thermal monitoring of north pacific volcanoes from space long term thermal modeling of volcanoes using satellite imagery provides an effective tool for monitoring remote yet dangerous volcanoes in the north pacific this region includes volcanoes in alaska the aleutian islands and the kamchatkan peninsula thermal infrared data collected multiple times per day from weather satellites show distinct signatures for three different types of volcanic activity at different volcanic centers near real time automated techniques are being developed to monitor relative changes in radiant temperature at volcanoes in this region radiant temperature values as a function of time are extracted and compared to background values for a series of active volcanoes by establishing a long term thermal record for these volcanoes significant deviations indicative of an impending eruption can be detected this tool is used to search for precursors to explosive eruptions in order to increase warning times and hazard mitigation for these potentially catastrophic events a six year archive of satellite imagery has been compiled for this active region and is available for study

chronology of bezymianny volcano activity 1956 2010 abstract bezymianny volcano is one of the most active volcanoes in the world in 1955 for the first time in history bezymianny started to erupt and after six months produced a catastrophic eruption with a total volume of eruptive products of more than 3 km3 following explosive eruption a lava dome began to grow in the resulting caldera lava dome growth continued intermittently for the next 57 years and continues today during this extended period of lava dome growth 44 vulcanian type strong explosive eruptions occurred between 1965 and 2012 this paper presents a summary of activity at bezymianny volcano from 1956 to 2010 with a focus on descriptive details for each event

eruptive processes and caldera formation in a nested downsagcollapse caldera cerro panizos central andes mountains abstract the cerro panizos ignimbrite center in the central andes mountains produced two ignimbrite sheets and many lava flows the ignimbrite of quebrada cienago was erupted at 7 9 ma and effusive eruptions continued until the two cooling units of the crystal rich dacitic cerro panizos ignimbrite were emplaced at 6 7 ma the lower unit has no laterally continuous flow breaks and was erupted from a single vent or small cluster of vents with limited fluctuation in discharge lithic fragments reach significant concentrations 5 only in the uppermost two meters of this cooling unit where they document vent wall collapse or the opening of a new vent the upper cooling unit contains many flow units with variations in welding thicknesses and lithic fragment concentrations implying an unsteady eruption column the opening of many vents and probable caldera collapse triangulation of anisotropy of magnetic susceptibility flow direction measurements locate a single vent for the lower cooling unit whereas the upper cooling unit had many vents within the present dome cluster a 15 km diameter topographic depression marked by inward dips of 4 8 at the cooling unit contact is centered on the vent area of the lower cooling unit the depression is interpreted as a downsag caldera formed during emplacement of the lower cooling unit collapse began late in the eruption of the lower cooling unit and continued through the emplacement of the upper cooling unit resurgent magmatism occurred as lava flows that mundated the caldera area a ring of dacite domes erupted until at least 6 1 ma in the northern half of the downsag caldera traces the margin of a collapse caldera associated with the upper cooling unit maximum caldera subsidence 353 km 3 is not enough to account for the erupted volume 652 km 3 dre minimum the ash poor crystal rich nature up to 50 crystals in the pumice 75 in the matrix of the cerro panizos pyroclastic flows resulted in poor retention of gases and there is little evidence of fluidization the high crystal content however favored modified grain flow processes in which several particle support mechanisms combine with grain dispersive forces it is postulated that the flows were initially partially fluidized but rapidly lost their gases and grain flow processes grew in relative importance grain flow processes destroyed evidence of fluidization before deposition

the effect of paleotopography on lithic distribution and facies associations of small volume ignimbrites the wtt cupa roccamonfina volcano italy abstract the distribution of lithic clasts within two trachytic small volume pumiceous ignimbrites are described from the quaternary white trachytic tuff cupa formation of roccamonfina volcano italy the ignimbrites show a downslope grading of lithics with a maximum size where there is a major break in the volcano s slope rather than at proximal locations this is also the location where ignimbrites are thickest and most massive the break in slope is interpreted to have reduced flow capacity and velocity increasing the sedimentation rate so that massive ignimbrite formed by hindered settling sedimentation ignimbrite cc exhibits no vertical grading of lithics though it does show downslope grading with maximum size at the major break in slope and a rapid decrease further downslope ignimbrite cc thins away from the break in slope and shows an upward fining of the grain size within the topmost few decimeters of the unit the ignimbrite is stratified proximally and grades to massive facies at the break in slope and distally to stratified facies with numerous inverse graded beds the simplest mechanism accounting for these downslope variations is progressive aggradation from a quasi steady nonuniform pyroclastic density current the changes in deposit thickness and facies are interpreted to record downcurrent changes in sedimentation rate the upward fining reflects waning flow inversely graded bedded depositional facies in distal areas is interpreted to reflect flow unsteadiness and a decrease in suspended sediment load ignimbrite cd shows vertical as well as downslope grading of lithics this characteristic coupled with the widespread massive facies of the deposit and the tabular unit geometry are features that can be reconciled with both the debris flow plug analogy for pyroclastic flows sparks 1976 and the progressive aggradation model branney and kokelaar 1992 however none of them appears to satisfy completely the field evidences implying that when dealing with massive ignimbrites other evidence than lithic grading needs to be presented to better understand the related transport and depositional processes

linear inverse problem for inferring eruption source parameters from sparse ash deposit data as viewed from an atmospheric dispersion modeling perspective determination of the volcanic eruption source parameters total grain size distribution and vertical ash mass distribution vmd within the source is carried out on a collection of measured area samples and granulometry data for this the geophysical inverse methods and hybrid particle and concentration transport model hypact driven by wind and turbulence fields simulated with the regional atmospheric modeling system rams are used a two step inversion procedure is proposed to obtain approximate but physically meaningful solution when the total number of ashfall samples is small and it is not possible to make a good initial guess of the source parameters first a spectrum of particle fall velocities is estimated by selecting a best fit subset of aerodynamically distinct subpopulations of free and aggregate particles from the trial set used to simulate a polycomponent ashfall the singular value decomposition svd analysis is then employed to identify spatial components of the ash emissions vertical distribution as resolvable by the observations model validation experiments are conducted for the january 12 2011 short duration vulcanian explosion at kizimen and paroxysmal phase of the december 24 2006 sub plinian eruption at bezymianny the derived vmds exhibit high variability in fine ash content 60 100 wt as well as strong secondary maxima in the lower troposphere likely reflecting the contribution of ash particles fallen out of co pyroclastic flow ash clouds and partially collapsing eruption columns

the interaction of ash flows with ridges using both laboratory experiments and theoretical models we examine the different flow regimes that may develop when an ash flow encounters a ridge for very small ridges all the flow may pass over the ridge for intermediate size ridges the flow may be partially blocked with a fraction of the flow reflected upstream as a travelling bore in this case the remainder of the flow which does pass over the ridge is hydraulically controlled at the ridge crest finally if the ridge is sufficiently high then the flow will be totally blocked new laboratory experiments show that the sedimentation patterns associated with these flow regimes may be very different most importantly flows that involve partial blocking and the formation of upstream propagating bores display enhanced sedimentation upstream of the ridge analogous to valley ponded and caldera fill deposits in contrast under some circumstances if the flow is able to scale a ridge the deposit may be relatively unaffected by the presence of the ridge the minimum ridge height that leads to total blocking of the flow increases with mass eruption rate and has a complex variation with distance from the source in a one dimensional channel the minimum ridge height that causes blocking increases with distance downstream this is because the flow becomes less dense through sedimentation of particles and entrainment of air and so requires less energy to scale a ridge of a particular height in axisymmetric flow the minimum ridge height initially decreases with distance downstream as the flow spreads radially but subsequently increases as the flow becomes less dense through sedimentation and entrainment a new quantitative model of dilute ash flows propagating over ridges indicates that flows with mass fluxes in excess of 108 109 kg s can partially scale barriers as high as 1000 m at distances of tens of kilometres from the source whereas smaller flows are likely to be totally blocked by such an obstacle our results shed new insight on the possible long range transport mechanism of several large flows including the ata fisher and aniakchak pyroclastic flows

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

instantaneous dynamic pressure effects on the behaviour of lithic boulders in pyroclastic flows the abrigo ignimbrite tenerife canary islands a method for estimating the instantaneous dynamic pressure near the base of ancient pyroclastic flows using large lithic boulders from the late pleistocene abrigo ignimbrite is proposed here the minimum instantaneous dynamic pressure is obtained by determining the minimum aerodynamic drag force exerted by a pyroclastic flow onto a stationary boulder that will allow the boulder to overcome static friction with the underlying substrate and move within the flow consideration is given to the properties of the boulder shape roughness size density and orientation relative to the flow substrate type and hill slope angle boulder substrate interface looseness of boulder coefficient of static friction and flow coefficient of aerodynamic drag nineteen boulders from massive lithic rich ignimbrite deposits at two localities on tenerife were assessed in this study minimum dynamic pressures required for abrigo pyroclastic flows to move these boulders ranged from 5 to 38 kpa which are comparable to dynamic pressures previously calculated from observations of the damage caused by recent pyroclastic flows considering the maximum possible range in flow density the derived minimum velocity range for the abrigo pyroclastic flows is 1 3 to 87 m s 1

geochronology and stratigraphy of the ignimbrites from the 21 30 s to 23 30 s portion of the central andes of northern chile the central volcanic zone cvz of the andes which extends from 14 to 28 s is one of the largest provinces of late tertiary to recent ignimbrite volcanism in the world in the 21 30 s to 23 30 s portion of the cvz in northern chile ignimbrite volcanism was initiated at the beginning of the late miocene 10 4 ma ago and continued until the recent the stratigraphy is dominated by the products of five major dacitic ignimbrite eruptions 100 km3 the artola ignimbrite member 9 4 ma the sifon ignimbrite member 8 3 ma the pelon ignimbrite member 5 5 ma the puripicar ignimbrite member 4 2 ma and the atana ignimbrite member 4 1 ma at least three of these represent only portions of larger ignimbrite sheets erupted from centres of sw bolivia two of the ignimbrites the sifon and atana ignimbrites must represent erupted volumes in excess of 1000 km3 each the major units which represent 90 of the total volume of ignimbrite in this area are intercalated with smaller 50 km3 less extensive volcanic units some of which were erupted from source structures within the study area the upper tertiary to recent volcanic stratigraphy has been revised using the large ignimbrites as the major stratigraphic horizons the ignimbrite formations can be divided into two groups on a geographic basis those in the northern and central portions of the study area are known as the san bartolo group while those in the southern portion belong to the silapeti group these two groups appear to be contemporaneous although the silapeti group may represent a period of ignimbrite volcanism which was initiated later about 6 ma ago the ignimbrite formation of sw bolivia and the punense arancaniano formation of nw argentina are equivalent to the san bartolo and silapeti groups based on correlation of the stratigraphy into adjacent areas in sw bolivia and nw argentina the beginning of the late miocene 10 4 ma marks the onset of the most intense phase ignimbrite volcanism in the cvz this phase of volcanism is suggested to be the result of crustal melting in response to crustal thickening during the quechua phase of deformation and subduction approximately 10 000 km3 of ignimbrite erupted over a period of 9 ma in the 21 30 23 30 s portion and led to the development of a major ignimbrite province

columnar jointing in vapor phase altered non welded cerro galan ignimbrite paycuqui argentina columnar jointing is thought to occur primarily in lavas and welded pyroclastic flow deposits however the non welded cerro galan ignimbrite at paycuqui argentina contains well developed columnar joints that are instead due to high temperature vapor phase alteration of the deposit where devitrification and vapor phase crystallization have increased the density and cohesion of the upper half of the section thermal remanent magnetization analyses of entrained lithic clasts indicate high emplacement temperatures above 630 c but the lack of welding textures indicates temperatures below the glass transition temperature in order to remain below the glass transition at 630 c the minimum cooling rate prior to deposition was 3 0 10 3 8 5 10 2 c min depending on the experimental data used for comparison alternatively if the deposit was emplaced above the glass transition temperature conductive cooling alone was insufficient to prevent welding crack patterns average 4 5 sides to each polygon and column diameters average 75 cm are consistent with relatively rapid cooling where advective heat loss due to vapor fluxing increases cooling over simple conductive heat transfer the presence of regularly spaced complex radiating joint patterns is consistent with fumarolic gas rise where volatiles originated in the valley confined drainage system below joint spacing is a proxy for cooling rates and is controlled by depositional thickness valley width we suggest that the formation of joints in high temperature non welded deposits is aided by the presence of underlying external water where vapor transfer causes crystallization in pore spaces densifies the deposit and helps prevent welding

incorporation and redistribution of locally derived lithic fragments within a pyroclastic flow the lower miocene peach springs tuff exposed in the newberry mountains california was deposited within a paleovalley trending s65 w exposures within the paleovalley contain lithic breccia intercalated with ash rich ignimbrite the clast assemblage of the lithic breccias matches the rock types of the paleovalley walls and therefore the clasts were not derived from a distant eruptive vent flow direction breccia bed thickness grain size data and sedimentary textures indicate that the lithic breccias were deposited from density currents within the pyroclastic flow that moved down tributaries and into the main paleovalley to be intermingled with the ash rich pyroclastic flow a model is proposed whereby a turbulent boundary layer at the base of the pyroclastic flow is induced by surface roughness of the substrate and incorporates loose material from the substrate to produce a high density ground layer that decouples from the lower density ash rich pyroclastic flow after decoupling has occurred the high density lithic rich ground layer moves independently from the ash rich pyroclastic flow the lithic breccia horizons have many characteristics of proximal lag breccias and caution must be used when inferring distance from vent in ancient ignimbrites based on the occurrence of coarse breccias

three different types of plumbing system beneath the neighboring active volcanoes of tolbachik bezymianny and klyuchevskoy in kamchatka

propagation and hindered settling of laboratory ash flows the fluidal behavior of pyroclastic flows is commonly attributed to high gas pore pressures and associated fluidization effects we carried out experiments on flows of fluidized volcanic ash at 170 c which is hot enough to reduce cohesive effects of moisture the flows were generated in a 3 m long horizontal lock exchange flume the ash was fluidized and expanded uniformly in the flume reservoir by up to 43 above loose packing and was then released each flow defluidized progressively down the flume until motion ceased initial expansion e and initial height h0 were varied independently of one another the flows traveled in a laminar manner flow fronts exhibited three main phases of transport 1 a brief initial phase of gravitational slumping 2 a dominant approximately constant velocity phase and 3 a brief stopping phase phase 2 frontal velocities scaled with equation image like other types of dam break flow deposition from initially expanded flows took place by progressive sediment aggradation at a rate that was independent of distance and varied only with e despite rates of shear up to 80 s 1 aggradation rates were identical to those determined independently at the same value of e in quasi static collapse tests sedimentation caused the flows to thin progressively during transit until they ran out of volume the dynamics were governed to a first order by two dimensionless parameters 1 the initial aspect ratio h0 x0 in the lock reservoir and 2 the ratio tsett tgrav of two timescales a particle settling time tsett and a gravitational acceleration time tgrav

assembling an ignimbrite mechanical and thermal building blocks in the bishop tuff california abstract the building blocks that control ignimbrite physical characteristics are here defined as mechanical flow units and flow packages and thermal cooling units ignimbrite construction from these mechanical and thermal building blocks is illustrated by a longitudinal profile of the bishop tuff in the owens river gorge california in the bishop ignimbrite flow unit boundaries can be defined only locally but known or inferred multiple flow units combine to form eruptive packages showing imbricate offlapping relationships such that each package is thickest successively farther from the source in these packages the presence or absence of flow unit boundaries does not necessarily reflect directly the presence or absence respectively of time breaks thus massive ignimbrite need not be the product of continuous accumulation progressive aggradation the intrinsic thermal properties of each package or parts thereof have combined with local thicknesses of accumulated material to control the weld

satellite thermal observations of the bezymianny lava dome 1993 2008 precursory activity large explosions and dome growth 1 fifteen years worth of advanced very high resolution radiometer avhrr data is presented and used to quantitatively assess processes occurring at bezymianny this andesitic volcano is one of kamchatka s most dangerous volcanoes with 16 eruptions in the last decade that have dispersed ash into north pacific air routes all known episodes of increased activity for which data were available were detected in band 3 3 53 3 93 m avhrr thermal data twenty three peaks can be seen in the data nineteen peaks correspond to known explosions while the remaining three peaks correspond to known phases of dome growth that were not believed to have been accompanied by explosive activity start and end dates of extrusive phases defined by the thermal data are presented repose times between phases of extrusion vary from four months to just over two and half years with an average of just less than a year using rank order statistics a maximum time interval between consecutive explosions of 1288 170 days is determined this could serve as a cut off time for declaring the current dome growth activity over the calculated cumulative erupted volume 0 28 km3 and time averaged extrusion rate 0 6 m3 s 1 from 1993 to 2008 corresponds to values found at bezymianny from 1956 to 1976 showing that the satellite based methodology provides a good way of quantitatively assessing dome growth three different types of precursors to explosive behavior have been identified at bezymianny 1 values that cluster around the mode of the data set prior to explosion potentially due to endogenous dome growth 2 upward trends that commence 15 20 days prior to explosion and reach sensor saturation levels are due to significant extrusion and 3 a gradual upward trend that starts 5 days prior to explosion probably due to ramping up of extrusion this work shows that retrospectively analyzing and modeling of a volcano s thermal signal provides increased insight into its characteristic behavior the methods used in this paper can be used at other dome building volcanoes around the world the insights presented here can be used to improve monitoring capabilities to aid in providing early warnings to large explosions at bezymianny

preliminary report on the activity at unzen volcano japan november 1990 november 1991 dacite lava domes and pyroclastic flows abstract the eruption of unzen volcano commenced on 17 november 1990 phreatic and phreatomagmatic eruptions occurred by early may 1991 no large scale explosive eruptions preceded the extrusion of lava domes lava domes appeared in a summit crater on 20 may 1991 and they grew on the steep slope of mt fugen at unzen volcano rockfalls from the margins of the domes frequently generated pyroclastic flows major pyroclastic flows occurred on 3 june 8 june and 15 september 1991 the 3 june pyroclastic flow killed forty three persons many of the pyroclastic flows seem to have resulted from the simple rockfalls except one flow on 8 june which was accompanied by an explosion from the crater many of the rockfalls that generated pyroclastic flows were witnessed as of november 1991 unzen volcano was still active with a nearly constant magma supply rate of about 0 3 106 m3 d the total magma output exceeded 45 106 m3 by the beginning of november 1991 the volume of the lava domes is more than 23 106 m3

the evolution of volcanic systems following sector collapse abstract sector collapses affect volcanic edifices across all tectonic settings and involve a rapid redistribution of mass comparable in scale to the largest magmatic eruptions the eruptive behaviour of a volcano following sector collapse provides a test of theoretical relationships between surface loading and magma storage which imply that collapse driven unloading may lead to changes in eruption rate and erupted magma compositions large sector collapses are infrequent events globally with all historical examples being relatively small in comparison to many of the events documented in the geological record as a result exploration of the impacts of sector collapse on eruptive behaviour requires detailed investigation of prehistoric collapses but this is often hindered by poorly resolved stratigraphic relationships and dating uncertainties nevertheless observations from a number of volcanoes indicate sharp changes in activity following sector collapse here a global synthesis of studies from individual volcanoes in both arc and intraplate settings is used to demonstrate a number of common processes in post collapse volcanism multiple examples from large 5 km3 sector collapses in arc settings show that collapse may be followed by compositionally anomalous large volume and often effusive eruptions interpreted to originate via disruption of a previously stable upper crustal reservoir these anomalous eruptions highlight that magma compositions erupted during periods of typical i e unperturbed by sector collapse volcanism may not be representative of the range of compositions stored within a vertically extensive crustal reservoir if eruptible magma is not present upper crustal reservoirs may rapidly solidify following collapse without further eruption allowing more mafic compositions to ascend to the surface with only limited upper crustal modification resulting in edifice regrowth at temporarily elevated eruption rates subsequent re establishment of an upper crustal reservoir further supports a relationship between surface loading and crustal storage but long term chemical and mineralogical differences between pre and post collapse evolved magmas imply that a newly developed reservoir can overprint the influence of a preceding reservoir forming a spatially and compositionally distinct plumbing system these broad patterns are replicated in intraplate settings despite differences in scale and melting processes current evidence suggests that post collapse evolution of intraplate volcanoes can be explained by unloading induced destabilisation of the magma plumbing system rather than increased melt production what emerges from an apparently diverse set of observations is a systematic behaviour that strongly supports a coupling between edifice growth and magma ascent storage and pressurisation eruption rates erupted compositions and the style of volcanism at any particular system may thus be modulated from the surface and long term shifts in surface behaviour may occur without any changes in the deep parts of magmatic systems observations of sharp post collapse changes in erupted compositions including the ascent of primitive mafic magmas also require a crystal dominated mid to upper crustal reservoir consistent with recent models of crustal magmatic systems

recent eruptions at bezymianny volcano a seismological comparison abstract for the past few decades bezymianny volcano has erupted once to twice per year here i examine eight eruptive events between 2006 and 2010 this is the first time period for which proximal or broadband seismic data have been recorded at bezymianny several recurring patterns are demonstrated in advance of eruptions eruptions are generally preceded by 12 36 h of tremor energy elevated by 2 to 3 orders of magnitude locatable earthquake activity is quite erratic in the days before eruptions for eruptions of juvenile magma however the cumulative moment magnitude increases with the repose time since the previous eruption though tenuous this relationship is statistically significant and could improve forecasts of bezymianny eruptions the most energetic eruptions demonstrate increasing multiplet activity in the run up followed by a rapid cessation at the time of eruption when present this behavior marks increasing pressure in the conduit system as degassing eclipses the capacity for venting very long period seismicity 20 s periods accompanies some eruptions these tend to be the same short lived high energy eruptions that exhibit multiplet precursors four eruptions are examined in detail to illustrate the variety in eruption mechanisms lava dome collapses sustained eruptions singular paroxysmal explosions and post explosion lava flows occur in different combinations demonstrating that more than one eruption trigger is regulating bezymianny compared to bezymianny s fifty year modern history recent eruptions have been shorter lived and separated by longer repose times some evidence suggests that these eruptions may be increasingly explosive a speculation that carries significant hazard implications if true however this threat is tempered by solid evidence that the most explosive eruptions are preceded by the clearest precursors suggesting an ability to improve the already excellent eruption forecasts available for bezymianny

particle velocity fields and depositional processes in laboratory ash flows with implications for the sedimentation of dense pyroclastic flows we conducted laboratory experiments on dam break flows of sub 250 m volcanic ash generated by the release of gas fluidized and variably non expanded to expanded up to 35 beds in order to gain insights into the internal kinematics of pyroclastic flows the flows were typically several cm thick and had frontal speeds of up to 2 m s 1 high speed videos taken through the transparent sidewall of the 3 m long channel were analyzed with a particle tracking algorithm providing a spatial and temporal description of transport and sedimentation the flows deposited progressively as they traveled down the flume being consumed by sedimentation until they ran out of volume deposition commenced 5 20 cm rearward of the flow front and for a given expansion proceeded at a rate independent of distance from the lock gate deposit aggradation velocities were equal to those inferred beneath quasi static bed collapse tests of the same ash at the same initial expansions implying that shear rates of up to 300 s 1 have no measurable effect on aggradation rate the initially non expanded and just fluidized flow deposited progressively at a rate indicative of an expansion of a few percent perhaps due to shear induced reynolds dilation during initial slumping the fronts of the flows slid across the flume floor on very thin basal shear layers but once deposition commenced a no slip condition was established at the depositional interface within the flows the trajectory of the constituent particles was linear and sub horizontal the velocities of the particles increased with height above the depositional interface reached a maximum then declined slightly towards the flow surface perhaps due to air drag at a given location the velocity profiles were translated upwards as the deposit aggraded the results show that even cm thin poorly expanded flows of ash deposit progressively as inferred for many pyroclastic flows the change from frontal slip to rearward no slip conditions at the bases of the laboratory flows are qualitatively consistent with some textural features of pyroclastic flow deposits

anisotropy of magnetic susceptibility studies of depositional processes in the campanian ignimbrite italy the late pleistocene trachytic campanian ignimbrite underlies much of the campanian plain near naples italy and occurs in valleys in the mountainous area surrounding the plain out to about 80 km from its source the campi flegrei caldera at sites within 15 km of the campi flegrei anisotropy of magnetic susceptibility ams principal directions indicate that in the absence of significant topography deposition came from a flow moving in a roughly radial direction ams studies of the more distal ignimbrite reveal downhill and or downvalley flow directions prior to deposition even where these directions are at high angles to a generally radial transport direction from the vent on the flanks of roccamonfina volcano flow was directly downhill as if the source of the ignimbrite was the summit of the volcano in most localities the ignimbrite consists of a single massive deposit in a few localities in the apennine mountains however the confluence of multiple drainage systems off mountains resulted in multiple local flow units that cannot be correlated between valleys a detailed study of the ignimbrite in the flat titerno river valley near massa shows that the ams fabrics are not due to late stage creeping during deposition or compaction well defined but non parallel ams fabrics from vertical and lateral sections in the massa area are best explained by the merging of gravity currents flowing down the valley and steep valley sides to form a single aggradational deposit clast compositions and ams axes at mondragone indicate that the pyroclastic flow encountered the monte massico massif and was partially blocked so that flow during deposition was toward the campi flegrei similar ams data from sites along the edge of the campanian plain indicate back flow off the first ridge of the apennine mountains reached at least 5 km from their base the campanian ignimbrite was deposited from a density stratified pyroclastic flow the depositional system consisted of the lower denser portion of the current and was controlled by topography the grouping of the ams axes is interpreted to indicate that deposition occurred under laminar flow conditions

aster and field observations of the 24 december 2006 eruption of bezymianny volcano russia abstract an explosive eruption occurred at bezymianny volcano kamchatka peninsula russia on 24 december 2006 at 09 17 utc seismicity increased three weeks prior to the large eruption which produced a 12 15 km above sea level asl ash column we present field observations from 27 december 2006 and 2 march 2007 combined with satellite data collected from 8 october 2006 to 11 april 2007 by the advanced spaceborne thermal emission and reflection radiometer aster as part of the instrument s rapid response program to volcanic eruptions pixel integrated brightness temperatures were calculated from both aster 90 m pixel thermal infrared tir data as well as 30 m pixel short wave infrared swir data four days prior to the eruption the maximum tir temperature was 45 c above the average background temperature 33 c at the dome which we interpret was a precursory signal and had dropped to 8 c above background by 18 march 2007 on 20 december 2006 there was also a clear thermal signal in the swir data of 128 c using aster band 7 2 26 m the maximum swir temperature was 181 c on the lava dome on 4 january 2007 decreasing below the detection limit of the swir data by 11 april 2007 on 4 january 2007 a hot linear feature was observed at the dome in the swir data which produced a maximum temperature of 700 c for the hot fraction of the pixel using the dual band technique this suggests that magmatic temperatures were present at the dome at this time consistent with the emplacement of a new lava lobe following the eruption the eruption also produced a large 6 5 km long by up to 425 m wide pyroclastic flow pf deposit that was channelled into a valley to the south southeast the pf deposit cooled over the following three months but remained elevated above the average background temperature a second field investigation in march 2007 revealed a still warm pf deposit that contained fumaroles it was also observed that the upper dome morphology had changed in the past year with a new lava lobe having in filled the crater that formed following the 9 may 2006 eruption these data provide further information on effusive and explosive activity at bezymianny using quantitative remote sensing data and reinforced by field observations to assist in pre eruption detection as well as post eruption monitoring

transport of pyroclastic flows across the sea during the explosive rhyolitic eruption of the kos plateau tuff greece the kos plateau tuff kpt is dominated by a sequence of nonwelded rhyolitic ignimbrites some of which were deposited more than 60 km from source on islands in the eastern aegean sea greece palaeo shoreline reconstruction at the time of the kpt eruption 161 ka suggests that northward directed pyroclastic flows travelled over an extensive landmass although the proximal zone may have been sea in comparison flows directed to the southeast and east most likely crossed wide expanses of sea depositing ignimbrite on islands and peninsulas the ignimbrites include basal coarse lithic rich breccias overlain by thick massive pumiceous zones and generally have low abundances of fine ash they are interpreted to have been deposited from pyroclastic flows that were relatively dilute and stratified with lower denser lithic rich zones and upper expanded pumice rich zones high velocity inherited from the intensity of the eruption combined with turbulence and low bulk density favoured transport across water the pyroclastic flows remained hot even after crossing 35 km of the sea heat capacity equations indicate that a depth of 1 cm of water ingested over the outflow path would have cooled the flows by only a few degrees the ignimbrites deposited prior to the eruption climax have distributions restricted by 300 m high topographic barriers and they thicken in topographic depressions these ignimbrites show significant decreases in grain size proportion of lithic clasts and thickness with distance from source in comparison during the eruption climax the coarsest most voluminous and widespread kpt ignimbrite was deposited this ignimbrite has relatively even thickness and uniform componentry and texture regardless of topographic relief or distance from source textural analysis indicates that crossing 35 km water to the southeast had little effect on the pyroclastic flow generated during the eruption climax except for the loss of the coarsest 20 cm vent and conduit derived lithic clasts preferential loss of lithic clasts is related to the mechanism by which they were transported on land large dense clasts could be saltated over the ground surface at the base of the pyroclastic flow in the case of transport over water these large dense clasts sank and were permanently removed from the transport system outflow across water had a greater effect on the pre climax pyroclastic flows the ignimbrites formed at this stage are significantly thinner and slightly finer grained and lack basal lithic breccias and lithic clasts 5 cm where the pyroclastic flows crossed the sea reflecting the lower velocities of the flows all kpt ignimbrites to the east of the source were deposited from pyroclastic flows that crossed 25 km of water ignimbrites in this sector are markedly finer grained possibly as a result of blocking of coarser pyroclasts by a topographic barrier close to source

the bishop tuff new insights from eruptive stratigraphy the 0 76 ma bishop tuff from long valley caldera in eastern california consists of a widespread fall deposit and voluminous partly welded ignimbrite the fall deposit f exposed over an easterly sector below and adjacent to the ignimbrite is divided into nine units f1 f9 with no significant time breaks except possibly between f8 and f9 maximum clast sizes are compared with other deposits where accumulation rates are known or inferred to estimate an accumulation time for f1 f8 as ca 90 hrs the ignimbrite ig is divided into chronologically and or geographically distinct packages of material earlier packages ig1 were emplaced mostly eastward are wholly intraplinian coeval with fall units f2 f8 lack phenocrystic pyroxenes and contain few or no glass mountain derived rhyolite lithic fragments earlier packages ig2 were erupted mostly to the north and east are at least partly intraplinian interbedded with fall unit f9 to the east contain pyroxenes and have lithic fractions rich in g

ranking welding intensity in pyroclastic deposits welding of pyroclastic deposits involves flattening of glassy pyroclasts under a compactional load at temperatures above the glass transition temperature progressive welding is recorded by changes in the petrographic e g fabric and physical e g density properties of the deposits mapping the intensity of welding can be integral to studies of pyroclastic deposits but making systematic comparisons between deposits can be problematical here we develop a scheme for ranking welding intensity in pyroclastic deposits on the basis of petrographic textural observations e g oblateness of pumice lapilli and micro fabric orientation and measurements of physical properties including density porosity point load strength and uniaxial compressive strength our dataset comprises measurements on 100 samples collected from a single cooling unit of the bandelier tuff and parallel measurements on 8 samples of more densely welded deposits the proposed classification comprises six ranks of welding intensity ranging from unconsolidated rank i to obsidian like vitrophyre rank vi and should allow for reproducible mapping of subtle variations in welding intensity between different deposits the application of the ranking scheme is demonstrated by using published physical property data on welded pyroclastic deposits to map the total accumulated strain and to reconstruct their pre welding thicknesses

high emission rate of sulfuric acid from bezymianny volcano kamchatka high concentrations of primary sulfuric acid h2so4 in fumarolic gases and high emission rate of sulfuric acid aerosol in the plume were measured at bezymianny volcano an active dome growing andesitic volcano in central kamchatka using direct sampling filter pack sampling and differential optical absorption spectroscopy measurements we estimated an average emission of h2so4 at 243 75 t d in addition to an average so2 emission of 212 65 t d the fumarolic gases of bezymianny correspond to arc gases released by several magma bodies at different stages of degassing and contain 25 92 of entrained air h2so4 accounts for 6 87 mol of the total sulfur content 42 8 mol on average and so2 is the rest the high h2so4 in bezymianny fumaroles can be explained by catalytic oxidation of so2 inside the volcanic dome because sulfate aerosol is impossible to measure remotely the total sulfur content in a plume containing significant h2so4 may be seriously underestimated

mobility of a large volume pyroclastic flow emplacement of the campanian ignimbrite italy abstract the trachytic campanian ignimbrite originally exposed over a 30 000 km 2 area around naples italy is the product of a highly energetic gas rich eruption the deposit lies in valleys and isolated watersheds and in its medial and distal extent to the south north and east of naples the campanian pyroclastic current encountered mountains exceeding 1000 meters anisotropy of magnetic susceptibility ams measurements indicate that the campanian pyroclastic current the transport system traveled radially outward from the phlegrean fields area but the ignimbrite forming flow the deposition system that developed from the base of the transport system moved downslope from mountainsides to valleys including slopes facing the eruption source and flowed down drainage systems from intermontane basins the campanian pyroclastic current flowed 35 km over the water of the bay of naples to deposit 43 m of ignimbrite on the south shore and also overtopped a 685 1000 m high ridge of the sorrento peninsula to deposit more on the other side the distribution of the ignimbrite and the measured flow directions suggest that the campanian pyroclastic current moved across the landscape as an expanded and therefore turbulent decompressing flow rather than as a high density nonturbulent sheet like current moving over mountains by momentum acquired by eruption column collapse strong expansion is corroborated by shard morphology that indicates derivation from highly inflated pumice and suggests vesicles must have been at least 80 by volume of the original magma

the influence of palaeotopography on facies architecture and pyroclastic flow processes of a lithic rich ignimbrite in a high gradient setting the abrigo ignimbrite tenerife canary islands abstract the late pleistocene 188 19 ka abrigo ignimbrite represents the last major explosive caldera forming eruption on tenerife it consists almost entirely of a moderate volume 1 8 km 3 light grey phonolitic lithic rich ignimbrite deposit although a possible abrigo member thin fall deposit is locally preserved beneath the ignimbrite suggesting an initial short lived stable plinian eruption column the ignimbrite deposit is dispersed radially around the lower flanks of the las canadas edifice and correlates to a clast supported lithic breccia on the eastern and northern caldera wall much of the ignimbrite was probably deposited offshore or within the caldera now buried by more recent lavas two major depositional units separated by a co ignimbrite ash cloud deposit and which display dramatic variations in thickness pyroclastic flows were channelised along and deposited within the same valleys that exist today and were commonly continuous and sheet like across the interfluves the basal zones of pyroclastic flows are envisaged as a bed load of coarse lithic lapilli and blocks transported under their own momentum and with the support of the surrounding fine ash gas granular flow

phase equilibria constraints on pre eruptive magma storage conditions for the 1956 eruption of bezymianny volcano kamchatka russia abstract phase equilibria experiments were performed on andesites from the catastrophic 1956 eruption of bezymianny volcano kamchatka russia to determine pre eruptive magma storage conditions fifteen experiments were conducted under water saturated conditions with oxygen fugacity equal to the ni nio oxygen buffer at temperatures between 775 and 1100 c and pressures between 50 and 200 mpa simultaneous amphibole and plagioclase crystallization is reproduced at 850 c and 200 mpa the simultaneous crystallization temperature range of the plagioclase clinopyroxene orthopyroxene fe ti oxide assemblage increases with decreasing pressure from 840 to 940 c at 150 mpa to 940 1020 c at 50 mpa melt inclusion compositions in plagioclase phenocrysts and matrix glass match experimental melt compositions reproduced at 50 100 mpa and 50 mpa respectively presence of the silica phase in groundmass and mature amphibole breakdown rims suggests that magma has been stored at ca 3 km depth prior to the final ascent for at least 40 days syn eruptive ascent led to decompression driven crystallization which caused a temperature increase from 850 900 c to 950 1000 c

the magma plumbing system of bezymianny volcano insights from a 54 year time series of trace element whole rock geochemistry and amphibole compositions abstract samples from 33 individual eruptions of bezymianny volcano between 1956 and 2010 provide an opportunity to study in detail the temporal evolution of an arc volcano major element and icp ms trace element analyses show that the eruptive products shifted progressively from relatively silicic magma in 1956 60 4 sio2 to more mafic compositions e g 56 8 sio2 in 2010 amphibole compositions changed concurrently from low al2o3 to high al2o3 whole rock element element variation diagrams show tight compositional arrays some with a distinct kink in the late 1970s which cannot be reproduced by fractionation of a single magma along a liquid line of descent amphibole thermobarometry indicates amphibole crystallization in two separate reservoirs one between 200 and 300 mpa and another between 500 and 750 mpa liquid compositions calculated from the amphibole analyses show that liquids stored in each reservoir become increasingly mafic from 1956 to 2010 suggesting that each reservoir received magma inputs from more mafic sources throughout the eruptive cycle end member mixing analysis of the dataset allows calculation of three end member compositions that can be combined in varying proportions to reproduce major and trace element whole rock compositions the end member mixing proportions vary systematically between 1956 and 2010 with maxima for end members a b and c during 1956 1977 and 2010 respectively major element compositions of phenocrysts combined with published trace element partition coefficients show that each end member may have evolved from a common parental magma by fractionation of three different mineral assemblages possibly due to different pressures of crystallization and volatile contents the petrologic data are consistent with three magma reservoirs at different depths magmas from the shallowest reservoir erupted first with increasing proportions of deeper reservoirs over time past studies have demonstrated similarities in eruptive style between bezymianny and both mount st helens and soufriere hills volcanoes contrasting time series data show that the magma plumbing systems of mount st helens and bezymianny have little in common while soufriere hills may be a better analog similar eruptive styles at the surface do not necessarily reflect similar systems of magma supply and evolution at depth

explosive rhyolitic volcanism in the jemez mountains vent locations caldera development and relation to regional structure the jemez volcanic field straddles the western margin of the rio grande rift where the rift is intersected by the jemez lineament in north central new mexico the field has a record of volcanism extending back to before 13 ma initial basaltic activity was related to active rifting with minor rhyolitic eruptions occurring along n s rift bounding faults between 10 and 7 ma voluminous andesitic volcanism took place in the central jemez mountains area overwhelming contemporaneous basaltic and rhyolitic magmatism an apparent tectonic lull took place from 7 to 4 ma accompanied by lower eruption rates during this interval dacitic magmas were erupted to form the tschicoma volcanic center but mafic and rhyolitic volcanism virtually ceased since 4 ma accompanying resumption of rifting a growing silicic magma system has been present under the central part of the jemez mountains ultimately evolving to the magma body that produced the voluminous rhyolitic bandelier tuffs explosive rhyolitic eruptions from this large magma body have occurred many times since 3 to 4 ma early eruptions 3 6 2 8 ma produced high silica rhyolite ignimbrites restricted to the southwest part of the jemez mountains formation of these units may have been accompanied by caldera collapse these events were followed by the two caldera forming bandelier tuff ignimbrite eruptions 1 45 and 1 12 ma post caldera explosive and effusive rhyolite eruptions have also tapped the magma body from vents generally located along ring fractures after both bandelier events vent and caldera locations for the rhyolitic eruptions during 3 4 ma have been inferred from grain size characteristics dispersal patterns and facies variations in the plinian deposits and ignimbrites lithic breccia zones of the pre bandelier ignimbrites indicate possible caldera sources in the southwest part of the present valles caldera during the eruption of both bandelier tuffs initial plinian falls and early pyroclastic flows emanated from vents centrally located in the jemez mountains in the lower bandelier tuff eruption a transition to ring fracture vents occurred before the emission of later pyroclastic flows but there is no strong evidence to suggest such a transition occurred during the upper bandelier eruption calderas associated with the lower and upper bandelier tuffs toledo and valles respectively are almost identical in location as are the plinian vent sites for these two large eruptions the toledo embayment northeast of the valles caldera contains lava domes from up to 3 6 ma and may be a caldera or crater associated with early explosive dacitic volcanism in the tschicoma volcanic center post 1 4 ma lava domes also fill this depression the main volcanic features of the jemez mountains field including the valles caldera complex eruption vents and the apical graben of the post valles redondo resurgent block appear to be aligned along the ne sw trending jemez fault zone this zone the local expression of a precambrian basement feature the jemez lineament has exerted strong control on the location and style of eruptions from the bandelier rhyolitic magma system

the kizilkaya ignimbrite an unusual low aspect ratio ignimbrite from cappadocia central turkey abstract the 4 3 m y old medium volume low aspect ratio kizilkaya ignimbrite 50 100 km3 dre is one of the most widespread in the cappadocian volcanic province covering about 8500 10 600 km2 the ignimbrite rests on a relatively fine grained fan of plinian pumice fall deposit md of 1 0 1 80 mm in proximal locations the eruptive center was located in the misli plain northeast of nigde as deduced from thickness and grain size variations of the fall deposit flow direction indicators welding patterns of the ignimbrite and the distribution of certain types ofxenoliths the massive ignimbrite generally about 15 m thick covers a paleoplain throughout at least two thirds of its areal extent it comprizes two flow units identified by local pumice enrichment in the upper part of the lower unit the ignimbrite is completely welded in many places in other places the lower flow unit is non welded particularly where the initial pumice fall deposit was eroded a fine grained ground layer was deposited and undulating or cross laminations with antidunes were developed the ground layer was derived from the ignimbrite ground mass by loss of fines depositional characteristics indicate that the ignimbrite was emplaced as high concentration flows with relatively low velocity and low heat loss during runout local development of a ground layer and internal bedding structures indicate local increased turbulence only within individual flow portions due to agitated fluidization from engulfed air the degree of welding of the lower flow unit was controlled by this turbulence and is not related to thickness variations

magma source beneath the bezymianny volcano and its interconnection with klyuchevskoy inferred from local earthquake seismic tomography abstract we present a new 3d model of p and s wave velocities and vp vs ratio to 20 km depth beneath the active klyuchevskoy and bezymianny volcanoes kamchatka russia in this study we use travel time data from local seismicity recorded by temporary stations of the pire experiment from october 24 to december 15 2009 and permanent stations operated by the kamchatkan branch of geophysical survey kbgs the calculations were performed using the lotos code koulakov 2009 the resolution limitations were explored using a series of synthetic tests with checkerboard patterns in the horizontal and vertical sections at shallow depths the resulting vp and vs anomalies tend to alternate on opposite sides of the lineation connecting the most active volcanic centers of the klyuchevskoy volcanic group kvg this prominent lineation suggests the presence of a large fault zone passing throughout the kvg consistent with regional tectonics we suggest that this fault zone weakens the crust creating a natural pathway for magmas to reach the upper crust beneath bezymianny volcano we observe a shallow anomaly of high vp vs ratio extending to 5 6 km depth beneath klyuchevskoy another high vp vs anomaly is observed at deeper depths of 7 and 15 km these findings are consistent with the regional scale model of koulakov et al 2013a and provide some explanation for how very different eruption styles can be maintained at two volcanoes in close proximity over numerous eruption cycles

the flow dynamics of an extremely large volume pyroclastic flow the 2 08 ma cerro galan ignimbrite nw argentina and comparison with other flow types the 2 08 ma cerro galan ignimbrite cgi represents a 630 km3 dense rock equivalent vei 8 eruption from the long lived cerro galan magma system 6 ma it is a crystal rich 35 60 pumice 10 generally and lithic poor 5 generally rhyodacitic ignimbrite lacking a preceding plinian fallout deposit the cgi is preserved up to 80 km from the structural margins of the caldera but almost certainly was deposited up to 100 km from the caldera in some places only one emplacement unit is preserved in proximal to medial settings and in most distal settings suggesting constant flow conditions but where the pyroclastic flow moved into a palaeotopography of substantial valleys and ridges it interacted with valley walls resulting in flow instabilities that generated multiple depositional units often separated by pyroclastic surge deposits the cgi preserves a widespread sub horizontal fabric defined by aligned elongate pumice and lithic clasts and minerals e g biotite a sub horizontal anisotropy of magnetic susceptibility fabric is defined by minute magnetic minerals in all localities where it has been analysed the cgi is poor in both vent derived accessory lithics and locally derived lithics from the ground surface accidental lithics locally derived lithics are small 20 cm and were not transported far from source points all data suggest that the pyroclastic flow system producing the cgi was characterised throughout by high sedimentation rates resulting from high particle concentration and suppressed turbulence at the depositional boundary layer despite being a low aspect ratio ignimbrite based on these features we question whether high velocity and momentum are necessary to account for extensive flow mobility it is proposed that the cgi was deposited by a pyroclastic flow system that developed a substantial high particle concentration granular under flow which flowed with suppressed turbulence high particle concentration and fine ash content hindered gas loss and maintained flow mobility in order to explain the contemporaneous maintenance of high particle concentration high sedimentation rate at the depositional boundary layer and a high level of mobility it is also proposed that the flow s was continuously supplied at a high mass feeding rate it is also proposed that internal gas pressure within the flow directed downwards onto the substrate over which the flow was passing reduced the friction between the flow and the substrate and also enhanced its mobility the pervasive sub horizontal fabric of aligned pumice lithic and even biotite crystals indicates a consistent horizontal shear force existed during transport and deposition in the basal granular flow consistent with the existence of a laminar shearing granular flow regime during the final stages of transport and deposition

an ignimbrite veneer deposit the trail marker of a pyroclastic flow abstract the term ignimbrite veneer deposit ivd is proposed for a new kind of pyroclastic deposit which is found associated with and passes laterally into taupo ignimbrite of valley pond type in new zealand it forms a thin layer mantling the landscape over 15 000 km 2 and is regarded as the deposit from the trailing tail of a pyroclastic flow where a relaxation of shear stress favoured the deposition of the basal part of the flow the ivd differs little in grain size from the associated ignimbrite but it shows a crude internal stratification attributed to the deposition of a succession of layers one after the passage of each pulse of the pyroclastic flow it locally contains laterally discontinuous lenses of coarse pumice lee side lenses on the far vent side of topographic obstacles in nearvent exposures the taupo ivd shows lensoid and cross stratified bed forms even where it stands on a planar surface attributed to deposition from a flow travelling at an exceedingly high velocity an ivd can be distinguished from a poorly sorted pyroclastic fall deposit because the beds in it show more rapid lateral variations in thickness it may show a low angle cross stratification and it contains carbonised wood from trees not in the position of growth from the deposit of a wet base surge because it lacks vesicles and strong antidune like structures and contains carbonised vegetation and from a hot and dry pyroclastic surge deposit because it possesses a high content of pumice and fines the significance of an ivd is that it records the passage of a pyroclastic flow where the flow itself has moved farther on

inviscid behaviour of fines rich pyroclastic flows inferred from experiments on gas particle mixtures abstract experiments were carried out on granular flows generated by instantaneous release of gas fluidised bidisperse mixtures and propagating into a horizontal channel the mixture consists of fine 100 m particles of same density with corresponding grain size ratios of 2 to 9 initial fluidisation of the mixture destroys the interparticle frictional contacts and the flow behaviour then depends on the initial bed packing and on the timescale required to re establish strong frictional contacts at a fines mass fraction below that of optimal packing 40 the initial mixtures consist of a continuous network of coarse particles with fines in interstitial voids strong frictional contacts between the coarse particles are probably rapidly re established and the flows steadily decelerate some internal friction reduction appears to occur as and the grain size ratio increases possibly due to particle rolling and the lower roughness of internal shear surfaces segregation only occurs at large grain size ratio due to dynamical sieving with fines concentrated at the flow base in contrast at above that for optimal packing the initial mixtures consist of coarse particles embedded in a matrix of fines flow velocities and run outs are similar to that of the monodisperse fine end member thus showing that the coarse particles are transported passively within the matrix whatever their amount and grain size are these flows propagate at constant height and velocity as inviscid fluid gravity currents thus suggesting negligible interparticle friction we have determined a froude number of 2 61 0 08 consistent with the dam break model for fluid flows and with no significant variation as a function of the grain size ratio and the initial bed expansion very little segregation occurs which suggests low intensity particle interactions during flow propagation and that active fluidisation is not taking place strong frictional contacts are only re established in the final stages of emplacement and stop the flow motion we infer that fines rich i e matrix supported pyroclastic flows propagate as inviscid fluid gravity currents for most of their emplacement and this is consistent with some field data

mantle and crustal sources of magmatic activity of klyuchevskoy and surrounding volcanoes in kamchatka inferred from earthquake tomography

physics of crustal fracturing and chert dike formation triggered by asteroid impact 3 26 ga barberton greenstone belt south africa archean asteroid impacts reflected in the presence of spherule beds in the 3 2 3 5 ga barberton greenstone belt bgb south africa generated extreme seismic waves spherule bed s2 provides a field example it locally lies at the contact between the onverwacht and fig tree groups in the bgb which formed as a result of the impact of asteroid possibly 50 km diameter scaling calculations indicate that very strong seismic waves traveled several crater diameters from the impact site where they widely damaged onverwacht rocks over much of the bgb lithified sediments near the top of the onverwacht group failed with opening mode fractures the underlying volcanic sequence then failed with normal faults and opening mode fractures surficial unlithified sediments liquefied and behaved as a fluid these liquefied sediments and some impact produced spherules filled near surface fractures today represented by swarms of chert dikes strong impact related tsunamis then swept the seafloor p waves and rayleigh waves from the impact greatly exceeded the amplitudes of typical earthquake waves the duration of extreme shaking was also far longer probably hundreds of seconds than that from strong earthquakes dynamic strains of 10 3 occurred from the surface and downward throughout the lithosphere shaking weakened the onverwacht volcanic edifice and the surface layers locally moved downhill from gravity accommodated by faults and open mode fractures coast parallel opening mode fractures on the fore arc coast of chile formed as a result of megathrust events are the closest modern analogs it is even conceivable that dynamic stresses throughout the lithosphere initiated subduction beneath the onverwacht rocks

estimates of total ash content from 2006 and 2009 explosion events at bezymianny volcano with use of a regional atmospheric modeling system abstract the december 24 2006 and december 16 2009 strong explosion events at bezymianny volcano kamchatka peninsula were accompanied by extensive ash falls in proximal and medium distal area

the 26 5 ka oruanui eruption new zealand an introduction and overview abstract the 26 5 ka oruanui eruption from taupo volcano in the central north island of new zealand is the largest known wet eruption generating 430 km3 of fall deposits 320 km3 of pyroclastic density current pdc deposits mostly ignimbrite and 420 km3 of primary intracaldera material equivalent to 530 km3 of magma erupted magma is 99 rhyolite and 90 pdc deposits range from mm to cm thick ultra thin veneers enclosed within fall material to 200 m thick ignimbrite in proximal areas the farthest travelled 90 km most energetic pdcs velocities 100 m s 1 occurred during phase 8 but the most voluminous pdc deposits were emplaced during phase 10 grain size variations in the pdc deposits are complex with changes seen vertically in thick proximal accumulations being greater than those seen laterally from near source to most distal deposits modern lake taupo partly infills the caldera generated during this eruption a 140 km2 structural collapse area is concealed beneath the lake while the lake outline reflects coeval peripheral and volcano tectonic collapse early eruption phases saw shifting vent positions development of the caldera to its maximum extent indicated by lithic lag breccias occurred during phase 10 the oruanui eruption shows many unusual features its episodic nature wide range of depositional conditions in fall deposits of very wide dispersal and complex interplay of fall and pdc activity

surface deformation of bezymianny volcano kamchatka recorded by gps the eruptions from 2005 to 2010 and long term long wavelength subsidence abstract since bezymianny volcano resumed its activity in 1956 eruptions have been frequent recently with up to 1 2 explosive events per year to investigate deformation related to this activity we installed a gps network of 8 continuous and 6 campaign stations around bezymianny the two striking observations for 2005 2010 are 1 rapid and continuous network wide subsidence between 8 and 12 mm yr which appears to affect kamnet stations more than 40 km away where we observe 4 5 mm yr of subsidence and 2 only the summit station bz09 shows slight deviations from the average motion in the north component at times of eruptions the network wide subsidence cannot be explained by tectonic deformation related to the build up of interseismic strain due to subduction of the pacific plate a first order model of surface loading by eruptive products of the kluchevskoy group of volcanoes also explains only a fraction of the subsidence however a deep sill at about 30 km under kluchevskoy that constantly discharges material fits our observations well the sill is constrained by deep seismicity which suggests 9 5 km width 12 7 km length and a 13 dip angle to the south east we infer a closing rate of 0 22 m yr which implies a volume loss of 0 027 km 3 yr 0 16 m yr and 0 019 km 3 yr considering surface loading additional stations in the near and far field are required to uniquely resolve the spatial extent and likely partitioning of this source we explain the eruption related deformation at bz09 with a very shallow reservoir likely within bezymianny s edifice at a depth between 0 25 km and 1 5 km with a volume change of 1 4 10 4 km 3 much of the material erupted at bezymianny may be sourced from deeper mid crustal reservoirs with co eruptive volume changes at or below the detection limit of the gps network installation of more sensitive instruments such as tiltmeters would allow resolving of subtle co eruptive motion