile bearing glasses were synthesized at 1250 c and 1000 mpa in a piston cylinder with h 2 o or mixtures of h 2 o co 2 they were then heated in situ on the x ray beamline at 1 atm bubble growth was observed in situ using x ray radiography the 3d bubble size distributions in the quenched samples and a natural stromboli pumice were studied by synchrotron x ray microtomography the results show that bubble nucleation and growth in basaltic melts are volatile concentration dependent bubbles can easily form in melts initially containing high volatile concentrations the effect of co 2 on bubble nucleation and growth becomes significant at large co 2 concentrations of 880 to 1480 ppm but is not important at lower concentrations multiple nucleation events occur in most of these degassing experiments and they are more pronounced in more supersaturated melts bubble growth is controlled by viscosity near glass transition temperatures and by diffusion at higher temperatures bubbles begin to pop 10 to 20 s after a foam is developed at vesicularities of 65 to 83 bubble size distributions follow power law relations at vesicularities of 1 to 65 and bubble size distributions evolve from power law relations to exponential relations at vesicularities of 65 to 83 this evolution is associated with the change from far from equilibrium degassing to near equilibrium degassing during far from equilibrium degassing multiple nucleation events are pronounced and possibly account for the generation of power law relations when the system reaches near equilibrium degassing coalescence is dominant and leads to the formation of bubbles of similar size therefore bubble size distributions are described by exponential relations

rate of sediment yield following small scale volcanic eruptions a quantitative assessment at the merapi and semeru stratovolcanoes java indonesia sediment yields were calculated on the anks of merapi and semeru volcanoes in java indonesia using two different methods during the rst year following the 22 november 1994 eruption of merapi a sediment yield in excess of 1 5 105 m3 km 2 yr 1 was calculated in the boyong river drainage basin based on the volumes of sediment that were trapped by ve check dams at semeru sediment discharges were assessed in the curah lengkong river from direct measurements on the lahars in motion and on the most signi cant stream ows the calculated rate of sediment yield during one year of data in 2000 was 2 7 105 m3 km 2 yr 1 sediment yields are dominated by rain triggered lahars which occur every rainy season in several drainage basins of merapi and semeru volcanoes mostly during the rainy season extending from october to april the return period of lahars carrying sediment in excess of 5 105 m3 is about one year in the curah lengkong river at semeru at merapi the volume of sediments transported by a lahar did not exceed 2 8 105 m3 in the boyong river during the rainy season 1994 95 on both volcanoes the sediments are derived from similar sources pyroclastic ow surges deposits rockfalls from the lava domes and old material from the riverbed and banks however daily explosions of vulcanian type at semeru provide a more continuous sediment supply than at merapi therefore sediment yields are larger at semeru copyright 2004 john wiley sons ltd

surface deformation and coherence measurements of kilauea volcano hawaii from sir c radar interferometry the shuttle imaging radar c x synthetic aperture radar sir c x sar radar on board the space shuttle endeavor imaged kilauea volcano hawaii in april and october 1994 for the purpose of measuring active surface deformation by the methods of repeat pass differential radar interferometry observations at 24 cm l band and 5 6 cm c band wavelengths were reduced to interferograms showing apparent surface deformation over the 6 month interval and over a succession of 1 day intervals in october a statistically significant local phase signature in the 6 month interferogram is coincident with the pu u o o lava vent interpreted as deformation the signal implies centimeter scale deflation in an area several kilometers wide surrounding the vent peak deflation is roughly 14 cm if the deformation is purely vertical centered southward of the pu u o o caldera delays in the radar signal phase induced by atmospheric refractivity anomalies introduce spurious apparent deformation signatures at the level of 12 cm peak to peak in the radar line of sight direction though the phase observations are suggestive of the wide area deformation measured by global positioning system gps methods the atmospheric effects are large enough to limit the interpretation of the result it is difficult to characterize centimeter scale deformations spatially distributed over tens of kilometers using differential interferometry without supporting simultaneous spatially distributed measurements of refractivity along the radar line of sight studies of the interferometric correlation of images acquired at different times show that l band is far superior to c band in the vegetated areas even when the observations are separated by only 1 day these results imply longer wavelength instruments are more appropriate for studying surfaces by repeat pass observations

wind forced motion on the northern great barrier reef abstract observations of current bottom pressure and wind from the shelf of the northern great barrier reefare interpreted using a two layer frictional step shelf model forced by propagating wind stress distinguishing features of the region are the many reefs on the shallow shelf the well mixed nature of the shelf waters and the steep continental slope the instrument army was deployed from april to october 1982 and comprised 14 current meters nine pressure gauges and two weather stations low pass 0 6 cycles per day cpd filtered velocity and pressure data are analyzed separately using a time domain empirical orthogonal function eof analysis the first eofs of both velocity and pressure data are found to account for most of the observed variance on the shelf time series of these two eofs are both highly coherent with the local longshore wind stress at weatherband frequencies 0 3cpd however the frequency transfer functions of the wind to the current and of the wind to the pressure ar

pyroclastic flow deposits of the 1991 eruption of volcan de colima mexico the april 16 1991 eruption of volcan de colima represents a classical example of partial dome collapse with the generation of progressively longer runout merapi type pyroclastic flows that traveled up to 4 km along the el cordoban gullies east central and west the flows filled the gullies with block and ash flow deposits up to 10 m thick of which after 7 years of erosion only remnants remained in the el cordoban west and east gullies the el cordoban central gully however provided a well preserved and incised longitudinal section of the 1991 deposits the deposits were emplaced as proximal and distal facies separated by a change in slope angle from 30 to 20 the proximal facies consists of massive clast supported flow units up to 1 m thick with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading the distal facies consists of a massive matrix supported deposit up to 8 m thick which contains dispersed andesite blocks in a fine ash matrix in the distal facies a train of blocks marks flow unit upper boundaries and although sorting is poor some grading is present thin finely stratified or dune bedded layers of fine ash material are locally present above or below units of both facies sedimentologic parameters show that the size or fraction of large pyroclasts larger than 1 decreases from proximal to distal facies as the percentage of matrix 0 to 4 increases especially immediately beyond the break in slope we propose that the propagation of the colima pyroclastic flows is critically dependent on local slope angle the presence of erodible slope debris and the decrease in grain size with distance from the vent the progressive fining is probably caused by some combination of erosion clast breakup and deposition of larger pyroclasts and is itself influenced by the slope angle in the proximal region the flows moved as granular avalanches in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud the maximum runout distance of the avalanches was controlled by the angle of repose of the material and the volume and grain size of source and eroded material because the slope angle is close to the repose angle for this debris granular avalanches were not able to propagate far beyond the change in slope if however an avalanche had enough mass in finer grain size fractions at least part of the flow continued beyond the break in slope and across the volcano apron propagating in a turbulent state and depositing surge layers or in an otherwise settling modified state and depositing block and ash flow layers

toward a revised hazard assessment at merapi volcano central java abstract of 1 1 million people living on the flanks of the active merapi volcano 440 000 are at relatively high risk in areas prone to pyroclastic flows surges and lahars for the last two centuries the activity of merapi has alternated regularly between long periods of viscous lava dome extrusion and brief explosive episodes at 8 15 year intervals which generated dome collapse pyroclastic flows and destroyed part of the pre existing domes violent explosive episodes on an average recurrence of 26 54 years have generated pyroclastic flows surges tephra falls and subsequent lahars the 61 reported eruptions since the mid 1500s killed about 7000 people the current hazard zone map of merapi pardyanto et al 1978 portrays three areas termed forbidden zone first danger zone and second danger zone based on successively declining hazards revision of the hazard map is desirable because it lacks details necessary to outline hazard zones with accuracy in particular the valleys likely to be swept by lahars and excludes some areas likely to be devastated by pyroclastic gravity currents such as the 22 november 1994 surge in addition risk maps should be developed to incorporate social technical and economic factors of vulnerability eruptive hazard assessment at merapi is based on reconstructed eruptive history on eruptive behavior and scenarios and on existing models and preliminary numerical modeling firstly the reconstructed eruptive activity in particular for the past 7000 years and from historical accounts of eruptions helps to define the extent and recurrence frequency of the most hazardous phenomena newhall et al 2000 camus et al 2000 pyroclastic flows traveled as far as 9 15 km from the source pyroclastic surges swept the flanks as far as 9 20 km away from the vent thick tephra fall buried temples in the vicinity of yogyakarta 25 km to the south and subsequent lahars spilled down the radial valleys as far as 30 km to the west and south at least one large edifice collapse has occurred in the past 7000 years newhall et al 2000 camus et al 2000 secondly four eruption scenarios are portrayed as hazardous zones on two maps and derived from the past eruptive behavior of merapi and from the most affected areas in the past thirdly simple numerical simulation based on a digital elevation model a stereo pair of spot satellite images and one 2d orthoimage helps to simulate pyroclastic and lahar flowage on the flanks and in radial valley channels and to outline areas likely to be devastated three major threats are identified 1 a collapse of the summit dome in the short to mid term that can release large volume pyroclastic flows and high energy surges towards the south southwest sector of the volcano 2 an explosive eruption much larger than any since 1930 may sweep all the flanks of merapi at least once every century 3 a potential collapse of the summit area involving the fumarolic field of gendol and part of the southern flank which can contribute to moderate scale debris avalanches and debris flows

dynamic observations of vesiculation reveal the role of silicate crystals in bubble nucleation and growth in andesitic magmas abstract bubble nucleation and growth control the explosivity of volcanic eruptions and the kinetics of these processes are generally determined from examinations of natural samples and quenched experimental run products these samples however only provide a view of the final state from which the initial conditions of a time evolving magmatic system are then inferred the interpretations that follow are inexact due to the inability of determining the exact conditions of nucleation and the potential detachment of bubbles from their nucleation sites an uncertainty that can obscure their nucleation location either homogeneously within the melt or heterogeneously at the interface between crystals and melts we present results of a series of dynamic real time 4d x ray tomographic microscopy experiments where we observed the development of bubbles in crystal bearing silicate magmas experimentally synthesized andesitic glasses with 0 25 0 5 wt h 2 o and seed silicate crystals were heated at 1 atm to induce bubble nucleation and track bubble growth and movement in contrast to previous studies on natural and experimentally produced samples we found that bubbles readily nucleated on plagioclase and clinopyroxene crystals that their contact angle changes during growth and that they can grow to sizes many times that of the silicate on whose surface they originated the rapid heterogeneous nucleation of bubbles at low degrees of supersaturation in the presence of silicate crystals demonstrates that silicates can affect when vesiculation ensues influencing subsequent permeability development and effusive vs explosive transition in volcanic eruptions

potentially active volcanoes of peru observations using landsat thematic mapper and space shuttle imagery landsat thematic mapper tm images and space shuttle color photograph have been used to make a synoptic study of the volcanoes of southern peru 14 17 s the northernmost portin of the central volcanic zone cvz 14 28 s of the andes apart from providing consistent coverage the chief merit of the tm for this study has been the spatial resolution provided by the 30 m pixel size the optimal 20 m resolution variable lighting and viewing geometry and stereo capability of the shuttle photography provided an invaluable ancilliary data set at the resolution available subtle glacial morphological features such as valley and terminal moraines can be confidently identified and these features have been used to determine the relative ages of volcanoes volcanoes have been classified as potentially active if they have i a well preserved summit crater ii pristine lava flow texture and morphology iii flank lava flows with low albedo and iv evidence of postglacial 10 000 years activity eight major volcanoes are postulated to be potentially active most are large dominantly andesitic composite cones with edifice heights of up to 2500 m some of which threaten nearby settlements one of them sabancaya was active as recently as july 1988 other little known postglacial volcanic features include huaynaputina site of a major explosive rhyolitic eruption in 1600 a d and several fields of monogenetic scoria cones and lava flows the active volcanic front is some 200 km east of the peru chile trench and the volcanoes lie on a trenchparallel trend oblique to the ew subduction this narrow volcanic zone is thought to reflect the steep dip of the nazca plate through the zone of magma generation the break in the trend of the volcanic front in the northern extremity of the volcanic zone is thought to reflect the complexity of the crustal stress field above a major segment boundary in the subducting plate the fields of mafic monogenetic centers also occur in this region in comparison with the southern part of the cvz the general paucity of older volcanic edifices north of 17 s suggests a more recent onset of volcanism north of this latitude probably resulting from the oblique subduction of the nazca ridge and the consequent northward migration of its intersection with the pere chile trench this coupled with the lack of any large silicic caldera systems and youthful dacite domes like those found further south suggest that there are real differences between the volcanic evolution of different parts of the cvz

strain localization in vesicular magma implications for rheology and fragmentation the rheology of two or three phase magmas has been the focus of much interest because it controls magma ascent and eruption behavior research on magma rheology has typically considered homogeneous fl ow here we demonstrate based on natural examples that strain resulting from viscous fl ow preceding explosive fragmentation localizes into shear zones at a microscopic scale strain localization affects the rheological behavior of magmas modifying predictions based on experiments localization leads to high strain rate shear zones where elongated sheared vesicles and shear heating have a weakening effect surrounding regions of relatively low strain rate where subequant vesicles have a strengthening effect thus energy is dissipated more effi ciently into localized bands where strain rate increases through feedback effects and can lead to melt fragmentation

oblique synoptic images produced from digital data display strong evidence of a new caldera in southwestern guatemala abstract the synoptic view of broad regions of the earth s surface as displayed in landsat and other satellite images has greatly aided in the recognition of calderas ignimbrite plateaus and other geologic landforms remote sensing images that include visual representation of depth are an even more powerful tool for geologic interpretation of landscapes but their use has been largely restricted to the exploration of planets other than earth by combining landsat images with digitized topography we have generated regional oblique views that display compelling evidence for a previously undocumented late cenozoic caldera within the active volcanic zone of southwestern guatemala this new caldera herein called xela is a depression about 30 km wide and 400 600 m deep which includes the quezaltenango basin the caldera depression is breached only by a single river canyon the caldera outline is broadly circular but a locally scalloped form suggests the occurrence of multiple caldera collapse events or local slumping of steep caldera walls or both within its northern part xela caldera contains a toreva block about 500 m high and 2 km long that may be incompletely foundered pre caldera bedrock xela contains several post caldera volcanoes some of which are active a bouguer gravity low tens of milligals in amplitude is approximately co located with the proposed caldera the oblique images also display an extensive plateau that dips about 2 away from the north margin of xela caldera we interpret this landform to be underlain by pyroclastic outflow from xela and nearby atitlan calderas field mapping by others has documented a voluminous rhyolitic pumiceous fallout deposit immediately east of xela caldera we speculate that xela caldera was the source of this deposit if so the age of at least part of the caldera is between about 84 ka and 126 ka the ages of deposits that stratigraphically bracket this fallout most of the floor of xela caldera is covered with los chocoyos pyroclastics 84 ka deposits erupted from atitlan caldera oblique images produced from digital data are unique tools that can greatly facilitate initial geologic interpretation of morphologically young volcanic and other terrains where field access is limited especially because conventional visual representations commonly lack depth perspective and may cover only part of the region of interest

contrasts between debris flows hyperconcentrated flows and stream flows at a channel of mount semeru east java indonesia abstract in order to differentiate between different types of sediment laden flows in volcanic channels we carried out observation of debris flows hyperconcentrated flows and stream flows in the curah lengkong river on the southeast slope of mount semeru in east java indonesia the aims of this study are 1 to provide quantitative data for these flows in motion 2 to compare the data for different types of flow that occur in the same river 3 to assess the influence of rainfall on debris flows hyperconcentrated flows and streamflow generation the curah lengkong river transports large volumes of sediment in the range of 1 10 5 to 5 10 5 m 3 per debris flow and 10 3 to 10 5 m 3 per hyperconcentrated flow and stream flow large sediment discharges result from the following factors continuous and voluminous sediment supply of fine juvenile material by daily explosions of the semeru volcano pyroclastic source material emplaced on steep slopes strong erosion of weathered river banks and strong rainfall intensities the occurrence of the flows focuses in the period from november through april and the daily timing of it is the mid to late afternoon nearly all debris flows are triggered by stationary rainfall confined to the upper slopes of mount semeru whereas hyperconcentrated flows and stream flows are mainly generated by migratory or regional rains driven upwards on the eastern slope this slope receives its maximum of annual rainfall 3800 mm at 800 m asl the peak surface velocity of debris flows is always greater than the peak frontal velocity the peak discharge of debris flows occurs several minutes after the passage of the flow front volumetric concentrations of sediment are high 48 to 69 between the debris flow front and the point of peak discharge after the peak discharge it usually decreases gradually contrary to the case of debris flows high concentration of sediment appears in various portion of hyperconcentrated flows and stream flows near the front in the mid point or at the back of flows although the concentration of sediments in them is much less than in of debris flows relationships between sediment discharge total volume and peak discharge show a very strong positive correlation for debris flows and hyperconcentrated flows therefore sediment discharge can be roughly estimated from direct visual observation

tidal jets nutrient upwelling and their influence on the productivity of the alga halimeda in the ribbon reefs great barrier reef abstract a field experiment was carried out to study water circulation and benthic biological productivity near a passage through the ribbon reefs in the northern great barrier reef of australia the currents through the passage were phase locked with the tide during rising tides strong currents through the passage generated localized upwelling on the upper continental slope enriching the depleted surface waters in nutrients particularly nitrate and phosphate simultaneously on the shelf side of the passage a tidal jet vortex pair system developed which separated from the ribbon reefs so that the coral reefs themselves received little of the upwelled water this was propagated as a bottom trapped layer towards the meadows of the calcareous alga halimeda situated several kilometres inshore of the reefs halimeda can accumulate nutrients particularly nitrate from the relatively low concentrations available from the upwelling events the quantity of nitrogen upwelled was more than sufficient to supply the total nitrogen requirements of the halimeda vegetation a tidal jet also formed offshore from the reef passage during falling tides and the coral covered offshore side of the ribbon reefs may be sustained by the subsequent vertical turbulent entrainment into the jet of deep nutrient rich water immediately offshore from the reef passages these processes require a continuous barrier reef with only narrow passages several kilometers apart numerical models successfully reproduce the observations of jet driven upwelling and of the dynamics of the tidal jet vortex pair system the model predictions are very sensitive to the details of the bathymetry of reef passages as such data are presently unavailable it is not yet possible to use these models to calculate the jet driven nutrient upwelling for the whole great barrier reef

delayed disequilibrium degassing in rhyolite magma decompression experiments and implications for explosive volcanism recent numerical models and analog shock tube experiments show that disequilibrium degassing during magma ascent may lead to violent vesiculation very near the surface in this study a series of decompression experiments using crystal free rhyolite melt were conducted to examine the development of large supersaturations due to delayed homogenous spontaneous bubble nucleation melts were saturated at 900 c and 200 mpa with either 5 2 wt dissolved h2o or with 4 2 wt h2o and 640 ppm co2 and isothermally decompressed at linear rates of either 0 003 0 025 or 8 5 mpa s to final pressures between 25 and 175 mpa additional isobaric saturation experiments 900 c 200 25 mpa using pure h2o or mixed h2o co2 fluids establish reference equilibrium solubility curves values homogenous nucleation is triggered in both h2o only and h2o co2 experiments once the supersaturation pressure pss reaches 120 150 mpa and the melt contains two times its equilibrium water contents bubble number density and nucleation rate depend on the supersaturation pressure with values on the order of 102 cm3 and 1 cm3 s for pss 120 mpa 106 cm3 and 103 105 cm3 s for pss 130 150 mpa and 107 cm3 and 106 cm3 s for pss 160 175 mpa nucleation rates are consistent with classical nucleation theory and infer an activation energy for nucleation of 1 5 10 18 j nucleus a critical bubble radius of 2 10 9 m and an effective surface tension for rhyolite at 5 2 wt h2o and 900 c of 0 10 0 11 n m the long nucleation delay limits the time available for subsequent diffusion such that disequilibrium dissolved h2o and co2 contents persist to the end of our runs the disequilibrium degassing paths inferred from our experiments contrast markedly with the equilibrium or quasi equilibrium paths found in other studies where bubble nucleation occurs heterogenously on crystals or other discontinuities in the melt at low pss homogenous and heterogenous nucleation rates are comparable however as are bubble number densities so that at a given decompression rate it appears that nucleation mechanism rather than nucleation rate determines degassing efficiency by fixing the pressure depth at which vesiculation commences and hence the time available for equilibration prior to eruption although real systems are probably never truly crystal free our results show that rhyolitic magmas containing up to 104 crystals cm3 and perhaps as high as 106 crystals cm3 are controlled by homogenous rather than heterogenous nucleation during ascent

sediment transportation and deposition by rain triggered lahars at merapi volcano central java indonesia abstract a lahar is a general term for a rapidly flowing mixture of rock debris and water other than normal streamflow from a volcano and refers to the moving flow located in the populated area of central java the stratovolcano merapi 2965 m is prone to lahar generation due to three main factors 1 millions of cubic meters of pyroclastic deposits are the product of frequent pyroclastic flows which have occurred on 2 to 4 year intervals 2 rainfall intensity is high often 40 mm in 2 h on average during the rainy season from november to april and 3 drainage pattern is very dense following the 22 november 1994 eruption of merapi 31 rain triggered lahar events were recorded in the boyong river between december 1994 and may 1996 on merapi s slopes instantaneous sediment concentration at any given time of the lahars varies widely over time and space lahars are transient sediment water flows whose properties are unsteady so that the sediment load fluctuates during the flow the boundary between the flow types debris flow with sediment concentration 60 volume or hyperconcentrated flow with sediment concentration ranges from 20 to 60 volume may fluctuate within the flow itself grain size distribution physical composition of sediments shear stress yield stress and water temperature play each a role on this boundary natural self damming and rapid breakout are partly responsible for the sediment variations of the flows debris flow phases at merapi typically last a few minutes to 10 min and are often restricted to the lahar front debris flow surges are sometimes preceded and always followed by longer hyperconcentrated flow phases as a result mean sediment concentration of the lahars is low commonly from 20 to 50 volume besides transient normal streamflow phases sediment concentration low sediment load and frequent transient flows in the merapi channels may result from at least three factors 1 several breaks in slope along the channel increase the deposition rate of sediment and hinder the bulking capacity of the lahars 2 source material is mainly coarse debris of merapi type block and ash flows consequently the remobilization of coarse debris is more difficult and the clast deposition is accelerated 3 variations of rainfall intensity over time and space common in tropical monsoon rainfall also influence the sediment load variations of the lahars sedimentologic analyses of the lahar deposits in the boyong river at merapi encompass clast supported and matrix supported debris flow deposits hyperconcentrated flow deposits and streamflow deposits the stratigraphic succession of massive and stratified beds observed immediately after any given lahar event in the boyong river indicates that the sediment concentration varies widely over time and space during a single lahar event sedimentation rate varies from 3 to 4 5 cm min during relatively long lived surges to as much as 20 cm min during short lived surges these results indicate that the sediment load fluctuates during lahar flow further demonstrating that lahars are transient sediment water flows with unsteady flow properties

preliminary analyses of sir b radar data for recent hawaii lava flows abstract the shuttle imaging radar sir b experiment acquired two l band 23 cm wavelength radar images at about 28 and 48 incidence angles over the kilauea volcano area of southeastern hawaii geologic analysis of these data indicates that although as lava flows and pyroclastic deposits can be discriminated pahoehoe lava flows are not readily distinguished from surrounding low return materials preliminary analysis of data extracted from isolated flows indicates that flow type i e as or pahoehoe and relative age can be determined from their basic statistics and illumination angle

in flow evolution of lahar deposits from video imagery with implications for post event deposit interpretation mount semeru indonesia abstract the hazardous and unpredictable nature of lahars makes them challenging to study yet the in flow processes characterizing these events are important to understand as a result much of the previous research on lahar sedimentation and flow processes has been derived from experimental flows or stratigraphic surveys of post event deposits by comparison little is known on the time dependent sediment and flow dynamics of lahars in natural environments using video footage of seven lahars on the flanks of semeru volcano east java indonesia the present study offers new insights on the in flow evolution of sediment in natural lahars video analysis revealed several distinctive patterns of sediment entrainment and deposition that varied with time related fluctuations in flow these patterns were used to generate a conceptual framework describing possible processes of formation for subsurface architectural features identified in an earlier lateral survey of lahar deposits on semeru volcano gomez and lavigne 2010a the formation of lateral discontinuities was related to the partial erosion of transitional bank deposits followed by fresh deposition along the erosional contact this pattern was observed over the course of several lahar events and within individual flows observations similarly offer potential explanations for the formation of lenticular features depending on flow characteristics these features appeared to form by preferential erosion or deposition around large stationary blocks and by deposition along channel banks during episodes of channel migration or channel constriction finally conditions conducive to the deposition of fine laminated beds were observed during periods of attenuating and surging flow these results emphasize the difficulties associated with identifying process structure relationships solely from post event deposit interpretation and illustrate that an improved understanding of the time dependent sediment dynamics in lahars may be advantageous when interpreting post event structural features

the eastern flank of the merapi volcano central java indonesia architecture and implications of volcaniclastic deposits abstract merapi volcano in central java island is considered to be the most active and dangerous andesitic volcano in indonesia the volcanic history of merapi volcano is complex and often perturbed by frequent episodes of eruptive edifice building and subsequent erosion and collapse in this paper we present a detailed field literature and gis study of the well preserved eastern flank of merapi which has been spared from major eruptions in order to reconstruct the geologic and geomorphic history of the edifice here the most recent deposits arise from the remobilization of the old volcanic materials by lahar gravitational collapse of massive lava flow and local landslide processes in this study we describe the specific deposits and subsequent alteration and removal processes the stratigraphic analysis was performed with respect to the distinct phases of construction due to eruptions and dismantling of the volcano by erosion gravitational collapse and the associated local to distal re sedimentation based on gis analysis and field surveys a drainage network anomaly was detected in two main rivers the soka and the brambang rivers we infer that an apex fan of volcaniclastic material was deposited into a central paleo pusur river and explains the abnormal divergence of the rivers a new lithological 3d conceptual model is proposed based on the characterization of the lithological facies and their temporal and spatial evolution along the eastern flank of merapi volcano

instrumental lahar monitoring at merapi volcano central java indonesia abstract more than 50 volcanic debris flows or lahars were generated around mt merapi during the first rainy season following the nuees ardentes of 22 november 1994 the rainfalls that triggered the lahars were analyzed using such instruments as weather radar and telemetered rain gauges lahar dynamics were also monitored using new non contact detection instrumentation installed on the slopes of the volcano these devices include real time seismic amplitude measurement rsam seismic spectral amplitude measurement ssam and acoustic flow monitoring afm systems calibration of the various systems was accomplished by field measurements of flow velocities and discharge contemporaneously with instrumental monitoring the 1994 1995 lahars were relatively short events their duration in the boyong river commonly ranging between 30 min and 1 h 30 min the great majority 90 of the lahars was recognized at kaliurang village between 13 00 and 17 30 h due to the predominance of afternoon rainfalls the observed mean velocity of lahar fronts ranged between 1 1 and 3 4 m s whereas the peak velocity of the flows varied from 11 to 15 m s under the gardu pandang viewpoint location at kaliurang to 8 10 m s at a section 500 m downstream from this site river slopes vary from 28 to 22 m km at the two sites peak discharges recorded in various events ranged from 33 to 360 m3 s with the maximum value of peak discharge 360 m3 s on 20 may 1995 to improve the lahar warning system along boyong river some instrumental thresholds were proposed large and potentially hazardous lahars may be detected by rsam units exceeding 400 ssam units exceeding 80 on the highest frequency band or afm values greater than 1500 mv on the low gain broad band setting

sir b radar imagery of volcanic deposits in the andes the andean cordillera of western south america between 16 s and 28 s and south of 34 s latitude have been two of the most volcanically active areas in the world for the last 25 million years ma synthetic aperture radar imagery from the shuttle imaging radar mission b sir b was collected in october 1984 over the central andes between 20 s and 24 s and also south of 42 s despite signal strength problems that drastically reduced the signal to noise s n ratio of the images volcanic features of both areas show up well in particular ignimbrite sheets formed by large explosive eruptions stand out as very strong radar reflectors due to their characteristically rough erosional surface high backscatter is apparently caused by erosional relief on the ignimbrites at scales ranging from the radar wavelength 23 cm for sir b to the 30 200 m scale of quebradas gullies and canyons the quebradas are steep sided and straight and have a similar southeast orientation in ignimbrites separated by as much as 450 km spatially and 6 ma temporally the consistent regional erosional pattern appears unrelated to the emplacement of the ignimbrites and is probably caused by preferential eolian erosion in the direction of the prevailing wind hand held space photographs ground observations and landsat thematic mapper tm imagery support the interpretation of the ignimbrite radar signature the chilean volcano michinmahuida 43 s was imaged by four radar data takes at different incidence angles which show tectonic glacial and volcanic features of that nearly inaccessible and often cloud covered region

response of a bubble bearing viscoelastic fluid to rapid decompression implications for explosive volcanic eruptions we conducted rapid decompression experiments using bubble bearing viscoelastic fluid in a vertical shock tube we varied vesicularity and pressure difference between the inside pg and the outside po of the bubbles dp pgpo to understand the behavior of bubbly magmas under rapid decompression we find that the potential energy which depends on the initial vesicularity pg and po determines the expansion velocity of the bubbly fluid during rapid decompression higher potential energy caused by a higher and a larger dp leads to faster expansion the expansion style also depends on the vesicularity and on the pressures pg and po we observe five different styles of expansion during the rapid decompression that depend on and dp when both and dp are small bnothingq occurs as and dp increase the bubbly fluid reacts more violently first the surface of the bubbly fluid bdeformsq and the fluid elongates in the vertical direction for sufficient elongation the fluid can bdetachq from the tube wall as and dp continue to increase bubble walls can break a process we refer to as bpartial ruptureq finally for still larger dp and both bubble walls and plateau borders break allowing the fluid to bfragmentq into discrete pieces and erupt explosively our experiments show that a larger potential energy which results from higher and larger dp causes a faster expansion of magma which in turn promotes fragmentation and thus explosive eruption if we assume that the pressure inside bubbles pg scales with the depth of bubbly magma measuring the magma vesicularity in conduits or domes as a function of the depth before eruption would help assess volcanic hazard d 2005 elsevier b v all rights reserved

geology tectonics and the 2002 2003 eruption of the semeru volcano indonesia interpreted from high spatial resolution satellite imagery abstract the paper illustrates the application of high spatial resolution satellite images in interpreting volcanic structures and eruption impacts in the tengger semeru massif in east java indonesia we use high spatial resolution images ikonos and spot 5 and aerial photos in order to analyze the structures of semeru volcano and map the deposits geological and tectonic mapping is based on two dems and on the interpretation of aerial photos and four spot and ikonos optical satellite images acquired between 1996 and 2002 we also compared two thermal surface kinetic temperature aster images before and after the 2002 2003 eruption in order to delineate and evaluate the impacts of the pyroclastic density currents semeru s principal structural features are probably due to the tectonic setting of the volcano a structural map of the tengger semeru massif shows four groups of faults orientated n40 n160 n75 and n105 to n140 conspicuous structures such as the se trending horseshoe shaped scar on semeru s summit cone coincide with the n160 trending faults the direction of minor scars on the east flank parallels the first and second groups of faults the semeru composite cone hosts the currently active jonggring seloko vent this is located on and buttressed against the mahameru edifice at the head of a large scar that may reflect a failure plane at shallow depth dipping 35 towards the se this failure plane may correspond to a weak basal layer of weathered volcaniclastic rocks of tertiary age we suggest that the deformation pattern of semeru and its large scar may be induced by flank spreading over the weak basal layer of the volcano it is therefore necessary to consider the potential for flank and summit collapse in the future the last major eruption took place in december 2002 january 2003 and involved emplacement of block and ash flows we have used the 2003 aster surface kinetic temperature image to map the 2002 2003 pyroclastic density current deposits we have also compared two 10 m pixel images acquired before and after the event to describe the extent and impact of an estimated volume of 5 45 106 m3 of block and ash flow deposits an ash rich pyroclastic surge escaped from one of the valley confined block and ash flows at 5 to 8 km distance from the crater and swept across the forest and tilled land on the sw side of the bang river valley downvalley the temperature of the pyroclastic surge decreased and a mud rich deposit coated the banks of the bang river valley thus hazard mitigation at semeru should combine 1 continuous monitoring of the eruptive activity through an early warning system and 2 continuous remote sensing of the morphological changes in the drainage system due to the impact of frequent pyroclastic density currents and lahars

sediment yield following severe volcanic disturbance a two decade perspective from mount st helens explosive volcanic eruptions perturb water and sediment fluxes in watersheds consequently posteruption sediment yields can exceed preeruption yields by several orders of magnitude annual suspended sediment yields following the catastrophic 1980 mount st helens eruption were as much as 500 times greater than typical background level and they generally declined nonlinearly for more than a decade although sediment yields responded primarily to type and degree of disturbance streamflow fluctuations significantly affected sediment yield trends consecutive years 1995 1999 of above average discharge reversed the nonlinear decline and rejuvenated yields to average values measured within a few years of the eruption after 20 yr the average annual suspended sediment yield from the 1980 debris avalanche deposit remains 100 times 10 4 mg megagrams km 2 above typical background level 10 2 mg km 2 within five years of the eruption annual yields from valleys coated by lahar deposits roughly plateaued and average yields remain about 10 times 10 3 mg km 2 above background level yield from a basin devastated solely by a blast pyroclastic current diminished to background level within five years these data demonstrate longterm instability of eruption generated detritus and show that effective mitigation measures must remain functional for decades

an approach using sar ers images to relate extension fractures to volcanic vents examples from iceland and madagascar abstract a new approach to the study of geometric relationships between tectonic structures and volcanic vents is presented it is based on the mapping of tectonic and volcanic features using high resolution imagery including synthetic aperture radar sar images of the european remote sensing satellite number one ers 1 we have evidenced new faults 1 n striking normal faults in the husavik fault zone of the north atlantic ridge and 2 nw striking faults belonging to the husavik transform fault zone associated to drag folds which testify to a dextral strike slip movement component we show that most of the volcanic edifices are located on extension fractures responsible for fissure eruptions volcanic linear clusters and elongated volcanoes this relationship is studied first in iceland where the geodynamics is well known using sar ers 1 imagery applied to the montagne d ambre in northern madagascar using aerial photographs this approach makes it possible to identify faults and the regional plio quaternary direction of extension i e n65 e to n85 e volcanoes forming linear clusters together with elongated volcanoes are interpreted to be located on extension fractures s or z shape of the linear clusters allowed us to determine the tips of extension fractures and consequently the orientation of the regional tension alignments of extension fractures depending on their s or z shape permitted us to infer conjugated faults

deflation of mount etna monitored by spaceborne radar interferometry ground based measurements of volcano deformation can be used to assess eruptive hazard but require the costly and often hazardous installation and maintenance of an instrument network here we show that spaceborne radar interferometry which has already shown its utility in mapping earthquake related deformation1 can be used to monitor long term volcano deformation two families of synthetic aperture radar images acquired from ascending and descending orbits by the satellite ers 1 and looking at mount etna from opposite sides cover the time period from 17 may 1992 to 24 october 1993 and include the second half of etna s most recent eruption despite artefacts of the interferometric technique we can observe a volcano wide deflation which is an expected consequence of the eruption but which had not previously been appreciated we quantify it using a simple model based on the change of pressure in a sphere located in an elastic half space the modelled deformation increases linearly with time until the end of the eruption our results show that it will be possible to use this technique to detect the inflation of volcanic edifices that usually precedes eruptions

the threat of hazards in the semeru volcano region ineast java indonesia abstract semeru volcano 3676 m the highest volcano in java is one of the most active volcanoes in indonesia its activity has occurred almost continuously since 1967 the activity is manifested by mostly strombolian type eruptions with lava extrusions which extend into a lava tongue in kobokan breach southeast slope of the volcano the lava tongue is unstable after reaching a certain volume the tongue collapses and causes pyroclastic flows to the southeast direction traveling a maximum of about 11 km downslope the collapse is sometimes triggered by volcanic eruptions the main dangers are not due to eruption and collapse of the lava tongue but caused by the secondary dangers the secondary dangers are more destructive and distributed over a wider area tens of kilometres from the source the natural hazards in the semeru region are not only related to volcanic activity which is so called lahar but also non volcanic processes such as debris flow this phenomenon is related to the heavy rainfall which causes landslides in the altered volcanic deposit areas the flow of the mixture of water and landslide materials has devastated large areas the occurrences of the secondary flow is unpredictable and its viscosity is much lower than lahar this flow is distributed over a wide area and threatens cultivated land and densely populated and developing urban areas

changes in water clarity in response to river discharges on the great barrier reef continental shelf 2002 2013 abstract water clarity is a key factor for the health of marine ecosystems the australian great barrier reef gbr is located on a continental shelf with 35 major seasonal rivers discharging into this 344 000 km2 tropical to subtropical ecosystem this work investigates how river discharges affect water clarity in different zones along and across the gbr for each day over 11 years 2002 2013 we calculated photic depth as a proxy measure of water clarity calibrated to be equivalent to secchi depth for each 1 km2 pixel from modis aqua remote sensing data long term and seasonal changes in photic depth were related to the daily discharge volumes of the nearest rivers after statistically removing the effects of waves and tides on photic depth the relationships between photic depths and rivers differed across and along the gbr they typically declined from the coastal to offshore zones and were strongest in proximity to rivers in agriculturally modified catchments in most southern inner zones photic depth declined consistently throughout the 11 year observation period such long term trend was not observed offshore nor in the northern regions averaged across the gbr photic depths declined to 47 of local maximum values soon after the onset of river floods and recovery to 95 of maximum values took on average 6 months range 150 260 days the river effects were strongest at latitude 14 5 19 0 s where river loads are high and the continental shelf is narrow here even offshore zones showed a 40 seasonal decline in photic depth and 17 24 reductions in annual mean photic depth in years with large river nutrients and sediment loads our methodology is based on freely available data and tools and may be applied to other shelf systems providing valuable insights in support of ecosystem management

characterization of debris flows by rainstorm condition at a torrent on the mount yakedake volcano japan abstract we analyzed rainstorm control on debris flow magnitude and flow characteristics using the 14 sets of rainstorm and debris flow data obtained from 1980 to 2005 at the kamikamihorizawa creek of mount yakedake with the principal component analysis on five parameters of debris flows frontal velocity peak velocity peak flow depth peak discharge and total discharge and with video record of boulder dams in motion and the preceding rainfall intensities we conclude that the 14 debris flows could be categorized into three groups the flows in the first group have large hydraulic magnitude and massive and turbulent boulder dams filled with slurry matrix the flows in the second group have small hydraulic magnitude and boulder dams scarcely filled with slurry matrix and the dam is observed to alternate between stopping and starting the flows in the third group have small hydraulic magnitude and boulder dams filled with slurry matrix analysis of hillslope hydrology and debris flow data asserted that the antecedent rainfall conditions control not only the hydraulic magnitude of debris flows but also the boulder dam features large rainstorms of high intensity and durations as short as 10 minutes induces fast and large storm runoff to the headwaters and the source reaches of debris flow while rainstorms with durations as long as 24 h raises water content in the bottom deposits along the debris flow growth reaches and generates substantial runoff from the tributaries classification of the three groups is done based on water availability to debris flows on the source and growth reaches at the occurrence of debris flow

bubble nucleation in rhyolite and dacite melts temperature dependence of surface tension surface tension profoundly influences the ability of gas bubbles to nucleate in silicate melts to determine how temperature impacts experiments were carried out in which high silica rhyolite melts with 5 wt dissolved water were decompressed at temperatures that ranged from 775 to 1 085 c decompressions were also carried out using dacite melts with 4 3 wt dissolved water at 1 150 c water bubbles nucleated in rhyolite only when decompressions exceeded 95 mpa at all temperatures bubbles nucleated in number densities that increased as decompression increased and at hotter temperatures at a given amount of decompression after correcting decompression amounts for temperature differences values for were estimated from nucleation rates and found to vary between 0 081 and 0 093 n m 1 surface tension decreases as temperature increases from 775 to 875 c but then increases as temperature increases to 1 085 c those values overlap previous results but only when melt viscosity is less than 104 pa s for low viscosity rhyolite there is a strong correlation of with temperature in which increases by 6 9 10 5 n m 1 c 1 that variation is robust for 5 9 wt dissolved water as long as melt viscosity is 104 pa s more viscous rhyolite deviates from that correlation probably because nucleation is retarded in stiffer melts bubbles nucleated in dacite when decompressions exceeded 87 mpa and occured in one or more events as decompression increased surface tension is estimated to be 0 083 0 001 n m 1 and when adjusted for temperature agrees well with previous results for colder and wetter dacite melts at a given water content dacite melts have lower surface tensions than rhyolite melts when corrected to a fixed temperature

gas driven filter pressing in magmas insights into in situ melt segregation from crystal mushes gas driven filter pressing is the process of melt expulsion from a volatile saturated crystal mush induced by the buildup and subsequent release of gas pressure filter pressing is inferred to play a major role in magma fractionation at shallow depths 10 km by moving melt and gas relative to the solid crystalline framework however the magmatic conditions at which this process operates remain poorly constrained we present novel experimental data that illustrate how the crystal content of the mush affects the ability of gas driven filter pressing to segregate melt hydrous haplogranite 2 1 wt water in the melt and dacite 4 2 wt water in the melt crystal mushes with a wide range of crystallinities 34 80 vol crystals were investigated using in situ high temperature 500 800 c synchrotron x ray tomographic microscopy with high spatial 3 m pixel and temporal resolution 8 s per three dimensional data set our experimental results show that gas driven filter pressing operates only below the maximum packing of bubbles and crystals 74 vol above this threshold the mush tends to fracture and gas escapes via fractures therefore the efficiency of gas driven filter pressing is promoted close to the percolation threshold and in situations where a mush inflates slowly relative to build up of pressure and expulsion of melt such observations offer a likely explanation for the production of eruptible crystal poor magmas within earth s crust

defining conditions for bulking and debulking in lahars through measurements at semeru volcano east java we define the conditions under which bulking entrainment of sediment and pore water and debulking dilution and sedimentation occur in rain triggered volcanic floods lahars two observation sites were installed 510 m apart along the curah lengkong river 11 5 km southeast of semeru s summit this 30 m wide box valley with a gravel and lava base represents a real world flume analogy pore pressure sensors provided stage measurements a broad band seismograph gave insight into sediment content and frictional collisional behavior video cameras were used to measure surface velocities and direct bucket samples were taken eight rainfall induced lahars were recorded lasting 1 3 h with heights of 0 5 2 m peak velocities of 3 7 m s and discharges of 25 250 m3 s flows ranged from typical 40 wt sediment to coarse and dense hyperconcentrated flows 50 60 wt sediment multiple distinct flow packets occurred within the complex lahars and were used to determine internal changes between sites from the multiparameter data set at each site volumetric bulking and wave shortening due to portions of the lahar accelerating toward the flow front are identified initial debulking of lahars between sites may reflect drainage into the dry substrate estimates of discharge and volume at each site lead to the quantification of bulking and debulking by these actively flowing lahars along the channel reach from this we observe that bulking can be localized to certain parts of lahars resulting in intraevent increases in peak discharge that are greater than what would occur if bulking was evenly distributed throughout the flow such data are essential for the development of numerical descriptions and hazard models for mass flows

the 2006 pyroclastic deposits of merapi volcano java indonesia high spatial resolution ikonos images and complementary ground based observations abstract on 16 june 2006 an overpass of ikonos coincided with the emplacement of an active block and ash flow fed by a lava dome collapse at merapi volcano java indonesia it was the first moving pyroclastic flow recorded on a satellite image the very high spatial resolution of the image indicated the extent and impact of pyroclastic material that was deposited during and prior to the day of image acquisition a number of features associated with the hazardous block and ash flows emplaced in narrow deep gorges were mapped interpreted and analysed the high spatial resolution ikonos imagery worked extremely well for identifying pyroclastic deposits the block and ash flow and surge deposits recognized in the ikonos images include 1 several channel confined flow lobes and tongues in the box shaped gorge 2 thin ash cloud surge deposit and knocked down trees in constricted areas on both slopes of the gorge 3 fan like overbank deposits on the gendol tlogo interfluves from which flows were re routed in the tlogo minor valley 4 massive overbank flow lobes on the right bank of the gendol river which destroyed the village of kaliadem 0 5 km from the main channel a small part of this flow was re channelled into the opak tributary valley the high resolution ikonos images also helped us to identify geomorphic obstacles that enabled flows to ramp up and spill out from the sinuous channel as flow avulsion flow avulsions are dangerous as the redirect flows to unexpected areas away from the main channel valley fills from previous deposits channel bends and anthropogenic barriers in the channel locally known as sabo dams influence the down valley passage of the flows sabo dams originally built to ameliorate the effect of high sediment load streams caused block and ash flows to avulse of the containing channel and devastate populated areas

emplacement history of a low viscosity fountain fed pantelleritic lava flow abstract the strongly peralkaline 8 ka flow mayor island new zealand was emplaced as a low viscosity fountain fed lava flow the flow stratigraphy comprises from top to base a finely vesicular pumiceous carapace an upper obsidian layer central crystalline rhyolite a lower obsidian layer incorporating a crumble breccia above a fall lapilli unit rare relict clasts welded within the lowermost 0 5 m of the lower obsidian layer support a fountain fed origin for the 8 ka flow five physical parameters density porosity microlite size void and autoclast aspect ratios and water content were measured throughout the thickness of the lava flow and show that prolonged vesiculation occurred in the upper 33 of the flow thickness and that autoclast and pyroclast shapes and microlite lengths were influenced by the thermal conditions of the lava after eruption crystallisation of the flow interior commenced before the flow stopped moving compared with calc alkaline rhyolites the high flow temperature 950 c and peralkaline chemistry contributed to a less polymerised low viscosity melt log 6 4 pa s these data and structural observations of the 8 ka flow suggest that near complete homogenisation and remobilisation of spatter from a lava fountain occurred on the caldera rim producing a distally tapering lava sheet that also spilled back down the caldera wall towards the vent

automated block detection in lahars through 3 bands spectral analysis of video images abstract lahars present a particular problem for automated block detection using machine vision because their patterns and apparent sizes and shapes vary with the flow to address this difficulty we developed a simple algorithm to detect blocks in lahars at semeru volcano based on traditional rgb red green blue 25 frame per second videos the detection algorithm is based on the combination of two methods 1 a determination of blocks by color segregation and 2 objects movements detection after image processing we converted the data into a signal that emphasizes the presence of large blocks results compare very well with video images since 100 of peaks of amplitude 300 corresponded to large blocks traveling down the channel this method ultimately aims at contributing to lahars automatic detection systems where little funding is available since it only requires a traditional camera and a computer

lahars at merapi volcano central java an overview abstract merapi volcano in central java is one of the most active volcanoes in the world at least 23 of the 61 reported eruptions since the mid 1500s have produced source deposits for lahars the combined lahar deposits cover about 286 km 2 on the flanks and the surrounding piedmonts of the volcano at merapi lahars are commonly rain triggered by rainfalls having an average intensity of about 40 mm in 2 h most occur during the rainy season from november to april and have average velocities of 5 7 m s at 1000 m in elevation a wide range of facies may be generated from a single flow which may transform downvalley from debris flow to hyperconcentrated streamflow because of the high frequency and magnitude of the lahar events lahar related hazards are high below about 450 600 m elevation in each of the 13 rivers which drain the volcano hazard zone maps for lahar were produced by pardyanto et al volcanic hazard map merapi volcano central java 1 100 000 geol surv of indonesia bandung ii 4 1978 and the japanese indonesian cooperation agency master plan for land conservation and volcanic debris control in the area of mt merapi jakarta 1980 but these maps are of a very small scale to meet modern zoning requirements more recently a few large scale maps 1 10 000 and 1 2000 scale and risk assessments have been completed for a few critical river systems

volcanic hazards at mount semeru east java indonesia with emphasis on lahars mt semeru the highest mountain in java 3 676 m is one of the few persistently active composite volcanoes on earth with a plain supporting about 1 million people we present the geology of the edifice review its historical eruptive activity and assess hazards posed by the current activity highlighting the lahar threat the composite andesite cone of semeru results from the growth of two edifices the mahameru old semeru and the seloko young semeru on the se flank of the summit cone a n130 trending scar branched on the active jonggring seloko vent is the current pathway for rockslides and pyroclastic flows produced by dome growth the eruptive activity recorded since 1818 shows three styles 1 the persistent vulcanian and phreatomagmatic regime consists of short lived eruption columns several times a day 2 increase in activity every 5 to 7 years produces several kilometer high eruption columns ballistic bombs and thick tephra fall around the vent and ash fall 40 km downwind dome extrusion in the vent and subsequent collapses produce block and ash flows that travel toward the se as far as 11 km from the summit and 3 flank lava flows erupted on the lower se and e flanks in 1895 and in 1941 1942 pyroclastic flows recur every 5 years on average while large scale lahars exceeding 5 million m3 each have occurred at least five times since 1884 lumajang a city home to 85 000 people located 35 km e of the summit was devastated by lahars in 1909 in 2000 the catchment of the curah lengkong river on the ese flank shows an annual sediment yield of 2 7 105 m3 km 2 and a denudation rate of 4 105 t km 2 yr 1 comparable with values reported at other active composite cones in wet environment unlike catchments affected by high magnitude eruptions sediment yield at mt semeru however does not decline drastically within the first post eruption years this is due to the daily supply of pyroclastic debris shed over the summit cone which is remobilised by runoff during the rainy season three hazard prone areas are delineated at mt semeru 1 a triangle shaped area open toward the se has been frequently swept by dome collapse avalanches and pyroclastic flows 2 the s and se valleys convey tens of rain triggered lahars each year within a distance of 20 km toward the ring plain 3 valleys 25 km s se and the ring plain 35 km e toward lumajang can be affected by debris avalanches and debris flows if the steep sided summit cone fails

preliminary ers 1 observations of alaskan and aleutian volcanoes abstract we used ers 1 radar images collected between october 1991 and february 1993 to study volcanic landforms of the alaska peninsula and aleutian islands these data were used to map a little eroded even textured unit that is a thick low mobility pyroclastic deposit around aniakchak caldera also we have identified possible caldera remnants at black peak and located volcanically related collapse pits and depressions in the summit glacier of veniaminof observations of westdahl and mt spurr both of which erupted during our observation period demonstrate that new lava flows and debris flows can be mapped by virtue of their high radar backscatter and contrast with the surrounding terrain these data demonstrate the utility of frequent orbital radar observations in this area regional mapping can be carried out for volcanoes that are difficult to study in the field due to adverse working conditions e g frequent cloud cover bad weather long periods of darkness during winter and remote locations timely acquisition of images soon after or during an eruption can assist in the monitoring of active volcanoes the 23 incidence angle causes strong foreshortening and there is sometimes up to 35 days between repeat observations of certain locations however we conclude that the routine collection of sar data from ers 1 can provide valuable rapid information for assessing volcanic hazards in this region whatever the weather or time of year the situation will be improved with the additional use of jers 1 data and the launch of the radarsat spacecraft in 1995

geologic analyses of shuttle imaging radar sir b data of kilauea volcano hawaii analyses of imaging radar data of volcanic terranes on earth and venus have emphasized the need for a clearer understanding of how these data can be most effectively used to accomplish important volcanological goals including the interpretation of eruptive styles and the characterization of the geologic history of volcanic centers the second shuttle imaging radar experiment sir b obtained two digital images over the summit caldera and the southwest rift zone of kilauea volcano in 1984 our geologic analyses of these images indicate that sir b data are particularly useful for delineating the distribution and surface textural variations of a9a lava flows for mapping large scale topographic features with radar facing slopes and for identifying an areally extensive pyroclastic deposit analyses of the sir b data of kilauea however do not permit unambiguous identification of landforms such as pahoehoe lava flows cinder cones and fissures although separation of low return units such as pahoehoe lava flows and adjacent pyroclastic ash is not greatly improved using standard image enhancement techniques the texture analysis technique applied here did facilitate discrimination of such smooth surfaced volcanic deposits although analyses of the sir b data permit a generally accurate interpretation of the eruptive history of kilauea the inability to distinguish low return pahoehoe flows results in misinterpretation of several aspects of kilauea volcanism suggesting that caution should be exercised in the interpretation of sar data of volcanic terranes

scaling vesicle distributions and volcanic eruptions models of coalescence decompressive expansion of the later stages of bubble growth predict that for diverse types of volcanic products the vesicle number densities n v are of the scaling form text n left text v right propto text v text b 3 1 where v is the volume of the vesicles and b3 the 3 dimensional scaling power law exponent we analyze cross sections of 9 pumice samples showing that over the range of bubble sizes from 10 m to 3 cm they are well fit with b3 0 85 we show that to within experimental error this exponent is the same as that reported in the literature for basaltic lavas and other volcanic products the importance of the scaling of vesicle distributions is highlighted by the observation that they are particularly effective at packing bubbles allowing very high vesicularities to be reached before the critical percolation threshold a process which for highly stressed magmas would trigger explosion in this way the scaling of the bubble distributions allows them to be key actors in determining the rheological properties and in eruption dynamics

experimental study of bubble coalescence in rhyolitic and phonolitic melts abstract we have experimentally studied the process of bubble coalescence in rhyolite and phonolite melts of natural composition the experiments involved decompression of water saturated melts equilibrated at pressures and temperatures from 100 to 150 mpa and 775 to 840 c in vertically oriented rapid quench capable cold seal pressure vessels one type of experiments rhyolite mcr 100 120 150 and phonolite lsp 120 series approximates a static bubble coalescence case where we held the decompressed samples for 5 seconds to 4320 minutes 3 days before quenching the second type rhyolite lpc 100 series replicates an expanding bubble coalescence environment where we continually decompressed the experiments at a rate of 0 5 mpa s examining samples quenched at ending pressures between 10 and 80 mpa our static case mcr 100 120 and 150 and lsp 120 results show significant increases in the modal bubble sizes and in the sizes of the largest bubbles corresponding to measurable broadening in the size distributions their bubble number densities nv decrease as a function of hold time at their final pressures pf and can be fit well by power law functions our expanding case experiments lpc 100 show a significant drop in nv during the duration of the experiments that can be fit by an exponential equation as nv vs either time or pf average estimates of bulk coalescence rates indicate a 1 order of magnitude drop in nv for static case rhyolites in a 2 3 day period and 2 orders of magnitude for phonolites within a 3 day period despite a 2 order of magnitude difference in viscosity coalescene in the phonolite is only slightly faster than the rhyolite the expanding case experiments show a 1 order of magnitude drop in nv over 180 seconds thus nv s decrease 4 orders of magnitude faster in expanding vs static bubbly rhyolite melts our results imply that significant bubble coalescence can occur in rhyolite magmas at relatively fast 20 m s ascent rates in the conduit thus bubble interconnectivity leading to high permeability is possible during ascent bubble coalescence may occur during second boiling in magma bodies that are stalled in the crust the timescales over which this occurs is much faster than the estimated rise rates for bubbles to reach the top of the magma chamber

strain induced outgassing of three phase magmas during simple shear a major factor determining the explosivity of silicic eruptions is the removal of volatiles from magma through permeability controlled outgassing we studied the microstructural development of permeability during deformation of highly viscous magma by performing simple shear experiments on bubble 0 12 0 36 volume fraction and crystal bearing 0 0 42 volume fraction silicate melts experiments were performed under torsion at high temperature and pressure 723 873 k and 150 200 mpa in a paterson deformation apparatus at bulk shear strains between 0 and 10 the experimental setup allows for gas escape if bubble connectivity is reached on the sample periphery three dimensional imaging and analysis of deformed bubbles was performed using x ray tomography the development of localized deformation in all samples enhanced by crystal content leads to brittle fracture at bulk strains 2 and sample wide fracturing in samples deformed to strains 5 a decrease in both bubble fraction and dissolved volatile content with increasing strain along with strain hardening rheological behavior suggests significant shear induced outgassing through the fracture networks applicable to shallow conduit degassing in magmas containing crystal fractions of 0 0 42 this study contributes to our understanding of highly viscous magma outgassing and processes governing the effusive explosive transition

boundary crossing and non linear theory in earth system sciences a proof of concept based on tsunami and post eruption scenarios on java island indonesia although volcanic eruptions are well known to be the trigger of some weather and climatic changes land cover changes by pyroclastic flows and lahars do not get this recognition neither do major hazards such as tsunami these two earth processes are even lesser considered as being able to modify other earth processes they are not directly connected to such as landslides or river discharge in non connected basins more than a hundred kilometres away in this contribution the authors argue that these ideas are mainly driven by the process of being educated in a single academic discipline and once put to the test interactions and retroactions between earth processes and atmospheric processes are far more reaching than commonly thought for this study the site of java island indonesia was chosen to conduct 1 an analysis of a major tsunami impact in the same area as the 2006 java tsunami and 2 an analysis of the post eruption impacts of merapi volcano after a major eruption excluding any ejecta in the atmosphere for the sake of the demonstration the atmospheric feedback simulations were conducted using the regional climate model regcm 4 with calibration from weather stations in java island as a result both simulations have proven that large scale deposits of pyroclasts not introducing the ejectas sent in the atmosphere and tsunamis can have outstanding impacts on the atmospheric situation and the bio geomorphologic evolution of the landscape in the following weeks to months interestingly enough these impacts are not limited to the area impacted by the earth process and the effect are not linear in time as they work following thresholds these rainfalls tele impacts are important enough to in turn modify earth surface processes in areas remote from the original phenomenon this system acts in the same manner as a famous butterfly in africa that could trigger a hurricane on the other side of the atlantic ocean copyright 2012 john wiley sons ltd

bubble nucleation in rhyolitic melts experiments at high pressure temperature and water content abstract we report the first measurement of bubble nucleation in hydrated rhyolitic melts in response to pressure release two rhyolitic obsidians one containing less than 1 of microlites of fe ti oxides and the other about 20 of various crystals were hydrated at 150 mpa and 780 850 c after saturation was reached 5 3 5 5 wt water pressure was lowered and the samples were allowed to nucleate and grow bubbles for various amounts of time before the final rapid quenching of the experiments the results demonstrate the importance of heterogeneous nucleation microlites of fe ti oxides are very efficient as sites for bubble nucleation in their presence modest nucleation was observed even after decompression by 6 10 8 bubbles cm 3 in the absence of microlites no nucleation occurred at p mpa at p 10 mpa bubbles also nucleated on crystals of biotite zircon and apatite modest nucleation 10 3 10 5 cm 3 took place even in crystal free samples but it was still heterogeneous when p exceeded 80 mpa nucleation in crystal free samples became extensive 10 5 10 7 cm 3 the lack of correlation of bubble density with either time or decompression suggests that nucleation was still heterogeneous nucleation rates were controlled mainly by the availability of sites rates were faster than 10 6 cm 3 s 1 when microlites were present and faster than 10 5 cm 3 s 1 in the absence of microlites at p 70 mpa narrow size distributions in most samples suggests that nucleation took place immediately after the pressure drop the experimental data we present here indicate that the presence or absence of efficient nucleation sites can lead to two distinct modes of bubble formation when a large number of efficient sites e g fe ti oxide are present bubble nucleation requires very little supersaturation and to a good approximation gas and magma are in equilibrium in magmas that are crystal free or contain crystals that are inefficient at nucleating bubbles very high degrees of supersaturation are required in order to initiate nucleation these two modes of exsolution may lead to contrasting styles of convection pressure build up and eruption

experimental constraints on degassing and permeability in volcanic conduit flow this study assesses the effect of decompression rate on two processes that directly influence the behavior of volcanic eruptions degassing and permeability in magmas we studied the degassing of magma with experiments on hydrated natural rhyolitic glass at high pressure and temperature from the data collected we defined and characterized one degassing regime in equilibrium and two regimes in disequilibrium equilibrium bubble growth occurs when the decompression rate is slower than 0 1 mpa s 1 while higher rates cause porosity to deviate rapidly from equilibrium defining the first disequilibrium regime of degassing if the deviation is large enough a critical threshold of super saturation is reached and bubble growth accelerates defining the second disequilibrium regime we studied permeability and bubble coalescence in magma with experiments using the same rhyolitic melt in open degassing conditions under these open conditions we observed that bubbles start to coalesce at 43 vol porosity regardless of decompression rate coalescence profoundly affects bubble texture and size distributions and induces the melt to become permeable we determined coalescence to occur on a time scale 180 s independent of decompression rate we parameterized and incorporated our experimental results into a 1d conduit flow model to explore the implications of our findings on eruptive behavior of rhyolitic melts with low crystal contents stored in the upper crust compared to previous models that assume equilibrium degassing of the melt during ascent the introduction of disequilibrium degassing reduces the deviation from lithostatic pressure by 25 the acceleration at high porosities 50 vol by a factor 5 and the associated decompression rate by an order of magnitude the integration of the time scale of coalescence to the model shows that the transition between explosive and effusive eruptive regimes is sensitive to small variations of the initial magma ascent speed and that flow conditions near fragmentation may significantly be affected by bubble coalescence and gas escape

experimental constraints on degassing of magma isothermal bubble growth during continuous decompression from high pressure numerical models predict that rapid ascent of hydrous magma can lead to supersaturation of dissolved volatile constituents possibly leading to explosive eruption we have performed controlled decompression experiments to investigate the ascent rates required to maintain bubble melt equilibrium high silica rhyolitic melts were saturated with water at 200 mpa and 825 c decompressed to lower pressures at constant rates of 0 025 0 25 0 5 and 1 0 mpa s 1 and then rapidly quenched isobarically other samples were saturated with water over the pressure range investigated to determine equilibrium water solubility in order to quantify degassing efficiency during decompression at a decompression rate of 0 025 mpa s 1 melt vapor equilibrium was maintained over the entire pressure range examined 200 to 17 5 mpa a single bubble nucleation event occurred in response to decompression and quenched bubble sizes can be modeled by a equilibrium bubble growth model that takes into account the number density of bubbles at decompression rates of 0 25 0 5 and 1 0 mpa s 1 rhyolitic melts could not degas in equilibrium when pressure decreased from 200 mpa to 140 mpa and water supersaturation p in the melt reached up to 60 mpa with higher values at faster decompression rates further pressure release resulted in near equilibrium degassing and p dropped significantly in each case p decreased when bubbles exceeded 10 vol a single heterogeneous bubble nucleation event occurred in each experiment when p 20 mpa no other bubbles nucleated despite p reaching 60 mpa which is probably too low to trigger homogeneous nucleation compared to estimates for magma decompression rates during lava dome eruptions our results indicate that magmas can degas efficiently throughout their ascent to the surface in explosive eruptions decompression rates may exceed those of this study and hence melts may become supersaturated with water such fast decompressions are expected however only when magma is highly vesicular which would aid approach to equilibrium degassing

coupled effect of magma degassing and rheology on silicic volcanism abstract explosive volcanism such as the 1991 mt pinatubo philippines and the 2008 mt chaiten chile eruptions is caused by violent vesiculation of hydrous magma however gas may efficiently separate from magma owing to the enhancement of gas permeability by shear deformation of magma flowing in a volcanic conduit this makes it difficult to maintain the driving force of explosive volcanism although explosive volcanism is actually common here we propose that shear localization in a volcanic conduit controls the eruption style and explosivity based on deformation experiments of vesicular magma linked with synchrotron radiation x ray radiography and computed tomography we observed for the first time in situ that the shear localization caused magma fracturing and formed a slip plane and thus inhibited deformation and outgassing elsewhere we also observed the compaction of vesicular magma into a dense lava as a result of outgassing when shear localization did not occur in a natural setting shear localizes along the edges of a volcanic conduit where the strain rate is high causing a highly permeable fracturing layer to form at the conduit s edge and leaving less sheared and less outgassed magma at its center the less outgassed magma in the center may ascend rapidly and cause explosive volcanism non explosive lava effusion may occur only when shear localization does not occur effectively this new view explains the rapid ascent of viscous magma and the formation of pyroclasts with contrasting vesicularity pyroclastic obsidian and highly vesiculated pumice

strain induced magma degassing insights from simple shear experiments on bubble bearing melts experiments have been performed to determine the effect of deformation on degassing of bubble bearing melts cylindrical specimens of phonolitic composition initial water content of 1 5 wt and 2 vol bubbles have been deformed in simple shear torsional configuration in an internally heated paterson type pressure vessel at temperatures of 798 848 k 100 180 mpa confining pressure and different final strains micro structural analyses of the samples before and after deformation have been performed in two and three dimensions using optical microscopy a nanotomography machine and synchrotron tomography the water content of the glasses before and after deformation has been measured using fourier transform infrared spectroscopy ftir in samples strained up to a total of 2 the bubbles record accurately the total strain whereas at higher strains 10 the bubbles become very flattened and elongate in the direction of shear the residual water content of the glasses remains constant up to a strain of 2 and then decreases to about 0 2 wt at 10 results show that strain enhances bubble coalescence and degassing even at low bubble volume fractions noticeably deformation produced a strongly water under saturated melt this suggests that degassing may occur at great depths in the volcanic conduit and may force the magma to become super cooled early during ascent to the earth s surface potentially contributing to the genesis of obsidian

initiation and flow behavior of the 1980 pine creek and muddy river lahars mount st helens washington two large high velocity lahars volcanic debris flows were triggered by a pyroclastic surge during the first few minutes of the may 18 1980 eruption of mount st helens the initial surge cloud evolved progressively by gravity segregation from a gas mobilized highly inflated density flow to a dense water mobilized basal debris flow lahar and accompanying ash cloud as it flowed down the east flank of the volcano the main source of the water for the lahars was probably from eroded snow and ice incorporated into the flow by turbulent mixing but ground water expelled together with the rock debris by the initiating volcanic explosions also may have contributed peak lahar discharge from the pine muddy fan upper smith creek and ape canyon probably exceeded 250 000 m 3 s initially but decreased exponentially in the downstream direction total volume of the lahars was in excess of 1 4 10 7 m 3 initial peak flow velocities in excess of 30 m s also decreased markedly downstream where flow was not impeded velocity was strongly related to the depth slope term r 2 3 s 1 2 from the manning uniform flow equation as a power law function during much of the route traveled lahar flow appears to have been supercritical deposits left in channels were generally thin relative to flow depth 0 to 2 5 m particles up to small boulder size were randomly distributed in the poorly sorted nonstratified matrix indicating complete suspension in a fully developed debris flow slurry however much larger clasts were transported as bed load computed sediment concentrations of matrix slurry samples ranged from 84 to 91 solids by weight and were similar for the two lahars two indirect methods for computing peak flow velocity previously only tentatively applied to debris flows were tested for accuracy by comparing computed lahar arrival times with recorded arrival times at swift reservoir the computed velocities appear to be 15 slower than the recorded velocities which is consistent with the restriction that the velocity formulas produce only minimum values

transverse architecture of lahar terraces inferred from radargrams preliminary results from semeru volcano indonesia semeru volcano is the highest mountain of java indonesia and a vulcanian explosion occurs every 15 minutes on average since 1967 thus a constantly renewed stock of material and the heavy monsoon rainfall 3700 mm yr 1 at 1500 m above sea level a s l provide a perfect setting for the study of lahars and their deposits hence we examined the architecture of lahars terraces 9 5 km from the summit in the curah lengkong valley we first used ground penetrating radar gpr over vertical exposures of the lahars cut bank terraces this allowed us to better understand transversal radargrams across terraces which are not visually accessible in the field preliminary results from a single radargram are very instructive since 1 they prove that the lateral architecture does not correspond to that observed from banks only 2 we could observe the presence of lenses and stratigraphic discontinuities 3 the setting of the various units can also help reconstruct deposition processes and the chronology of different units in order to finalize these preliminary results we however need to perform multiple gpr radargrams and provide a complete set of results copyright 2010 john wiley sons ltd

so2 emissions at semeru volcano indonesia characterization and quantification of persistent and periodic explosive activity we present the first measurements of so2 emissions at semeru volcano indonesia using an so2 camera activity at semeru is characterized by quiescent degassing interspersed with short lived explosive events with low ash burden the interval between explosions was measured at 32 1 15 7 min in a webcam survey of the volcano between the months of june and december 2013 we distinguish between two types of events shorter events type i similar to 5 min duration with emissions returning quickly to baseline levels and longer events type ii similar to 15 min duration often showing multiple pulses and a longer period of increased emissions before a return to quiescent levels type i events represent 90 of the activity and release an average of 200 500 kg of so2 per event the single type ii event we documented with the so2 camera released a total of 1460 kg of so2 we estimate the daily average emissions of semeru to be 21 71 t d 1 of so2 amounting to a yearly output of 8 26 gg 8000 26 000 metric tons with 35 65 released during explosive events the time series patterns of degassing are consistent with the existence of a viscous plug at the top of the conduit which seals the conduit immediately prior to explosive events causing pressurization of the underlying magma followed by a sudden release of gas and fragmented magma c 2015 elsevier b v all rights reserved

insights into lahar deposition processes in the curah lengkong semeru volcano indonesia using photogrammetry based geospatial analysis near surface geophysics and cfd modelling abstract semeru volcano is an active stratovolcano located in east java indonesia where historic lava flows occasional pyroclastic flows and vulcanian explosions on average every 5 min to 15 min generate a stock of material that is remobilized by lahars mostly occurring during the rainy season between october and march every year several lahars flow down the curah lengkong valley on the south east flank of the volcano where numerous lahar studies have been conducted in the present contribution the objective was to study the spatial distribution of boulder size clasts and try to understand how this distribution relates to the valley morphology and to the dynamic and deposition dynamic of lahars to achieve this objective the method relies on a combination of 1 aerial photogrammetry derived geospatial data on boulders distribution 2 ground penetrating radar data collected along a 2 km series of transects and 3 a cfd model of flow to analyse the results from the deposits results show that

the net water circulation in the far northern great barrier reef abstract the 500 km long far northern great barrier reef fngbr is a semi enclosed sea with little connectivity with the rest of the gbr further south its mean circulation is controlled by the prevailing southeasterly northwestward wind that generates a wind driven mean longshore flow that is enabled by an inflow of oceanic water in the south from an examination of single point mid depth current meter data at ten sites over one year it appears that there is no net current during calm weather which implies that the northward north queensland coastal current in the adjoining coral sea does not intrude in the fngbr only about 20 40 of the wind driven longshore transport continues northward to exit the fngbr through torres strait because of blockage by reefs shoals and islands and by the tidal friction effect in shallow waters the remaining 60 80 of the flow appears to be deflected seaward to the coral sea in the north an observation that appears to be supported by oceanographic modelling this situation differs from that in the central and southern great barrier reef where the southward flowing east australian current intrudes on the shelf and generates a net current even during calm weather

in situ x ray tomographic microscopy observations of vesiculation of bubble free and bubble bearing magmas magma degassing is thought to play a major role in magma fractionation transport storage and volcanic eruption dynamics however the conditions that determine when and how magma degassing operates prior to and during an eruption remain poorly constrained we performed experiments to explore if the initial presence of gas bubbles in magma influences the capability of gas to escape from the magma vesiculation of natural h2o poor 1 wt silicic obsidian glasses was investigated by in situ high temperature above the glass transition experiments using synchrotron based x ray tomographic microscopy with high spatial 3 m pixel and temporal resolution 1 second per 3d dataset as a validation a second set of experiments was performed on identical starting materials using a karl fisher titration setup to quantify the amount of extracted gas that escapes via volatile diffusion and or bubble coalescence during vesiculation in both sets of experiments vesiculation was triggered by heating the samples at room pressure our results suggest that the presence of pre existing gas bubbles during a nucleation event significantly decreases the tendency of bubbles to coalesce and inhibits magma outgassing in contrast in initially bubble free samples the nucleation and growth of bubbles is accompanied by significant coalescence and outgassing we infer that volatile undersaturated i e bubble free magmas in the reservoirs are more likely to erupt effusively while the presence of excess gas already at depth i e bubble bearing systems increases the likelihood of explosive eruptions

high resolution unstructured meshes for hydrodynamic models of the great barrier reef australia accuracy and mesh generation are key issues for the high resolution hydrodynamic modelling of the whole great barrier reef our objective is to generate suitable unstructured grids that can resolve topological and dynamical features like tidal jets and recirculation eddies in the wake of islands a new strategy is suggested to refine the mesh in areas of interest taking into account the bathymetric field and an approximated distance to islands and reefs such a distance is obtained by solving an elliptic differential operator with specific boundary conditions meshes produced illustrate both the validity and the efficiency of the adaptive strategy selection of refinement and geometrical parameters is discussed

river plumes coral reefs and mixing in the gulf of papua and the northern great barrier reef abstract the mean annual freshwater discharge in the gulf of papua principally from the fly kikori and purari rivers is estimated to be 13000 m 3 s 1 water from these rivers forms a low salinity surface layer in the gulf where it has a residence time of about two months and flows generally eastward a small fraction of this water intrudes through bligh entrance on the great barrier reef continental shelf horizontal patchiness and mixing of these intruding waters with shelf waters are considerably enhanced by secondary circulation wakes around coral reefs the wakes shapes visible in enhanced landsat imagery are similar to those around cylinders and plates in laboratory experiments at low reynolds numbers topographically enhanced mixing may explain why the cross shelf gradients of temperature and of the structure of fish communities are smaller in the northern region than in the central region of the great barrier reef

erosion and aggradation on persistently active volcanoes a case study from semeru volcano indonesia erosion processes on active volcanoes in humid climates result in some of the highest sediment yields on earth episodic sediment yields after large eruptions have been evaluated but not the long term and continuous patterns on persistently active volcanoes we have used high spatial resolution satellite imagery and dems dsms along with field based geologic mapping to assess accurately sediment budgets for the active semeru volcano in java indonesia patterns of aggradation and degradation on semeru differ from that of other active volcanoes because 1 both episodic pyroclastic density currents pdc and continuous supplies of tephra generate pulses of sediment 2 sediment is transferred via cycles of aggradation and degradation that continue for 15 years in river channels after each pdc producing eruption and 3 rain triggered lahars remove much greater material than fluvial transport during long intense rainfall events the geomorphic response of two of semeru s rivers to volcanic sediment migration indicates that 1 each river experiences alternating aggradation and degradation cycles following pdc producing eruptions and 2 spatial patterns of sediment transfer are governed by geomorphic characteristics of the river reaches usually high degradation in the steep source reach is followed by a long bypassing middle reach aggradation predominates in the depositional reaches further down valley on the ring plain average sediment yields 103 105 t km2 year at persistently active volcanoes are two to three orders of magnitude lower than sediment yields after large and infrequent eruptions but the continuous and steady sediment transfer in rivers removes more sediment on a mid term 10 years to long term 30 years basis in contrast to the trend observed on composite cones after large and infrequent eruptions decay of sediment yields is not exponential and river channels do not fully recover at steadily active volcanoes as episodic inputs from baf eruptions superimposed on the background remobilization of daily tephra have a greater cumulative effect

synchrotron based x ray tomographic microscopy for rock physics investigations abstractsynchrotron radiation x ray tomographic microscopy is a nondestructive method providing ultra high resolution 3d digital images of rock microstructures we describe this method and to demonstrate its wide applicability we present 3d images of very different rock types berea sandstone fontainebleau sandstone dolomite calcitic dolomite and three phase magmatic glasses for some samples full and partial saturation scenarios are considered using oil water and air the rock images precisely reveal the 3d rock microstructure the pore space morphology and the interfaces between fluids saturating the same pore we provide the raw image data sets as online supplementary material along with laboratory data describing the rock properties by making these data sets available to other research groups we aim to stimulate work based on digital rock images of high quality and high resolution we also discuss and suggest possible applications and research directions that can be pursued on the basis o

wind driven circulation on the northern great barrier reef continental shelf in summer abstract observations of wind atmospheric pressure sea levels and current are presented for the northern 9 14 s great barrier reef continental shelf for november 1981 to may 1982 strong low frequency non tidal oceanic fluctuations were observed resulting in alternating northward and southward transport and a weak mean circulation and are the result of long arrested topographic waves driven by a quasi steady longshore wind stress and damped by turbulent bottom friction the coefficient of friction for low frequency currents is found to be proportional to the tidal velocities the coefficient is also found to be much larger than that in the central 15 19 s region of the great barrier reef continental shelf and this difference is attributed to the greatly enhanced energy dissipation by secondary circulation around coral reefs in the reef studded northern region sough of cape york 10 5 s the primary effect of the cross shelf wind is to complement the geostrophic set up due to the longshore current intense tidal currents in the vicinity of cape york combined with a dissipative western boundary in torres strait appear to prevent long wave propagation north of cape york where a steady state analytical model is used to show that both cross and longshore wind components generate the reversing currents observed through bligh entrance

factors controlling permeability porosity relationships in magma a model has been developed to investigate the sensitivity of magma permeability k to various parameters power law relationships between k and porosity are revealed in agreement with previous experimental and theoretical studies these relationships take the form mathtype mtef 2 1 feaaeaart1ev0aaatcvaufkttlearuavtnhis1mbaexatlxbi9gbae rbd9wdylwzybwexlmbbxgbcf2cpn2qvrwzqf2zlnharyavp1wzzbit ldhis9wbh5garqqtubsr4rnchbgeagqivci8ffyjh8sipiydhavhbb f9v8qqaqfr0xc9pk0xbba9q8wqffeay bilkvclq jhqpepeea0 as 0fb9pgeayrxxe9vr0 vr0 vqpwqaaeaabigaciaacaqabeaadaabau aaaoqaaiqbdugarzaajagaeyypa0jaem4aasmaei4la8iaemocai3a awbaasqabeaacqaiyagmaagccqgh9aqpcqwghbqycqggoaakcqahgp gzcqghsislcqahgpgzdawgaawcbagaem4yammaemocaihabeaakiab cmcapmaacaaaleqabagaemoyaigaaaaa 4ce4 hat k k r 2 a phi phi cr b where r is the mean bubble radius cr is the percolation threshold below which permeability is zero and a and b are constants it is discovered that mathtype mtef 2 1 feaaeaart1ev0aaatcvaufkttlearuavtnhis1mbaexatlxbi9gbae rbd9wdylwzybwexlmbbxgbcf2cpn2qvrwzqf2zlnharyavp1wzzbit ldhis9wbh5garqqtubsr4rnchbgeagqivci8ffyjh8sipiydhavhbb f9v8qqaqfr0xc9pk0xbba9q8wqffeay bilkvclq jhqpepeea0 as 0fb9pgeayrxxe9vr0 vr0 vqpwqaaeaabigaciaacaqabeaadaabau aaaoqaaiqbdugarzaajagaeyoei0iaeqoxdygaaa 3cdb hat k phi relationships are independent of bubble size the percolation threshold was found to lie at around 30 porosity polydisperse bubble size distributions bsds give permeabilities around an order of magnitude greater than monodisperse distributions at the same porosity if bubbles are elongated in a preferred direction then permeability in this direction is increased but perpendicular to this direction permeability is unaffected in crystal free melts the greatest control on permeability is the ease of bubble coalescence in viscous magmas or when the cooling time scale is short bubble coalescence is impeded and permeability is much reduced this last effect can cause variations in permeability of several orders of magnitude

bubble growth in highly viscous melts theory experiments and autoexplosivity of dome lavas we examine the physics of growth of water bubbles in highly viscous melts during the initial stages diffusive mass transfer of water into the bubble keeps the internal pressure in the bubbles close to the initial pressure at nucleation growth is controlled by melt viscosity and supersaturation pressure and radial growth under constant pressure is approximately exponential at later stages internal pressure falls radial growth decelerates and follows the square root of time at this stage it is controlled by diffusion the time of transition between the two stages is controlled by the decompression melt viscosity and the peclet number of the system the model closely fit experimental data of bubble growth in viscous melts with low water content close fit is also obtained for new experiments at high supersaturation high peclet numbers and high variable viscosity near surface degassed silicic melts are viscous enough so that viscosity controlled growth may last for very long times using the model we demonstrate that bubbles which nucleate shortly before fragmentation cannot grow fast enough to be important during fragmentation we suggest that tiny bubbles observed in melt pockets between large bubbles in pumice represent a second nucleation event shortly before or after fragmentation the presence of such bubbles is an indicator of the conditions at fragmentation the water content of lavas extruded at lava domes is a key factor in their evolution melts of low water content 0 2 wt are too viscid and bubbles nucleated in them will not grow to an appreciable size bubbles may grow in melts with 0 4 wt water the internal pressure in such bubbles may be preserved for days and the energy stored in the bubbles may be important during the disintegration of dome rocks and the formation of pyroclastic flows

a multi scale model of the hydrodynamics of the whole great barrier reef an unstructured mesh parallel hydrodynamic model of the whole great barrier reef is presented this model simultaneously simulates most scales of motion it allows interactions between small and large scale processes the depth averaged equations of motion are discretized in space by means of a mixed finite element formulation while the time marching procedure is based on a third order explicit adams bashforth scheme the mesh is made up of triangles their size and shape can be modified easily so as to resolve a wide range of scales of motion from those of the regional flows to those of the eddies or tidal jets that develop in the vicinity of reefs and islands the forcings are the surface wind stress the tides and the inflow from the coral sea east australian current coral sea coastal current the latter two forcings being applied along the open boundaries of the computational domain the numerical results compare favourably with observations of both longshore currents and the local perturbations due to narrow reef passages comparisons are also performed with the simulations of a three dimensional model applied to a small domain centered on rattray island showing that both models produce similar horizontal flow fields for a structured mesh model to yield results of the same accuracy there is no doubt that the computational cost would be much higher

in situ bubble vesiculation in silicic magmas volatile degassing is a major process driving volcanic eruptions therefore a full understanding of mechanisms ranging from bubble nucleation growth coalescence to magma fragmentation is required we have simulated magma degassing during ascent in the volcanic conduit by depressurizing hydrated haplogranite melts in high pressure and high temperature optical cells a hydrothermal diamond anvil cell and an internally heated pressure vessel fitted with sapphire windows this allowed the whole process of bubble nucleation growth and coalescence to be directly observed in situ through images captured from the recording videos bubble nucleation pressures number densities growth laws and characteristics of coalescence were estimated as a function of melt water content decompression rate and temperature melt vapor surface tension during bubble nucleation and coalescence was calculated our data show good agreement with those previously obtained in classical vessels methodological improvements are proposed for the experimental simulation of magma degassing in volcanic conduits

decoupling of small volume pyroclastic flows and related hazards at merapi volcano indonesia the november 1994 eruption at merapi volcano provided good evidence of decoupling of dome collapse pyroclastic flows and of large scale detachment of an ash cloud surge acs component from the basal block and ash flow baf timing and stratigraphic relationships of the largest 1994 acs indicate that this escaped from the valleys travelled well ahead of the baf arrived at the termination tens of seconds before it and deposited a discrete acs deposit beneath the baf unit this suggests that the acs detachment mostly occurred relatively high on the volcano slope likely at the foot of the proximal cone later pyroclastic flow eruptions in january 1997 and july 1998 also showed evidence of acs detachment although to a lesser extent suggesting that acss could be a frequent hazard at merapi volcano based on an extensive review of the available literature and on field investigations of historical deposits we show here that flow decoupling and acs detachment in the way inferred from the 1994 eruption is a common process at merapi the acs related destructions outside valleys were frequently reported in the recent past activity of the volcano i e in at least 16 pyroclastic flow eruptions since 1927 destruction occurred systematically in eruptions where maximum runout of the bafs was 6 5 km or more and occurred rarely for baf runouts of 4 5 km or less the acs deposits have been recognized beneath some valley filling baf units we attribute to some recent destructive eruptions i e the 1930 1954 1961 and 1969 eruptions topographic conditions at merapi volcano favouring acs detachment include a the high slope 30 of the proximal cone leading to high proximal velocities of the pyroclastic flows and thus to the transfer of large amounts of particles into the ash cloud b the strong break in slope at the foot of the proximal cone where the velocity of the basal baf is strongly reduced and a major acs component is thought to form and detach by shearing over the baf and c the small depth of most valleys in the first kilometres beyond the foot of the cone which allows minor acs components to escape from the valleys during travel of the baf however flow decoupling and acs detachment occur for only some of the numerous pyroclastic flows that follow the same path in a given eruption this indicates that topography alone cannot lead to flow decoupling we suggest two factors that control flow decoupling and its extent the main one is flow volume and thus flux as both are correlated in almost instantaneous dome collapse events as suggested by the observed relationship between flow decoupling and the travel distance of the pyroclastic flows the second factor is the amount of available ash in the flow at its early stage which influences the mass and thus momentum of the ash cloud the amount of ash in the pyroclastic flows of merapi may depend on several factors among which are a the physical and thermal state of the part of the active dome that collapses and b the proportion of older cold rocks incorporated in the flow either by undermining of surrounding summit rocks by the current pyroclastic flow activity or by erosion on the upper slopes

the effect of varying acquisition parameters on the interpretation of sir c radar data the virunga volcanic chain abstract in 1994 the spaceborne imaging radar experiment c sir c acquired five data takes with different acquisition parameters over the virunga volcanic chain zaire changes in incidence angle 20 0 48 1 look direction west and east looking and pulse bandwidth 10 mhz 20 mhz and 40 mhz affect the geologic interpretations drawn from these data we examine differences in spatial distortion of features near the summit of nyiragongo volcano finding that opposite look direction data are helpful in interpreting volcanic features such as the shape of small craters in areas of high relief the relative brightness of lava flows and vegetation change and actually reverse for different wavelengths and polarizations although l band data are best for mapping the outline of the flows c and x band cross polarization data show differences in backscatter intensity between and within flows in addition our ability to discriminate lava flows and vents from surrounding vegetation is strongly influenced by pulse bandwidth resolution and angle of incidence pulse bandwidth is the most important parameter in mapping small topographic features such as volcanic cones and a set of particularly thick flows on the flanks of karisimbi volcano these examples illustrate important considerations of the tradeoffs and priorities in acquisition parameters for future missions such as envisat as well as potential pitfalls for interpretation of existing data

determining flow type shear rate and shear stress in magmas from bubble shapes and orientations we interpret the shear environments that produced bubble textures in obsidian samples using the results of theoretical numerical and experimental studies on the deformation of bubbles in shear flows in particular we use the shapes and orientations of bubbles vesicles in obsidian to estimate shear rates and shear stresses and assess flow type simple vs pure shear this technique can be used to determine shear rates in volcanic conduits the origin of pyroclastic obsidian and the emplacement history and dynamics of obsidian flows a spherical bubble in a viscous fluid subjected to a low reynolds number steady flow field deforms until it reaches a steady shape and orientation bubble deformation is governed by the competing stresses from shearing that deforms and surface tension that rerounds the ratio of these stresses is the capillary number ca because the relationships among ca bubble orientation and shape differ for pure and simple shear we can distinguish between these flow types using preserved bubble geometries furthermore because ca is a function of shear rate we can use relationships between ca and the magnitude of deformation to calculate shear rates when melt viscosity and surface tension are known to demonstrate the potential of the technique we examine three obsidian samples chosen for diversity of origin and texture two of the samples have low crystallinities and banding defined by layers of different vesicularity bubble geometries in a spatter fed obsidian flow sample record deformation by pure shear whereas a juvenile obsidian clast from a pyroclastic fall deposit records predominantly simple shear a third sample from an obsidian flow has banding marked by variable concentrations of microlites and shows bubble deformation most consistent with dominantly simple shear and some bubble relaxation the highest shear rate and shear stress are recorded by the pyroclastic obsidian shear rate 0 01 s 1 shear stress 60 kpa the spatter fed obsidian flow sample deformed by pure shear records the lowest shear stress 4 9 kpa the obsidian flow sample deformed by simple shear records the lowest shear rates 10 6 6 10 6 9 s 1 despite high shear stresses 22 36 kpa because of the high viscosity of the degassed rhyolite 0 13 wt water

landscape and sedimentary response to catastrophic debris avalanches western taranaki new zealand abstract catastrophic volcanic debris avalanches reshape volcanic edifices with up to half of pre collapse cone volumes being removed deposition from this debris avalanche deposit often fills and inundates the surrounding landscape and may permanently change the distribution of drainage networks on the weakly incised mt taranaki ring plain volcanic debris avalanche deposits typically form a large wedge shape in plan view over all flat lying fans following volcanic debris avalanches a period of intense re sedimentation commonly begins on ring plain areas particularly in wet or temperate climates this is exacerbated by large areas of denuded landscape ongoing instability in the scarp source region damming of river stream systems and in some cases inherent instability of the volcanic debris avalanche deposits in addition on mt taranaki the collapse of a segment of the cone by volcanic debris avalanche often generates long periods of renewed volcanism generating large volumes of juvenile tephra onto unstable and unvegetated slopes or construction of new domes with associated rock falls and block and ash flows the distal ring plain impact from these post debris avalanche conditions and processes is primarily accumulation of long run out debris flow and hyperconcentrated flow deposits with a variety of lithologies and sedimentary character common to these post debris avalanche units is evidence for high water content flows that are typically non cohesive hence sedimentary variations in these units are high in lateral and longitudinal exposure in relation to local topography the post collapse deposits flank large scale fans and hence similar lithological and chronological sequences can form on widely disparate sectors of the ring plain these deposits on mt taranaki provide a record of landscape response and ring plain evolution in three stages that divide the currently identified warea formation 1 the deposition of broad fans of material adjacent to the debris avalanche unit 2 channel formation and erosion of stage 1 deposits primarily at the contact between debris avalanche deposits and the stage 1 deposits and the refilling of these channels and 3 the development of broad tabular sheet flows on top of the debris avalanche leaving sediments between debris avalanche mounds after a volcanic debris avalanche these processes represent an ever changing and evolving hazard scape with hazard maps needing to be regularly updated to take account of which stage the sedimentary system is in