catastrophic debris avalanche deposit of socompa volcano northern chile between 10 000 and 500 yr ago the socompa volcano in northern chile experienced a catastrophic collapse of a 70 deg sector of the original cone causing a debris avalanche that descended nearly 3000 m vertically and traveled more than 35 km from the volcano the deposits cover some 490 sq km and have a minimum volume of 15 cu km parts of the original cone slumped in a nearly coherent form and are now preserved as large blocks more than 400 m high the primary avalanche traveled northwestward over sloping ground before coming to rest transiently forming a prominent marginal ridge and then slid away northeastward to form a secondary flow overriding much of the primary avalanche deposit abundant prismatic jointed dacite blocks within the debris avalanche deposit and a thin fine grained pumiceous deposit beneath it suggest that the collapse was triggered by magmatic activity and may have been accompanied by a violent lateral blast collapse was followed by eruption of pumiceous pyroclastic flows and extrusion of voluminous dacite domes

on the mobility of pyroclastic currents in light of deposit thickness and clast size trends abstract pyroclastic currents pcs represent the most hazardous manifestations of explosive volcanic activity the evaluation of their mobility as related to the eruptive source parameters and the interactions with the surroundings along their path is crucial for hazard assessment at active volcanoes in order to define the areas exposed to their impacts here we report on two case studies from the latera volcanic complex vulsini volcanic district central italy that may approach the two end members of the classical spectrum of pc dynamics in terms of particle concentration and dominant flow regime i e dilute turbulent vs concentrated laminar pcs for the two examples we document specific and contrasting variation trends of deposit thickness and maximum lithic and pumice clast sizes with distance from vent which provide a further characterization in terms of forced vs inertial flow behavior in the first case thickness and maximum lithic and pumice sizes show a mild linear decrease with distance implying a sort of balance between forced and inertial regimes flow pressure and mass progressively drop via deposition along with flow competence for given source conditions i e mass eruption rate fountaining height erupting mixture etc and slope angle of topography the pc runout depends primarily on the waning density contrast between the flow and the surrounding atmosphere density current ending with the loft of the current the second case representative of moderate to large volume dense pcs derived by continuous feeding with high mass discharge rate i e from collapsing plinian columns or caldera forming events shows an increase of deposit thickness with distance which is accompanied by opposite lithic and pumice clast size distance trends i e decreasing lithic sizes and increasing pumice sizes downcurrent compatible with high particle concentration and forced non turbulent granular flow regime by analogy with the mobility of dry debris flows we suggest that the sliding component of transport which prevails in proximal to intermediate settings may account for the prevailing tendency of the pc to transport than to deposit which leaves behind relatively thin sheets with coarse lithics while the dominant spreading component downcurrent would result in increasing accumulation and the stacking of coarse pumice rich flow lobes in more distal settings the spreading component of transport would become more and more important with increasing material supply at pc source resulting in additional runout these findings cast new light on the first order controlling factors of flow mobility for the two pc end members laying the groundwork for determining the most relevant pc hazard parameters i e the maximum runout and the flow properties upon impact dynamic pressure burial potential temperature

mobility of pyroclastic flows and surges at the soufriere hills volcano montserrat the soufriere hills volcano on montserrat has produced avalanche like pyroclastic flows formed by collapse of the unstable lava dome or explosive activity pyroclastic flows associated with dome collapse generate overlying dilute surges which detach from and travel beyond their parent flows the largest surges partially transform by rapid sedimentation into dense secondary pyroclastic flows that pose significant hazards to distal areas different kinds of pyroclastic density currents display contrasting mobilities indicated by ratios of total height of fall h run out distance l area inundated a and volume transported v dome collapse flow mobilities characterised by either l h or a v2 3 resemble those of terrestrial and extraterrestrial cold rockfalls dade and huppert 1998 in contrast fountain fed pumice flows and fine grained secondary pyroclastic flows travel slower but for comparable initial volumes and heights can inundate greater areas

pyroclastic flows from the 1991 eruption of unzen volcano japan pyroclastic flows from unzen were generated by gravitational collapse of the growing lava dome as soon as the parental lobe failed at the edge of the dome spontaneous shattering of lava occurred and induced a gravity flow of blocks and finer debris the flows had a overhanging tongue like head and cone or rollershaped vortices expanding outward and upward most of the flows traveled from 1 to 3 km but some flows reached more than 4 km burning houses and killing people in the evacuated zone of kita kamikoba on the eastern foot of the volcano the velocities of the flows ranged from 15 to 25 m s on the gentle middle flank observations of the flows and their deposits suggest that they consisted of a dense basal avalanche and an overlying turbulent ash cloud the basal avalanche swept down a topographic low and formed to tongue like lobe having well defined levees it is presumed to have moved as a non newtonian fluid the measured velocities and runout distances of the flows can be matched to a bingham model for the basal avalanche by the addition of turbulent resistance the rheologic model parameters for the 29 may flow are as follows the density is 1300 kg m3 the yield strength is 850 pa the viscosity is 90 pa s and the thickness of the avalanche is 2 m the ash cloud is interpreted as a turbulent mixing layer above the basal avalanche the buoyant portions of the cloud produced ash fall deposits whereas the dense portions moved as a surge separated from the parental avalanche the ash cloud surges formed a wide devastated zone covered by very thin debris the initial velocities of the 3 june surges when they detached from avalanches are determined by the runout distance and the angle of the energy line slope a comparison between the estimated velocities of the 3 june avalanches and the surges indicates that the surges that extended steep slopes along the avalanche path detached directly from the turbulent heads of the avalanches the over running surge that reached kita kamikoba had an estimated velocity higher than that of the avalanche this farther travelled surge is presumed to have been generated by collapse of a rising ash cloud plume

grain scale pressure variations and chemical equilibrium in high grade metamorphic rocks in the classical view of metamorphic microstructures fast viscous relaxation and so constant pres sure is assumed with diffusion being the limiting factor in equilibration this contribution is focused on the only other possible scenario fast diffusion and slow viscous relaxation and brings an alter native interpretation of microstructures typical of high grade metamorphic rocks in contrast to the pressure vessel mechanical model applied to pressure variation associated with coesite inclusions in various host minerals a multi anvil mechanical model is proposed in which strong single crystals and weak grain boundaries can maintain pressure variation at geological time scales in a polycrystalline material in such a mechanical context exsolution lamellae in feldspar are used to show that feldspar can sustain large differential stresses 10 kbar at geological time scales furthermore it is argued that the existence of grain scale pressure gradients combined with diffusional equilibrium may explain chemical zoning preserved in reaction rims assuming zero net flux across the microstructure an equilibrium thermodynamic method is introduced for inferring pressure variation corresponding to the chemical zoning this new barometric method is applied to plagioclase rims around kyanite in fel sic granulite bohemian massif czech republic yielding a grain scale pressure variation of 8 kbar in this approach kinetic factors are not invoked to account for mineral composition zoning preserved in rocks metamorphosed at high grade

elasticity of plagioclase feldspars elastic properties are reported for eight plagioclase feldspars that span compositions from albite nasi3alo8 to anorthite casi2al2o8 surface acoustic wave velocities measured using impulsive stimulated light scattering and compliance sums from high pressure x ray compression studies accurately determine all 21 components of the elasticity tensor for these triclinic minerals the overall pattern of elasticity and the changes in individual elastic components with composition can be rationalized on the basis of the evolution of crystal structures and chemistry across this solid solution join all plagioclase feldspars have high elastic anisotropy a the direction perpendicular to the b and c axes is the softest direction by a factor of 3 in albite from albite to anorthite the stiffness of this direction undergoes the greatest change increasing twofold small discontinuities in the elastic components inferred to occur between the three plagioclase phases with distinct symmetry c1 i1 and p1 appear consistent with the nature of the underlying conformation of the framework linked tetrahedra and the associated structural changes measured body wave velocities of plagioclase rich rocks reported over the last five decades are consistent with calculated hill averaged velocities using the current moduli this confirms long standing speculation that previously reported elastic moduli for plagioclase feldspars are systematically in error the current results provide greater assurance that the seismic structure of the middle and lower crusts can be accurately estimated on the basis of specified mineral modes chemistry and fabric

simulation of block and ash flows and ash cloud surges of the 2010 eruption of merapi volcano with a two layer model a new depth averaged model has been developed for the simulation of both concentrated and dilute pyroclastic currents and their interactions the capability of the model to reproduce a real event is tested for the first time with two well studied eruptive phases of the 2010 eruption of merapi volcano indonesia we show that the model is able to reproduce quite accurately the dynamics of the currents and the characteristics of the deposits thickness extent volume and trajectory the model needs to be tested on other well studied eruptions and the equations could be refined but this new approach is a promising tool for the understanding of pyroclastic currents and for a better prediction of volcanic hazards

rapid topographic change measured by high resolution satellite radar at soufriere hills volcano montserrat 2008 2010 high resolution satellite radar observations of erupting volcanoes can yield valuable information on rapidly changing deposits and geomorphology using the terrasar x tsx radar with a spatial resolution of about 2 m and a repeat interval of 11 days we show how a variety of techniques were used to record some of the eruptive history of the soufriere hills volcano montserrat between july 2008 and february 2010 after a 15 month pause in lava dome growth a vulcanian explosion occurred on 28 july 2008 from a vent that was hidden by dense cloud we were able to show the civil authorities using tsx difference images of surface roughness change that this explosion had not disrupted the dome sufficiently to warrant continuation of a previous precautionary evacuation change difference images also proved to be valuable in mapping new pyroclastic flow deposits the valley occupying block and ash component tended to increase backscatter and the marginal surge deposits to reduce it with the pattern reversing after the event due to erosion and deposition by comparing east and west looking images acquired 12 h apart the deposition of some individual pyroclastic flows can be inferred from change differences some of the narrow upper sections of valleys draining the volcano received many tens of metres of rockfall and pyroclastic flow deposits over periods of a few weeks by measuring the changing radar shadows cast by these valleys in tsx images the changing depth of infill by deposits could be estimated in addition to using the amplitude data from the radar images we also used their phase information within the insar technique to calculate the topography during a period of no surface activity this enabled areas of transient topography crucial for directing future flows to be captured

sequential plug formation disintegration by vulcanian explosions and the generation of granular pyroclastic density currents at tungurahua volcano 2013 2014 ecuador following 84 years of repose tungurahua volcano ecuador initiated its present eruptive episode in october 1999 but its pdc activity only began in july 2006 a period of highly energetic vulcanian eruptions started in 2012 those of 14 july 2013 18 october 2013 and 1 february 2014 being the most important these eruptions were well monitored by a 5 station broadband seismic and acoustic array repeated repose intervals of 3 5 months between vulcanian events vei 2 suggest that gases in the ascending juvenile magma experienced sequential pressurization cycles as magma of preceding eruptive events solidified to form plugs that sealed the conduit every 34 months plug failure occurred abrupt decompression followed and the resulting vulcanian explosions are associated with the highest seismic and acoustic energies ever registered anywhere small to moderate sized pdc flows associated with the explosions and fountain collapses were generated and traveled 7 km down the steep n nw and w flanks of tungurahua s cone at velocities of 11 to 18 m s although a small lateral blast and its pdc were clocked at 33 m s descending the n flank the explosive fragmentation of the plugs a dense microcrystalline andesite and the juvenile magma a vesiculated glassy andesite comprise the principal rock fragments of the pdc deposits each deposit typically consisting of two layers a thin upper layer of large segregated and abraded clasts with few fines and a thicker lower layer that is fines rich with few large clasts many deposits were studied and photographed within a few days of their formation which are presented

a comparison of pyroclastic flow and debris avalanche mobility many pyroclastic flows have runout distances longer than expected from basic frictional arguments in these cases the ratio of the height descended h and the runout l are as small as 0 2 a feature which has been attributed to fluidization however significant fluidization by gases is now considered unlikely during emplacement of debris avalanches where h l and volume are inversely related we determine whether pyroclastic flows are more mobile than debris avalanches of the same volume and if different emplacement mechanisms are needed to describe their runout h l and volume data were compiled for 34 nonvolcanic and 40 volcanic debris avalanche deposits as well as 15 pyroclastic flow deposits systematic differences in the volume versus h l plots were explored by statistical analysis results show an inverse relationship between h l and volume for both nonvolcanic and volcanic debris avalanche deposits as expected and also for pyroclastic flow deposits regression lines for plots of pyroclastic flow and volcanic debris avalanche data are statistically indistinguishable and the non volcanic debris avalanche line is parallel to the other two we argue that the nonvolcanic and volcanic debris avalanche differences are due to material properties rather than emplacement mechanisms therefore since pyroclastic flows and volcanic debris avalanches have indistinguishable h l versus volume it is unlikely that pyroclastic flows have a significantly different primary emplacement mechanism based on the data in hand we conclude that it is unnecessary to invoke gas fluidization to explain the mobility of the types of pyroclastic flows examined or the excess runout of large volume debris avalanches

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

a conceptual model for block and ash flow basal avalanche transport and deposition based on deposit architecture of 1998 and 1994 merapi flows the 1998 block and ash flow baf deposits on the western flanks of merapi were described both immediately following emplacement and after one and two wet seasons of erosion this afforded a unique combination of data on deposit morphology and internal structure from proximal to distal reaches the deposits of the basal avalanches from individual baf events were classified into three major and two minor facies in channelised reaches primarily resulting from effects of channel confinement and slope termination reaches were classified into three facies related to preevent topography the deposit facies architecture was interpreted to understand particle transport and deposition within the framework of granular flow systematics the transport model we propose for these basal avalanches involves unsteady flow conditions generated by pulses of collapse as the source and or by development of kinetic waves during the granular flow the coarsest clasts along with low density material migrated to the wave pulse fronts within these flows whereas in bulk flow grain dispersive pressures and kinetic sieving result in coarsest clasts being buoyed to the flow top with this tendency being greatest on higher slopes greater kinetic energy and with greater flow confinement maximising particle collisions deposition begins as the flow reaches near its full extent an initial pulse or flow wave freezes rapidly from its base upward and its rear forward as it looses kinetic energy and dispersive pressure such that an upper higher energy part of the flow is still able to move downstream over the frozen base later waves or pulses then accrete progressively horizontally upslope banking up onto or overtopping earlier deposited sediment hence the overall flow freezes from its front to its tail at termination reaches in unconfined areas the overflowing upper part of flow gradually deposits from its base upward resulting in a slightly tapering sheet formed deposit marked by a front made up of wood fragments and large boulders on sudden slope breaks in termination areas piling up of sediment occurs in flat reaches producing whaleback type forms as the flows rapidly lost competence one implication of this model is that each kinetic wave or flow pulse crest developed within the basal avalanche represents a portion of greater flow depth or stage height hence development of these crests control the ability of parts of the basal avalanche to escape from confined channels and generate unexpected hazards

catastrophic debris avalanche from ancestral mount shasta volcano california a debris avalanche deposit extends 43 km northwestward from the base of mount shasta across the floor of shasta valley california where it covers an area of at least 450 km 2 the surface of the deposit is dotted with hundreds of mounds hills and ridges all formed of blocks of pyroxene andesite and unconsolidated volcaniclastic deposits derived from an ancestral mount shasta individual hills are separated by flat topped laharlike deposits that also form the matrix of the debris avalanche and slope northwestward about 5 m km radiometric ages of rocks in the deposit and of a postavalanche basalt flow indicate that the avalanche occurred between about 300 000 and 360 000 yr ago an inferred average thickness of the deposit plus a computed volume of about 4 km 3 for the hills and ridges indicate an estimated volume of about 26 km 3 making it the largest known quaternary landslide on earth

using tandem x to measure pyroclastic flow source location thickness and volume application to the 3rd june 2018 eruption of fuego volcano guatemala abstract the estimation of the volume of volcanic flows during an ongoing eruption is challenging but this information is crucial for improving risk assessment and for forecasting future events although previous studies have shown the ability of tandem x satellite data to derive the thickness and the volume of lava flow fields during effusive eruptions the method has not been explored yet for pyroclastic flows using bi static interferometry we produce tandem x dem on fuego volcano guatemala to measure the significant topographic changes caused by the 3rd june 2018 eruption which destroyed the town of san miguel los lotes we estimate the volume of the pyroclastic density currents pdcs to be 15 1 4 2 106 m3 the deposits are likely to be the source of lahars during future rainy seasons we identify the main channel of deposition positive elevation changes and the source region of pyroclastic material areas of significant substrate erosion and vegetation destruction negative elevation changes our results show that the june 3rd 2018 pyroclastic flow was predominantly composed of material which had gravitationally collapsed from a location close to the vent the eroded material increased the volume of the flow bulking and likely caused the run out distance of the 2018 pdc to be larger than previous eruptions 1999 2017 this study highlights the potential of remote sensing techniques for actively monitoring topography changes in inaccessible locations and to rapidly derive deposit volumes

a statistical study of trees damaged by the 22 november 1994 eruption of merapi volcano java indonesia relationships between ash cloud surges and block and ash flows abstract on 22 november 1994 after 2 years of dome growth merapi volcano generated pyroclastic flows and surges this eruption destroyed the south southwest flank that had been intact for several decades about 9 5 km 2 of forest were blown down a study of tree damage correlated with geological and eyewitness observations is used here to reconstruct the dynamics of the pyroclastic surges and block and ash flows of the 22 november eruption the main results are summarised in the form of maps showing blown down trunk directions and zones indicating the percentage of broken and downed trees these maps provide evidence for various aspects of the emplacement of the 1994 flows 1 pyroclastic flow generation from gravitational collapse of part of the active lava dome without significant initial explosion 2 the control of topography cliffs hills river channels on damage distribution and range 3 the genesis and decoupling of ash cloud surges from block and ash flows

the 2006 lava dome eruption of merapi volcano indonesia detailed analysis using modis tir abstract merapi is one of indonesia s most active and dangerous volcanoes prior to the 2010 vei 4 eruption activity at merapi during the 20th century was characterized by the growth and collapse of a series of lava domes periods of very slow growth were punctuated by short episodes of increased eruption rates characterized by dome collapse generated pyroclastic density currents pdcs an eruptive event of this type occurred in may june 2006 for effusive eruptions such as this detailed extrusion rate records are important for understanding the processes driving the eruption and the hazards presented by the eruption we use thermal infrared tir images from the moderate resolution imaging spectrometer modis instrument on nasa s aqua and terra satellites to estimate extrusion rates at merapi volcano during the 2006 eruption using the method of harris and ripepe 2007 we compile a set of 75 nighttime modis images of the eruptive period to produce a detailed time series of thermal radiance and extrusion rate that reveal multiple phases of the 2006 eruption these data closely correspond to the published ground based observational record and improve observation density and detail during the eruption sequence furthermore additional analysis of radiance values for thermal anomalies in band 21 3 959 m of modis images results in a new framework for detecting different styles of activity we successfully discriminate among slow dome growth rapid dome growth and pdc producing dome collapse we also demonstrate a positive correlation between pdc frequency and extrusion rate and provide evidence that extrusion rate can increase in response to external events such as dome collapses or tectonic earthquakes this study represents a new method of documenting volcanic activity that can be applied to other similar volcanic systems

the 1984 nuee ardente deposits of merapi volcano central java indonesia stratigraphy textural characteristics and transport mechanisms for many centuries merapi volcano has generated hot avalanches of blocks lapilli and ashes derived from the destruction of partially solidified viscous lava domes merapi type nuees ardentes on 15 june 1984 at least four nuees ardentes came down the southwest slope of the merapi the first and the last being responsible for more than 99 of the deposits which are now exposed the first nuee ardente a merapi type nuee ardente was produced by the destruction of the dome travelled 7 km from the crater leaving a measured deposit 2 7 m thick 4 km from the crater near its upper depositional limit regularly increasing to a maximum measured thickness of 12 m at the front of the deposit the lower contact is sharp non erosive with pines still rooted in the underlying paleosol the deposit consists of 50 ash 33 lapilli and 17 blocks with two subpopulations one rosin and one normal and is finespoor with less than 4 of fine ash d finer than 4 the deposit displays reverse population grading of both vesiculated and massive clasts and of the maximum grain size the maximum size significantly increases regularly down current over most of the exposed length of unit 1 and bed thickness increases for the entire length of the deposit the deposit of the second nuee ardente is only 6 21 cm thick and of very limited lateral extent it is a normally graded coarse to fine ash with a finespoor base the third unit consists of fines poor normally graded coarse ash exposed in low amplitude 20 40 cm 12 m wavelength dunes the deposit of the fourth nuee ardente rests in sharp erosive contact on the underlying unit increasing in thickness down flow it consists of transitional coarse and fine grained strata 6 130 c cm thick dipping 5 10 down flow the deposit made up of two subpopulations one rosin and one normal is normally graded over the entire bed but coarsegrained strata are reversely graded the relative content of vesiculated clasts increases up bed in both strata types from 12 at the base to 40 at the top the characteristics of unit 1 suggest that it accumulated from a concentrated suspension of cohesionless solids exhibiting non newtonian behavior where dispersive pressure played an important role in the suspension of the clasts units 2 and 3 were probably deposited from dilute turbulent suspensions whereas the upper unit 4 is a classic example of deposition from a high density turbulent suspension leading to the formation of multiple traction carpets driven by the overlying lower density surge the horizontal distance travelled by a hot rock avalanche may be influenced by its transport mechanism debris flows are mobile on very low slopes as low as 1 whereas grain flows even density modified grain flows require relatively high slopes more than 6 at merapi to maintain their mobility if the present merapi dome were to collapse and produce a debris flow its present volume coupled with the minimal 1 5 km vertical drop could travel a distance ranging between 15 and 30 km however if transport were by grain flow mechanisms the mass could come to rest as it reaches a 5 10 slope

simply pyroclastic currents gravity driven ground hugging gas pyroclast mixtures produced during explosive volcanic eruptions define a full spectrum of particle concentration flow regime and particle support mechanisms to describe these phenomena the term pyroclastic density current pdc has become increasingly popular in the last few tens of years here i question the general application of the term pdc to the whole flow spectrum and instead i propose the simpler term pyroclastic current

stratigraphy sedimentology and inferred flow dynamics from the july 2015 block and ash flow deposits at volcan de colima mexico abstract the july 2015 block and ash flow baf events represent the first documented series of large volume and long runout bafs generated from sustained dome collapses at volcan de colima this eruption is particularly exceptional at this volcano due to 1 the large volume of baf material emplaced 0 0077 0 001 km3 2 the long runout reached by the associated bafs max 10 km and 3 the short period 18 h over which two main long sustained dome collapse events occurred on 10 and 11 july respectively stratigraphy and sedimentology of the 2015 baf deposits exposed in the southern flank of the volcano based on lithofacies description grain size measurements and clast componentry allowed the recognition of three main deposit facies i e valley confined overbank and ash cloud surge deposits correlations and lithofacies variations inside three main flow units from both the valley confined and overbank deposits left from the emplacement of the second series of bafs on 11 july provide detailed information about 1 the distribution volumes and sedimentological characteristics of the different units 2 flow parameters i e velocity and dynamic pressure and mobility metrics as inferred from associated deposits and 3 changes in the dynamics of the different flows and their material during emplacement these data were coupled with geomorphic analyses to assess the role of the topography in controlling the behaviour and impacts of the successive baf pulses on the volcano flanks finally these findings are used to propose a conceptual model for transport and deposition mechanisms of the july 2015 bafs at volcan de colima in this model deposition occurs by rapid stepwise aggradation of successive baf pulses flow confinement in a narrow and sinuous channel enhance the mobility and runout of individual channelized baf pulses when these conditions occur the progressive valley infilling from successive sustained dome collapse events promote the overspill and lateral spreading of the upper and marginal regions of the main flow body generating highly mobile overbank flows that travel outside of the main valley volume and distance dependent critical channel capacities for the generation of overbank flows are used to better estimate the inundation area of these hazardous unconfined pyroclastic flows these results highlight the importance of including and correctly assessing the hazards posed by large volume and long runout bafs associated with frequent small vei sustained dome collapse eruptions

nuees ardentes of 22 november 1994 at merapi volcano java indonesia nuees ardentes associated with dome collapse on 22 november 1994 at merapi volcano traveled to the south southwest as far as 6 5 km and collectively accumulated roughly 2 5 3 million cubic meters of deposits the damaged area comprises 9 5 km2 and is covered by two nuee ardente facies a conventional merapi type valley fill block and ash flow facies and a pyroclastic surge facies the proximal deposits reflect the accumulation of dozens of nuees ardentes with many subsidiary flow units the distal deposits are more simply organized as only a few individual events reached to distances 3 5 km the stratigraphic relationships north of turgo hill indicate that the surge deposits are a facies of particularly mobile nuees ardentes that also deposited channeled block and ash flow facies they further suggest that the surge facies beyond the channel margins correlate laterally with a finer grained sublayer locally developed at the base of the block and ash flow facies eyewitness reports suggest that the emplacement of the block and ash flow facies in the distal part of the boyong river may have followed by a short time interval the destruction and deposition of the surge facies at turgo village the stratigraphy is in accord with the eyewitness reports the surge facies was emplaced by a dilute surge current detached from the same dome collapse nuee ardente that as a separate flow unit subsequently emplaced the distal block and ash deposit in the boyong valley the detachment occurred at higher elevations likely at or above the slope break at about 2000 m elevation this flow separation enabled the surge current to shortcut over the landscape and to emplace its deposit even as the block and ash flow continued its tortuous southward movement in the boyong channel dome collapse nuee ardente activity formed the bulk of the eruption which was accompanied by virtually no significant vertical summit explosive activity

the latest explosive eruptions of ciomadul csomad volcano east carpathians a tephrostratigraphic approach for the 51 29 ka bp time interval abstract the most recent mainly explosive eruptions of ciomadul the youngest volcano in the carpatho pannonian region have been constrained by detailed field volcanological studies major element pumice glass geochemistry luminescence and radiocarbon dating and a critical evaluation of available geochronological data these investigations were complemented by the first tephrostratigraphic studies of the lacustrine infill of ciomadul s twin craters st ana and mohos that received tephra deposition during the last eruptions of the volcano our analysis shows that significant explosive activity collectively called eppa early phreatomagmatic and plinian activity started at ciomadul in or around the present day mohos the older crater at 51 ka bp these eruptions resulted in a thick succession of pyroclastic fall deposits found in both proximal and medial distal localities around the volcano characterized by highly silicic rhyolitic glass chemical compositions ca 75 2 79 8 wt sio 2 the eppa stage was terminated by a subplinian plinian eruption at 43 ka bp producing pumiceous pyroclastic fall and flow deposits of similar glass composition probably from a proto st ana vent located at or around the younger crater hosting the present day lake st ana after a quiescent period with a proposed lava dome growth in the st ana crater a new explosive stage began defined as mpa middle plinian activity in particular a significant two phase eruption occurred at 31 5 ka bp producing pyroclastic flows from vulcanian explosions disrupting the preexisting lava dome of sf ana and followed by pumiceous fallout from a plinian eruption column related pyroclastic deposits show a characteristic less evolved rhyolitic glass composition ca 70 2 74 5 wt sio 2 and occur both in proximal and medial distal localities up to 21 km from source the mpa eruptions that may have pre shaped a crater similar to but possibly smaller than the present day st ana crater was followed by a so far unknown but likewise violent last eruptive stage from the same vent creating the final morphology of the crater this stage referred to as lspa latest st ana phreatomagmatic activity produced pyroclastic fall deposits of more evolved rhyolitic glass composition ca 72 8 78 8 wt sio 2 compared to that of the previous mpa stage according to radiocarbon age constraints on bulk sediment charcoal and organic matter from lacustrine sediments recovered from both craters the last of these phreatomagmatic eruptions that draped the landscape toward the east and southeast of the volcano occurred at 29 6 ka bp some 2000 years later than the previously suggested last eruption of ciomadul

investigation of surge derived pyroclastic flow formation by numerical modelling of the 25 june 1997 dome collapse at soufriere hills volcano montserrat deposits from ash cloud surges associated with dome collapse can under certain conditions be remobilised to form surge derived pyroclastic flows sdpfs using numerical modelling we reproduce the emplacement of these flows and investigate the conditions that favour their genesis we use the new version of the numerical model volcflow which simulates the two components of a pyroclastic flow the basal avalanche and the overriding ash cloud surge the basal avalanche primary block and ash flows and sdpfs are simulated using three previously published rheological laws plastic frictional and frictional velocity weakening rheologies applied to the 25 june 1997 dome collapse at soufriere hills volcano the models reproduce to different degrees the deposit footprints formed by the block and ash flows the ash cloud surges and the sdpfs in the plastic model sdpfs occur if the ash cloud surge deposit exceeds a threshold thickness that allows it to remobilise and flow in the frictional models sdpfs occur only if ash cloud surge deposition takes place on a slope exceeding the friction angle of the ash results also highlight that sdpfs appeared so clearly in 1997 at montserrat due to a combination of topographic factors i a bend in the mosquito ghaut drainage that allowed the ash cloud surges to detach ii a depositional area on the watershed between the eastern and western drainage channels and iii a network of tributaries that drained all the remobilised mass into dyer s river to form a single large sdpf our model could be a promising tool for the future forecasting of hazards posed by surge derived pyroclastic flows

tracing the evolution of 2010 merapi volcanic deposits indonesia based on object oriented classification and analysis of multi temporal very high resolution images abstract we compare identification delineation and recording of freshly erupted deposits around active volcanoes from very high resolution optical images with that done by traditional geologic mapping object oriented classification ooc and normalized difference spectral indices of vegetation moisture and soil redness ndvi ndwi and ndrsi have been applied to sub metric geoeye 1 and pleiades images to identify and map pyroclastic and lahar deposits and trace their spatio temporal evolution over two years following the 2010 eruption of merapi volcano indonesia we could identify several categories of pyroclastic depositional areas and also map the damaged forest and destroyed cultivated terraces and settlements in the gendol and opak river basins on the south flank of the volcano more than 75 of erupted deposits were delineated semi automatically unlike the ground geological map based on photo interpretation of the 2010 geoeye image and field observations a temporal image analysis using bivariate scatter diagrams of the three spectral indices between 2010 and 2012 and a combination of ndwi and ndvi separated areas affected by surges from unscathed vegetation use of ndrsi and ndwi allowed us to differentiate overbank pyroclastic density current deposits from wet lahar deposits ndrsi values close to 0 refer to scoria rich pyroclastic deposits about 40 of the devastated upper catchment was recolonized by vegetation between 2010 and 2012 the recovery also took place in the forested valley margins affected by ash cloud surges the morphometric analysis of the initial drainage network digitized from the 2011 2012 images demonstrated 1 the resurfacing of pristine 2010 pdc deposits by runoff and 2 incision or remobilization by lahars it took two years following the eruption in the rugged upper catchment devastated by high energy surges to fully develop the hydrographic network it is however still rudimentary on gently sloping fans created by overbank pdc deposits in the middle valley thus suggesting the importance of slope gradient grain size permeability and thickness of deposits as much as 35 of the 2010 pdc deposits emplaced in the vicinity of the river channels were remobilized by lahars over the two post eruption rainy seasons and also by constant mining activities studies on the erosion of the pyroclastic deposits after 2012 need to concentrate on the upper reach of the catchment on the south flank

evaluation of geophysical mass flow models using the 2006 block and ash flows of merapi volcano java indonesia towards a short term hazard assessment tool abstract the dynamics and depositional processes associated with block and ash flows bafs are most commonly inferred to be a function of granular or inertial grain flow similar to debris flows and cold rock avalanches existing geophysical mass flow models are either based on frictional mohr coulomb behavior the titan2d model developed at the state university of new york at buffalo usa or another rheological law i e a constant retarding stress eventually adding some viscous and turbulent components the volcflow model developed at the laboratoire magmas et volcans clermont ferrand france the 2006 bafs of merapi present a rare opportunity to test these two well established models against a well constrained field example integration of high resolution field based data into numerical simulations allows the validity of these models to be tested and rapid quantification of best fit input parameters we first show that with the incorporation of spatially varying bed friction angles titan2d is capable of reproducing the paths runout distances areas covered and deposited volumes of the 2006 merapi flows over highly complex topography however some discrepancies with field data are noted and the velocity and travel time of the flows do not match entirely using a single free parameter a constant retarding stress simulations obtained with the volcflow model also reproduce the morphology and distribution of the natural deposits as well as the time of emplacement and velocities of the flows the results suggest that the performance of these models in simulating actual events is critically dependent on 1 the calibration of the model by using extensive field based data such as deposit distribution and processes of flow generation transport and deposition 2 the incorporation of a suitable numerical topographic dataset i e high resolution digital elevation model and 3 the choice of input parameters such as location and volume of the initial pile of material and source characteristics single or multiple dome collapse dome collapse duration and total volume of collapsed material sensitivity analyses and inundation maps based on the probability of impact were used to produce a suite of potentially inundated areas from future gravitational dome collapse events affecting the gendol valley and adjacent areas on the southern flank of the volcano our results provide the basis for defining hazard zonations of key areas at risk from bafs which will be generated during future comparable eruptions at merapi

mass budget partitioning during explosive eruptions insights from the 2006 paroxysm of tungurahua volcano ecuador how and how much the mass of juvenile magma is split between vent derived tephra pdc deposits and lavas i e mass partition is related to eruption dynamics and style estimating such mass partitioning budgets may reveal important for hazard evaluation purposes we calculated the volume of each product emplaced during the august 2006 paroxysmal eruption of tungurahua volcano ecuador and converted it into masses using high resolution grainsize componentry and density data this dataset is one of the first complete descriptions of mass partitioning associated with a vei 3 andesitic event the scoria fall deposit near vent agglutinate and lava flow include 28 16 and 12 wt of the erupted juvenile mass respectively much 44 wt of the juvenile material fed pyroclastic density currents i e dense flows dilute surges and co pdc plumes highlighting that tephra fall deposits do not depict adequately the size and fragmentation processes of moderate pdc forming event the main parameters controlling the mass partitioning are the type of magmatic fragmentation conditions of magma ascent and crater area topography comparisons of our dataset with other pdc forming eruptions of different style and magma composition suggest that moderate andesitic eruptions are more prone to produce pdcs in proportions than any other eruption type this finding may be explained by the relatively low magmatic fragmentation efficiency of moderate andesitic eruptions these mass partitioning data reveal important trends that may be critical for hazard assessment notably at frequently active andesitic edifices this article is protected by copyright all rights reserved

dramatic effects of stress on metamorphic reactions thermodynamic calculations predict mineralogy from temperature and pressure and vice versa such calculations assume that stress is isotropic despite the fact that differential stresses prevail in earth resulting from large scale tectonics and or differences between fluid and rock pressures in porous rocks new calculations show that differential stress can have significant effects on thresholds for metamorphic reactions depending on the grain scale reaction pathways a differential stress may depending on the reaction pathway have an effect equivalent to a pressure difference on the order of assemblage volume reaction volume change differential stress the multiplying factor is typically 10 or more for example the onset of a garnet clinopyroxene breakdown reaction may be offset up or down by the equivalent of 500 mpa in pressure for a 50 mpa differential stress the effect is equivalent to a temperature difference on the order of assemblage volume reaction entropy change differential stress for example the onset of muscovite quartz breakdown may be offset up or down by the equivalent of 130 c for a 50 mpa differential stress much of earth is under differential stress so the new calculations invite a reappraisal of metamorphic mineralogy and microstructure indicating that new insights into stresses and fluid pressures on earth can be gained

emplacement of pyroclastic flows during the 1998 1999 eruption of volcan de colima mexico after three years of quiescence volcan de colima reawakened with increasing seismic and rock fall activity that reached its peak on november 20 1998 when a new lava dome forced its way to the volcano s summit the new lava rapidly reached the s sw edge of the summit area beginning the generation of merapi type pyroclastic flows that traveled down la lumbre and the el cordoban western and eastern ravines reaching distances of 3 4 5 and 3 km respectively on december 1 1998 the lava flow split into three fronts that in early 1999 had reached 2 8 3 1 and 2 5 km in length advancing down the el cordoban ravines the lava flow fronts disaggregated into blocks forming pyroclastic flows one of the best examples occurred on december 10 1998 as the lava flow ceased moving in early 1999 activity became more explosive strong blasts were recorded on february 10 may 10 and july 17 1999 the last event developed a 10 km high eruptive column from which a pyroclastic flow developed from the base traveling 3 3 km sw from the summit into the san antonio montegrande ravines regardless of the mechanism of pyroclastic flow generation each flow immediately segregated into a basal avalanche that moved as a granular flow and an upper ash cloud in which particles were sustained in turbulent suspension when the basal avalanche lost velocity and eventually stopped the upper ash cloud continued to move independently as a dilute pyroclastic flow that produced a massive pyroclastic flow deposit and an upper dune bedded surge deposit the dilute pyroclastic flow scorched and toppled maguey plants and trees and sandblasted vegetation in the direction of the flow at the end of the dilute pyroclastic flow path the suspended particles lifted off in a cloud from which a terminal ash fall was deposited the basal avalanche emplaced block and ash flow deposits up to 8 m thick that filled the main ravines and consisted of several flow units each flow unit was massive monolithologic matrix supported and had a clast supported steep front ca 1 5 to 2 m thick composed of boulders up to 1 7 m in diameter the juvenile lithic clasts had an average density of 1800 kg m3 the dilute pyroclastic flow emplaced overbank deposits found on valley margins or beyond the tip of block and ash flow deposits they consist from bottom to top of a massive medium to coarse sand size flow layer 2 4 cm thick a dune bedded surge layer 2 10 cm thick and a massive silt size layer 0 5 cm thick the total estimated volume of the pyroclastic flow deposits produced during the 1998 1999 eruption is 24 105 m3

very rapid cooling of the energetic pyroclastic density currents associated with the 5 november 2010 merapi eruption indonesia abstract understanding the thermal behavior of pyroclastic density currents pdcs is crucial for forecasting impact scenarios for exposed populations as it affects their lethality and destructiveness here we report the emplacement temperatures of pdc deposits produced during the paroxysmal explosive eruption of merapi central java on 5 november 2010 based on the reflectance of entombed charcoal fragments this event was anomalously explosive for merapi and destroyed the summit dome that had been rapidly growing with partial collapses and associated pdcs since october 26 results show mean reflectance values mainly between 0 17 and 0 41 these new data provide a minimum temperature of the flow of 240 320 c consistent with previous estimations determined from independent field engineering and medical observations published in the literature for this eruption a few charcoal fragments recorded higher values suggestive of temperatures up to 450 c and we suggest that this is due to the thermal disequilibrium of the deposits with larger block size clasts being much hotter than the surrounding ash matrix charring temperatures show no major differences between proximal and distal pdc deposits and are significantly lower than those that may be associated with a fast growing dome dominated by dense and vitric non vesicular rocks we therefore infer that the decrease in temperature from that at fragmentation 900 c occurred in the very initial part of the current

pyroclastic density current volume estimation after the 2010 merapi volcano eruption using x band sar abstract pyroclastic density current deposits remobilized by water during periods of heavy rainfall trigger lahars volcanic mudflows that affect inhabited areas at considerable distance from volcanoes even years after an eruption here we present an innovative approach to detect and estimate the thickness and volume of pyroclastic density current pdc deposits as well as erosional versus depositional environments we use sar interferometry to compare an airborne digital surface model dsm acquired in 2004 to a post eruption 2010 dsm created using cosmo skymed satellite data to estimate the volume of 2010 merapi eruption pdc deposits along the gendol river kali gendol kg results show pdc thicknesses of up to 75 m in canyons and a volume of about 40 106 m3 mainly along kg and at distances of up to 16 km from the volcano summit this volume estimate corresponds mainly to the 2010 pyroclastic deposits along the kg material that is potentially available to produce lahars our volume estimate is approximately twice that estimated by field studies a difference we consider acceptable given the uncertainties involved in both satellite and field based methods our technique can be used to rapidly evaluate volumes of pdc deposits at active volcanoes in remote settings and where continuous activity may prevent field observations

the merapi 2010 eruption an interdisciplinary impact assessment methodology for studying pyroclastic density current dynamics abstract the large explosive eruption of merapi volcano indonesia in 2010 presented a key and rare opportunity to study the impacts of a major explosive eruption in a densely populated area pyroclastic density currents pdcs produced throughout the 2010 eruption were unusually destructive causing near complete devastation across a 22 km 2 swath of the densely populated southern flanks and casualties to the end of their runout at 15 5 km from the volcano the majority 120 of the more than 200 fatalities occurred more than 12 km from the volcano where many people were caught in pdcs as they were evacuating the 2010 eruption vei 4 exhibited a range of pdc behaviour in a complex multi stage event that marked a change in eruption behaviour at merapi being the first eruption of this magnitude and style since 1872 this shift in style may mark a change in regime and so understanding the potential impact of such large explosive eruptions is essential for future risk assessment at merapi we describe a new impact assessment methodology that allowed us to collect important empirical geological damage and casualty information and reconstruct impact dynamics associated with the pdcs in contrast to previous pdc impact studies we combined remote field laboratory and gis assessments and were able to enter the affected areas safely and before their disturbance by rains or human activity by integrating the results of our geological damage and medical studies we could reconstruct the spatial and temporal dynamics of the pdcs and their main hazard characteristics our interdisciplinary methods and preliminary findings are discussed here in the areas damaged by pdcs we used empirical damage data and calculations of material and structural resistance to lateral force to estimate approximate dynamic pressures dynamic pressures associated with the 5 november paroxysm exceeded 15 kpa more than 6 km from source and rapidly attenuated over a distance of less than 1 km at the end of the pdc runouts analysis of thermal indicators such as deformed plastic and correlation with information on burns injuries and fires provided estimates of ambient temperatures associated with the pdcs even at the relatively low temperatures estimated for the pdcs 200 300 c they were lethal to people inside as well as outside buildings in part because of the building design that enabled the pdcs to rapidly infiltrate inside such detailed quantitative data can be used to support numerical pdc and impact modelling and risk assessment at dome forming volcanoes providing an improved understanding of the complexity of pdcs and their associated impacts on exposed populations

rain triggered lahars following the 2010 eruption of merapi volcano indonesia a major risk abstract the 2010 vei 4 eruption of merapi volcano deposited roughly ten times the volume of pyroclastic materials of the 1994 and 2006 eruptions and is recognized as one of the most intense eruption since 1872 however as the eruptive phase is now over another threat endangers local communities rain triggered lahars previous papers on lahars at merapi presented lahar related risk following small scale dome collapse pdcs thus the aim of this study is to provide new insights on lahar related risk following a large scale vei 4 eruption the paper highlights the high number of events 240 during the 2010 2011 rainy season october 2010 may 2011 the frequency of the 2010 2011 lahars is also the most important ever recorded at merapi lahars occurred in almost all drainages located under the active cone with runout distances exceeding 15 km the geomorphic impacts of lahars on the distal slope of the volcano are then explained as they directly threaten houses and infrastructures creation of large corridors avulsions riverbank erosion and riverbed downcutting are detailed through local scale examples related damage is also studied 860 houses damaged 14 sabo dams and 21 bridges destroyed sedimentological characteristics of volcaniclastic sediments in lahar corridors are presented with emphasis on the resource in building material that they represent for local communities risk studies should not forget that thousands of people are exposing themselves to lahar hazard when they quarry volcaniclastic sediment on lahar corridors finally the efficient community based crisis management is explained and shows how local people organize themselves to manage the risk 3 fatalities were reported although lahars reached densely populated areas to summarize this study provides an update of lahar risk issues at merapi with emphasis on the distal slope of the volcano where lahars had not occurred for 40 years and where lahar corridors were rapidly formed

merapi 2010 eruption chronology and extrusion rates monitored with satellite radar and used in eruption forecasting abstract despite dense cloud cover satellite borne commercial synthetic aperture radar sar enabled frequent monitoring of merapi volcano s 2010 eruption near real time interpretation of images derived from the amplitude of the sar signals and timely delivery of these interpretations to those responsible for warnings allowed satellite remote sensing for the first time to play an equal role with in situ seismic geodetic and gas monitoring in guiding life saving decisions during a major volcanic crisis our remotely sensed data provide an observational chronology for the main phase of the 2010 eruption which lasted 12 days 26 october 7 november 2010 unlike the prolonged low rate and relatively low explosivity dome forming and collapse eruptions of recent decades at merapi the eruption began with an explosive eruption that produced a new summit crater on 26 october and was accompanied by an ash column and pyroclastic flows that extended 8 km down the flanks this initial explosive event was followed by smaller explosive eruptions on 29 october 1 november then by a period of rapid dome growth on 1 4 november which produced a summit lava dome with a volume of 5 10 6 m 3 a paroxysmal vei 4 magmatic eruption with ash column to 17 km altitude destroyed this dome greatly enlarged the new summit crater and produced extensive pyroclastic flows to 16 km radial distance in the gendol drainage and surges during the night of 4 5 november the paroxysmal eruption was followed by a period of jetting of gas and tephra and by a second short period 12 h of rapid dome growth on 6 november the eruption ended with low level ash and steam emissions that buried the 6 november dome with tephra and continued at low levels until seismicity decreased to background levels by about 23 november our near real time commercial sar documented the explosive events on 26 october and 4 5 november and high rates of dome growth 25 m 3 s 1 an event tree analysis for the previous 2006 merapi eruption indicated that for lava dome extrusion rates 1 2 m 3 s 1 the probability of a large 1872 scale eruption was 10 consequently the order of magnitude greater rates in 2010 along with the explosive start of the eruption on 26 october the large volume of lava accumulating at the summit by 4 november and the rapid and large increases in seismic energy release deformation and gas emissions were the basis for warnings of an unusually large eruption by the indonesian geological agency s center for volcanology and geologic hazard mitigation cvghm and their volcano research and technology development center bpptk in yogyakarta warnings that saved thousands of lives

viscous relaxation of grain scale pressure variations in the presence of grain scale pressure variations there will be a natural tendency for deformation to flatten pressure gradients to establish pressure equilibrium we explore the time scale of the survival of pressure variations in the presence of power law creep such viscous relaxation turns out to be strongly dependent on the exponent in the power law creep constitutive relation for larger exponents there is the possibility of maintaining pressure variations for the order of a million years orders of magnitude longer than the viscoelastic relaxation time that is commonly used as a proxy for the pressure relaxation time petrologically this means that while pressure variations may only be transient their effect may contribute to mineral textural development even if not preserved in mineral assemblages and mineral compositions

giant debris avalanches from the colima volcanic complex mexico implications for long runout landslides 100 km and hazard assessment at least two giant volcanic debris avalanche deposits are associated with the colima volcanic complex located in the western part of the trans mexican volcanic belt one avalanche originated from volcan de colima 3820 m probably 4300 yr ago a much larger avalanche originated from nevado de colima 4240 m 18500 yr ago it traveled more than 120 km from its source and covered an area of at least 2200 km 2 almost twice the area of any previously described avalanche deposit this older debris avalanche is the second largest by volume known has the longest travel distance yet reported and has one of the lowest height length ratios 0 04 the avalanche material was probably hot during emplacement and after initial slope failure may have behaved similarly to a pyroclastic flow such large long runout landslides from volcanic or nonvolcanic constructs present a serious geologic hazard that must be considered in risk assessment

10 000 years of explosive eruptions of merapi volcano central java archaeological and modern implications abstract stratigraphy and radiocarbon dating of pyroclastic deposits at merapi volcano central java reveals 10 000 years of explosive eruptions highlights include 1 construction of an old merapi stratovolcano to the height of the present cone or slightly higher our oldest age for an explosive eruption is 9630 60 14 c y b p construction of old merapi certainly began earlier 2 collapse s of old merapi that left a somma rim high on its eastern slope and sent one or more debris avalanche s down its southern and western flanks impoundment of kali progo to form an early lake borobudur at 3400 14 c y b p hints at a possible early collapse of merapi the latest somma forming collapse occurred 1900 14 c y b p the current cone new merapi began to grow soon thereafter 3 several large and many small buddhist and hindu temples were constructed in central java between 732 and 900 a d roughly 1400 1000 14 c y b p explosive merapi eruptions occurred before during and after temple construction some temples were destroyed and or buried soon after their construction and we suspect that this destruction contributed to an abrupt shift of power and organized society to east java in 928 a d other temples sites though were occupied by caretakers for several centuries longer 4 a partial collapse of new merapi occurred 14 c y b p eruptions 700 800 14 c y b p 12 14th century a d deposited ash on the floors of still occupied candi sambisari and candi kedulan we speculate but cannot prove that these eruptions were triggered by the same partial collapse of new merapi and that the eruptions in turn ended caretaker occupation at candi sambisari and candi kedulan a new or raised lake borobudur also existed during part or all of the 12 14th centuries probably impounded by deposits from merapi 5 relatively benign lava dome extrusion and dome collapse pyroclastic flows have dominated activity of the 20th century but explosive eruptions much larger than any of this century have occurred many times during merapi s history most recently during the 19th century are the relatively small eruptions of the 20th century a new style of open vent less hazardous activity that will persist for the foreseeable future or alternatively are they merely low level background activity that could be interrupted upon relatively short notice by much larger explosive eruptions the geologic record suggests the latter which would place several hundred thousand people at risk we know of no reliable method to forecast when an explosive eruption will interrupt the present interval of low level activity this conclusion has important implications for hazard evaluation

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

transitions between explosive and effusive phases during the cataclysmic 2010 eruption of merapi volcano java indonesia transitions between explosive and effusive activity are commonly observed during dome forming eruptions and may be linked to factors such as magma influx ascent rate and degassing however the interplay between these factors is complex and the resulting eruptive behaviour often unpredictable this paper focuses on the driving forces behind the explosive and effusive activity during the well documented 2010 eruption of merapi the volcano s largest eruption since 1872 time controlled samples were collected from the 2010 deposits linked to eruption stage and style of activity these include scoria and pumice from the initial explosions dense and scoriaceous dome samples formed via effusive activity as well as scoria and pumice samples deposited during subplinian column collapse quantitative textural analysis of groundmass feldspar microlites including measurements of areal number density mean microlite size crystal aspect ratio groundmass crystallinity and crystal size distribution analysis reveal that shallow pre and syn eruptive magmatic processes acted to govern the changing behaviour during the eruption high an up to 80 mol an microlites from early erupted samples reveal that the eruption was likely preceded by an influx of hotter or more mafic magma transitions between explosive and effusive activity in 2010 were driven primarily by the dynamics of magma ascent in the conduit with degassing and crystallisation acting via feedback mechanisms resulting in cycles of effusive and explosive activity explosivity during the 2010 eruption was enhanced by the presence of a plug of cooled magma within the shallow magma plumbing system which acted to hinder degassing leading to overpressure prior to initial explosive activity

kinematic characteristics of pyroclastic density currents at merapi and controls on their avulsion from natural and engineered channels we herein report an example of pyroclastic density current avulsion on 14 june 2006 at merapi indonesia four discrete series of multiple dome collapses led to the generation of four individual block and ash flows into kali gendol valley all four pyroclastic density currents locally overflowed the channel margins to devastate cultivated terraces along each side of the box shaped canyon while propagating as much as 2 2 km within adjacent tributaries the largest destruction was caused by the second and third pyroclastic density currents both of these flows partially spilled out of the gendol valley at a travel distance of 4 9 km bypassing a sabo dam just upstream of the village of kaliadem and leaving the village almost completely destroyed and buried by several meters of overbank deposits the main mechanism of flow avulsion on june 14 was the overflow of up to 20 vol of the dense basal part of the pyroclastic density currents onto interfluves the relative proportions of valley escaped material increased dramatically in the succession of each of the four pyroclastic density currents the main geometric parameters controlling flow avulsion and their critical values were quantified through high resolution real time kinetic global positioning system rtk gps data of the pre event topography for each of the 14 june flows this case highlights the way in which a sabo dam can significantly increase the potential of flow avulsion key lessons are derived for the future hazard mitigation in valleys subject to volcanic mass flows flow observational and geometric data are combined into a model to derive the kinematic characteristics of the basal valley ponding avalanche and the valley escaping veneer flows which are otherwise hidden by overriding clouds of elutriated ash

bar form resistance in gravel bed rivers resistance to flow in unvegetated gravel bed rivers is basically dependent on the skin resistance due to surface bed material and bar form resistance due to accelerations and decelerations in the flow between pools and riffles although flow is generally nonuniform at riffle sections flow is locally uniform it is these sections which principally control the velocity depth characteristics of the reach since hydraulic conditions in the pool result from the backwater effect of the riffle isolating the effect of bar forms on flow resistance is achieved by first establishing the roughness height of the surface bed material on the riffle overall resistance to flow in terms of the total roughness height due to bed forms and grains for equivalent uniform flow is determined from the riffle and reach average flow geometry and the grain roughness height differences between total and grain roughness heights define the bar form effect field data from 62 sites in the united kingdom illustrate that at bankful

a unifying basis for the interplay of stress and chemical processes in the earth support from diverse experiments the interplay between stress and chemical processes is a fundamental aspect of how rocks evolve relevant for understanding fracturing due to metamorphic volume change deformation by pressure solution and diffusion creep and the effects of stress on mineral reactions in crust and mantle there is no agreed microscale theory for how stress and chemistry interact so here i review support from eight different types of the experiment for a relationship between stress and chemistry which is specific to individual interfaces chemical potential helmholtz free energy normal stress at interface molar volume the experiments encompass temperatures from 100 to 1300 degrees c and pressures from 1 bar to 1 8 gpa the equation applies to boundaries with fluid and to incoherent solid solid boundaries it is broadly in accord with experiments that describe the behaviours of free and stressed crystal faces next to solutions that document flow laws for pressure solution and diffusion creep that address polymorphic transformations under stress and that investigate volume changes in solid state reactions the accord is not in all cases quantitative but the equation is still used to assist the explanation an implication is that the chemical potential varies depending on the interface so there is no unique driving force for reaction in stressed systems instead the overall evolution will be determined by combinations of reaction pathways and kinetic factors the equation described here should be a foundation for grain scale models which are a prerequisite for predicting larger scale earth behaviour when stress and chemical processes interact it is relevant for all depths in the earth from the uppermost crust pressure solution in basin compaction creep on faults reactive fluid flow systems serpentinisation the deeper crust orogenic metamorphism the upper mantle diffusion creep the transition zone phase changes in stressed subducting slabs to the lower mantle and core mantle boundary diffusion creep

volcflow capabilities and potential development for the simulation of lava flows volcflow is a finite difference eulerian code based on the depth averaged approach and developed for the simulation of isothermal geophysical flows its capability for reproducing lava flows is tested here for the first time the field example chosen is the 2010 lava flow of tungurahua volcano ecuador the emplacement of which is tracked by projecting thermal images onto a georeferenced digital topography results show that at least for this case study the isothermal approach of volcflow is able to simulate the velocity of the lava through time as well as the extent of the solidified lava however the good fit between the modelled and the natural flow may be explained by the short emplacement time c 20 h of a thick lava c 5 m which could limit the influence of cooling on the flow dynamics thus favouring the use of an isothermal rheology

suitability of simple rheological laws for the numerical simulation of dense pyroclastic flows and long runout volcanic avalanches 1 the rheology of volcanic rock avalanches and dense pyroclastic flows is complex and it is difficult at present to constrain the physics of their processes the problem lies in defining the most suitable parameters for simulating the behavior of these natural flows existing models are often based on the coulomb rheology sometimes with a velocity dependent stress e g voellmy but other laws have also been used here i explore the characteristics of flows and their deposits obtained on simplified topographies by varying source conditions and rheology the coulomb rheology irrespective of whether there is a velocity dependent stress forms cone shaped deposits that do not resemble those of natural long runout events a purely viscous or a purely turbulent flow can achieve realistic velocities and thicknesses but cannot form a deposit on slopes the plastic rheology with e g bingham or without a velocity dependent stress is more suitable for the simulation of dense pyroclastic flows and long runout volcanic avalanches with this rheology numerical flows form by pulses which are often observed during natural flow emplacement the flows exhibit realistic velocities and deposits of realistic thicknesses the plastic rheology is also able to generate the frontal lobes and lateral levees which are commonly observed in the field with the plastic rheology levee formation occurs at the flow front due to a divergence of the driving stresses at the edges once formed the levees then channel the remaining flow mass the results should help future modelers of volcanic flows with their choice of which mechanical law corresponds best to the event they are studying

volcano tectonic control of merapi s lava dome splitting the november 2013 fracture observed from high resolution terrasar x data abstract volcanism at active andesite dacite volcanoes is often associated with the formation and collapse of circular shaped protrusions of extruded highly viscous lava the so called domes which are emplaced in the near summit region growing domes may experience stable and instable structural phases with a gradual transition in between dome collapse and the break off of instable blocks of viscous lava may lead to pyroclastic flows one of the most lethal hazards at stratovolcanoes at merapi volcano indonesia a new dome started growing in the summit region in the amphitheater formed in the course of the climactic 2010 eruption three years later the dome reached a height of approximately 100 m and diameters of 220 and 190 m with a plateau like surface area of 40 000 m2 approximately on 18 11 2013 an explosion occurred without identified precursors leaving a major fracture cutting the complete dome structure based on high resolution terrasar x satellite radar imagery we could identify the linear fracture traceable over 200 m in the long axis up to 40 m wide after geocoding of the radar amplitude imagery the fractures azimuthal trend could be compared to other structural lineaments indicative of a significant nnw sse structural direction that has formed on merapi volcano in the past the merapi dome fractured in a nw se direction and is consistent with the alignment of regional tectonic structures and of anticipated directions of pyroclastic flows the fracture may be part of a larger volcano tectonic system and may affect the dynamics and the stability of the merapi dome

harmonic ionospheric oscillation by the 2010 eruption of the merapi volcano indonesia and the relevance of its amplitude to the mass eruption rate abstract using continuous data from ground based global satellite navigation system gnss receivers in java and sumatra indonesia we studied the response of ionospheric total ionospheric electron content tec to the 2010 nov 5 eruption of the merapi volcano in central java we then compared the results with the case of the 2014 feb 13 eruption of the kelud volcano eastern java the tec showed a quasi periodic oscillation of a frequency 4 mhz with average amplitudes of 0 9 and 1 8 relative to background values lasting for 20 and 120 min for the merapi and kelud eruptions respectively by comparing the two cases together with the 2015 april eruption of the calbuco volcano chile we found the relative tec oscillation amplitude may scale with the mass eruption rate this suggests that the product of such tec oscillation amplitude and the duration provides a new measure for the total volume of the volcanic deposits

a two layer depth averaged model for both the dilute and the concentrated parts of pyroclastic currents pyroclastic currents are very destructive and their complex behavior makes the related hazards difficult to predict a new numerical model has been developed to simulate the emplacement of both the concentrated and the dilute parts of pyroclastic currents using two coupled depth averaged approaches interaction laws allow the concentrated current pyroclastic flow to generate a dilute current pyroclastic surge and inversely the dilute current to form a concentrated current or a deposit the density of the concentrated current is assumed to be constant during emplacement whereas the density of the dilute current changes depending on the particle supply from the concentrated current and the mass lost through sedimentation the model is explored theoretically using simplified geometries as a proxies for natural source conditions and topographies it reproduces the relationships observed in the field between the surge genesis and the topography the increase in surge production in constricted valleys the decoupling between the concentrated and the dilute currents and the formation of surge derived concentrated flows the strong non linear link between the surge genesis and the velocity of the concentrated flow beneath it could explain the sudden occurrence of powerful and destructive surges and the difficulty of predicting this occurrence a companion paper compares the results of the model with the field data for the eruption of merapi in 2010 kelfoun et al submitted and demonstrates that the approach is able to reproduce the natural emplacement of the concentrated and the dilute pyroclastic currents studied with good accuracy

pre explosive conduit conditions during the 2010 eruption of merapi volcano java indonesia the 2010 eruption is the largest explosive event at merapi volcano since 1872 the high energy of the initial 26 october explosions cannot be explained by simple gravitational collapse and the paroxysmal explosions were preceded by the growth of a lava dome not large enough to ensure significant pressurization of the system we sampled pumice from these explosive phases and determined the pre explosive depths of the pumices by combining textural analyses with glass water content measurements our results indicate that the magma expelled was tapped from depths of several kilometers such depths are much greater than those involved in the pre 2010 effusive activity we propose that the water rich magma liberated enough gas to sustain the explosivity our results imply that the explosive potential of volcanoes having dome forming effusive activity is linked to the depth from which fresh magma can be evacuated in a single explosion regardless of the evacuated volume

signs of magma ascent in lp and vlp seismic events and link to degassing an example from the 2010 explosive eruption at merapi volcano indonesia the link between seismicity and degassing is investigated during the vei 4 eruptions of merapi volcano indonesia in october and in early november 2010 seismicity comprised a large number and variety of earthquakes including volcano tectonic events a sustained period of long period seismicity lps i e long period events lp very long period events vlp and tremor lps seismicity is ascribed to the excitation of fluid filled cavity resonance and inertial displacement of fluids and magma we investigate here lps that occurred between 17 october and 4 november 2010 to obtain insights into the volcano eruption processes which preceded the paroxysmal phase of the eruption on 4 5 november we proceed to the moment tensor inversion of a well recorded large vlp event during the intrusion phase on 17 october 2010 i e before the first explosion on 26 october by using two simplified models crack and pipe we find a shallow source for this vlp event at about 1 km to the south of the summit and less than 1 km below the surface we analyze more than 90 lp events that occurred during the multi phase eruption 29 october 4 november we show that most of them have a dominant frequency in the range 0 2 4 hz we could locate 48 of those lp events at least 3 clusters of lp events occurred successively we interpret these observations as generated by different fluid filled containers in the summit area that were excited while magma rose we also observe significant variations of the complex frequency during the course of the eruption we discuss these changes in terms of a variable ratio of fluid to solid densities and or by possible conduit geometry change and or permeability of the conduit or the edifice and or by resonance of different fluid containers during the release of more than 0 4 tg of so2 and large but unknown masses of other volcanic gases finally we also discuss how the major explosions of the eruption were possibly triggered by passing waves resulting from regional tectonic earthquakes on 3 and 4 november

a comparison of the landsat image and laharz simulated lahar inundation hazard zone by the 2010 merapi eruption located above the java subduction zone merapi volcano is an active stratovolcano with a volcanic activity cycle of 1 5 years most merapi eruptions are relatively small with volcanic explosivity index vei of 1 3 however the most recent eruption which occurred in 2010 was quite violent with a vei of 4 and 386 people were killed in this study lahars and pyroclastic flow zones were detected using optical landsat images and the lahar and pyroclastic flow zone simulated using the laharz program to detect areal extents of lahar and pyroclastic flows using landsat images supervised classification was performed after atmospheric correction by using a cosine of the solar zenith correction cost model as a result the extracted dimensions of pyroclastic flows are nearly identical to the calatrava volcanic province cvp monthly reports then areas of potential lahar and pyroclastic flow inundation based on flow volume using the laharz program were simulated and mapped finally the detected lahars and pyroclastic flow zones were compared with the simulated potential zones using laharz program and verified results showed satisfactory similarity 55 63 between the detected and simulated zone the simulated zones using the laharz program can be used as an essential volcanic hazard map for preventing life and property damages for merapi volcano and other hazardous volcanic areas also the laharz program can be used to map volcano hazards in other hazardous volcanic areas

parametric analysis of lava dome collapse events and pyroclastic deposits at shiveluch volcano kamchatka using visible and infrared satellite data abstract for the years 2001 to 2013 of the ongoing eruption of shiveluch volcano a combination of different satellite remote sensing data are used to investigate the dome collapse events and the resulting pyroclastic deposits shiveluch volcano in kamchatka russia is one of the world s most active dome building volcanoes which has produced some of the largest known historical block and ash flows bafs globally quantitative data for deposits resulting from such large and long lived dome forming eruptions especially like those at shiveluch are scarce we use advanced spaceborne thermal emission and reflection radiometer aster thermal infrared tir shortwave infrared swir and visible near infrared vnir data to analyze the dome collapse scars and baf deposits that were formed during eruptions and collapse events in 2001 2004 2005 2007 2009 2010 and two events in 2013 these events produced flows with runout distances of as far as 19 km from the dome and with aerial extents of as much as 22 3 km2 over the 12 years of this period of investigation there is no trend in deposit area or runout distances of the flows through time however two potentially predictive features are apparent in our data set 1 the largest dome collapse events occurred when the dome exceeded a relative height from dome base to top of 500 m 2 collapses were preceded by thermal anomalies in six of the cases in which aster data were available although the areal extent of these precursory thermal areas did not generally match the size of the collapse events as indicated by scar area volumes are available for three collapse events linking the deposit distribution to the area location and temperature profiles of the dome collapse scars provides a basis for determining similar future hazards at shiveluch and at other dome forming volcanoes because of these factors we suggest that volcanic hazard analysis and mitigation at volcanoes with similar baf emplacement behavior may be improved with detailed synoptic studies especially when it is possible to access and interpret appropriate remote sensing data in near real time

numerical simulations of block and ash flows using the titan2d flow model examples from the 2006 eruption of merapi volcano java indonesia we present titan2d simulations of two well characterized block and ash flow baf events of the 2006 eruption of merapi java indonesia that affected the gendol valley on the volcano s southern flank and adjacent densely populated interfluve non valley areas 1 a single dome collapse event to the south that generated one of the smaller post june 14 flows and 2 a sustained multiple dome collapse event also directed to the south that produced the largest flows of the 2006 eruption emplaced in the afternoon of june 14 using spatially varying bed friction angles titan2d is capable of reproducing the paths velocities runout distance areas covered and deposited volumes of these flows over highly complex topography the model results provide the basis for estimating the areas and levels of hazards associated with bafs generated during relatively short as well as prolonged dome collapse periods and guidance during future eruptive crises at merapi

textural and micro petrological variations in the eruptive products of the 2006 dome forming eruption of merapi volcano indonesia implications for sub surface processes the interplay between magma ascent degassing and changing magmatic properties are widely recognized as critical factors controlling the style of silicic volcanic eruptions microlite textures in samples from the prolonged dome forming eruption of merapi in 2006 provide a record of changing magmatic ascent conditions and shallow conduit processes throughout the eruption analysis of microlite textural parameters including measurements of areal number density na mean microlite size crystal aspect ratio and groundmass crystallinity combined with the monitoring record and field observations indicate that magma ascent paths change between continuous ascent at varying rates from a deeper magma storage region to ascent being temporarily stalled at shallow depths in the latter stages of the eruption supporting the idea of an ephemeral shallow magma storage region at merapi plagioclase microlite compositions show evidence of decompression induced degassing often displaying rims of anorthoclase and more k rich alkali feldspar sanidine anorthite contents also support the textural data of later erupted magma being temporarily stalled at shallow depths crystal size distributions csds are interpreted to show that both growth dominated and nucleation dominated crystallisation regimes existed during the 2006 eruption resulting from changing conditions of undercooling t during variable magma ascent paths by contrast microlite textural analysis and feldspar microlite compositions of samples from the fast growing lava dome of the second phase of the 2010 eruption prior to the cataclysmic events on 5 november indicate faster ascent rates a crystallisation regime more strongly dominated by nucleation due to high t and interaction of the 2010 magma with more hotter magma from depth

remote sensing data types and techniques for lahar path detection a case study at mt ruapehu new zealand mt ruapehu is new zealand s most active onshore volcano in 2007 the volcano produced a large lahar following a break out from the summit crater lake here satellite and airborne remote sensing and image processing is used to extract the path of the lahar using aster and spot5 visible and near infra red imagery alos palsar l band synthetic aperture radar data and airborne lidar the results obtained from each of these datasets were compared to the lahar deposit manually digitized from aerial photography spot5 imagery produced the most accurate map of the lahar deposit 77 correct even though these data were acquired a year after the event this is attributed to the spatial resolution of the data the alos palsar coherence mapping calculated from images acquired 2 months before and nine months after the lahar was not as accurate as that obtained using the optical imagery 43 correct but this was still considered an important tool for acquiring data during cloudy periods lidar topographic data collected to constrain geomorphic changes caused by the lahar was the least accurate in terms of mapping the lahar path 28 correct no single technique was deemed to be the most accurate under all circumstances and a combination of data types would produce the best results by combining the satellite and lidar data it was possible to accurately classify 92 of the lahar path

the geological evolution of merapi volcano central java indonesia merapi is an almost persistently active basalt to basaltic andesite volcanic complex in central java indonesia and often referred to as the type volcano for small volume pyroclastic flows generated by gravitational lava dome failures merapi type nuees ardentes stratigraphic field data published and new radiocarbon ages in conjunction with a new set of 40k 40ar and 40ar 39ar ages and whole rock geochemical data allow a reassessment of the geological and geochemical evolution of the volcanic complex an adapted version of the published geological map of merapi wirakusumah et al 1989 peta geologi gunungapi merapi jawa tengah geologic map of merapi volcano central java 1 50 000 is presented in which eight main volcano stratigraphic units are distinguished linked to three main evolutionary stages of the volcanic complex proto merapi old merapi and new merapi construction of the merapi volcanic complex began after 170 ka the two earliest proto merapi volcanic edifices gunung bibi 109 60 ka a small basaltic andesite volcanic structure on merapi s north east flank and gunung turgo and gunung plawangan 138 3 ka 135 3 ka two basaltic hills in the southern sector of the volcano predate the merapi cone sensu stricto old merapi started to grow at 30 ka building a stratovolcano of basaltic andesite lavas and intercalated pyroclastic rocks this older merapi edifice was destroyed by one or possibly several flank failures the latest of which occurred after 4 8 1 5 ka and marks the end of the old merapi stage the construction of the recent merapi cone new merapi began afterwards mostly basaltic andesite pyroclastic and epiclastic deposits of both old and new merapi 11 792 90 14c years bp cover the lower flanks of the edifice a shift from medium k to high k character of the eruptive products occurred at 1 900 14c years bp with all younger products having high k affinity the radiocarbon record points towards an almost continuous activity of merapi since this time with periods of high eruption frequency interrupted by shorter intervals of apparently lower eruption rates which is reflected in the geochemical composition of the eruptive products the holocene stratigraphic record reveals that fountain collapse pyroclastic flows are a common phenomenon at merapi the distribution and run out distances of these flows have frequently exceeded those of the classic merapi type nuees ardentes of the recent activity widespread pumiceous fallout deposits testify the occurrence of moderate to large subplinian eruptions vei 3 4 during the mid to late holocene vei 4 eruptions as identified in the stratigraphic record are an order of magnitude larger than any recorded historical eruption of merapi except for the 1872 ad and possibly the october november 2010 events both types of eruptive and volcanic phenomena require careful consideration in long term hazard assessment at merapi

field observations and surface characteristics of pristine block and ash flow deposits from the 2006 eruption of merapi volcano java indonesia abstract a series of pristine block and ash flow deposits from the may june 2006 eruption of merapi represent an exceptional record of small volume pyroclastic flows generated by gravitational lava dome collapses over a period of about two months the deposits form nine overlapping lobes reaching 7 km from the summit in the gendol river valley on the volcano s southern flank which were produced by successive flows generated during and after the major dome collapse event on june 14 both single pulse post june 14 events and multiple pulse pyroclastic flows generated by sustained dome collapses on june 14 are recognised and three types of deposits spread over an area of 4 7 km are distinguished totalling 13 3 10 6 m 3 1 valley confined basal avalanche deposits 11 7 10 6 m 3 in the gendol river valley 2 overbank pyroclastic flow and associated surge deposits 1 4 10 6 m 3 where parts of the basal avalanche spread laterally onto interfluves and were subsequently channeled into the surrounding river valleys and 3 dilute ash cloud surge deposits 0 2 10 6 m 3 along valley margins variations in the distribution surface morphology and lithology of the deposits are related to the source materials involved in individual pyroclastic flow forming events and varying modes of transport and deposition of the different flows inferred flow velocities of the largest block and ash flows generated on june 14 vary from 43 8 13 5 m s for the basal avalanche and from 62 6 24 2 m s for the ash cloud surge the minimum temperatures range from 400 c for the basal avalanche to 165 c for the overlying ash cloud due to the potential of being re channeled into adjacent river valleys and flowing laterally away from the main river channel the overbank pyroclastic flows are considered the most hazardous part of the block and ash flow system the conditions that lead to their development during flow transport and deposition must be taken into account when assessing future pyroclastic flow hazards at merapi and similar volcanoes elsewhere

decoupling of pyroclastic currents hazards assessments gravitational settling of fragments gas elutriation and boundary layer processes cause concentration values to change within different parts of sediment gravity flows during movement these processes result in flow transformations density stratification and decoupling of single currents into separate sediment gravity flows density can change by an increase in solids concentration in basal zones of currents by downward fall of particles or by incorporation of particles from the substrate thereby leaving their upper parts more dilute in some flows upward streaming gases and elutriation of fines cause dilute turbulent currents to develop at the top of a dense current increasing concentration dampens turbulent action transforming the turbulent to the nonturbulent state commonly at the current s base conversely dilute parts of currents become or remain turbulent currents consisting of turbulent and nonturbulent parts can decouple by shearing past one another because of differing flow properties with each part taking separate paths the manner by which a pyroclastic flow moves affects its predicted runout distance its distribution as continuous sheets or in isolated basins and whether it can cross barriers such as high mountain ranges or water bodies during the eruption of unzen volcano on june 3 1991 decoupling of a pyroclastic surge from the top of a pyroclastic flow caused the deaths of harry glicken maurice krafft katia krafft and 40 japanese citizens mapping volcanic hazard zones requires that consideration be given to decoupling processes to help prevent similar tragedies in the future

kinetics and duration of metamorphic mineral growth in a subduction complex zircon and phengite in the nagasaki metamorphic complex western kyushu japan we applied interface controlled kinetics including interface controlled ostwald ripening and non hydrostatic dissolution precipitation to metamorphic zircon and phengite growth in a high pressure high p metamorphic complex this kinetic modeling yields the growth duration of metamorphic zircon based on the assumption that dissolution and precipitation of zircon is much slower than that of phengite the model was applied to zircon and phengite growth in the nishisonogi unit of the high p nagasaki metamorphic complex western kyushu japan given that detrital zircons that are tens of microns in size remain after metamorphism our model assumption is justified our results show that the duration of metamorphic zircon growth in an individual rock ranges from 10 to 20 myr in general the duration of metamorphic zircon growth in the whole nishisonogi unit is ca 30 myr this prolonged duration implies that high p metamorphism is sustained by continuous subduction of hydrated oceanic crust and overlying trench fill sediments the continuous subduction and accretion of these materials may supply the metamorphic fluid into the high p metamorphic domain in the deeper part of the accretionary prism thereby contributing to interface controlled kinetics in the metamorphic complex

tracking metamorphic dehydration reactions in real time with transmission small and wide angle synchrotron x ray scattering the case of gypsum dehydration we present a review of a unique non destructive method for the real time monitoring of phase transformations and nano pore evolution in dehydrating rocks transmission small and wide angle synchrotron x ray scattering saxs waxs it is shown how saxs waxs can be applied to investigating rock samples dehydrated in a purpose built loading cell that allows the coeval application of high temperature axial confinement and fluid pressure or flow to the specimen because synchrotron sources deliver extremely bright monochromatic x rays across a wide energy spectrum they enable the in situ examination of confined rock samples with thicknesses of 1 mm at a time resolution of order seconds hence fast kinetics with reaction completion times of about hundreds of seconds can be tracked with beam sizes of order tens to hundreds of micrometres it is possible to monitor multiple interrogation points in a sample with a lateral extent of a few centimetres thus resolving potential lateral spatial effects during dehydration and enlarging sample statistics significantly therefore the saxs waxs method offers the opportunity to acquire data on a striking range of length scales for rock samples with thicknesses of 10 3 m and widths of 10 2 m a lateral interrogation point spacing of 10 5 m can be achieved within each irradiated interrogation point volume information concerning pores with sizes between 10 9 and 10 7 m and the crystal lattice on the scale of 10 10 m is acquired in real time this article presents a summary of the physical principles underpinning transmission x ray scattering with the aim of providing a guide for the design and interpretation of time resolved saxs waxs experiments it is elucidated 1 when and how saxs data can be used to analyse total porosity internal surface area and pore size distributions in rocks on length scales from 1 to 300 nm 2 how waxs can be employed to track lattice transformations in situ and 3 which limitations and complicating factors should be considered during experimental design data analysis and interpretation to illustrate the key capabilities of the saxs waxs method we present a series of dehydration experiments on a well studied natural gypsum rock volterra alabaster our results demonstrate that saxs waxs is excellently suited for the in situ tracking of dehydration kinetics and the associated evolution of nano pores the phase transformation from gypsum to bassanite is correlated directly with nano void growth on length scales between 1 and 11 nm for the first time a comparison of the saxs waxs kinetic results with literature data emphasises the need for future dehydration experiments on rock specimens because of the impact of rock fabric and the generally heterogeneous and transient nature of dehydration reactions in nature it is anticipated that the saxs waxs method combined with in situ loading cells will constitute an invaluable tool in the ongoing quest for understanding dehydration and other mineral replacement reactions in rocks quantitatively

flow and deposition of pyroclastic granular flows a type example from the 1975 ngauruhoe eruption new zealand small volume pyroclastic density currents pdcs are generated frequently during explosive eruptions with little warning assessing their hazard requires a physical understanding of their transport and sedimentation processes which is best achieved by the testing of experimental and numerical models of geophysical mass flows against natural flows and or deposits to this end we report on one of the most detailed sedimentological studies ever carried out on a series of pristine small volume pdc deposits from the 1975 eruption of ngauruhoe volcano whose emplacement were also witnessed during eruption using high resolution gps surveys a series of lateral excavations across the deposits and bulk sedimentological analysis we constrained the geomorphology internal structure and texture of the deposits with respect to laterally varying modes of deposition deposition from these pdcs began only on slopes at or around the material s angle of repose c 30 in unconfined settings the granular pdcs are interpreted to have been quasi steady forming sheets and lobes around the angle of repose where flows were confined sheet like proximal facies made up around 10 of the deposit volume at the angle of repose but 90 of the material was deposited from apparently unsteady inertial granular pdcs as a distal levee and channel facies on slopes well below the repose angle hence confined pdcs were able to travel up to 50 farther than unconfined flows in the distal facies the deposit width is inversely correlated to the local slope and the height of the levees above the deposit centreline is positively correlated with slope internally the deposits comprise three parts a coarse grained fines free sole layer that laterally connects to levees zone i an ashy matrix supported central body zone ii and an overlying coarse plaster of clasts zone ii trends in grain size data suggests these zones derive from a continuous un mixing of coarse particles from the initial bulk material by granular segregation that preferentially drives large particles to the upper free surface of the flow where they are concentrated at the front of flow before being deposited and overrun by comparison to analogue experiments we suggest a model of flow and deposition where the temporally and spatially varying mode of deposition is determined by the flow velocity the local slope the vertical velocity gradient the velocity gradient at the free surface and the vertical deposition rate using this model estimated vertical deposition rates of c 5 cm s 1 from the ngauruhoe pdcs agree with those determined in laboratory experiments on inertial granular flows

deposits associated with the 1990 1995 eruption of unzen volcano japan abstract the 1990 1995 eruption of unzen volcano in japan was characterized by lava dome growth and block and ash flows triggered by dome collapse the repeated dome collapse events produced block and ash flow ash cloud surge and fine grained ash fall deposits block and ash flow deposits which are confined to valleys are massive to reversely graded very poorly sorted and contain non vesiculated to poorly vesiculated blocks up to 10 m across the deposits often display finer grained basal parts coarse clast depleted flow units which have intermediate grain size distribution between main flow and surge deposits occur as marginal part of block and ash flow deposits ash cloud surge deposits which spread more widely are finer grained and better sorted than block and ash flow deposits ash fall deposits which were derived from ash clouds of block and ash flows and were dispersed around the volcano are very fine grained and are as well sorted as the surge deposits lahars resulting from remobilization of pyroclastic debris devastated the base of the volcano and their deposits are moderately fines depleted and occasionally display two different lahar facies debris flow and hyperconcentrated flow units

evaluation of the impact of the 2010 pyroclastic density currents at merapi volcano from high resolution satellite imagery field investigations and numerical simulations the 2010 pyroclastic density currents pdc at merapi have presented a rare opportunity to collect a uniquely detailed dataset of the source extent lateral variations and impact of various pdc deposits on a densely populated area using traditional volcanological field based methods and a multi temporal dataset of high resolution satellite imagery a total of 23 pdc events have been recognized including 5 main channeled flows 15 overbank flows derived from overspill and re channelization of the main pdcs into adjacent tributaries and two main surge events the 2010 pdc deposits covered an area of 22 3 km2 unequally distributed between valley filling 6 9 overbank 22 4 and surge and associated fallout deposits 71 7 their total estimated non dre volume is 36 3 106 m3 with 50 2 of this volume accounting for valley filling deposits 39 3 for overbank deposits and 10 5 for surge and associated fallout deposits more than 70 of the total volume was deposited during the third eruptive phase 4 5 november and only 16 6 11 5 and 0 9 during the first 26 29 october second 30 october 3 november and fourth phase 6 23 november respectively the internal architecture and lithofacies variations of the 2010 pdc deposits were investigated using data collected from 30 stratigraphic sections measured after one rainy season of erosion the results show that complex local scale variations in flow dynamics and deposit architectures are apparent and that the major factors controlling the propagation of the main flows and their potential hazards for overbanking were driven by 1 the rapid emplacement of several voluminous pdcs associated with the steady infilling of the receiving landscape after the two first phases of the eruption 2 longitudinal changes in channel capacity following increased sinuosity in the valley and decreased containment space and 3 the effects of varying source mechanisms gravitational dome collapse vertical or lateral dome explosions and column collapse and source materials involved during individual pdc forming events integration of these data into numerical simulations of the channeled and overbank pdcs of the third eruptive phase 4 5 november using two well established geophysical mass flow models titan2d and volcflow allow us to evaluate the ability of these models to reproduce the main features of the natural deposits and some of the flow overbanking processes observed in the field using such a multi technique approach the dataset obtained in this study not only characterizes the pdcs and related hazards at merapi but will allow comparisons with similar events at other volcanoes around the globe

deposit architecture and dynamics of the 2006 block and ash flows of merapi volcano java indonesia the internal architecture of the 2006 block and ash flow deposits of merapi volcano java indonesia was investigated using data collected from 27 stratigraphic sections measured immediately after flow emplacement and after one and two rainy seasons of erosion identification of different depositional units and their longitudinal and lateral facies variations provide detailed information about i the distribution volumes and sedimentological characteristics of the different units ii flow types and mobility as inferred from associated deposits and iii changes in the dynamics of the different flows and their material during emplacement two main types of block and ash flows short runout to medium runout block and ash flows and long runout block and ash flows are defined based on flow generation mechanism flow volume travel distance deposit morphology distribution lithology and grain size distribution conceptual models for the transport and depositional mechanisms of these two types of block and ash flows are presented variations in the runout distances observed for short runout to medium runout block and ash flows are linked directly to different initial flow volumes degree of fragmentation and material properties of the moving mass during transport with the largest and finer grained flows having the greatest mobility deposition occurs only over a narrow range of basal inclinations close to the angle of repose for pyroclastic material indicating that such flows behave in a similar way to granular free surface flows on unconfined planes the flow mechanisms of long runout block and ash flows at merapi are interpreted to be similar in many respects to unsteady cohesionless grain flows with an inertial flow regime where collisional forces largely overcome frictional forces flow unsteadiness causes the main body to be segmented into different pulses that run closer to each other as the flow moves downslope deposition occurs stepwise with rapid aggradation of stacked sub units from different parts of the major flow pulses in such a model the arrival of each flow pulse front at selected sites in the main river valley controls the generation and development of highly mobile unconfined pyroclastic flows outside valley regions and their associated overbank deposits

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

paroxysmal dome explosion during the merapi 2010 eruption processes and facies relationships of associated high energy pyroclastic density currents an 11 minute sequence of laterally directed explosions and retrogressive collapses on 5 november 2010 at merapi indonesia destroyed a rapidly growing dome and generated high energy pyroclastic density currents pdcs spreading over 22 km2 with a runout of 8 4 km while contemporaneous co genetic valley confined pdcs reached 15 5 km this event formed stage 4 of the multi stage 2010 eruption the most intense eruptive episode at merapi since 1872 the deposits and the widespread devastating impact of associated high energy pdcs on trees and buildings show striking similarities with those from historical volcanic blasts montagne pelee martinique bezymianny russia mount st helens usa soufriere hills montserrat we provide data from stratigraphic and sedimentologic analyses of 62 sections of the first unequivocal blast like deposits in merapi s recent history we used high resolution satellite imagery to map eruptive units and flow direction from the pattern of extensive tree blowdown the stratigraphy of stage 4 consists of three depositional units u0 u1 u2 that we correlate to the second third and fourth explosions of the seismic record both u1 and u2 show a bi partite layer stratigraphy consisting each of a lower l1 layer and an upper l2 layer the lower l1 layer is typically very coarse grained fines poor poorly sorted and massive and was deposited by the erosive waxing flow head the overlying l2 layer is much finer grained fines rich moderately to well sorted with laminar to wavy stratification l2 was deposited from the waning upper part and wake of the pdc field observations indicate that pdc height reached 330 m with an internal velocity of 100 m s 1 within 3 km from the source the summit s geometry and the terrain morphology formed by a major transversal ridge and a funneling deep canyon strongly focused pdc mass towards a major constriction thereby limiting the loss of kinetic energy this favored elevated pdc velocities and high particle concentration promoted overspilling of pdcs across high ridges into other river valleys and generated significant dynamic pressures to distances of 6 km that caused total destruction of buildings and the forest the merapi 2010 eruption highlights that explosive and gravitational disintegration of a rapidly growing dome can generate devastating high energy high velocity pdcs this constitutes a credible high impact scenario for future multi stage eruptions at merapi and at other volcanoes that pose particular monitoring crisis response and risk reduction challenges

volcanic hazards from bezymianny and bandai type eruptions major slope failures are a significant degradational process at volcanoes slope failures and associated explosive eruptions have resulted in more than 20 000 fatalities in the past 400 years the historic record provides evidence for at least six of these events in the past century several historic debris avalanches exceed 1 km3 in volume holocene avalanches an order of magnitude larger have traveled 50 100 km from the source volcano and affected areas of 500 1500 km2 historic eruptions associated with major slope failures include those with a magmatic component bezymianny type and those solely phreatic bandai type the associated gravitational failures remove major segments of the volcanoes creating massive horseshoe shaped depressions commonly of caldera size the paroxysmal phase of a bezymianny type eruption may include powerful lateral explosions and pumiceous pyroclastic flows it is often followed by construction of lava dome or pyroclastic cone in the new crater bandai type eruptions begin and end with the paroxysmal phase during which slope failure removes a portion of the edifice massive volcanic landslides can also occur without related explosive eruptions as at the unzen volcano in 1792 the main potential hazards from these events derive from lateral blasts the debris avalanche itself and avalanche induced tsunamis lateral blasts produced by sudden decompression of hydrothermal and or magmatic systems can devastate areas in excess of 500km2 at velocities exceeding 100 m s 1 the ratio of area covered to distance traveled for the mount st helens and bezymianny lateral blasts exceeds that of many pyroclastic flows or surges of comparable volume the potential for large scale lateral blasts is likely related to the location of magma at the time of slope failure and appears highest when magma has intruded into the upper edifice as at mount st helens and bezymianny debris avalanches can move faster than 100 ms 1 and travel tens of kilometers when not confined by valley walls avalanches can affect wide areas beyond the volcano s flanks tsunamis from debris avalanches at coastal volcanoes have caused more fatalities than have the landslides themselves or associated eruptions the probable travel distance l of avalanches can be estimated by considering the potential vertical drop h data from a catalog of around 200 debris avalanches indicates that the h l rations for avalanches with volumes of 0 1 1 km3 average 0 13 and range 0 09 0 18 for avalanches exceeding 1 km3 h l ratios average 0 09 and range 0 5 0 13 large scale deformation of the volcanic edefice and intense local seismicity precede many slope failures and can indicate the likely failure direction and orientation of potential lateral blasts the nature and duration of precursory activity vary widely and the timing of slope faliure greatly affects the type of associated eruption bandai type eruptions are particularly difficult to anticipate because they typically climax suddenly without precursory eruptions and may be preceded by only short periods of seismicity