analysis of shuttle multispectral infrared radiometer measurements of the western saudi arabian shield during the november 12 14 1981 mission of the space shuttle columbia the shuttle multispectral infrared radiometer smirr recorded radiances in ten channels along a 100 m wide groundtrack across the western saudi arabian shield the ten channels are located in the 0 5 to 2 4 m region with five positioned between 2 0 and 2 40 m for measuring absorption features that are diagnostic of oh bearing and co3 bearing minerals this exceptionally well exposed area consists of late proterozoic metamorphic intermediate to silicic intrusive and interlayered clastic sedimentary and intermediate silicic volcanic rocks that have not been studied previously using smirr data plots or traces of unnormalized smirr channel ratios were examined before field studies to locate areas with high spectral contrast especially in the 2 0 m to 2 40 m channels reflectance spectra were measured in the laboratory for rock and soil samples collected in these areas and the mineralogic causes of the main absorption features w

predicting yield strengths and effusion rates of lava domes from morphology and underlying topography abstract to investigate the effects of slope on the morphology of lava domes laboratory experiments were conducted with a peg kaolin slurry erupted into cold water on slopes ranging from 0 to 60 in each experiment the slope effusion rate and water temperature were varied producing four distinct morphologies spiny lobate platy and no crust each morphology is correlated with b and slope where b is defined as the ratio of the timescale of solidification to the timescale of advection as the underlying slope increases from 0 to 40 each morphology forms at a lower value of b than it would on a horizontal surface above 40 the transitions between morphologies become independent of slope and the platy morphology is no longer observed once a range of b values for a dome is determined based on its morphology and slope its yield strength or effusion rate can be calculated in the case of active domes observations of the effusion rate can be used to calculate yield strength while for prehistoric domes an assumption of yield strength based on composition is used to determine the effusion rate for active domes we estimate yield strengths of 0 4 7 3 10 5 pa and effusion rate ranges for prehistoric domes of 0 1 330 m 3 s 1 these values compare well with yield strengths of 1 0 2 0 10 5 pa measured in the laboratory and effusion rates of 0 1 40 m 3 s 1 observed during historically active dome eruptions

morphological analysis of nevado de toluca volcano mexico new insights into the structure and evolution of an andesitic to dacitic stratovolcano abstract we present a morphological analysis of nevado de toluca volcano located 80 km wsw of mexico city based on digital elevation model study where slope and aspect maps have been generated and analysed aerial photograph and satellite image observations improve the morphological analysis the synoptic view which is offered by this analysis allowed for recognition and localization of the main volcanic and tectonic features of the area on the basis of digital elevation model value distribution and surface textures five morphological domains were defined the most interesting domain south of the crater reflects the occurrence of an ancient complex volcano distinct from the adjacent areas interaction between the volcanic and volcano tectonic evolution and the basement produced the other domains single volcanic edifices like lava domes and scoria cones and eruptive fractures were recognized finally flank collapse scarps opened to the east and to the north were identified and four relevant morphostructural lineaments and their possible role in the nevado de toluca geological and structural evolution are discussed

control on the emplacement of the andesite lava dome of the soufriere hills volcano montserrat by degassing induced crystallization lava solidification is controlled by two mechanisms external cooling and gas exsolution the latter inducing crystallization due to increasing liquidus temperature the andesite lava dome of the soufriere hills volcano montserrat is an extrusion dominated by crystallization caused by gas exsolution where cooling is unimportant in controlling emplacement in the magma chamber the magma has an estimated viscosity of 7 106 pa s during ascent gas exsolution caused the magma to extrude in a highly crystalline state with only 5 15 residual melt viscosities in the range 1013 1014 pa s and mechanical strength 1 mpa deformation can be heterogeneous with extrusion along shear zones rheological stiffening in the upper conduit also causes large overpressures shallow seismicity and cyclic patterns of dome extrusion gas rich porphyritic andesites tend to be the least mobile kind of lava because transition from magma into hot crystalline material was reached during ascent

repeated fracture and healing of silicic magma generate flow banding and earthquakes textures in an exceptionally preserved effusive rhyolite conduit at torfajokull iceland indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit rfh process anastomosing tuffisite veins filled by fine grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval welding of the particulate material during subsequent deformation led to thorough healing of veins allowing repeated fracture of the same body of magma we propose that the rfh process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions the rfh process may also form the flow banding that is nearly ubiquitous in obsidian

endogenous growth of dacite dome at unzen volcano japan 1993 1994 a dacite dome at unzen volcano grew mainly exogenously when it was small and the effusion rate was high but endogenously when the dome became large and the effusion rate declined the endogenous dome that has grown since late 1993 shows a shape classified as pelean whereas the earlier stage had a low lava dome shape the carapace of the endogenous dome moved like the crust of a basaltic lava pillow although the dome is several hundred times larger than such pillows the surface carapace was carried from the inside of the dome where it had been produced and it thickened as it cooled the crater floor was strongly deformed by the advancing endogenous dome the movement and crater floor deformation can be compared to that of a tractor tread moving on unconsolidated ground

field based density measurements as tool to identify preeruption dome structure set up and first results from unzen volcano japan for an improvement in the quality of conduit flow and dome related explosive eruption models knowledge of the preeruption or precollapse density of the rocks involved is necessary as close investigation is impossible during eruption the best substitute comes from quantitative investigation of the eruption deposits the porosity of volcanic rocks is of primary importance for the eruptive behaviour and accordingly a key parameter for realistic models of dome stability and conduit flow fortunately this physical property may be accurately determined via density measurements we developed a robust battery powered device for rapid and reliable density measurements of dry rock samples in the field the density of the samples sealed in plastic bags at 250 mbar is determined using the archimedean principle we have tested the device on the deposits of the 1990 1995 eruption of unzen volcano japan short setup and operation times allow up to 60 measurements per day under fieldwork conditions the rapid accumulation of correspondingly large data sets has allowed us to acquire the first statistically significant data set of clast density distribution in block and ash flow deposits more than 1100 samples with a total weight of 2 2 tons were measured the data set demonstrates that the deposits of the last eruptive episode at unzen display a bimodal density distribution with peaks at 2 0 0 1 and 2 3 0 1 g cm3 corresponding to open porosity values of 20 and 8 vol respectively we use this data set to link the results of laboratory based fragmentation experiments to field studies at recently active lava domes

a new high resolution unstructured grid finite volume arctic ocean model ao fvcom an application for tidal studies 1 a spherical coordinate version of the unstructured grid 3 d fvcom finite volume coastal ocean model has been applied to the arctic ocean to simulate tides with a horizontal resolution ranging from 1 km in the near coastal areas to 15 km in the deep ocean by accurately resolving the irregular coastlines and bathymetry in the arctic ocean coastal regions this model reproduces the diurnal k1 and o1 and semidiurnal m2 and s2 tidal wave dynamics and captures the complex tidal structure along the coast particularly in the narrow straits of the canadian archipelago the simulated tidal parameters harmonic constituents of sea surface elevation and currents agree well with the available observational data high resolution meshes over the continental shelf and slope capture the detailed spatial structure of topographic trapped shelf waves which are quite energetic along the greenland siberia and spitsbergen continental slope and shelf break areas water stratification influences the vertical distribution of tidal currents but not the water transport and thus tidal elevation the comparison with previous finite difference models suggests that horizontal resolution and geometric fitting are two prerequisites to simulate realistically the tidal energy flux in the arctic ocean particularly in the canadian archipelago

rock fracture as a precursor to lava dome eruptions at mount st helens from june 1980 to october 1986 following its plinian eruption on 18 may 1980 mount st helens washington state usa entered a period of intermittent lava dome extrusion until 1986 renewed extrusion was frequently preceded by accelerating rates of seismicity with more precursory seismicity observed prior to eruptions later in the sequence here the failure forecasting method ffm is used to investigate changes in the observed rate of volcano tectonic vt seismicity the analysis indicates that 1 all vt crises resulted in an eruption within 3 weeks usually less than 10 days 2 the majority of eruptions had vt precursors and 3 patterns of precursory seismicity showed fluctuations about the ideal model trend thus although these seismic events could be used to warn of an impending eruption specific forecasts were subject to an uncertainty of weeks or more it is proposed that 1 increased seismicity prior to later eruptions is a result of a larger and more solidified dome acting as a greater impediment to magma ascent 2 the consistency of seismic swarms resulting in an eruption indicates that stresses high enough to initiate fracturing in the country rock and lava dome carapace were only achieved once the approach to an eruption had already begun and 3 discrepancies between models of accelerating rock fracture and the observed seismicity may arise due to a significant amount of the rocks deforming through ductile mechanisms rather than seismogenic fracture

exogenous and endogenous growth of the unzen lava dome examined by satellite infrared image analysis abstract phase 1 of the most recent eruption of unzen volcano japan occurred between 1991 and 1993 and involved the endogenous and exogenous addition of magma to a growing summit lava dome the temporal variation between endogenous and exogenous styles of dome growth has an important bearing on the hazard posed by dome collapse and explosive events however such data are difficult to acquire and have previously only been obtained in a fully quantitative manner for the mount st helens dome in that case using detailed photogrammetry here we investigate these competing dome growth processes at unzen via analysis of their thermal emission signals present in shortwave infrared swir satellite imagery we find that both the endogenous and exogenous growth styles exhibit identifiable swir signatures whose magnitude can be related to their respective magma supply rates we find that the swir radiant area corresponding to endogenous growth is around four times larger than that corresponding to exogenous growth at the same magma discharge rate analysis of time series imagery indicates that like mount st helens unzen experienced a temporally decreasing magma discharge rate during phase 1 as time progressed and the discharge rate fell the growth style of the unzen dome changed from exogenous only through exogenous decreasing and endogenous increasing to endogenous only thus relative growth rates at the endogenous and exogenous areas of the unzen dome appear to be at least partly controlled by the overall magma discharge rate as with mount st helens the cause of this relationship was most likely the formation and strengthening of a brittle crust at the surface vent which impeded exogenous growth more effectively as time elapsed and the discharge rate fell these results suggest the similarity of the processes operating at the unzen and mount st helens domes though important differences remain in that dome growth was basically continuous at unzen whilst at mount st helens growth episodes were interspersed by significant periods of repose

collapse and reconstruction of monowai submarine volcano kermadec arc 1998 2004 monowai submarine volcano is one of the three most historically active volcanoes of the kermadec arc repeat multibeam surveys of monowai cone from september 1998 and september 2004 and t wave data recorded by the reseau sismique polynesien network for the same period document the collapse and subsequent regrowth of the cone within this 6 a period grid differencing of the two bathymetric data sets acquired 6 a apart reveals that a landslide 2230 m long occurred between the surveys within which a postcollapse cone and talus ridge 0 023 km3 in volume subsequently formed the volume of this collapse minus postcollapse construction is 0 085 km3 we interpret an unusual strong amplitude t wave event on 24 may 2002 as recording hot landsliding where the 100 to 160 m thick collapse has unroofed the uppermost parts of the vent conduit with the subsequent explosive interaction and cooling of hot magma and volcaniclastic rubble with ambient seawater this interpretation is consistent with the lack of emergent events sharp onset and large amplitude of the 24 may 2002 t waves the subsequent 2500 t wave events between november 2002 and september 2004 occurred in swarms with emerging and waning activity and with typical explosive volcanic acoustic signatures which are interpreted as recording the regrowth of an 90 m high cone back to a near 1998 elevation at an average rate of 47 m a 1 this study provides 1 a lower bound for frequency magnitude relationships of landsliding for submarine arc volcanoes and 2 estimates of 0 013 km3 a 1 of submarine cone growth during eruptive cycles

a 3 d prognostic numerical model study of the georges bank ecosystem part i physical model abstract the influence of tidal forcing and tidal and wind mixing on circulation and stratification over georges bank and adjacent regions in the gulf of maine has been examined using the 3 d semi implicit version of the blumberg and mellor 1987 primitive equation ocean circulation model the numerical domain covered the gulf of maine georges bank region with an open boundary starting at the new jersey coast and ending at the nova scotia coast with increased spatial resolution over georges bank numerical experiments were conducted using both smoothed and non smoothed high resolution 15 s bottom topography the model was forced by specifying the m 2 elevation and phase on the open boundary and several forms of the bottom roughness parameter z o were used the model provided a reasonable simulation of the m 2 tidal elevations and currents the model when run as an initial value problem with early summer stratification exhibited tidal mixing fronts around the 40 60 m isobath over georges bank and nantucket shoals and 100 m isobath on brown bank the formation of these tidal mixing fronts significantly enhanced the along isobath tidal rectified current over georges bank and the other two shoal regions a cool water band developed within the frontal zone along the eastern and southern flanks of georges bank and nantucket shoal and it became cooler owing to wind mixing and upwelling as a mean summer wind stress was added tidal mixing and turbulent dissipation varied in time asymmetrically over georges bank over georges bank tidal mixing was generally characterized as a local 1 d balance between turbulent shear production and dissipation the spatial structure of the tidal residual flow and local turbulent dissipation rate depended critically on the spatial resolution of the bottom topography and the spatial distribution of z 0 analysis of the 3 d momentum balance and the residual flow over the center of georges bank indicates that earlier results based on a 2 d cross bank model correctly captured the basic dynamics of stratified tidal rectification and tidal mixing in this idealized model setting

identification of structural controls in an active lava dome with high resolution dems volcan de colima mexico monitoring the topography of active lava domes is critical for detecting changes that may trigger or influence collapse or explosive activity internal dome structure and conditions are more difficult to elucidate but also play vital roles here we describe the exposure following an explosion of significant scarps in the active dome at volcan de colima mexico that are interpreted as evidence of brittle failure planes and a complex internal dome morphology in the first use of automated 3d computer vision reconstruction techniques structure from motion and multi view stereo sfm mvs on an active volcanic dome we derive high resolution surface models from oblique and archive photographs taken with a consumer camera the resulting 3d models were geo referenced using features identified in a web sourced orthoimage no ground based measurements were required in december 2010 the dome 2 14 106 m3 had a flat upper surface reflecting an overall ductile emplacement regime between then and may 2011 a period of low explosivity was accompanied by a small volume loss 0 4 105 m3 and arcuate steps appeared in the dome surface suggesting the presence of localized planes of weakness the complex array of summit scarps was exposed following a significant explosion in june 2011 and is interpreted to be the surface expression of fault planes in the dome the 1 m resolution dems indicated that the region of greatest volume loss was not coincident with the assumed location of the conduit and that heterogeneity within the dome may have been important during the june explosion

a new type of volcano flank failure the resurgent caldera sector collapse ischia italy 1 this study is the first description of recurrent and rapid lateral failure of the resurgent portion of a caldera complex the sliding planes and the characteristics of debris avalanche deposits resemble those of cone sector collapses but the main triggering mechanism proposed at ischia caldera italy is related to intermittent resurgence during the last 33 ka the increase in resurgence rate produced major collapses southward due to three main mechanisms that contributed to an increase in shear stress i magma driven uplift which produced increase in static loading ii faulting and associated deformation which induced tilting and steepening of the original layering and iii earthquake shaking due to coseismic faulting the largest episodes of flank failure occurred in the interval 8 6 5 7 ka bp these were followed by magma eruption and a decrease in the resurgence rate recognition of this phenomenon is particularly important in recent active calderas located near the coast as it can trigger tsunamis

a model for submarine rhyolite dome growth ponza island central italy abstract the late pliocene rhyolitic submarine volcanic rocks of ponza island italy can be interpreted as the subaqueous equivalent of subaerial dome complexes in terms of geometry and structure three coalescing domes of about 1 km radius and aligned along a ne trending regional fracture have been identified the main difference between subaqueous and subaerial lava domes is that in a subaqueous environment lava is likely to undergo pervasive hyaloclastic brecciation so that domes are mainly composed of variously brecciated in situ to clast rotated hyaloclastite rather than coherent lava we suggest that the shape and rheologic behaviour through time of submarine domes are closely controlled by the development and thickness of the particulate hyaloclastic carapace which assumes the role of the solid crust of domes in subaerial environment the thickness of the hyaloclastic carapace at ponza is greater than 150 m and emplaced during several different pulses or eruptions in the earliest pulses lava is directly extruded on the seafloor and produces hyaloclastite the degree of brecciation of which decreases inward to the coherent flow banded rhyolite lava of the feeder dike once the hyaloclastic carapace is formed further pulses of magma combined with increase in height of the dome result in a local stress pattern characterised by a vertical 1 2 3 producing concentric and radial fractures and normal faults the newly rising magma shielded by the hyaloclastic carapace can intrude along these fault and fracture systems and invade previously emplaced but still water saturated hyaloclastite this produces the characteristic pattern of dikes observed at ponza as a series of concentric dikes that are progressively less inclined outward with respect to the dome centre these late stage dikes in turn produce hyaloclastite at their margins but generally less fragmented than the embedding hyaloclastite probably because the ascending magma is better shielded from direct contact with sea water periodic gravity collapses of the dome maintain the equilibrium between height and radius of the dome as suggested at ponza by the presence of mass flow deposits and the development of small topographic basins on top of the domes probably related to debris removal some of these topographic depressions host subaqueous pyroclastic deposits suggesting that if due to vertical growth of the dome water depth above the dome becomes shallower hydromagmatic explosions may occur

simulation of barotropic and baroclinic tides off northern british columbia abstract the tidal response of northern british columbia coastal waters is studied through simulations with a three dimensional prognostic primitive equation model the model is forced at the boundaries with the leading semidiurnal and diurnal constituents and experiments with stratified and homogeneous fluid are compared the barotropic response shows good agreement with previously published studies of tides in the region a comparison with tide gauge measurements indicates that average relative rms differences between observations and the model surface elevation field are less than 5 for the largest constituents an internal tide is generated in cases where the model is initialized with a vertical stratification diagnostic calculations of the baroclinic energy flux are used to identify regions of generation and propagation of internal tidal energy with a representative summer stratification the integrated offshore flux is about 0 5 gigawatts higher than previously estimated from theoretical model

multispectral remote sensing as stratigraphic and structural tool wind river basin and big horn basin areas wyoming stratigraphic and structural analyses of the wind river basin and big horn basin areas of central wyoming are in progress one result has been the development of an approach to stratigraphic and structural analysis that uses photogeologic and spectral interpretation of multispectral image data to characterize the attitude thickness and lithology of strata new multispectral systems that have only been available since 1982 are used with topographic data to map upper paleozoic and mesozoic strata exposed on the southern margin of the bighorn mountains landsat acquired thematic mapper tm data together with topographic data are used to map lithologic contacts measure dip and strike and develop a stratigraphic column that is correlated with conventional surface and subsurface sections aircraft acquired airborne imaging spectrometer ais and thermal infrared multispectral scanner tims data add mineralogic information to the tm column including the stratigraphic distribution of quartz calcite dolomite smectite and gypsum results illustrate an approach that has general applicability in other geologic investigations that could benefit from remotely acquired information about areal variations in attitude sequence thickness and lithology of strata exposed at the earth s surface application of our methods elsewhere is limited primarily by availability of multispectral and topographic data and quality of bedrock exposures

anatomy of a lava dome collapse the 20 march 2000 event at soufriere hills volcano montserrat abstract a second extrusive phase of the currently ongoing 1995 2003 eruption of soufriere hills volcano shv montserrat commenced in mid november 1999 following 19 months during which no fresh lava had reached the surface by mid march 2000 a new andesite lava dome constructed within a collapse scar girdled by remnants of the 1995 1998 dome complex had attained an estimated volume of 29 3 million m3 mm3 on 20 march 2000 during a period of heavy rainfall on the island a significant collapse event ensued that removed 95 of the new lava dome 28 3 mm3 during 5 hours of activity that generated 40 pyroclastic flows and at least one magmatic explosion the associated ash cloud reached an altitude of 9 km and deposited ash on the island of guadeloupe to the southeast and a number of lahars and debris flows occurred in valleys on the flanks of shv a large quantity of observational data including contemporaneous field observations and continuous data from the broadband seismic network on montserrat allow a detailed reconstruction of this dome collapse event in contrast to most of the large dome collapses at shv the 20 march 2000 event is distinguished by a lack of short term precursory elevated seismicity at shallow depths beneath the lava dome broadband seismic amplitude data recorded during the event are used to infer the cumulative volume of collapsed dome as the collapse progressed these data indicate that the high velocity pyroclastic flows observed at the climax of the event removed by far the largest portion 68 of the lava dome at peak discharge rates estimated from the seismic record of 2 104 m3 s 1 following the 20 march 2000 collapse lava dome growth recommenced immediately and continued without significant interruption until another larger dome collapse occurred on 29 july 2001 the 29 july 2001 event also coincided with heavy rainfall on montserrat matthews et al 2002 geophys res lett 29 doi 10 1029 2002gl014863 and lacked precursory elevated seismic activity we attribute the initiation of the 20 march 2000 collapse to a prolonged spell of heavy rainfall on the lava dome prior to and during the event the precise causal mechanism remains controversial though some combination of mechanical erosion and or destabilization of a critically poised face of the lava dome the action of pressurized steam or water on potential failure surfaces within the dome rapid cooling of hot lava and small phreatic explosions seems likely anecdotal evidence exists for other rainfall induced activity on montserrat and the triggering of explosive or pyroclastic flow activity by rainfall has been noted at dome forming volcanoes elsewhere including merapi indonesia voight et al 2000 j volcanol geotherm res 100 69 138 unzen japan yamasato et al 1997 papers meteorol geophys 48 santiaguito guatemala smithsonian institution global volcanism network bull 15 1990 and mount st helens usa mastin 1994 geol soc am bull 106 175 185 hazard mitigation plans at dome forming volcanoes would therefore benefit from the inclusion of meteorological forecasting and rain monitoring equipment particularly in the tropics

scaling of columnar joints in basalt 1 we describe field work analysis and modeling of columnar joints from the columbia river basalt group this work is focused on the regions around the grand coulee snake river and columbia gorge which form parts of this unusually homogeneous and very large sample of columnar basalt we examine in detail the scaling relationship between the column width and the size of the striae and relate these quantitatively to thermal and fracture models we found that the column radius and stria size are proportional to each other and inversely proportional to the cooling rate of the lava near a flow margin our results put observational constraints on diffusive thermal models of joint formation deeper than a few meters into a colonnade our measurements are consistent with a simple advection diffusion model of two phase convective cooling within the joints regardless of the direction of cooling this model allows an accurate comparison of igneous columnar jointing and joints due to desiccation in laboratory analog systems we also identify a new length scale in which wavy columns can appear in some colonnades the mechanisms leading to the wavy columns are likely related to those underlying similar wavy cracks in 2 d analog systems

energy flux and generation of diurnal shelf waves along vancouver island abstract recent observations along the west coast of vancouver island reveal among diurnal period currents due to a tidally driven continental shelf wave superimposed upon a kelvin wave the energy flux of this system is investigated here it is shown that both the kelvin wave and the first mode continental shelf wave transport energy toward the northwest in the direction of phase propagation but when the two waves are superimposed the combined energy flux vectors form meanders and gyres over the continental shelf the pattern repeats in the alongshore direction every wavelength of the shelf wave near southern vancouver island these waves combine to form a gyre in which the nearshore side carries energy to the southeast toward juan de fuca strait kinetic energy flows up strait until it is dissipated in narrow tidal channels the total alongshore energy flux in the shelf wave alone can be determined from a fit of a model baroclinic shelf wave to current meter observations along vancouver island energy

coastal flooding in scituate ma a fvcom study of the 27 december 2010 nor easter 1 a nested finite volume coastal ocean model fvcom inundation forecast model has been developed for scituate ma as part of the northeast coastal ocean forecast system necofs scituate harbor is a small coastal lagoon oriented north south with a narrow entrance with opposing breakwaters opening eastward onto massachusetts bay and the gulf of maine on 27 december 2010 a classic nor easter produced a 0 9 m high surge which when added to the 1 5 m high tide and seasonal higher mean water level produced significant inundation in scituate the scituate fvcom inundation model includes flooding drying seawall breakwater and wave current interaction capabilities and was driven by one way nesting with necofs hindcasts of the 27 december nor easter event were made with two different resolution scituate fvcom grids with and without inclusion of wave current interaction to examine the influence of spatial resolution and model dynamics on the predicted flooding in all simulations a wind driven coastal current flowed southward across the harbor entrance with an attached separation eddy forming downstream of the northern breakwater and rapid decrease in wave energy entering the harbor with wave current interaction the southward coastal current was strongly enhanced and currents within the separation eddy increased to more than 1 m s making it highly nonlinear with large lateral shears comparisons of the model water elevation time series with harbor tide station measurements showed that inclusion of wave current interaction increased the peak model surge by 8 cm in closer agreement with the observed peak

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

classification and idealized limit equilibrium analyses of dome collapses at soufriere hills volcano montserrat during growth of the first lava dome november 1995 march 1998 abstract styles of dome collapse at soufriere hills volcano shv november 1995 march 1998 are classified by relations between extrusion rate prior to collapse and collapse volume four separate modes of collapse behavior are apparent notably moderate rates of extrusion are shown to result in two disparate modes of collapse small to large collapses on steeply inclined failure planes that switch to collapse volumes an order of magnitude larger that cut deeply into the dome core for constant effusion rates this bifurcation in behavior is explained by the monotonic growth of a soft core that ultimately promotes the development of a deep seated failure over previously favored shallow failure modes models are developed to test this hypothesis that first constrain magnitudes of cohesive and frictional strength with observed dome collapse morphologies and volumes evaluations of dome strengths confirm the important role of a soft core in promoting deep failure a nested model representing a cohesive dome core surrounded by a frictional rind with constant rate of magma input confirms the observed bifurcation in behavior and for invariant effusive activity importantly failure volumes are shown to increase by close to an order of magnitude for a few percent change in the proportion of dome core comprising cohesive material this model is capable of replicating a posteriori the approximate timing of failure for both small 250 m and large 325 m domes the timing and style of the 17 september 1996 and june to november 1997 collapses are honored

remote sensing of geological structure in temperate agricultural terrains agricultural patterns dominate most remotely sensed images of lowland north europe and camouflage shadow patterns related to topography and hence to underlying geological structure images of those parts of the near infrared spectrum close to absorption features controlled by h o h bond stretching in plant cells and soil moisture largely remove this hindrance to interpretation if they are acquired at an early stage in the growing season the most easily available and most useful images of this type are those of band 5 from the landsat thematic mapper spatial filtering techniques applied to digital images can enhance them for structural interpretation if filter matrices and viewing scales are chosen to match the dimensions of the most common elements of the landscape and the peak of visual acuity filters to enhance directional attributes of an agricultural scene give appealing results but contain spurious linear features that masquerade as faults

possible techniques for lithologic discrimination using the short wavelength infrared bands of the japanese ers 1 abstract the possible techniques for lithologic discrimination using sensor data with the short wavelength infrared swir bands of the japanese ers 1 satellite were examined in a preliminary manner prior to its expected operation in 1991 reflectance data of typical minerals and rocks measured by the iris spectroradiometer were used in the examination to simulate hypothetical sensor response patterns prior to actual measurements by the satellite sensor which is currently being manufactured by using the simulated swir bands data three typical techniques band ratios spectral indices and hsi color transform were compared in terms of the capability to discriminate different rocks and minerals band ratios among bands 6 7 and 8 might be useful to separate some pure minerals from the other but may not correctly estimate concentration of a certain component in a mixture of minerals spectral indices linear combinations of the spectral bands will be able to avoid this problem and are thus more appropriate than band ratios two indices corresponding to the response patterns of alunite and calcite are proposed as to be useful for discrimination of the minerals and the rock types the hsi color transform applied to the three dimensional data structure is another possible way to express sensor response patterns and will allow us to create a color image useful for visual interpretation of different rock types

ductile rebound of an orogenic root case study and numerical model of gravity tectonics in the western gneiss complex caledonides southern norway the main caledonian deformation in the western gneiss complex southern norway has been interpreted as resulting from the gravity driven ductile rebound of the orogenic root detailed field data from the sognefjord profile a 60 km long continuously exposed shore section through the complex are compared with the results of a numerical scale model of root rebound dimensioned according to reconstructions of the overall tectonic evolution the strain pattern in the model can be closely tied to the previously recognized structural regimes from east to west r1 little deformed precambrian basement stiff orogenic lid basal part of upper crust r2 heterogeneously sheared basement simple shear domain at upper crust lower crust boundary r3 completely overprinted basement with eclogitic remnants pure shear regime in the lower crust of the rebounded root subsequent to root rebound the profile remained practically unaffected by later tectonic events except for tilting uplift erosion providing a unique example of deep seated gravity tectonics

deformation and seismic precursors to dome collapse and fountain collapse nuees ardentes at merapi volcano java indonesia 1994 1998 abstract following the eruption of january 1992 episodes of lava dome growth accompanied by generation of dome collapse nuees ardentes occurred in 1994 1998 in addition nuees ardentes were generated by fountain collapse in january 1997 and the 1998 events also suggest an explosive component significant tilt and seismic precursors on varying time scales preceded these events deformation about the summit has been detected by electronic tiltmeters since november 1992 with inflation corresponding generally to lava dome growth and deflation or decreased inflation corresponding to loss of dome mass strong short term days to weeks accelerations in tilt rate and seismicity occurred prior to the major nuees ardentes episodes apart from those of 22 november 1994 which were preceded by steadily increasing tilt for over 200 days but lacked short term precursors because of the combination of populated hazardous areas and the lack of an issued warning about 100 casualties occurred in 1994 in contrast the strong precursors in 1997 and 1998 provided advance warning to observatory scientists enabled the stepped raising of alert levels and aided hazard management as a result of these factors but also the fortunate fact that the large nuees ardentes did not quite descend into populated areas no casualties occurred the nuee ardente episode of 1994 is interpreted as purely due to gravitational collapse whereas those of 1997 and 1998 were influenced by gas pressurization of the lava dome

mechanisms for rainfall concurrent lava dome collapses at soufriere hills volcano 2000 2002 the evolution of rainfall concurrent dome collapses at soufriere hills volcano is followed using a limit equilibrium model for rain infiltration into a hot lava carapace magma infusing into the dome both supplies heat and builds the slopes the dome rocks are cooled by episodic rain infiltration and climatic cooling rainfall infiltrates fractures that develop in the hot dome carapace occludes the void space and staunches effusive gas flow gases may originate from juvenile de gassing of the dome interior or result from the vaporization of infiltrating water gas pressures build in cracks blocked off by rain and may destabilize the dome the effects of dome growth heating by magma infusion and cooling by rain infiltration and climatic influences are combined to follow the growth of the dome towards ultimate collapse for a fixed suite of strength and transport parameters and for measured magma influx rates the evolution of instability may be followed the evolving factor of safety tracks the observed march 2000 and july 2001 rainfall concurrent collapse events which evolve over months however the resolution of the hindcast is unable to discriminate between the effects of closely timed rainfall events order of hours the heightening of the dome is shown to exert the principal influence on average slopes and in the evolution of instability collapse removes the over heightened dome and temporarily restores stability

radiometric dating of three large volume flank collapses in the lesser antilles arc abstract it is now recognised that flank collapses are a recurrent process in the evolution of the lesser antilles arc volcanoes large magnitude debris avalanche deposits have been identified off the coast of dominica martinique and st lucia with associated volumes up to 20 km 3 deplus c le friant a boudon g komorowski j c villemant b harford c segoufin j cheminee j l 2001 submarine evidence for large scale debris avalanches in the lesser antilles arc earth planet sci lett 192 145 157 we present new radiometric dating of three major events using the k ar cassignol gillot technique in the qualibou depression of st lucia a collapse has been constrained by dome emplacement prior to 95 2 ka in dominica where repetitive flank collapse events have occurred le friant a boudon g komorowski j c deplus c 2002 l ile de la dominique a l origine des avalanches de debris les plus volumineuses de l arc des petites antilles c r geoscience 334 235 243 the plat pays event probably occurred after 96 2 ka inside the depression caused by this event scotts head which is interpreted as a proximal megabloc from the subsequent soufriere avalanche event has been dated at 14 1 ka providing an older bound for this event on martinique three different domes within the carbets structure dated at 337 5 ka constrain the age of this high magnitude event finally these results obtained from three of the most voluminous flank collapses provide constraints to estimate the recurrence of these events which represent one of the major hazards associated with volcanoes of the lesser antilles arc

fracture and compaction of andesite in a volcanic edifice the failure mode of lava dilatant or compactant depends on the physical attributes of the lava primarily the porosity and pore size and the conditions under which it deforms the failure mode for edifice host rock has attendant implications for the structural stability of the edifice and the efficiency of the sidewall outgassing of the volcanic conduit in this contribution we present a systematic experimental study on the failure mode of edifice forming andesitic rocks porosity from 7 to 25 from volcan de colima mexico the experiments show that at shallow depths 1 km while low porosity 10 lava remains dilatant the failure of high porosity lava is compactant and driven by cataclastic pore collapse although inelastic compaction is typically characterised by the absence of strain localisation we observe compactive localisation features in our porous andesite lavas manifest as subplanar surfaces of collapsed pores in terms of volcano stability faulting in the upper edifice could destabilise the volcano leading to an increased risk of flank or large scale dome collapse while compactant deformation deeper in the edifice may emerge as a viable mechanism driving volcano subsidence spreading and destabilisation the failure mode influences the evolution of rock physical properties permeability measurements demonstrate that a throughgoing tensile fracture increases sample permeability i e equivalent permeability by about a factor of two and that inelastic compaction to an axial strain of 4 5 reduces sample permeability by an order of magnitude the implication of these data is that sidewall outgassing may therefore be efficient in the shallow edifice where rock can fracture but may be impeded deeper in the edifice due to compaction the explosive potential of a volcano may therefore be subject to increase over time if the progressive compaction and permeability reduction in the lower edifice cannot be offset by the formation of permeable fracture pathways in the upper edifice the mode of failure of the edifice host rock is therefore likely to be an important factor controlling lateral outgassing and thus eruption style effusive versus explosive at stratovolcanoes

late pleistocene flank collapse triggered by dome growth at tacana volcano mexico guatemala and its relationship to the regional stress regime during late pleistocene time the extrusion of an andesitic dome at the summit of tacana volcano caused the collapse of its northwestern flank the stratocone collapse was nearly parallel to the min stress direction suggesting that failure was controlled by the regional stress field the event produced a debris avalanche that was channelized in the san rafael river and moved 8 km downstream the deposit covered a minimum area of 4 km2 had a volume of 0 8 0 5 km3 with an h l vertical drop to horizontal transport distance ratio of 0 35 defining a degree of mobility that is atypical for volcanic debris avalanches the flank failure undermined the summit dome leading to its collapse and the generation of a series of block and ash flows that were emplaced in quick succession and covered the avalanche surface the collapse event left a 600 m wide summit amphitheatre with a 30 degree opening to the northwest and 200 m thick debris that blocked the san rafael river remobilization of this material produced debris flows that eroded the primary deposits and cascaded into the coatan river after the collapse the activity of tacana continued with the emission of the agua zarca lava flow dated at 10 6 ka 40ar 39ar and pyroclastic surges dated at 10 610 330 315 yr bp 14c which provide a minimum age for the collapse event during the holocene tacana has been very active producing explosive and effusive eruptions that ended with the extrusion of two summit domes that today occupy the amphitheatre the 1950 and 1986 phreatic outbursts occurred along the pleistocene collapse scar currently 300 000 inhabitants live within a 35 km radius of tacana and could conceivably be impacted by future events of similar magnitude

modelling the lava dome extruded at soufriere hills volcano montserrat august 2005 may 2006 part ii rockfall activity and talus deformation abstract during many lava dome forming eruptions persistent rockfalls and the concurrent development of a substantial talus apron around the foot of the dome are important aspects of the observed activity an improved understanding of internal dome structure including the shape and internal boundaries of the talus apron is critical for determining when a lava dome is poised for a major collapse and how this collapse might ensue we consider a period of lava dome growth at the soufriere hills volcano montserrat from august 2005 to may 2006 during which a 100 10 6 m 3 lava dome developed that culminated in a major dome collapse event on 20 may 2006 we use an axi symmetrical finite element method model to simulate the growth and evolution of the lava dome including the development of the talus apron we first test the generic behaviour of this continuum model which has core lava and carapace talus components our model describes the generation rate of talus including its spatial and temporal variation as well as its post generation deformation which is important for an improved understanding of the internal configuration and structure of the dome we then use our model to simulate the 2005 to 2006 soufriere hills dome growth using measured dome volumes and extrusion rates to drive the model and generate the evolving configuration of the dome core and carapace talus domains the evolution of the model is compared with the observed rockfall seismicity using event counts and seismic energy parameters which are used here as a measure of rockfall intensity and hence a first order proxy for volumes the range of model derived volume increments of talus aggraded to the talus slope per recorded rockfall event approximately 3 10 3 13 10 3 m 3 per rockfall is high with respect to estimates based on observed events from this it is inferred that some of the volumetric growth of the talus apron perhaps up to 60 70 might have occurred in the form of aseismic deformation of the talus forced by an internal laterally spreading core talus apron growth by this mechanism has not previously been identified and this suggests that the core hosting hot gas rich lava could have a greater lateral extent than previously considered

the m2 tide and its residual on the outer banks of the gulf of maine abstract tidal computations are reported for the gulf of maine with emphasis on its seaward banks georges bank browns bank nantucket shoals and the nearshore region off cape sable the model is 3d and nonlinear with quadratic vertical viscosity stratification is ignored the objective is to establish a theoretical baseline for tidal and residual currents on detailed topography against which seasonal changes may be examined two triangular meshes are used the base case corresponds to earlier studies with roughly 6 km resolution on the banks a more refined and extended mesh provides resolution at 2 3 km in critical areas and has boundaries farther removed from the banks both meshes provide very good fits with observed m2 elevations comparison of computed and observed m2 current profiles at 76 sites reveals general agreement that improves with resolution for the refined mesh and the 48 sites with records exceeding 60 days average deviations for m2 ellipse parameters are 6 1 4 7 cm s 1 for the

mineralogic information from a new airborne thermal infrared multispectral scanner a new six channel aircraft multispectral scanner has been developed to exploit mineral signature information at wavelengths between 8 and 12 micrometers preliminary results show that igneous rock units can be identified from their free silica content and that carbonate as well as clay bearing units are readily separable on the digitally processed images

clastic and core lava components of a silicic lava dome the formation of a lava dome involves fractionation of the lava into core and clastic components we show that for three separate successive andesitic lava domes that grew at soufriere hills volcano montserrat between 1999 and 2007 the volumetric proportion of the lava converted to talus or pyroclastic flow deposits was 50 90 of the lava extruded currently only 8 of the total magma extruded during the 1995 2007 eruption remains as core lava the equivalent representation in the geological record will probably be even lower most of the lava extruded at the surface flowed no further than 150 300 m from the vent before disaggregation resulting in a lava core whose shape tends to a cylinder moderate to high extrusion rates at the soufriere hills domes may have contributed to the large clastic fraction observed creating talus dissipates much of the energy that would otherwise be stored in the core lava of domes the extreme hazards from large pyroclastic flows and blasts posed by wholesale collapse of a lava dome depend largely on the size of the lava core and hence on the aggregate history of the partitioning process not on the size of the dome

eruptive response of oceanic islands to giant landslides new insights from the geomorphologic evolution of the teide pico viejo volcanic complex tenerife canary large sector collapses are a major component of oceanic islands evolution here we show that voluminous events such as the icod landslide on tenerife canary islands cause dramatic changes on the magma feeding system and control the subsequent volcanic and geomorphologic evolution of the eruptive complex over a period of more than 150 kyr instantaneous unloading by the icod landslide is marked by the development of a large phonolitic explosive eruption dated at 175 3 ka and interpreted as reflecting the immediate emptying of a shallow pre existing magma chamber geochronological geomorphological and geochemical analyses carried out on the post landslide volcanic succession sampled in a 4 4 km long underground water recovery gallery provide further evidence for an enhanced extrusion of primitive lavas starting in the 10 kyr time interval following the failure rapid construction 40 kyr of a thick basaltic volcano in the landslide scar at high eruptive rates up to 8 km3 kyr 1 increased the lithostatic pressure which then favored the intermittent storage of basic magma under the edifice this resulted in more episodic construction evidenced by a significant decrease in output rates and the increasing occurrence of lavas with intermediate composition from 117 7 to 52 7 ka an apparent volcanic gap is observed between 52 7 and 18 1 ka after which highly differentiated lavas have been dominantly erupted we propose that part of the gap can be explained by the individualization of a shallow magma reservoir a few kilometers below the base of the teide volcano during recent periods vertical and lateral extrusions of trachytic and phonolitic viscous bodies from this storage area contributed to increase the slope of the main edifice up to 35 overall favoring its present day instability

overview of the 2006 eruption of mt merapi abstract in the last part of the 20th century and the beginning of the 21st century mt merapi in central java indonesia erupted about every 2 5 years most of the eruptions were low in explosivity with vei 3 or less eruptions usually involve the formation of a lava dome either in the beginning or in the end of the eruptive episode for the 2006 eruption the precursory signal was first observed in the middle of the year 2005 with a decrease in edm slope distances to points on the rim an increase of seismicity and a possible increase of so 2 emissions those early events marked the beginning of a more continuous period of inflation which led to the eruption in total the pre eruption displacement of the southern rim reached at least 2 4 m toward the measuring station in kaliurang kal from late april until june 2006 a lava dome grew on the summit with a volume that gradually increased until it reached about 4 1 million m 3 in 38 days the total of erupted magma was about 5 3 million m 3 dense rock equivalent dre the dome subsequently collapsed in three steps from june 4 to june 14 leaving an open scar on its southeast side in this paper we detail the changes of dome morphology that were monitored by taking successive photographs from similar positions the eruption in 2006 marked a significant change in summit morphology from west southwestward opening during the 20th century to the currently southeast orientation also an mw 6 4 earthquake occurred on 26 may midway through the eruption which adds interesting questions about the relationship of the eruption and the earthquake edm data from 2006 and previous eruptions show that the summit remains inflated after each eruption i e no significant deflation occurs following eruptions the lack of post eruption deflation suggests that magma remains in the shallow parts of the edifice after the eruption as a result the complex of summit lava domes and their intrusive roots grow with time and merapi s rim and summit become progressively more unstable and prone to collapse

an assessment of hydrothermal alteration in the santiaguito lava dome complex guatemala implications for dome collapse hazards a combination of field mapping geochemistry and remote sensing methods has been employed to deter mine the extent of hydrothermal alteration and assess the potential for failure at the santiaguito lava dome complex guatemala the 90 year old complex of four lava domes has only experienced relatively small and infrequent dome collapses in the past which were associated with lava ex trusion however existing evidence of an active hydrother mal system coupled with intense seasonal precipitation also presents ideal conditions for instability related to weakened clay rich edifice rocks mapping of the santiaguito dome complex identified structural features related to dome growth dynamics potential areas of weakness related to erosion and locations of fumarole fields x ray diffraction and backscat tered electron images taken with scanning electron microsco py of dacite and ash samples collected from around fumaroles revealed only minor clay films and little evidence of alter ation mineral mapping using aster and hyperion satellite images however suggest low temperature 150 c silicic alteration on erosional surfaces of the domes but not the type of pervasive acid sulfate alteration implicated in collapses of other altered edifices to evaluate the possibility of internal alteration we re examined existing aqueous geochemical data from dome fed hot springs the data indicate significant wa ter rock interaction but the na mg kg eoindicator suggests only a short water residence time and 18 o dr atios show only minor shifts from the meteoric water line with little precipitation of secondary alteration minerals based on available data hydrothermal alteration on the dome complex appears to be restricted to surficial deposits of hydrous silica but the study has highlighted importantly that the 1902 eruption crater headwall of santa maria does show more advanced argillic alteration we also cannot rule out the pos sibility of advanced alteration within the dome complex inte rior that is not accessible to the methods used here it may therefore be prudent to employ geophysical methods to make further assessments in the future

geological mapping of the francistown area in northeastern botswana by surface temperature and spectral emissivity information derived from advanced spaceborne thermal emission and reflection radiometer aster thermal infrared data abstract we identified geological units in the francistown area in northeastern botswana by using advanced spaceborne thermal emission and reflection radiometer aster thermal infrared tir data which contains both surface temperature and spectral emissivity information a scatter plot of aster l1b daytime tir digital values and l2 daytime temperature indicates that in the aster l1b daytime tir data bands 10 11 and 12 contain spectral emissivity and temperature information whereas surface temperature dominates the spectral emissivity information in bands 13 and 14 visual interpretation of the aster tir false color composite fcc images generated by assigning red green and blue to band 14 band 12 band 10 using l1b daytime data allowed us to identify mafic to ultramafic units and quartz rich felsic units mafic to ultramafic units such as gabbro dolerite and dunite appear white in aster l1b daytime tir fcc images due to their high spectral emissivities in the 8 9 m region bands 10 and 12 and high surface temperatures mafic to ultramafic units have higher surface temperatures than other geological units because they absorb more solar radiation due to their lower albedos and they have a lower thermal inertia quartz rich felsic units such as granite and dry river sand appear reddish in the aster l1b daytime tir fcc image because the spectral emissivity of quartz is lower in the 8 9 m region bands 10 and 12 than in the 10 12 m region band 14 mafic to ultramafic and granitic units are important targets for mineral exploration because they are potential geological units to host or accompany mineralization the proposed aster l1b daytime tir fcc images can be prepared very simply and they provide valuable information for geological mapping and mineral exploration

numerical modelling of the growth dynamics of a simple silicic lava dome 1 two dimensional axisymmetrical computational models have been developed using finite element techniques to represent the rheological stiffening due to degassing induced crystallisation and the effects of a brittle carapace within a simple lava dome the dome is modelled numerically considering the effects of temperature pressure and rate of extrusion using these state variables the bulk viscosity is derived from empirical equations and the bulk rheology approximated using a solidification viscosity dividing the dome into solid dominated and fluid dominated domains elastoplastic equations for the solid component and fluid mechanical equations for the fluid domain are solved simultaneously allowing continuous stress across the fluid solid interface to ensure the two components move in unison we apply this model a hookean solid carapace model and a purely fluid lava dome model to the case of the october 1980 lava dome at mount st helens the results show that dynamic growth models involving a solid carapace are required to simulate this lava dome

rheological properties of dome lavas case study of unzen volcano abstract transitions between effusive and explosive styles of lava dome eruptions are likely accompanied by changes in lava rheology the common presence of crystals in dome lavas produces a complex non newtonian rheology thus models of such complex rheology are essential for volcanic eruption models here we have measured the rheology of natural unzen lavas with a compressive uniaxial press operating at stresses between 1 and 70 mpa and temperatures between 940 and 1010 c crystal rich unzen lavas are characterised by two essential rheological features which produce non newtonian effects the first is an instantaneous response of the apparent viscosity to applied stress which requires that the magma be described as a visco elastic fluid that exhibits shear thinning the second effect takes the form of a time dependence of the viscosity at moderate to high stress 10 mpa in this regime the apparent viscosity slowly decreases as increasing fracturing of the phenocrysts and the groundmass occurs fragmentation of crystals and alignment of crystal fragments are observed to produce flow banding effects which in turn lower the apparent viscosity of natural dome lavas ultimately deformation may lead to complete rupture of the lava if the stress is sufficient cracking thus stands as an important process in natural dome lava rheology the ubiquitous non newtonian rheology of dome lavas observed experimentally here needs to be adequately treated in order to generate appropriate eruption models

catastrophic lava dome failure at soufriere hills volcano montserrat 12 13 july 2003 the lava dome collapse of 12 13 july 2003 was the largest of the soufriere hills volcano eruption thus far 1995 2005 and the largest recorded in historical times from any volcano 210 million m3 of dome material collapsed over 18 h and formed large pyroclastic flows which reached the sea the evolution of the collapse can be interpreted with reference to the complex structure of the lava dome which comprised discrete spines and shear lobes and an apron of talus progressive slumping of talus for 10 h at the beginning of the collapse generated low volume pyroclastic flows it undermined the massive part of the lava dome and eventually prompted catastrophic failure from 02 00 to 04 40 13 july 2003 large pyroclastic flows were generated these reached their largest magnitude at 03 35 when the volume flux of material lost from the lava dome probably approached 16 million m3 over two minutes the high flux of pyroclastic flows into the sea caused a tsunami and a hydrovolcanic explosion with an associated pyroclastic surge which flowed inland a vulcanian explosion occurred during or immediately after the largest pyroclastic flows at 03 35 13 july and four further explosions occurred at progressively longer intervals during 13 15 july 2003 the dome collapse lasted approximately 18 h but 170 of the total 210 million m3 was removed in only 2 6 h during the most intense stage of the collapse

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

estimate of pyroclastic flow velocities resulting from explosive decompression of lava domes apparently benign silicic domes or lava flows can travel for several kilometres and then suddenly collapse to generate pyroclastic phenomena capable of causing widespread destruction as happened recently at mount unzen in japan1 two sources have been proposed for the energy that propels such pelean or merapi type2 pyroclastic flows gravitational col lapse supplemented by heating and expansion of air and sudden expansion of pressurized gases from inside the lava flow if gravity controls the energy transfer then areas likely to be affected can be predicted on the basis of topography3 and the resulting deposits will bear a simple relationship to the part of the lava flow from which they issued but if gas pressure adds a significant contribution hazard assessment becomes more difficult because gas decompression adds velocities beyond those acquired by gravitational forces putting much larger areas at risk and forming pyroclastic deposits that are much more difficult to relate to their source here we estimate the initial velocities of pyroclastic flows generated by dome disintegration for a range of lava compositions and volatile contents and offer a conceptual framework for correlating the dynamics of dome front collapse with the resulting sediment record our results indicate that explosive decompression at distal portions of domes can cause velocities comparable to gravitational collapse especially in cases where volatiles become locally concentrated above equilibrium values

volcanic geomorphology an overview abstract the review examines the role of geomorphology in analyzing the volcanoes on earth five objectives are stressed first classifications of volcanic landforms should be improved to take care of the complexity in volcanic landform generation as magmatic systems style of eruption and the erupted material all influence the morphology second geomorphology should contribute to the science of volcanology through its capability in reconstructing growth stages in complex volcanoes and also in analyzing the structural factors which contribute to the catastrophic collapse of volcanoes third geomorphology can contribute to physical volcanology by assessing the effects of topography on transport erosion and deposition of volcanogenic flows and identifying the sources and climatic tectonic conditions which govern the emplacement of volcaniclastic deposits fourth volcanic geomorphology a identifies sedimentary facies associations b constructs facies models for dynamic volcano delivery systems and c analyzes the characteristics of sediment gravity flows in order to determine relevant parameters for modelling their behaviour fifth process oriented geomorphology is critical in developing accurate methods for measuring rates of geomorphic processes that shape ephemeral volcanic constructs and for evaluating and comparing geomorphic impacts on disturbed catchments and the related hydrologic response before during and after eruptions this should help to refine parameters for the exponential decay model finally volcanic geomorphology is essential for risk assessment through geomorphic hazard zonation and composite risk zonation such treatments are necessary in order to face the enhanced challenge posed by the combination of natural hazards and the increasing number of people who are at risk around volcanoes

self stabilization of toppling and hillside creep in layered rocks abstract toppling and hillside creep in layered rocks share the characteristics of rotation of layers under gravity it has been observed that some toppling processes tend toward self stabilization the potential for self stabilization of these processes is greatly influenced by the degree of constraint provided by surrounding material the degree of constraint is reduced by the toppling surface daylighting on the slope surface toppling slope failure typically involves a daylighting failure surface whereas hillside creep by toppling of layers can occur on a surface which may be parallel to the slope surface the failure surface is termed the toppling hinge surface for both block and flexural toppling a review of published field photographs and selected field examples identified as hillside creep of layered rocks indicates that it is common for the rotated layers to form a mirror image symmetry across the toppling hinge surface the mirror image condition is a unique condition in which the strain parallel to the slope is equal in the initial and toppled orientations prior to reaching the mirror image condition the strain parallel to the slope is less than the initial condition resulting in low confining stress across layer boundaries thus facilitating motion rotation beyond the mirror image condition causes extensional strain parallel to the slope which cannot be accommodated without additional disturbance such as freedom of movement of blocks at the slope toe and or crest structural data collected in the maitai valley south island new zealand gives an example of the field observations associated with self stabilized creep toppling

cross section electrical resistance tomography of la soufriere of guadeloupe lava dome summary the electrical resistivity distribution at the base of la soufriof guadeloupe lava dome is reconstructed by using transmission electrical resistivity data obtained by injecting an elec trical current between two electrodes located on opposite sides of the volcano several pairs of injection electrodes are used in order to constitute a data set spanning the whole range of azimuths and the electrical potential is measured along a cable covering an angular sector of 120 alongthebasisofthedome thedataareinvertedtoperformasliceelectricalresistivity tomography sert with specific functions implemented in the eidors open source package dedicated to electrical impedance tomography applied to medicine and geophysics the result ing image shows the presence of highly conductive regions separated by resistive ridges the conductive regions correspond to unconsolidated material saturated by hydrothermal fluids two of them are associated with partial flank collapses and may represent large reservoirs that could have played an important role during past eruptive events the resistive ridges may represent massive andesite and are expected to constitute hydraulic barriers

pathways for degassing during the lava dome eruption of mount st helens 2004 2008 the ability of volatiles to escape rising magma regulates the explosivity of a volcanic system during silicic lava dome eruptions strain localization at the conduit margin occurs during magma ascent creating a damage halo with implications for gas escape here we report the first systematic study of permeability network anisotropy across the marginal shear zone of the a d 2004 2008 lava dome at mount st helens washington state usa the results show increasingly large permeability anisotropy of as much as four orders of magnitude over 4 m moving from the interior of the spine through the damage halo we find the permeability to be essentially isotropic in the spine interior but highly anisotropic in the damage zone and fault core our examination of the dome rocks reveals that the permeability anisotropy depends strongly on the presence of vertically oriented shear layers here we show that the rate of escape of volatiles will be several orders of magnitude higher vertically through a conduit margin shear zone than horizontally into the conduit wall

dome growth and coulee spreading controlled by surface morphology as determined by pixel offsets in photographs of the 2006 merapi eruption abstract at many explosive volcanoes viscous domes extrude which are destroyed by complete or partial collapses although the growth and development of silicic domes and the associated flow and collapse mechanisms are of vital importance for understanding the occurrence and scale of pyroclastic flows quantitative measurements of dome deformations are limited we report on a sequence of photographs taken of a growing and deforming dome a sequence in 2006 featuring the merapi dome taken from similar camera positions allow the application of a digital image correlation algorithm the aim being to detect and explore the temporal evolution of pixel offsets the results suggest that the dome underwent deformation in two regions between september and october 2006 i dome growth and spreading at the volcano summit and ii coulee flow through a narrow canyon the latter is associated with strain localization and flow acceleration which indicates that the displacements and flow velocities at silicic domes are governed by the topographic structure into which the flows develop the downslope motion of the distal parts of the flow and apron slumps continued during episodes of dome extrusion by gravitational spreading an analysis of the 2006 merapi dome and coulee displacement also provides insights into processes that may occur along the newly established southerly eruption direction which also may have influenced pyroclastic flows associated with the 2010 eruption

impact of current wave interaction on storm surge simulation a case study for hurricane bob 1 hurricane bob moved up the u s east coast and crossed over southern new england and the gulf of maine with peak marine winds up to 54 m s 100 mph on 19 20 august 1991 causing significant damage along the coast and shelf a 3 d fully wave current coupled finite volume community ocean model system was developed and applied to simulate and examine the coastal ocean responses to hurricane bob results from process study oriented experiments showed that the impact of wave current interaction on surge elevation varied in space and time more significant over the shelf than inside the inner bays while sea level change along the coast was mainly driven by the water flux controlled by barotropic dynamics and the vertically integrated highest water transports were essentially the same for cases with and without water stratification the hurricane induced wave current interaction could generate strong vertical current shear in the stratified areas leading to a strong offshore transport near the bottom and vertical turbulent mixing over the continental shelf stratification could also result in a significant difference of water currents around islands where the water is not vertically well mixed

a high resolution assimilating tidal model for the northeast pacific ocean a high resolution nonlinear barotropic finite element tidal model is developed for removing tidal elevations from satellite altimeter observations in the northeast pacific ocean surface elevations and currents for the constitutents m2 s2 n2 k2 k1 o1 p1 and q1 are computed using boundary forcing from the oregon state university global tidal model tpxo 3 and the effects of the tidal potential earth tide and ocean self attraction and loading amplitudes and phases computed from the harmonic analyses of altimeter time series at crossover locations along the tracks of the topex poseidon satellite are assimilated into the model and the corrected harmonics are compared with pelagic and coastal tide and pressure gauge measurements and with the tpxo 3 and fes95 2 1 global models diurnal tidal currents along the british columbia and alaska continental shelves are shown to be strongly influenced by the presence of continental shelf waves the surface manifestation of these waves is clearly evident in k1 coamplitude plots k1 and m2 energy fluxes are calculated along these shelves and the potential generation of internal tides is discussed barotropic tidal dissipation is estimated in several key subregions and the m2 total for the gulf of alaska is found to be approximately half that of previous estimates

observations and model simulations of wave current interaction on the inner shelf wave directions and mean currents observed for two 1 month long periods in 7 and 2 m water depths along 11 km of the southern shoreline of martha s vineyard ma have strong tidal modulations wave directions are modulated by as much as 70 over a tidal cycle the magnitude of the tidal modulations in the wavefield decreases alongshore to the west consistent with the observed decrease in tidal currents from 2 1 to 0 2 m s along the shoreline a numerical model swan and deflt3d flow simulating waves and currents reproduces the observations accurately model simulations with and without wave current interaction and tidal depth changes demonstrate that the observed tidal modulations of the wavefield primarily are caused by wave current interaction and not by tidal changes to water depths over the nearby complex shoals

a comparison of georges bank gulf of maine and new england shelf tidal dynamics abstract the semidiurnal tidal currents associated with the near resonant response of the gulf of maine bay of fundy system are amplified over the relatively shallow depths of georges bank thus leading to enhanced energy dissipation vertical mixing and secondary flows on the bank within the western gulf of maine the tidal sea level amplitudes are larger but currents are less energetic than those observed on georges bank while on the new england shelf the tidal response is the least energetic of the three regions in this paper we explore some of the details of the tidal dynamics in these three very different tidal regimes by estimating terms in the volume integrated momentum equations using observations of current and bottom pressure the computations are performed for the m2 semidiurnal tidal constituent which is the dominant tide in all of the regions and are presented in terms of an instantaneous stress balance results show that in the across isobath direction on george bank the m2 inertial te

experiments on internal strain in lava dome cross sections simple experiments have been conducted to study the strain evolution in lava dome cross sections a viscous fluid is injected vertically from a reservoir into a feeding conduit silicone putty is used as analogue magma two dimensional experiments allow the assessment of the internal strain within the dome particle paths are symmetrical on either side of a central line passing through the feeding conduit and display parabolic trajectories the highest strain zone is located above the extrusion zone in cross sections stretch trajectories show a remarkable concentric pattern wrapping around the extrusion zone of the analogue magma to the lateral margins a triple junction of stretch trajectories defines an isotropic point in the strain field in the main central part of the dome an intermediate zone of reversed sense of shearing is caused by a change in the sign of the velocity gradient with respect to that in the upper and lower zones knowledge of this evolving strain pattern can provide a better understanding of the evolution of natural domes also it can help to unravel the kinematic history of ancient domes partly removed by erosion

mineral discrimination using a portable ratio determining radiometer the instrument has ten bands in the visible and near infrared portion of the spectrum 0 5 2 4 mu m measurements and statistical analyses were performed on 66 samples which were characterized by microscopic and x ray diffraction analyses on the ability to discriminate between 16 mineralogical groups 91 percent classification accuracy was achieved modified journal abstract

wave effects on sediment dynamics in a macro tidal estuary darwin harbour australia during the monsoon season abstract darwin harbour is a flood dominated estuary with a large tidal range tides are considered to be the dominant factor influencing sediment resuspension and transport in the harbour during the dry season however the sediment dynamics during the wet or monsoon season have been little explored using either field data or numerical hydrodynamic modelling this study focused on understanding the sediment dynamics during the monsoon and the dominant factors controlling the suspended sediment concentration ssc in darwin harbour using the finite volume coastal ocean model fvcom coupled with the simulating waves nearshore swan model we investigated the effect of waves on the ssc during a particular wet season ssc distributions modelled with tidal currents and wave in the outer harbour were significantly different to those only with tidal currents due to the narrow harbour entrance strong monsoonal waves in the outer harbour barely propagated into the inner harbour the ssc in the inner harbour was therefore almost hardly affected by waves numerical results show that the criterion of neglecting wave forcing in a macro tidal environment when the tidal range is larger than 3 m is inaccurate and that the effects of waves on the ssc can still be important in waters with a large tidal range such as darwin harbour

interaction between the tidal and seasonal variability of the gulf of maine and scotian shelf region abstractas part of a broader study of ocean downscaling the seasonal and tidal variability of the gulf of maine and scotian shelf and their dynamical interaction are investigated using a high resolution 1 36 circulation model the model s seasonal hydrography and circulation and its tidal elevations and currents are compared with an observed seasonal climatology local observations and results from previous studies numerical experiments with and without density stratification demonstrate the influence of stratification on the tides the model is then used to interpret the physical mechanisms responsible for the largest seasonal variations in the m2 surface current that occur over and to the north of georges bank the model generates a striation pattern of alternating highs and lows aligned with georges bank in the m2 surface summer maximum speed in the gulf of maine the striations are consistent with observations by a high frequency coastal radar system and can be explained in terms of a li

the ischia debris avalanche first clear submarine evidence in the mediterranean of a volcanic island prehistorical collapse sector or flank collapse with related debris avalanches is increasingly recognized as a relatively common volcanic behaviour in particular for large hot spot related oceanic islands here we report the case of a catastrophic collapse that occurred at ischia volcanic island in prehistorical times and was driven by the volcano tectonic uplift of mt epomeo the major relief of the island the collapse left a subaerial to submarine horseshoe scar on the southern flank of the island and generated a debris avalanche incorporating thousands of giant blocks dispersed as far as 50 km from the island during the emplacement part of the debris avalanche evolved into a debris flow covering an area of 250 300 km2 this constitutes the first clear evidence of a submarine debris avalanche in the mediterranean sea the major collapse was followed and probably also preceded by recurrent less catastrophic terrestrial and underwater failures two other undersea hummocky deposits are found north and west of the island and might tentatively be correlated to the major southern collapse such volcanic behaviour previously unknown for ischia volcano has likely triggered tsunami waves over the entire bay of naples raising the question of their impact on prehistorical historical communities

modelling the mean barotropic circulation in the bay of fundy and gulf of maine abstract two dimensional nonlinear numerical models are used to study the residual barotropic circulation generated by tides and steady winds in the bay of fundy and gulf of maine the first a multi grid model is used to examine the bay of fundy with a coarse look at the gulf of maine the circulation in the upper bay of fundy is predominantly tidally driven the model clearly reproduces the major gyres observed at the head of the bay steady wind stresses have some effect on the strength of these currents but little cited on the pattern the counterclockwise gyre observed in the body of the bay of fundy is not reproduced in the model the second model covers the lower bay of fundy and the gulf of maine with a single fine grid and is used to look at details in the gulf of maine a clockwise circulation around georges bank and nantucket shoals is clearly indicated from tidal forcing alone as is a gyre over the shallow part of browns bnak different steady wind stress fields give rise to variations in

microshear zones in a miocene submarine dacite dome of southwest japan microscopic shear zones have been found in the groundmass of glassy rocks of a miocene submarine dacite dome in southwest japan similar textures have been reported previously but only in dykes these textures give a valuable insight into the deformation of the dome during its emplacement by recording the orientations of the principal strains detailed textural analysis indicates that the microshear zones formed as a result of flattening and stretching of the magma simultaneously with quenching measured stretching directions are near parallel suggesting the magma flowed in one dominant direction rather than in a radial pattern the strain is believed to also be influenced by high magma pressure inside the dome being imposed on the high viscosity outer part of the dome

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

multiple edifice collapse events in the eastern mexican volcanic belt the role of sloping substrate and implications for hazard assessment abstract the citlaltepetl cofre de perote volcanic chain forms an important physiographic barrier that separates the central altiplano 2500 masl from the gulf coastal plain gcp 1300 masl the abrupt eastward drop in relief between these provinces gives rise to unstable conditions and consequent gravitational collapse of large volcanic edifices built at the edge of the altiplano eastward sloping substrate caused by the irregular configuration of the basement rocks is the dominant factor that controls the direction of collapsing sectors in all major volcanoes in the region to be preferentially towards the gcp these collapses produced voluminous debris avalanches and lahars that inundated the well developed drainages and clastic aprons that characterize the coastal plain large catastrophic collapses from citlaltepetl las cumbres and cofre de perote volcanoes are well documented in the geologic record some of the avalanches and transformed flows have exceptionally long runouts and reach the gulf of mexico traveling more than 120 km from their source so far no direct evidence has been found for magmatic activity associated with the initiation of these catastrophic flank collapses apparently instability of the volcanic edifices has been strongly favored by very intense hydrothermal alteration abrupt topographic change and intense fracturing in addition to the eastward slope of the substrate the reactivation of pre volcanic basement structures during the late tertiary and the e w to ene ssw oriented regional stress regimes may have played an important role in the preferential movement direction of the avalanches and flows in addition to magmatic hydrothermal processes high amounts of rainfall in the area is another factor that enhances alteration and eventually weakens the rocks it is very likely that seismic activity may be the principal triggering mechanism that caused the flank collapse of large volcanic edifices in the eastern mexican volcanic belt however critical pore water pressure from extraordinary amounts of rainfall associated with hurricanes or other meteorological perturbation cannot be ruled out particularly for smaller volume collapses there are examples in the area of small seismogenic debris flows that have occurred in historical times showing that these processes are not uncommon assessing the stability conditions of major volcanic edifices that have experienced catastrophic sector collapses is crucial for forecasting future events this is particularly true for the eastern mexican volcanic belt where in many cases no magmatic activity was associated with the collapse therefore edifice failure could occur again without any precursory warning

thermal hydrologic mechanism for rainfall triggered collapse of lava domes hazardous gravitational collapses involving hot lava domes can be triggered by intense rainfall both in periods of active dome growth and volcanic repose the collapses can evolve into energetic failures involving as much as 90 of the dome or 100 3 10 6 m 3 of dome lava retrogressively removed over several hours under standing such potentially lethal phenomena is vital but traditional explanations for rain induced slope failure are problematic for rainfall on hot typically 400 8c crystalline lava in this paper we quantitatively develop a new thermal hydrologic mechanism that can cause such failures pressure buildup within fissures due to effusive gas trapped by a rain saturated dome carapace results in increased destabilizing forces and the loss of mass strength and ultimately results in failure of the dome our mechanistic models are consistent with field observations and provide a quantification of threshold rainfall intensities and durations required to trigger failure

reconstructing magma failure and the degassing network of dome building eruptions volcanic eruptions are regulated by the rheology of magmas and their ability to degas both detail the evolution of stresses within ascending subvolcanic magma but as magma is forced through the ductile brittle transition new pathways emerge as cracks nucleate propagate and coalesce constructing a permeable network current analyses of magma dynamics center on models of the glass transition neglecting important aspects such as incremental strain accommodation and the key monitoring tool of seismicity here in a combined methods study we report the first high resolution 20 m neutron computed tomography and microseismic monitoring of magma failure under controlled experimental conditions the data reconstruction reveals that a competition between extensional and shear fracturing modes controls the total magnitude of strain to failure and importantly the geometry and efficiency of the permeable fracture network that regulates degassing events extrapolation of our findings yields magma ascent via strain localization along conduit margins thereby providing an explanation for gas and ash explosions along arcuate fractures at active lava domes we conclude that a coupled deformation seismicity analysis holds a derivation of fracture mechanisms and network and thus holds potential application in forecasting technologies

tidal dynamics in the gulf of maine and new england shelf an application of fvcom 1 the unstructured grid finite volume community ocean model fvcom was used to simulate the tides in the gulf of maine gom and new england shelf nes for homogeneous and summer stratified conditions fvcom captures the near resonant nature of the semidiurnal tide and energy flux in the gom and the complex dynamics governing the tide in the nes stratification has limited impact on tidal elevation but can significantly modify the tidal current profile internal tides are energetic in the stratified regions over steep bottom topography but their contribution to the total tidal energy flux is only significant over the northeast flank of georges bank the model suggests that the tidal flushing induced eddy east of monomoy island is the dynamic basis for the locally observed phase lead of the m2 tide the southward propagating tidal wave east of cape cod encounters the northeastward propagating tidal wave from the nes south of nantucket island forming a zone of minimum sea level along a southeast oriented line from nantucket island these two waves are characterized by linear dynamics in which bottom friction and advection are negligible in the momentum balance but their superposition leads to a strong nonlinear current interaction and large bottom stress in the zone of lowest sea elevation

mechanical discontinuities monitoring at merapi volcano using kinematic gps merapi volcano java indonesia is in almost continuous activity with growth of an andesitic lava dome this dome frequently collapses to form potentially deadly glowing avalanches explosions and nuees ardentes to monitor the evolution of surface displacements and to model the associated magmatic sources we established a global positioning system gps network in 1993 and have measured it each year using the static gps method however the limited number of benchmarks and the geometry of the network did not allow us to precisely locate major mechanical discontinuities within the edifice precisely locating these discontinuities is of central importance because they delimit areas of potential instability and provide means to evaluate potential volumes of falling material the kinematic gps method offers a way to partially solve the problem of temporal and spatial sampling of the displacement field but its accuracy is usually insufficient to monitor small displacements we propose here a strategy of field measurements and adjustments which combines kinematic positioning 1 min and rapid static baselines 15 min to get a 1 5 cm error 95 confidence at merapi summit we have installed about 50 benchmarks covering the area around the main crater field measurements of this new network with our method take a few hours and the data processing has been automated we present the results of 8 surveys from 1999 to 2002 a period that includes a dome collapse in january 2001 our results show large horizontal displacements towards the northwest starting in july 2000 and reaching about 50 cm in amplitude in november 2000 that we interpret as precursors to the dome collapse we also locate two presently active discontinuities at the summit of the volcano this approach can be implemented easily on other active volcanoes

an exceptional case of endogenous lava dome growth spawning pyroclastic avalanches the 1999 bocca nuova eruption of mt etna italy abstract during an eruption at the bocca nuova one of the summit craters of mt etna in october november 1999 a part of the crater floor near its wnw rim was uplifted to form a dome shaped feature that consisted of older lava and pyroclastics filling the crater this endogenous dome grew rapidly over the crater rim thus being perched precariously over the steep outer slope of the bocca nuova and near continuous collapse of its steep flanks generated swiftly moving pyroclastic avalanches over a period of several hours these avalanches advanced at speeds of 10 20 m s and extended up to 0 7 km from their source on top of lavas emplaced immediately before their deposits were subsequently covered by lava flows that issued from vents below the front of the dome and from the bocca nuova itself growth of the dome was caused by the vertical intrusion of magma in the marginal western part of the crater which deformed and uplifted previously emplaced still hot and plastically deformable eruptive products filling the crater the resulting avalanches had all the characteristics of pyroclastic flows spawned by collapse of unstable flanks of lava domes but in this case the magma involved was of mafic hawaiitic composition and would under normal circumstances have produced fluid lava flows the formation of the dome and the generation of the pyroclastic avalanches owe their occurrence to the rheological properties of the eruptive products filling the crater which were transformed into the dome and to the morphological configuration of the bocca nuova and its surroundings the density contrast between successive erupted products may also have played a role although events of this type are to be considered exceptional at etna their recurrence might represent a serious hazard to visitors to the summit area

surface morphology of columnar joints and its significance to mechanics and direction of joint growth columnar joints in basaltic lava flows display conspicuous bands oriented normal to column axes new observations show that each band contains a single plumose structure and thus represents an individual crack or joint segment formed during a discrete growth event analysis of plumose structure and intersections of cracks leads to a new kinematic model of columnar jointing and provides the first direct proof that columnar joints grow incrementally from exterior to interior regions of solidifying magma bodies columnar joints form by nucleation and growth of new cracks on the edges of older cracks each new crack begins at a point and propagates mostly normal to column axes and along the leading edge of a developing column face where thermal stress is concentrated inward propagation of cracks toward hotter regions is limited by a decrease of thermal stress and by the brittle ductile transition of lava outward and lateral propagation is limited by mechanical interaction with previous cracks and by low thermal stress in already fractured lava cracks often diverge slightly from the planes of previous cracks probably because of spatial and temporal changes in directions of local principal stresses mechanical interaction causes a diverging crack to overlap curve toward and usually intersect the previous crack behind its edge leaving a blind tip that points in the overall growth direction of the columnar joints this and other directional criteria are applied to determine joint growth patterns in several lava flows of the western united states in two tiered and multi tiered flows downward growing columnar joints usually meet upward growing joints well below the middle of the flows which indicates very rapid cooling of upper portions relative to lower portions this supports the idea that convection of water in columnar joints connected to the surface may be an important mechanism for cooling the upper portions of these flows whereas conduction is probably the dominant cooling mechanism at the bases

geologic remote sensing remote sensing techniques are now being used routinely in geologic interpretation for mineral and energy exploration plant siting waste disposal and the development of models for regional and continental tectonics new spaceborne methods and associated technologies are being developed to produce data from which geologic information about large areas can be derived much more rapidly than by conventional techniques

sector collapses and large landslides on late pleistocene holocene volcanoes in kamchatka russia on kamchatka detailed geologic and geomorphologic mapping of young volcanic terrains and observations on historical eruptions reveal that landslides of various scales from small 0 001 km3 to catastrophic up to 20 30 km3 are widespread moreover these processes are among the most effective and most rapid geomorphic agents of 30 recently active kamchatka volcanoes at least 18 have experienced sector collapses some of them repetitively the largest sector collapses identified so far on kamchatka volcanoes with volumes of 20 30 km3 of resulting debris avalanche deposits occurred at shiveluch and avachinsky volcanoes in the late pleistocene during the last 10 000 yr the most voluminous sector collapses have occurred on extinct kamen 4 6 km3 and active kambalny 5 10 km3 volcanoes the largest number of repetitive debris avalanches 10 during just the holocene has occurred at shiveluch volcano landslides from the volcanoes cut by ring faults of the large collapse calderas were ubiquitous large failures have happened on both mafic and silicic volcanoes mostly related to volcanic activity orientation of collapse craters is controlled by local tectonic stress fields rather than regional fault systems specific features of some debris avalanche deposits are toreva blocks huge almost intact fragments of volcanic edifices involved in the failure some have been erroneously mapped as individual volcanoes one of the largest toreva blocks is mt monastyr a 2 km3 piece of avachinsky somma involved in a major sector collapse 30 40 ka bp long term forecast of sector collapses on kliuchevskoi koriaksky young cone of avachinsky and some other volcanoes highlights the importance of closer studies of their structure and stability

susceptibility of lava domes to erosion and collapse by toppling on cooling joints the shape of lava domes typically leads to the formation of radial patterns of cooling joints these cooling joints define the orientation of the columnar blocks which plunge toward the center of the dome in the lower parts of the dome the columns plunge into the dome at low angles and are relatively stable higher in the dome the columns plunge into the dome at steep angles these steeply plunging columns are susceptible to toppling and if the lower part of a dome is partially removed by erosion or collapse the unstable part of the dome becomes exposed leading to toppling failure examples of this process are provided from coastal erosion of lava domes at katsura island shimane peninsula western japan an analogue model is presented to demonstrate the mechanism it is proposed that the mechanism can contribute to collapse of lava domes during or after emplacement

trends in the aggregated rate of pre eruptive volcano tectonic seismicity at kilauea volcano hawaii accelerating rates of volcano tectonic vt earthquakes are commonly observed during volcanic unrest understanding the repeatability of their behaviour is essential to evaluating their potential to forecast eruptions quantitative eruption forecasts have focused on changes in precursors over intervals of weeks or less previous studies at basaltic volcanoes in frequent eruption such as kilauea in hawaii and piton de la fournaise on reunion suggest that vt earthquake rates tend to follow a power law acceleration with time about 2 weeks before eruption but that this trend is often obscured by random fluctuations or noise in vt earthquake rate these previous studies used a stacking procedure in which precursory sequences for several eruptions are combined to enhance the signal from an underlying acceleration in vt earthquake rate such analyses assume a common precursory trend for all eruptions this assumption is tested here for the 57 eruptions and intrusions recorded at kilauea between 1959 and 1984 applying rigorous criteria for selecting data e g maximum depth restricting magnitudes to be greater than the completeness magnitude 2 1 we find a much less pronounced increase in the aggregate rate of earthquakes than previously reported the stacked trend is also strongly controlled by the behaviour of one particular pre eruptive sequence in contrast a robust signal emerges among stacked vt earthquake rates for a subset of the eruptions and intrusions the results are consistent with two different precursory styles at kilauea 1 a small proportion of eruptions and intrusions that are preceded by accelerating rates of vt earthquakes over intervals of weeks to months and 2 a much larger number of eruptions that show no consistent increase until a few hours beforehand the results also confirm the importance of testing precursory trends against data that have been filtered according to simple constraints on the spatial distribution and completeness magnitude of the vt earthquakes

triggering of a volcanic dome collapse by rainwater infiltration 1 the thermodynamic processes in a one dimensional model of a porous lava dome are considered in the presence of a rising magmatic gas flux through the void spaces and rainfall interacting with the dome surface the steady state surface temperature of the dome depends on both magmatic gas mass flux and rainfall rate a critical rainfall rate is determined that cools the dome surface to 100 c rainfall rates above this critical value allow liquid infiltration into the void spaces of the dome thus restricting the escape of magmatic gas a model which restricts the gas flow through the surface predicts internal gas pressures much higher than the overburden pressure in the top few meters approximately one hour after the onset of rainfall for a marginally stable dome this could cause small vulcanian explosions which depending on their location could trigger a dome collapse on a timescale consistent with observations

magma degassing and intermittent lava dome growth 1 after its 1980 explosive eruption mount st helens developed a lava dome that grew intermittently for several years each growth episode was followed by a long repose suggesting that the magma column above the reservoir was in hydrostatic equilibrium a mechanism allowing an increasingly thicker dome is proposed loading of the crater floor by the dome acts to prevent gas leakage from magma by closing fractures around the volcanic conduit fractures get closed down to a depth that increases as the dome grows calculations of dome thickness as a function of dome radius are in good agreement with observations renewed growth is triggered by the spreading of the dome gas retention over a larger depth extent allows smaller magma densities and a taller magma column above the reservoir according to this model small domes can in fact promote explosive volcanic conditions and be unstable

the k1 tide on the continental shelf from nova scotia to cape hatteras abstract a description is given of the k1 tide over the northeast continental shelf off north america from nova scotia to cape hatteras analyzed pressure data obtained from w brown and j irish university of new hampshire have been used to draw up the k1 cotidal map and existing current data have been analyzed to give the associated velocity map offshore there is a sweep of the tide from north to south in general agreement with what is known of the oceanic k1 tide in the north atlantic on the shelf there is a trapping of phase lines to the coast creating in particular a virtual amphidrome south of cape cod maximum amplitudes of around 15 cm are found in the gulf of maine lowest around 7 cm south of cape cod the k1 currents are generally barotropic and current ellipses are aligned with the local topography maximum currents of about 10 cm s 1 are found south of cape cod a simple model for the k1 pressure field is developed using the free and forced inviscid barotropic waves on a two dimensi

evolution and volcanic hazards of taapaca volcanic complex central andes of northern chile taapaca volcanic complex is a large dacitic volcano 35 km 3 located in the western border of the active zone of the central andes of northern chile apart from early poorly preserved silicic andesites taapaca volcanic complex has generated remarkably similar porphyritic hornblende biotite dacites with distinctive sanidine megacrysts for at least 1 5 ma the main products of the volcano are dacite lavas and domes with associated block and ash flow deposits there have also been several sector collapses to generate debris avalanches which are closely associated with volcanic blasts and episodes of dome growth four stages of evolution are recognized with volcanism occurring in short bursts between much longer periods of dormancy volcanism has built a substantial stratovolcano and has migrated 4 5 km towards the sw with time late pleistocene to holocene activity has involved at least three sector collapses of the hydrothermally altered flanks and domes volcanic blasts block and ash flows debris avalanches and lahars have been distributed down the southwestern flanks these areas are the main populated part of the chilean altiplano and the location of the main road between bolivia and the pacific ocean coast a future eruption will threaten these areas and the regional economy