sub volcanic crystallization at stromboli aeolian islands southern italy preceding the sciara del fuoco sector collapse evidence from monzonite lithic suite we describe texture mineralogy and whole rock composition of cognate monzonite sub volcanic clasts within debris flow deposits related to the 5000 years catastrophic phreatomagmatic eruption probably linked to the sciara del fuoco sector collapse the debris flows are at the top of accretionary lapilli rich ash deposits overlying potassic ks shoshonites lavas of the neostromboli period the monzonites are inferred to be crystallized in situ at low p at the side walls and or roof margins of a shallow magma chamber and to be cogenetic with the ks neostromboli extrusives they can be considered ideal orthocumulates since they approximately retain a bulk liquid composition and possibly represent slowly cooled equivalents of their ks shoshonite host rock the closure temperature of final solidification of the monzonite lithic suite was estimated through ternary feldspar geothermobarometry plagioclase k feldspar and k feldspar biotite equilibria and is in the range of 750 790 c with a maximum logfo2 around 15 1 15 3 the estimated pressure of crystallization is 0 5 kbar potassic lavas and dikes previously emplaced during the neostromboli period also resemble the monzonites in both major trace elements and mineral chemistry the cogenetic relationship between ks neostromboli extrusives and the monzonite host rock magma from which the sub volcanic clasts were derived is clear evidence that a shallow magma chamber existed between the caldera collapse of the vancori period and the sciara del fuoco sector collapse i e between 13 000 and 5000 years the monzonite clasts were derived from crystallization at very shallow depth ca 1 km and strongly support the hypothesis of violent decompression of the shallow magmatic plumbing system during the sciara del fuoco sector collapse climax of the regressive landslide event with maximum disruption of the chamber walls took place during emplacement of the debris flows i e during the late stage of the neostromboli phreatomagmatic eruption

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

numerical modeling of the emplacement of socompa rock avalanche chile 1 the 7 5 ka socompa sector collapse emplaced 25 km3 of fragmented rock as a thin but widespread 500 km2 avalanche deposit followed by late stage sliding of 11 km3 as toreva blocks most of the avalanche mass was emplaced dry although saturation of a basal shear layer cannot be excluded modeling was carried out using the depth averaged granular flow equations in order to provide information on the flow behavior of this well preserved long run out avalanche results were constrained using structures preserved on the surface of the deposit as well as by deposit outline and run up a proxy for velocity models assuming constant dynamic friction fail to produce realistic results because the low basal friction angles 1 to 3 5 necessary to generate observed run out permit neither adequate deposition on slopes nor preservation of significant morphology on the deposit surface a reasonable fit is obtained however if the avalanche is assumed simply to experience a constant retarding stress of 50 100 kpa during flow this permits long run out as well as deposition on slopes and preservation of realistic depositional morphology in particular the model explains a prominent topographic escarpment on the deposit surface as the frozen front of a huge wave of debris reflected off surrounding hills the result that socompa avalanche experienced a small approximately constant retarding stress during emplacement is consistent with a previously published analysis of avalanche data

failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

emplacement of the 18 may 1980 lateral blast deposit ene of mount st helens washington facies variations east northeast of mount st helens preserve a record of depositional processes in the 18 may 1980 lateral blast cloud this paper reports new field grain size and component data from the ene sector of the timber blowdown zone and presents a model for blast flow and sedimentation the first erupted ejecta was rich in juvenile components and extends to the distal blowdown limit the last erupted ejecta was rich in accidental lithics and reached no further than a few kilometres from the mountain due to waning discharge the blast cloud was a turbulent stratified flow which transported and deposited sediment in the manner of a high density turbidity current the possibility that the blast was emplaced as a giant shearing fluidised bed is not favoured by compositional zoning patterns depositional conditions were strongly influenced by the rate of suspended load fallout from the blast within about 8 km from vent rapid sedimentation caused deposition under moderate to high concentration conditions and formation of a basal hindered settling zone able to detach gravitationally and drain into local depressions the resulting proximal facies resembles a low aspect ratio ignimbrite fines depletion in the proximal facies is attributed to a combination of residual turbulence and rapid gas escape during particle settling and compaction through the hindered settling zone component data suggest that the blast head played no significant role in the generation of fines depletion in the blast deposit as suggested by previous workers with increasing distance from vent the rate of particle fallout declined and sedimentation took place under increasingly dilute and tractional conditions building up antidune like bedforms wavelengths of these bedforms range from 20 to 1 m and decrease away from vent there is a systematic relationship between antidune migration direction and depositional slope the transition from proximal ignimbrite like to distal surge like facies suggests a possible gradation in transport and deposition processes between conventional pyroclastic surges and high velocity pyroclastic flows

link between major flank slip and 2002 2003 eruption at mt etna italy 1 the 2002 2003 etna eruption is studied through earthquake distributions and surface fracturing in september 2002 earthquake induced surface rupture sinistral offset 0 48 m occurred along the e w striking pernicana fault pf on the ne flank in late october a flank eruption accompanied further 0 77 m surface rupturing reaching a total sinistral offset of 1 25 m the deformation then propagated for 18 km eastwards to the coastline sinistral offset 0 03 m and southwards along the nw se striking timpe dextral offset 0 04 m and later trecastagni faults dextral offset 0 035 m seismicity 4 km bsl on the e flank accompanied surface fracturing fault plane solutions indicate an overall ese wnw extension direction consistent with ese slip of the e flank also revealed by ground fractures a three stage model of flank slip is proposed inception september earthquake climax accelerated slip and eruption and propagation e and s migration of the deformation

deflection of dykes into sills at discontinuities and magma chamber formation abstract many rift zones contain composite volcanoes central volcanoes most of which are supplied with magma from shallow crustal magma chambers volcanotectonic studies of eroded rift zones such as in iceland as well as geophysical studies indicate that many shallow magma chambers evolve from sills here i provide field description of sills and extinct magma chambers in the quaternary and tertiary palaeorift zones of iceland focusing on the felsic pluton of slaufrudalur southeast iceland as a fine example of a magma chamber developed through the injection of sills in this paper i review analyse and develop further two related mechanisms for the deflection of dykes into sills and thus the potential initiation of a magma chamber namely a cook gordon debounding delamination and b stress barriers and propose a third mechanism c favourable material toughness ratios due to elastic mismatch difference in young s moduli or stiffnesses of layers in contact in the cook gordon mechanism a weak contact opens up as a result of dyke induced tensile stress this mechanism is likely to operate primarily at shallow depths as is supported by field observations and numerical models a stress barrier is a layer where the local stress is unfavourable to a particular type of rock fracture here a dyke field observations and numerical models show that on meeting a stress barrier a dyke either changes into a sill or becomes arrested the material toughness mechanism indicates that when the upper layer at a contact has the same or less stiffness than the lower layer hosting the dyke there is little tendency for the dyke to become deflected into the contact however when the upper layer is stiffer such as when a stiff basaltic lava flow is on the top of a soft pyroclastic layer the dyke tends to become deflected into the contact to form a sill field results suggest that all these mechanisms may cause dyke deflection into sills and may operate together particularly where the rock consists of alternating soft and stiff layers since the quaternary lava pile in iceland has many more soft hyaloclastite layers than the tertiary lava pile these mechanisms were probably very efficient in generating sills and by implication shallow magma chambers during the quaternary this may be one reason why in comparison with the tertiary lava pile the quaternary lava pile contains so many sills and extinct plutons and active shallow magma chambers

volcaniclastic dykes tell on fracturing explosive eruption and lateral collapse at stromboli volcano italy abstract in the upper part of the stromboli volcano in the le croci and bastimento areas two dyke like bodies of volcanic breccia up to two metre thick crosscut and intrude the products of vancori and neostromboli volcanoes we describe the lithofacies association of these unusual volcaniclastic dykes interpret the setting of dyke forming fractures and the emplacement mechanism of internal deposits and discuss their probable relationships with the explosive eruption and major lateral collapse events that occurred at the end of the neostromboli period the dyke volcaniclastic deposits contain juvenile magmatic fragments pyroclasts suggesting a primary volcanic origin their petrographic characteristics are coincident with the neostromboli products the architecture of the infilling deposits comprises symmetrically nested volcaniclastic units separated by sub vertical boundaries which are parallel to the dyke margins the volcanic units are composed of distinctive lithofacies the more external facies is composed of fine and coarse ash showing sub vertical laminations parallel to the contact wall the central facies comprises stratified lithic rich breccia and lapilli tuff whose stratification is sub horizontal and convolute discordant to the dyke margins only at le croci dyke the final unit shows a massive tuff breccia facies the volcaniclastic dykes experienced a polyphasic geological evolution comprising three stages the first phase consisted in fracturing explosive intrusion related to magma rising and upward injection of magmatic fluids and pyroclasts the second phase recorded the dilation of fractures and their role as pyroclastic conduits in an explosive eruption possibly coeval with the lateral collapse of the neostromboli lava cone finally in the third phase the immediately post eruption mass flow remobilization of pyroclastic deposits took place on the volcano slopes

coupled magma chamber inflation and sector collapse slip observed with synthetic aperture radar interferometry on mt etna volcano 1 volcanoes deform dynamically due to changes in both their magmatic system and instability of their edifice mt etna features vigorous and almost continuous eruptive activity from its summit craters and periodic flank eruptions even though its shape is that of a large stratovolcano its structure features two rift systems and a flank collapse structure similar to hawaiian shield volcanoes we analyze european remote sensing ers satellite differential interferometric synthetic aperture radar insar data 1993 1996 for mt etna spanning its quiescence from 1993 through the initiation of renewed eruptive activity in late 1995 we use synthetic aperture radar sar data from both ascending and descending ers satellite tracks comparison of independent interferograms covering the first 2 years of the inflationary period shows a pattern consistent with inflation of the volcano calculation of the tropospheric path delay based on meteorological data does not change this interpretation interferograms from late summer 1995 1996 show no significant deformation joint inversion of interferograms from ascending and descending satellite tracks require both inflation from a spheroidal magmatic source located beneath the summit at 5 km below sea level and displacement of the east flank of etna along a basal decollement both sources of deformation were contemporaneous within the resolution of our data and suggest that inflation of the central magma chamber acted to trigger slip of etna s eastern flank these results demonstrate that flank instability and recharge of a volcano s magma system must both be considered toward understanding how volcanoes work and in their hazard evaluation

what controls sheet intrusion in volcanoes structure and petrology of the stromboli sheet complex italy abstract a multidisciplinary study has been conducted on 109 intrusive sheets of stromboli the relation between sheet injection conditions with the magmatic and structural variations of the volcano and the parameters governing the preferential intrusion geometry inside the volcano in a time perspective have been determined during its subaerial activity the last 100 ka stromboli experienced periods of extrusive growth and sheet intrusions alternated to caldera and lateral collapses of the nw sciara del fuoco flank the sheet intrusions similar to the extrusive rocks span a large compositional range from calc alkaline to potassic through high k calc alkaline and shoshonitic series the most evolved compositions of the effusive rocks however have not been found as intrusions whereas some mafic and basic magmas of sheets were never erupted the repeated time change of location of the intrusions from strombolicchio to the ne sw trend passing trough the inferred paleostromboli summit cone and the southern flank could represent the expression of the shift of the magma chamber towards the southeast and the subsequent onset of a clear ne sw elongated magma chamber located along the main stromboli weakness zone the stromboli evolution in the last 100 ka has been characterized by the persistent n 10 55 e intrusion direction which reflects the influence of the edifice s state of stress on the magma feeding paths after 13 ka ago sheets mainly intruded along to the sector collapse scarps in a circum amphitheatre geometry which has been demonstrated to be influenced by the new cone morphostructure and not by different magma rheological characters

analytical and 3 d numerical modelling of mt etna italy volcano inflation summary since 1993 geodetic data obtained by different techniques gps edm sar levelling have detected a consistent inflation of the mt etna volcano the inflation culminating with the 1998 2001 strong explosive activity from summit craters and recent 2001 and 2002 flank eruptions is interpreted in terms of magma ascent and refilling of the volcanic plumbing system and reservoirs we have modelled the 1993 1997 edm and gps data by 3 d pressurized sources to infer the position and dimension of the magma reservoir we have performed analytical inversions of the observed deformation using both spheroidal and ellipsoidal sources embedded in a homogeneous elastic half space and by applying different inversion methods solutions for these types of sources show evidence of a vertically elongated magma reservoir located 6 km beneath the summit craters the maximum elevation of topography is comparable to such depth and strong heterogeneities are inferred from seismic tomography in order to assess their importance further 3 d numerical models employing source parameters extracted from analytical models have been developed using the finite element technique the deformation predicted by all the models considered shows a general agreement with the 1993 1997 data suggesting the primary role of a pressure source while the complexities of the medium play a minor role under elastic conditions however major discrepancies between data and models are located in the se sector suggesting that sliding along potential detachment surfaces may contribute to amplify deformation during the inflation for the first time realistic features of mt etna are studied by a 3 d numerical model characterized by the topography and lateral variations of elastic structure providing a framework for a deeper insight into the relationships between internal sources and tectonic structures

the holocene secche di lazzaro phreatomagmatic succession stromboli italy evidence of pyroclastic density current origin deduced by facies analysis and ams flow directions the edifice of stromboli volcano gravitationally collapsed several times during its volcanic history 100 ka present the largest holocene event occurred during the final stage of the neostromboli activity 13 5 ka and was accompanied by the emplacement of phreatomagmatic and lahar deposits known as the secche di lazzaro succession a stratigraphic and paleomagnetic study of the secche di lazzaro deposits allows the interpretation of the emplacement and the eruptive processes we identify three main units within the succession that correspond to changing eruption conditions the lower unit ua consists of accretionary lapilli rich thinly bedded parallel to cross stratified ash deposits interpreted to indicate the early stages of the eruption and emplacement of dilute pyroclastic density currents upward the second unit ub of the deposit is more massive and the beds thicker indicating an increase in the sedimentation rate from pyroclastic density currents the upper unit uc caps the succession with thick immediately post eruptive lahars which reworked ash deposited on the volcano s slope flow directions obtained by anisotropy of magnetic susceptibility ams analysis of the basal bed of ua at the type locality suggest a provenance of pyroclastic currents from the sea this is interpreted to be related to the initial base surges associated with water magma interaction that occurred immediately after the lateral collapse which wrapped around the shoulder of the sector collapse scar upward in the stratigraphy upper beds of ua and ub paleoflow directions change and show a provenance from the summit vent probably related to the multiple collapses of a vertical pulsatory eruptive column

middle miocene volcaniclastic dikes at kukedo shimane peninsula sw japan fluidization of volcaniclastic beds by emplacement of syn volcanic andesitic dikes abstract at kukedo northern shimane peninsula sw japan volcaniclastic peperite dikes extend parallel to andesitic dikes in volcaniclastic turbidites of the middle miocene takashibiyama formation they mainly comprise a poorly sorted mixture of volcaniclasts derived from the host volcaniclastic turbidites andesitic dikes in direct contact with the volcaniclastic turbidites have fluidal contacts locally protruding into the volcaniclastic turbidites volcaniclastic beds are disorganized in a zone up to 1 m wide and are partly welded within 1 30 cm from the contacts one major volcaniclastic dike 0 5 1 5 m wide extends upwards from the lower segment to the upper segment of a laterally offset andesitic dike 1 5 3 m wide coarse lithic clasts are locally concentrated along the wall of the dike and juvenile clasts derived from the andesitic dike are sparsely set in the poorly sorted volcaniclastic mixture juvenile clasts are poorly vesicular and microcrystalline and mainly polyhedral in shape sparse fluidal juvenile clasts are fractured in situ into small clasts by quench cracks fluidization of host volcaniclastic turbidites occurred to form volcaniclastic dikes during emplacement of andesitic dikes driven by the excess pore fluid pressure imparted from the stress concentration at the advancing magma head and heating of pore water in the host volcaniclastic beds the volcaniclastic dike extending directly from the andesitic dike was produced by small scale dynamic mixing of magma and watery volcaniclastic beds upon offsetting of the andesitic dike welding was favored by the increased water vapor pressures and high temperatures in direct contact with andesitic dikes

87sr 86sr ratios in hydrothermal waters and deposits from the east pacific rise at 21 n abstract 87 sr 86 sr ratios of three hydrothermal waters collected on the east pacific rise at 21 n define a mixing line between seawater and a hydrothermal end member at 0 7030 which is derived by seawater basalt interaction at ca 350 c and water rock ratio of about 1 5 sr concentrations are not affected in the process while mg uptake from seawater is almost complete up to2 3 of this hydrothermal component is involved in anhydrite precipitation while the sr isotopic ratio in sulfides chalcopyrite sphalerite cannot be distinguished from that of sulfate it is estimated that ca 1 10 10 moles of strontium are yearly cycled in the hydrothermal systems of mid oceanic ridges thereby affecting the 87 sr 86 sr budget of seawater mass balance between river runoff limestone precipitation and ridge basalt alteration suggests that the 87 sr 86 sr ratios of the river runoff are in the range 0 7097 0 7113 and are largely dominated by limestone alteration

mineralogy and geochemistry of epigenetic features in metalliferous sediment atlantis ii deep red sea finely laminated and undisturbed except in the area of the southwest basin in this part bedding resedimentation and brecciation are common in addition some sediment cores contain vein minerals precipitated in open fissures which crosscut unlithified metalliferous sediments these veins are the conduits by which new hot brine vents into the deep vein mineralogy is dominated by anhydrite talc smectite pyrite sphalerite and chalcopyrite vertical zonation due to cooling and reaction of the incoming brine as it rises through the metalliferous sediment near the southwest basin west basin transition metalliferous sediment has been locally recrystallized to a hematite magnetite pyroxene assemblage probably due to the intrusion of basalt into the metalliferous sediments modified journal abstract

geological constraints of a structural model of sector collapse at stromboli volcano italy this study is focused on the reconstruction of the structure and dynamics of the first lateral collapse that occurred at stromboli during the holocene which represents the structure inherited by all the following collapses that formed the present sciara del fuoco depression the first lateral collapse of stromboli occurred at the end of the vancori volcano activity at about 13 ka ago the neostromboli lava cone grew within this collapse amphitheater based on a comprehensive geologic and structural analysis of both vancori and neostromboli products we propose an innovative interpretation of the sliding surface once considered to be a homogeneous landslide along a deep seated sliding surface we demonstrate that the upper vancori failure was accommodated by a more complex deformation regime comprising an upper proximal domain of tilted megablocks toreva and a lower distal domain of fragmental landslide transport and deposition

near and far field survey report of the 30 december 2002 stromboli southern italy tsunami abstract in may 2002 stromboli one of the two active volcanoes in the aeolian islands southern tyrrhenian sea entered a new phase of explosive activity initially characterized by gas and ash emission from the summit craters on 30 december 2002 a massive submarine landslide followed by a subaerial one from the elevation of about 650 m above sea level a s l detached from the submerged part of the northwest slope of stromboli island producing a tsunami this huge mass movement was recorded by the ingv seismic stations installed respectively at stromboli and panarea in the following days a working group of ingv researchers and technicians was organized in order to perform a field survey of the tsunami effects in the near field including all the aeolian islands meanwhile a survey in the far field was planned along the coastline of campania and sicily where the effects of the 30 december tsunami were observed but not directly quantified visible material effects of the 30 december tsunami could be observed only along the northeast coast of stromboli island inundated by the wave with run up heights locally up to several meters many buildings were severely damaged on the other aeolian islands and in the far field the effects of the sea wave were documented only through eyewitness accounts to ensure a coherent collection of these accounts a standard interview form based on the advice of the intergovernmental oceanographic commission ioc was used a databank of all observations measurements interview forms and photographs was compiled in order to provide a useful base to test computer simulations hazard analyses and damage scenarios additional information was also made available at the emergeo link of ingv web pages http www ingv it emergeo and http www ov ingv it

high precision photogrammetry for monitoring the evolution of the nw flank of stromboli volcano during and after the 2002 2003 eruption high precision aerial photogrammetry has been used in addition to other geophysical techniques such as bathymetric surveys geodetic measurements microseismicity recording etc for monitoring slope deformations and the volcanic activity of stromboli island aeolian arc italy during the last effusive eruption which started on december 28 2002 and soon after the major landslide tsunami event of december 30 qualitative and quantitative description of topographic and morphological changes of the sciara del fuoco were possible thanks to a recent pre eruption photogrammetric survey performed in 2001 the comparisons of 12 multi temporal digital terrain models carried out during the period january june 2003 were used to evaluate the displaced mass by the landslide the lava accumulation and the erosion processes of the sciara del fuoco after the end of the eruption four additional photogrammetric surveys were performed between july 2003 and october 2005 to monitor the evolution of the slope and detect potential instability phenomena the slope appeared significantly modified and continued to evolve showing marked erosion both on the lower part and toward the craters terrace over the same period the new lava flows showed progressive contraction of the thicker part of the lava pile caused by its cooling and compaction and the possible sliding along the shear surface of the december 2002 deep seated movement the present morphology seems to be far from equilibrium and the deformation processes are still ongoing justifying a continuous monitoring activity to understand the evolution of these instability phenomena

a new geological map of stromboli volcano tyrrhenian sea italy based on application of lithostratigraphic and unconformity bounded stratigraphic ubs units

superheating in the red sea the heat mass balance of the atlantis ii deep revisited atlantis ii is the only hydrothermally active of the five central red sea deeps hot new brine being supplied by a geyser spring it is filled with two stratified anoxic brine layers namely the lower conductive layer lcl at the bottom and the upper conductive layer ucl above it the other deeps were filled by brine overspill hydrological and geochemical data on the atlantis ii deep show that between 1965 and 1977 only negligible amounts of lower brine have spilled over towards chain a deep and that in contrast the lower brine component of the ucl has increased significantly the heat mass balance of the atlantis ii deep lower brine between 1966 to 1977 is considered mass balance calculations are based on the published bathymetry of the deep and on the measured rising rate of the interface between the ucl and the lcl including a possible loss of mass out of the system heat balance equations involve 1 the conductive flow of heat at the bottom of the deep 2 the heat lost by conduction through the lower interface 3 the flow of heat due to hot brine advection and 4 the heat lost by lower brine advection out of the lcl the equation of pitzer et al 1984 57 extrapolated above 300 c is first used to calculate the c p s of the hydrothermal brine it predicts moderately increasing c p s with temperature heat mass balance equations solved with this c p model yield a spring temperature of 461 c for the time interval 1966 1977 this temperature is unrealistic as it is 70 c higher than 390 c the boiling temperature of the lower brine at 220 bar besides it is shown that none of the parameters in the calculation other than c p can attain values as to decrease t s below 390 c the modified equation of born predicts a near exponential increase of the hydrothermal brine c p s above 300 c spring temperatures of 342 c or 353 c are calculated with this c p model depending whether the mass lost towards the ucl is taken into account or not these temperatures compare favorably with the mean temperature of 330 c obtained for the trapping of fluid inclusions in epigenetic anhydrites from the discharge zone sediments 21 hence it is concluded that 1 the changes in the mass and temperature of the atlantis ii deep lower brine between 1965 and 1977 cannot be interpreted in terms of a realistic spring temperature unless the hydrothermal fluid has presented very high heat transport properties above 300 c 2 this can be either in the stable region below the boiling point as predicted by the equation of born or in the metastable region above 390 c superheated liquids indeed present heat capacities which increase exponentially with temperature two periods in the recent hydrothermal activity of the atlantis ii deep are distinguished 1 from 1965 to 1976 the deep has received an excess heat supply e g compatible with the influx of superheated liquids the spring flow rate including the mass of lower brine expelled towards the ucl 29 was around 367 kg s 1 2 the hydrothermal activity then decreased from 1976 to 1979 the influx of fluids with abnormal heat transport properties was greatly reduced and the mean spring flow rate probably dropped to 280kg s 1

strength of jointed rock masses jointed rock masses comprise interlocking angular par ticles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials the strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which in turn depends on the number orientation spacing and shear strength of the discontinuities a complete understanding of this problem presents formidable theoretical and experi mental problems and hence simplifying assumptions are required in order to provide a reasonable basis for estimating the strength of jointed rock masses for engineering design purposes this paper summarizes some of the basic information upon which such simplifying assumptions can be made a simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples des masses jointives de rochers comprennent des particules angulaires enchevetrees ou des

atlantis ii deep geothermal brine system chemical processes between hydrothermal brines and red sea deep water water samples and suspended matter taken in the atlantis ii deep area red sea during the expedition so 2 with rv sonne in november 1977 were investigated for chemical composition only slight changes have been found for most components since 1966 a strong decrease of the cu content from 100 500 g kg 1 according to brooks et al 1969 to values below 1 g kg 1 has however become evident comparison between theoretical concentrations in the intermediate brine layers resulting when using the lower or the upper homothermal layers respectively as end members of mixing processes with red sea deep water and the concentrations measured prove that precipitation and resolution processes have considerable influence on the concentrations found in solution components strongly involved in such processes are iron manganese copper oxygen sulfate and silica as could be shown from comparison of theoretical and measured concentration profiles along the water column investigations of the metals suspended in the brine confirm these processes compared to 1971 1972 the cu and zn values in suspension preferring the southwestern basin at that time are clearly reduced thus being in agreement with the recently lowered hydrothermal activity remarks on the hypothetical composition of the unknown hydrothermal brine discharging into the deepest basin are also included

subaerial submarine evidence of structures feeding magma to stromboli volcano italy and relations with edifice flank failure and creep abstract structural field data including parameters of 109 sheets strike mostly n10 55 e average dip angle mostly 70 90 average thickness two peaks at 1 2 m and 4 2 m and of 14 eruptive fissures and vents as well as bathymetric and numerical data suggest that stromboli experienced the development of a volcanic rift zone across the cone summit with a tendency to widen towards the lower submarine flanks during the last 100 ka inside this rift zone intrusive sheets mostly strike ne and become more abundant more steeply dipping and thicker on approaching the rift axis this rift persistence reflects the edifice s state of stress with a nw se horizontal least principal stress on the magma intrusion paths after 13 ka ago sheets mainly intruded with a horseshoe shaped geometry in plan view along the boundaries of the northwestern unstable volcano flank where four main lateral collapses occurred during the last 13 ka they also intruded with a ne strike across the volcano summit and the northeastern volcano flank the horseshoe shaped geometry is influenced by the lateral creep of the volcano flank which provides space for intrusion along the transtensional boundaries of the unstable sector where thinner sheets were emplaced when the collapse depression was filled up by new deposits ne striking thicker dykes emplaced across the northwestern volcano flank indicating a rapid re establishment of regional tectonic forces across the cone unbuttressing due to the present sciara del fuoco depression and ongoing flank creeping can account for intrusions also inside the sciara del fuoco the latter in 2007

flow rates in the axial hot springs of the east pacific rise 21 n implications for the heat budget and the formation of massive sulfide deposits abstract the first in situ measurements of flow rates in submarine hot springs temperatures between 275 and 350 c were made in the hot springs of the east pacific rise at 21 n during november 1981 the flow rates ranged between 0 7 and 2 4 m s we estimate that the total rates at which heat and mass are transported from the three hot spring areas obs national geographic and southwest vents are ca 2 2 108 w and 150 kg of fluid s respectively the very high rate of heat loss precludes the existence of hot springs as steady state features of the east pacific rise at 21 n we estimate that hot springs are active for a maximum of ca 40 000 years chemical and or mechanical clogging of the vents can drastically reduce the lifetime of the hot springs using a simple model of plume development 1 we calculated that less than 3 of the sulfide particles that are entrained in the hydrothermal plumes at 21 n settle from the plumes before dispersal by a lateral submarine current at a height of ca 250 m above the seafloor 2 the time that is required to form the sulfide mounds that surround the hot springs by the accumulation of sulfide particles that settle from the plumes is ca 70 85 years the current rate at which sulfide particles settle from the hydrothermal plumes and accumulate near the hot springs appears to be too small to lead to the formation of large massive sulfide deposits such as the mavrouni deposit on cyprus 3 within the time limits that are suggested by our thermal energy balance calculations

growth after collapse the volcanic and magmatic history of the neostromboli lava cone island of stromboli italy this study focuses on the holocene neostromboli lava cone which is part of the stromboli volcano aeolian islands italy it represents an important example of the structure and behaviour of lava cone re growth shortly after a large scale volcano sector collapse neostromboli s eruptive style is dominated by extrusion of sheet like a a lava flows and associated autoclastic breccias the lava cone developed during five phases of activity phases a to e representing discrete episodes of lava effusion characterised by rapid changes in magma composition spatial development of the feeder system and physical properties of erupted lavas through time although they all belong to the potassic series ks with sio2 49 55 wt and mgo 2 50 6 25 wt the neostromboli lavas have distinct petrogenetic characteristics ranging from leucite free and low sr shoshonitic basalts phases a and b to leucite bearing shoshonitic basalts with high phase c and intermediate phase d sr contents and to leucite free biotite bearing shoshonites phase e three different batches of mantle derived relatively primitive basic magmas fed the activity of phases a c and d the evolution phases a to b is inferred to have occurred in a continuously replenished tapped and crystallizing rtf magma chamber whereas phase e products were dominantly generated by fractional crystallization from phase d magmas the neostromboli cone shows summit flank and satellite vents and sheet intrusions with different geometry and location through time reflecting the interplay of regional tectonics precursory instability processes and volcano load

the effects of flank collapses on volcano plumbing systems the growth of large volcanoes is commonly interrupted by episodes of flank collapse that may be accompanied by catastrophic debris avalanches explosive eruptions and tsunamis el hierro the youngest island of the canary archipelago has been repeatedly affected by such mass wasting events in the last 1 ma our field observations and petrological data suggest that the largest and most recent of these flank collapses the el golfo landslide likely influenced the magma plumbing system of the island leading to the eruption of higher proportions of denser and less evolved magmas the results of our numerical simulations indicate that the el golfo landslide generated pressure changes exceeding 1 mpa down to upper mantle depths with local amplification in the surroundings and within the modeled magma plumbing system stress perturbations of that order might drastically alter feeding system processes such as degassing transport differentiation and mixing of magma batches

forecasting giant catastrophic slope collapse lessons from vajont northern italy rapid giant landslides or sturzstroms are among the most powerful natural hazards on earth they have minimum volumes of similar to10 6 10 7 m 3 and normally preceded by prolonged intervals of accelerating creep are produced by catastrophic and deep seated slope collapse loads similar to1 10 mpa conventional analyses attribute rapid collapse to unusual mechanisms such as the vaporization of ground water during sliding here catastrophic collapse is related to self accelerating rock fracture common in crustal rocks at loads similar to1 10 mpa and readily catalysed by circulating fluids fracturing produces an abrupt drop in resisting stress measured stress drops in crustal rock account for minimum sturzstrom volumes and rapid collapse accelerations fracturing also provides a physical basis for quantitatively forecasting catastrophic slope failure c 2003 elsevier science b v all rights reserved

dynamics of the december 2002 flank failure and tsunami at stromboli volcano inferred by volcanological and geophysical observations 1 the 2002 effusive flank eruption at stromboli volcano started on december 28 after several months of strong explosive activity at the summit craters on december 30 the seismic network recorded two large flank failures and associated tsunami waves this is the first time that a flank collapse and tsunami and their associated phenomena have been recorded by a multi disciplinary monitoring system volcanological and geophysical monitoring as well as thermal surveys performed immediately before and after the failure allowed us to define and interpret the sequence of events the still on going eruption has provided for the first time the opportunity to look into the dynamics of stromboli s effusive eruptions flank failure and landslide formation and their potential hazard

structural architecture of the 1980 mount st helens collapse an analysis of the rosenquist photo sequence using digital image correlation the collapse of mount st helens united states on 18 may 1980 is one of the only incidents of its kind that was visually witnessed and instrumentally recorded previous analyses determined that the northern flank of the mountain failed which resulted in a rockslide and disintegrated during its mobilization to form a blocky facies and hummocky terrain in the downslope region gary rosenquist9s iconic photographs of the initial 18 may collapse were here analyzed by using a modern photogrammetric method to track portions of the moving flank across the photographs in the sequence thirty years after the 1980 mount st helens rockslide the digital image correlation technique enabled a precise investigation of the associated displacement vectors and strain a listric basal detachment and several associated faults at the lateral edge of the rockslide were identified in addition the heterogeneous movements and a number of shear zones were detected within the sliding block which had previously been assumed to be cohesive the results of my study demonstrate the value of using optical images for strain analyses of active volcanoes even decades after recording

neutron activation analysis of 12 900 year old stone artifacts confirms 450 510 km clovis tool stone acquisition at paleo crossing 33me274 northeast ohio u s a the archaeologically sudden appearance of clovis artifacts 13 500 12 500 calibrated years ago across pleistocene north america documents one of the broadest and most rapid expansions of any culture known from prehistory one long asserted hallmark of the clovis culture and its rapid expansion is the long distance acquisition of exotic stone used for tool manufacture given that this behavior would be consistent with geographically widespread social contact and territorial permeability among mobile hunter gatherer populations here we present geochemical evidence acquired from neutron activation analysis naa of stone flaking debris from the paleo crossing site a 12 900 year old clovis camp in northeastern ohio these data indicate that the majority stone raw material at paleo crossing originates from the wyandotte chert source area in harrison county indiana a straight line distance of 450 510 km our analyses thus geochemically confirm an extreme stone source to camp site distance of a clovis site in eastern north america and thus provide strong inferential material evidence that the fast expansion of the clovis culture across the continent occurred as a result of a geographically widespread hunter gatherer social network

energy release in subvolcanic environments implications for breccia formation mechanical pdelta v energy is released from hydrous magmas in subvolcanic environments by the two generally sequential processes of second boiling and subsequent decompression the second boiling process h 2 o saturated melt crystals h 2 o vapor releases sufficient pdelta v energy in the model system previously established by burnham 1979 and burnham and ohmoto 1980 to cause fracture failure of even the strongest wall rocks tensile strength approximately 3 77 x 10 10 ergs kg super 1 to depths of 4 or 5 km following fracture failure moreover expansion of already exsolved h 2 o and exsolution of additional h 2 o upon decompression into the model fracture system releases additional pdelta v energy 9 7 x 10 10 ergs kg super 1 of magma sufficient to lift an equivalent mass of rock nearly 1 km in the absence of frictional resistance this latter energy although a conservative value is model dependent to the extent that it is affected by changing any one of the following six independent model parameters 1 bulk composition of the magma hornblende biotite granodiorite in the model 2 depth of emplacement of the magma body approximately 2 3 km p t 0 6 kb 3 mass fraction of h 2 o in the initial melt f o w 0 027 2 7 wt h 2 o 4 mass fraction of melt in the magma at the time of emplacement f o m 1 0 100 liquid 5 tensile strength of the wall rocks 3 77 x 10 10 ergs kg super 1 and 6 depth to the top of the fracture once formed approximately 2 3 km p f 0 3 kb although all of these parameters except the first are of major importance in the formation of hydrothermal breccias generally the mass fraction of h 2 o in the initial melt f o w is regarded as the single most important factor in the formation of breccia bodies in typical porphyry type systems f o w not only determines primarily whether or not the second boiling reaction releases enough pdelta v energy to produce fractures it also determines the magnitude of the decompressional energy released into the fractures if formed magmas in which f o w 0 02 to 0 04 at liquidus temperatures generally release sufficient pdelta v energy not only to produce extensive porphyry type fracture systems but also to produce the breccia bodies these systems commonly contain magmas in which f o w 0 02 on the other hand generally do not release sufficient energy for extensive breccia formation except in structurally weak wall rocks at depths shallower than approximately 2 km magmas in which f o w raquo 0 04 at near liquidus temperatures are incapable of emplacement in the subvolcanic environment

the secche di lazzaro pyroclastics of stromboli volcano a phreatomagmatic eruption related to the sciara del fuoco sector collapse widespread phreatomagmatic ash deposits secche di lazzaro pyroclastics overlying the lavas of the neostromboli period 13000 to ca 5000 years b p have been identified at stromboli volcano the deposits consist of accretionary lapilli rich ash fall layers and debris flows ash fall layers originated by phreatomagmatic explosive activity from a vent probably located in the uppermost part of the sector collapse scarp sciara del fuoco which formed at the end of neostromboli period stratigraphic position composition of fresh lapilli identical to the neostromboli lavas and an unusually large scale of explosions suggest that the secche di lazzaro pyroclastics were erupted in connection with the sciara del fuoco slope failure characteristics of the deposits are consistent with phreatomagmatic hydrothermal explosivity related to catastrophic decompression of the plumbing hydrothermal system occurrence of multiple ash fall episodes coupled with variation of nature of lithics lithology is suggestive of repeated explosions eventually triggered by multiple backward migrating block detachments

subaqueous rhyolitic dome top tuff cones a model based on the devonian bunga beds southeastern australia and a modern analogue the relics of two late devonian subaqueous rhyolitic dome top tuff and pumice cone successions are preserved in the bunga beds outlier of the boyd volcanic complex southeastern australia these cone successions and other rhyolitic volcanics of the bunga beds are associated with turbidite and other deep water massflow sedimentary rocks the two cone successions have a generally similar stratigraphy at the base flow banded variably autobrecciated and quench fragmented rhyolite representing an intrusive to extrusive dome is overlain by rhyolitesediment breccia representing extrusion of the dome through the deep water sediment pile and resedimentation down its flanks in the northern cone succession an overlying succession of bedded pumiceous crystal rich to crystal poor tuffs represents the onset of pyroclastic activity and growth of a tuff cone an overyling debris flow deposit represents degradation of part of the cone the topmost unit a stratified pumice succession is thought to represent another cone building eruptive phase and is separated from the underlying strata by a major slide surface the southern cone succession contains less tuff and abundant pumice and is also terminated by a debris flow deposit indicating cone degradation a modern analogue for the inferred eruptive style and sequence is the 1953 1957 rhyolite eruption that formed the tuluman island lava tuff cone complex in the bismarck sea the eruptions were often cyclical consisting of an initial inferred submarine lava forming stage passing into a pumicecone forming stage in some cases a subaeriallava forming stage and a final stage following the cessation of volcanism during which the cones collapsed gravitationally or were destroyed by wave erosion using observations from both the tuluman island eruptions and the preserved stratigraphies of the devonian tuff cones a dynamic model is proposed for the formation of subaqueous rhyolitic dome top tuff and pumice cones

emplacement mechanisms of contrasting debris avalanches at volcan mombacho nicaragua provided by structural and facies analysis we study the lithology structure and emplacement of two debris avalanche deposits dads with contrasting origins and materials from the quaternary holocene mombacho volcano nicaragua a clear comparison is possible because both dads were emplaced onto similar nearly flat 3 slope topography with no apparent barrier to transport this lack of confinement allows us to study in nature the perfect case scenario of a freely spreading avalanche in addition there is good evidence that no substratum was incorporated in the events during flow so facies changes are related only to internal dynamics mombacho shows evidence of at least three large flank collapses producing the two well preserved debris avalanches of this study one on its northern flank las isletas directed northeast and the other on its southern flank el crater directed south other south eastern features indicate that the debris avalanche corresponding to the third collapse la danta occurred before las isletas and el crater events the materials involved in each event were similar except in their alteration state and in the amount of substrata initially included in the collapse while el crater avalanche shows no signs of substratum involvement and has characteristics of a hydrothermal weakening related collapse the las isletas avalanche involves significant substratum and was generated by gravity spreading related failure the latter avalanche may have interacted with lake nicaragua during transport in which case its run out could have been modified through a detailed morphological and structural description of the mombacho avalanches we provide two contrasting examples of non eruptive volcanic flank collapse we show that remarkably even with two distinct collapse mechanisms the debris avalanches developed the same gross stratigraphy of a coarse layer above a fine layer this fine layer provided a low friction basal slide layer whereas dad layering and the run outs are roughly similar the distribution of structures is different and related to lithology las isletas has clear proximal faults replaced distally by inter hummock depressions where basal unit zones are exhumed whereas el crater has faults throughout but the basal layer is hidden in the distal zone hummocky forms depend on material type with steep hummocks being formed of coherent lava units and low hummocks by matrix rich units in both avalanches extensional structures predominate the upper layers exclusively underwent longitudinal and lateral extension this is consistent with evidence of only small amounts of block to block interactions during bulk horizontal spreading the base of the moving mass accommodated transport by large amounts of simple shear we suggest that contractional structures and inter block collisions seen in many other avalanches are artifacts related to topographic confinement

the 2002 2003 eruption of stromboli italy evaluation of the volcanic activity by means of continuous monitoring of soil temperature co2 flux and meteorological parameters 1 from december 2002 to july 2003 stromboli volcano was characterized by a new effusive stage of eruption after a period of extraordinary strombolian activity signals recorded in two continuous monitoring stations during the eruption which have already been presented in very recent papers evidenced anomalies in the co2 flux just before the onset of the eruption a more detailed analysis carried out on the data subset acquired during the eruption integrated by daily field observations of the scientific personnel working at the volcanological observatory in stromboli showed that co2 flux and soil temperature are strictly related to volcanic events furthermore the relative minima and maxima of the two parameters showed a strong correlation with wind speed and direction this fact was especially true at the summit station whereas at the coastal sites seasonal and meteorological effects masked the volcanic signal the analysis of the wind data particularly the relationships between wind speed and direction air and soil temperature and local circulation of atmospheric air masses revealed that during the eruption in the summit area of stromboli air movements were not only related to atmospheric circulation but were also significantly affected and in certain cases caused by volcanic activity this conclusion was reached by observing several anomalies such as the discrepancies in the wind direction between the two stations higher air temperatures at the summit site and inversion of direction for wind before and after the reopening of the conduit in a major explosion on 5 april 2003 the relationships found between volcanic activity soil temperatures co2 fluxes and wind speed and direction indicate that soil temperature measurements in an open conduit volcano such as in this case could be used to monitor the level of volcanic activity along with co2 flux furthermore the possible volcanic origin of a peculiar type of air circulation identified in the summit area of stromboli suggests that the separation between volcanic and atmospheric signals might not be obvious requiring monitoring over a wide area rather than a single location

multiple sector collapses at stromboli volcano italy how they work this paper demonstrates that four large sector collapses have affected the nw flank of the stromboli volcano in the past 13 ka alternating with growth phases in order to contribute to the evaluation of the critical conditions which trigger lateral collapses a reconstruction of the geometry of each collapse of the volcano edifice in the four stages that preceded the relative collapse events is also presented and a computation of the landslide volume this reconstruction is based on new field data plotted in three dimensions prior to the initial 13 ka collapse the volcano was 1125 100 m high above sea level the collapse had a volume of 2 23 0 87 km3 whereas the pre collapse volcano volume was 218 8 7 7 km3 the next edifice that failed was 900 70 m high a s l the collapse volume was 1 0 54 km3 with a precollapse volcano volume of 201 4 5 4 km3 the edifice then grew to 1000 60 m a s l the third collapse had a volume of 1 08 0 39 km3 and occurred within a volcano with a volume of 209 1 4 6 km3 this was followed by a new growth phase followed by the last collapse with a volume of 0 73 0 22 km3 the volcano volume was about the same as the present one the present active crater zone is at 780 m a s l in the first three collapses sliding surfaces cut the main magma conduit in the last collapse the upper scarp coincided with the conduit location dyking along a main ne trending weakness zone across the volcano summit exerted a lateral force for collapse inception the decrease of the landslide volumes with the age and the concentric scarps of the four collapses suggest that the younger sliding planes tended to become more superficial and to decrease the areal extent this is interpreted as due to a successively weaker eruptive products from dominantly lavas to dominantly pyroclastics and b the feedback effects between collapses and dykes that injected along the lateral segments of the first collapse slide plane

the november 2002 eruption at piton de la fournaise volcano la reunion island ground deformation seismicity and pit crater collapse an eruption on the eastern flank of piton de la fournaise volcano started on 16 november 2002 after 10 months of quiescence after a relatively constant level of activity during the first 13 days of the eruption lava discharge volcanic tremor and seismicity increased from 29 november to 3 december lava effusion suddenly ceased on 3 december while shallow earthquakes beneath the dolomieu summit crater were still recorded at a rate of about one per minute this unusual activity continued and increased in intensity over the next three weeks ending with the formation of a pit crater within dolomieu based on ground deformation measured by rapid static and continuous gps and an extensometer seismic data and lava effusion patterns the eruptive period is divided into five stages 1 slow summit inflation and sporadic seismicity 2 rapid summit inflation and a short seismic crisis 3 rapid flank inflation onset of summit deflation sporadic seismicity accompanied by stable effusion 4 flank inflation coupled with summit deflation intense seismicity and increased lava effusion and finally 5 little deflation intense shallow seismicity and the end of lava effusion we propose a model in which the pre intrusive inflation of stage 1 in the months preceding the eruption was caused by a magma body located near sea level the magma reservoir was the source of an intrusion rising under the summit during stage 2 in stage 3 the magma ponded at a shallow level in the edifice while the lateral injection of a radial dike reached the surface on the eastern flank of the basaltic volcano causing lava effusion pressure decrease in the magmatic plumbing system followed resulting in upward migration of a collapse front forming a subterranean column of debris by faulting and stoping this caused intense shallow seismicity increase in discharge of lava and volcanic tremor at the lateral vent in stage 4 and eventually the formation of a pit crater in stage 5

ancient long distance trade in western north america new ams radiocarbon dates from southern california abstract eleven olivella biplicata spire lopped shell beads from six sites located 250 365 km inland from the pacific coast of southern california produced ams dates between 11 200 and 7860 cal bp olivella shell beads were well documented items of prestige and media of exchange in native california and recovery of these examples from inland contexts indicates low level exchange between resident populations of the coast and the southwestern great basin by at least 10 300 10 000 cal years bp these findings represent some of the earliest unequivocal evidence for long distance trade in western north america and push the antiquity of this important form of inter group interaction back several thousand years earlier than previously thought

paleoindian technological provisioning strategies in the northwestern great basin abstract great basin populations during the pleistocene holocene transition pht are often characterized as being mobile and focused on wetlands however the factors that influenced where paleoindians selected residential campsites are poorly understood using predictions derived from optimal foraging based patch choice models and gis reconstructions of the pht landscape some researchers have argued that occupations in smaller wetlands should have been shorter than occupations in larger wetlands but such arguments have rarely been evaluated using empirical data the pht lithic record provides an opportunity to evaluate the relationship between wetland size and occupation span by applying kuhn s 1995 concept of technological provisioning kuhn expects more mobile populations to provision individuals and more sedentary populations to provision places and suggests that 1 a strategy of provisioning individuals should be reflected by a high proportion of more extensively used artifacts made on non local raw materials and 2 a strategy of provisioning places should be reflected by a high proportion of less extensively used artifacts made on local raw materials we apply the technological provisioning concept to lithic assemblages from two of the parman localities extensive pht sites in the northwestern great basin and compare local and nonlocal artifacts to determine if paleoindians shifted from provisioning individuals while moving to from the sites to provisioning the place while occupying them there is no relationship between artifact transport distance and artifact use intensity we interpret these findings as evidence that paleoindians did not alter their provisioning strategies while occupying the parman localities likely because occupations were brief within a small wetland poorly suited to support groups for long periods

the shiveluch volcanic eruption of 12 november 1964 explosive eruption provoked by failure of the edifice abstract restudy of deposits at shiveluch in comparison with other data has shown that the sequence of eruptive events at shiveluch volcano on 12 november 1964 was the following edifice failure involving 1 154 km3 of material at 07 07 a m phreatic explosion with ejection of resurgent ash with a volume of 0 01 km3 plinian activity between 07 20 and 07 47 a m during which andesitic juvenile tephra with a volume of 0 3 km3 erupted during the final stage of the eruption between 07 47 and 08 22 a m pyroclastic flows with a volume of 0 3 0 5 km3 were erupted in this sequence there was no catastrophic directed blast with generation of a destructive pyroclastic density current like those that took place at bezymianny volcano in 1956 and at mount st helens in 1980 the absence of a directed blast is attributed to the fact that the 1964 eruption occurred before magma had enough time to intrude into the edifice and build a cryptodome the failure of the edifice depressurized only a hydrothermal system that existed around the old domes this appears to have been insufficient for the generation of a catastrophic directed blast the case history of volcanic activity at shiveluch before 1964 suggests that if the edifice of the young shiveluch had been stronger and had not failed by landsliding the eruption of 1964 might have consisted of prolonged dome extrusion with relatively weak explosive activity

understanding the collapse eruption link at stromboli italy a microanalytical study on the products of the recent secche di lazzaro phreatomagmatic activity abstract the secche di lazzaro sdl phreatomagmatic activity with the associated neostromboli sector collapse represents the most powerful activity of the last 6 ky at stromboli as revealed by its present day activity stromboli is one of the most eruptive volcanoes in italy and flank instability along its nw flank is a common process volcano instability is often dramatised by explosive eruptions thus it is of crucial importance to understand the linking between volcano collapse and the plumbing system itself the possible role of pre eruptive magmatic processes as triggers of explosive eruptions can be mainly preserved by minerals and revealed by petrochemical studies we studied the juvenile components scoria and pumice of the pyroclastic deposits from the sdl phreatomagmatic activity with the aim to understand the eruption collapse link the sdl pyroclastic sequence has been investigated in three different outcrops at secche di lazzaro sdl sw sequence at vallone del monaco sdl s and along the old path from stromboli village to the active craters sdl n juvenile components are ks shoshonites similar to the most evolved lavas erupted at the end of the neostromboli potassic period our study indicates that the sdl system is strongly heterogeneous and made up by at least two different sequences sdl n and sdl sw sdl s with different textural characteristics of the deposits and composition of the juvenile components mineral chemistry data show a variable presence of recycled crystals antecrysts possibly deriving from the previous neostromboli activity up to 13 ky ago whole rocks are characterised by small but significant differences between the sdl n and the southern samples pointing out the presence of compositionally different potassic magmas and the crystallization and recycling of slightly different mineral assemblages a clear isotope heterogeneity has been also found and explained by the presence of 10 minimum of less radiogenic antecrysts whereas crustal contamination would have only affected the higher sr radiogenic residual melt these data suggest that the sdl phreatomagmatic eruptions were fed by compositionally distinct potassic magmas which rested and evolved in two shallow magma conduits when the magma supply ceased in the waning phase of the neostromboli activity our results also rule out the occurrence of new arrivals of refreshing magmas in the sdl feeding system as well as other internal magma related causes as triggers for the sdl explosive eruptions accordingly external collapse related causes seem effectively more suitable for triggering the sdl phreatomagmatic eruptions by decompression of the magmatic systems we also suggest the sdl n and sdl sw sdl s sequences are generated by two respective explosive events separated in time and or space they can be respectively related to multiple failures of sciara del fuoco which successively depressurised the sdl n and the sdl sw sdl s magma conduits

geological constraints on the emplacement mechanism of the parinacota debris avalanche northern chile the holocene parinacota volcanic debris avalanche ca 8 000 years b p is located in the central andes of northern chile the avalanche formed by the sector collapse of a major stratovolcano adjacent to a lake basin in a single catastrophic event the deposit has an estimated volume of ca 6 km3 a run out of over 22 km and covers more than 140 km2 of the surrounding terrain the values of the heim coefficient 0 08 and the ratio a v 2 3 ca 50 where a is the area covered and v the volume of the deposit indicate high mobility of the avalanche debris in transport two avalanche units can be distinguished the lower unit consists mainly of blocks of rhyodacitic lavas and domes and pyroclastic flow deposits and glacial fluvial and lacustrine sediments the upper unit consists of a coarse grained breccia with little matrix largely composed of andesite blocks which are angular with little or no rounding by abrasion the avalanche displays pronounced hummocky topography in which hummock volume and amplitude as well as maximum block size within individual hummocks tends to decrease with transport distance and towards the lateral margins of the avalanche deposit some surfaces of individual breccia blocks are covered by tens to thousands of small scale impact marks indicating that neighbouring blocks were vibrating and colliding without significant shearing motion most of the deformation and shearing was instead accommodated in a basal layer of wet structureless sediments incorporated into the avalanche debris from the inundated lake basin we propose that the ancestral parinacota stratovolcano collapsed because of loading of underlying fluvioglacial and lacustrine sediments the edifice disintegrated during collapse along existing fractures into large rock domains volumes from 10 to greater than 1 106 m3 which were transported with little internal deformation and then fragmented into hummocks of breccia as they were deposited the decrease of hummock volume with distance suggests that material that travelled further broke up and had an initial greater kinetic energy

stability of a collapsing volcano stromboli italy limit equilibrium analysis and numerical modelling abstract stromboli is an active island volcano belonging to the aeolian archipelago italy in the last 13 ka it experienced four lateral collapses affecting its northwestern flank with its most recent volcanic crisis december 2002 associated with landslides and related tsunami events this paper presents the first stability analysis of the stromboli volcanic edifice the main input is the geotechnical model of the volcano defined on the basis of stratigraphical lithological material properties and structural data collected from in situ surveys and laboratory tests two dimensional stability analysis was performed by limit equilibrium methods lem and finite difference modelling flac 4 0 code mainly focusing on the subaerial part of stromboli s nw flank sciara del fuoco the variability of the safety factor was studied by deterministic sensitivity and probabilistic analysis focusing on the effect of external forces such as magma pressure and seismicity as potential triggering mechanisms of lateral collapse the lem analyses were developed considering a maximum depth of 150 350 m for the sliding surface to which correspond collapse volumes of 95 000 185 000 m 3 m respectively the study shows that without external forces the investigated rock mass is stable and that the tectonic seismicity of the area alone does not destabilize the studied slope on the contrary magma pressure in dykes can represent a destabilizing factor numerical modelling results are concordant with those from lem in addition the simulation reveals that deformations and superficial landslides preannounce and contribute to retrogressive plasticization and maybe to failure surface deepening shallow submarine landslides represent a possible triggering mechanism and the landslide events of 30 december 2002 consistently fit the simulated evolution flac has revealed to be a useful tool for modelling such a complex system it allowed to calibrate the response of the geotechnical model test the validity of the assumptions simulate the stress strain evolution and prepare a possible model for future scenarios

maar diatreme phreatomagmatism at hopi buttes navajo nation arizona usa remnants of an extensive maar diatreme volcanic field are magnificently exposed at various depths of erosion in the hopi buttes volcanic field of northeastern arizona field and petrographic studies of both the maar and diatreme elements of a selection of volcanoes within the field show that 1 lower sections of the maar rim sequences are typically rich in sandy mudrock derived from the pre eruptive mio pliocene bidahochi formation and the muddy bidahochi sediment was soft and wet at the time of maar eruptions 2 beds higher within the rims contain generally increased proportions of sandstone clasts from the triassic wingate formation in the diatremes late emplaced breccia has deeper seated lithics than more marginal breccia emplaced earlier and 3 many vents are topped by megacryst enriched scoria and spatter and deep seated xenoliths are known only from upper diatreme and craterfilling tephra these observations show that 1 eruptions at hopi buttes involved interaction of magma with unconsolidated mudrock at shallow levels and the phreatomagmatic processes that provided the bulk of the energy involved in the violent eruptions were driven by the interaction of magma and wet sediment 2 the locus of explosive activity migrated downward as eruptions progressed and 3 the closing stage of many eruptions was characterized by rapid magma rise and relative depletion of water

the shallow plumbing system of stromboli island as imaged from 1 hz instantaneous gps positions 1 the stromboli volcano aeolian islands italy erupted suddenly on 28 december 2002 after a 17 year period of typically persistent but moderate eruptive activity followed two days later by a tsunamigenic landslide on its nw flank sciara del fuoco felt in the coastal areas of southern italy three continuous gps stations were quickly deployed near the volcano s rim sampling at 1 hz with instantaneous positions computed relative to a fourth station on its flank we report on two deformation episodes a vent migration on 16 17 february 2003 caused significant displacements at only one site and contributed to the decision not to issue a warning of an impending tsunamigenic landslide the second episode on 5 april 2003 a paroxystic explosion from the summit crater allowed us to model for the first time with geodetic data the shallow magma chambers that give rise to strombolian explosive activity

welded tuff infilling a volcanic vent at weolseong republic of korea a plug of parataxitically welded tuff with an elliptical 700 400 m cross section crops out in weolseong district republic of korea it intrudes late cretaceous granodiorite and extrusive tuffs of the chisulryoung volcanic formation and displays a steeply inclined welding foliation concordant with the intrusive contacts and a subvertical stretching lineation these fabrics are interpreted as resulting from laminar shearing in a boundary layer during deposition of the tuff by agglutination along the walls of a vent which served as a feeder for extrusive ignimbrites

two scales of inflation at lastarria cordon del azufre volcanic complex central andes revealed from asar envisat interferometric data abstract asar envisat interferometric synthetic aperture radar insar data collected over the lastarria cordon del azufre complex chile argentina between march 2003 and may 2005 show the persistence of the large wavelength ground inflation revealed by pritchard and simons in 2002 from the analysis of ers insar data nature 418 2002 167 170 after reducing the tropospheric contribution in the interferograms using a combination of data network adjustment and analysis of modis images we produced an accurate interferometric time series showing a 2 yr long temporal evolution of the ground displacements patterns two distinct inflating signals are detected the main signal covers an elliptical area with a 45 km nne ssw major axis and a 37 km minor axis it is correlated with a regional topographic dome we estimated its maximum inflation rate to 2 5 cm yr 1 we inverted the insar data for a range of source geometries spherical prolate ellipsoids penny shaped cracks the inferred source parameters for 2003 2005 period are consistent with an over pressured reservoir at shallow to intermediate crustal depths 7 15 km with an average volumetric rate of inflation of about 14 106 m3 yr 1 in addition to this main signal a new feature highlighted by the asar data is short wavelength inflation 6 km wide at the location of lastarria volcano on the northern margin of the large wavelength signal we explain this short wavelength signal by a spherical over pressured source lying 1000 m below the summit of lastarria volcano we estimate the average volumetric rate of inflation during the observation period to be 35 103 m3 yr 1 it is remarkable that both volumetric variations for the large and small inflations exhibit the same evolution during the 2003 2005 period suggesting that both processes could be related on the basis of the inversion results and of arguments provided by field evidences and a morpho structural analysis of the digital elevation model of the area we propose that the deep source have a magmatic origin while the shallow source is most likely related to hydrothermal fluids in our interpretation the on going deformation processes observed at lastarria cordon del azufre volcanic complex could represent an evolving pre caldera silicic system further field geological and geophysical investigations will be required to confirm these hypotheses and refine the proposed model mostly based on satellite observations

hydrothermal breccias in vein type ore deposits a review of mechanisms morphology and size distribution abstract breccias are among the most widely distributed rock textures found in hydrothermal vein type deposits previous studies have mainly been interested in developing qualitative descriptive approaches leading to a confusing profusion of terms brecciation originates in numerous ways resulting in highly complex classification systems and frequent misinterpretations of facies field observations are difficult to reconcile with physical theories of fragmentation partly due to the fact that few satisfactory quantitative tools have been developed a review of the main brecciation processes occurring in hydrothermal vein type deposits allows for the discrimination between chemical and physical mechanisms including tectonic comminution wear abrasion two types of fluid assisted brecciation hydraulic and critical volume expansion or reduction impact and collapse each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry including fragment morphology size distribution of the fragments fabric and dilation ratio the first two parameters are especially important because 1 the morphology of the fragments allows chemical and physical mechanical breccias to be distinguished and 2 the particle size distribution psd is a function of the energy input during breccia formation the slope of the cumulative psd fractal dimension ranges from high values for high energy brecciation processes to low values for low energy processes indicated by an isometric distribution the evolution of a vein system can be divided into three stages propagation wear and dilation these stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity these two thresholds also mark the transition between different types of brecciation mineralization occurs during all three stages and may display different textures due to pressure variations the use of quantitative parameters in fault related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment including structural setting and crustal level as well as fluid rock interactions recognition of the different breccia types could also be important during the early stages of mineral exploration

eruptive sequence and seismic activity of llaima volcano chile during the 2007 2009 eruptive period inferences of the magmatic feeding system abstract llaima volcano one of the most active volcanoes in south america has experienced intense activity during the last 100 years the most recent eruptive activity occurred during the period 2007 2009 with at least six energetic eruptions the january 1st 2008 vei 3 being the strongest episode most of the paroxysmal activity was characterized by a rapid increase in seismic energy minutes to hours and the absence of precursory signals as well as by an accelerated drop of the seismic energy and eruption intensity at the end moreover subtle changes in the increase of low energy long period lp seismicity and the occurrence of minor explosive activity six months before the onset of the eruptive cycle were the only remarkable changes observed in advance this is the first study that includes a detailed description of the 2007 2009 eruptive period and is based on a temporal analysis of the seismic records technical reports from the monitoring network and 2000 photos this set allows a characterization of the coeval eruptive styles including strombolian and hawaiian activity morphological changes of the active vents inside the main crater and two fractures located in the sw and se flanks ten phases were identified based on the eruptive style volcanic explosivity index vei and the salient features of the seismic events the seismicity that accompanied the eruptive phases was characterized by the predominance of a continuous tremor tr and discrete lp events and a remarkable absence of volcano tectonics vt earthquakes a waveform cross correlation analysis of lp events showed an overall low similarity between them which suggests multiple sources our observations and analysis suggest that the plumbing system is composed of multiple independent structures some of which reached the surface during this eruptive period indicating that the upper part of the cone could be an unstable and essentially weak zone the activity and seismicity observed are characteristic of an open vent system in which the magma can ascend rapidly from several km depth with little to no clear precursory activity these results are in agreement with petrological studies of the products of these eruptions

fissure ignimbrites fissure source origin for voluminous ignimbrites of the sierra madre occidental and its relationship with basin and range faulting the sierra madre occidental is mostly composed of middle tertiary large volume ignimbrites from the united states mexico border 318n the sierra madre occidental extends southward to its intersection with the mexican volcanic belt 218n ignimbrites of equivalent age extend into southern mexico as discontinuous outcrops considering the average thickness of 1000 m for these ignimbrites based on representative measured sections a conservative estimate of their total volume is 393 000 km 3 fewer than 15 calderas have been identified in this province and the source of most of these ignimbrites has been an unsolved problem we present geologic evidence indicating that fissures most of them with the regional trend of basin and range faults served as conduits for the ignimbrites these fissures can be several kilometers long and are represented by pyroclastic ignimbrite dikes rhyolitic lava dikes linearly aligned lava domes and elongated coignimbrite lithic lag breccias adjacent to basin and range faults considering that the basin and range extension overlapped in time and space with the ignimbrite flare up we propose a model in which batholith sized magma chambers reached shallow crustal levels and erupted their contents when they reached basin and range normal faults the faults acted as vents and caused fast decompression when the system was opened and large volumes of silicic magmas were explosively erupted finally devolatilized rhyolitic magmas were emplaced as domes or dikes we propose the term fissure ignimbrites for ignimbrites formed in this way

a diachronic perspective on great basin projectile point morphology from veratic rockshelter idaho abstract veratic rockshelter 10cl3 located in the birch creek valley on the northern border of the snake river plain has long been considered among the most significant prehistoric sites in southeastern idaho initially excavated by earl swanson in 1961 this site produced over a thousand stone tools from stratified contexts including hundreds of diagnostic projectile points ranging from the late paleoindian to the late prehistoric period from 13 cultural horizons this paper provides a new evaluation of the geochronology of the site using 18 new ams radiocarbon dates acquired from charcoal features sampled during the original excavation these new ages are then compared with metric analyses of diagnostic projectile points from the existing assemblage to examine diachronic variability and morphological discreteness in this artifact class to tie them to existing snake river plain and intermountain west projectile point typologies as well as answer questions about late paleoindian and archaic spear and dart point variability results indicate that 1 western stemmed tradition points at veratic date to significantly later than previously thought 9500 10 000 cal b p and have a relatively broad spectrum of morphological variability 2 elko and northern side notched points found in a middle holocene horizon 6000 cal b p are morphologically distinct from each other supporting the concept of an elko long chronology 3 elko corner notched and eared northern side notched stemmed indented base including gatecliff and possibly pinto forms humboldt and salmon river points were found together in multiple middle holocene components at veratic indicating a period of greater variability that ended with the onset of the late holocene by 3200 cal b p after which only elko corner notched forms continued

evidence of tectonic control on active arc volcanism the panarea stromboli tectonic link inferred by submarine hydrothermal vents monitoring aeolian arc italy 1 the combination of the latest geophysical instruments and geochemical methods applied to the arc volcanism aeolian islands italy has given new insights on the role of active tectonics on fluids migration a continuous monitoring of the hydrothermal system off the island of panarea has shown contemporaneous modifications of the vented fluids and the seismic activity of the nearby stromboli volcano the almost contemporary start of the last volcanic crisis at panarea and stromboli in 2002 besides the contemporary variation of the 3 he 4 he ratios at both the islands and the large number of submarine crater shaped structures at panarea bears testimony to interconnections between the volcanic edifices to confirm a tectonic drive of magmatic fluids over volcanic arcs implies that episodes of volcanic unrest can be triggered by the tectonic activity increasing the volcanic risk for the whole area and this might be the case of the stromboli panarea volcanic complex

root zone processes in the phreatomagmatic pipe emplacement model and consequences for the evolution of maar diatreme volcanoes abstract the understanding of processes within the root zone of maar diatreme volcanoes is important for the interpretation of the geology volcanology and even hazard assessment of these volcanoes in the phreatomagmatic model of pipe formation the irregularly shaped root zone is the site of the phreatomagmatic explosions and thus functions as the engine for pipe formation in this model the root zone grows over a period of time in a series of many single thermohydraulic i e phreatomagmatic explosions the explosions initially occur close to the surface and with ongoing explosive activity penetrate towards deeper levels the ejection of country rock clasts from the root zone results in a mass deficiency in the root zone that causes the overlying tephra and the adjacent country rocks to subside passively in a sinkhole like fashion into the root zone many phreatomagmatic eruptions consequently result in the formation of a cone shaped diatreme thus with ongoing eruptions the cone shaped diatreme has to grow systematically both in depth and diameter during its growth processes in the lower diatreme levels successively destroy the upper levels of the evolving root zone at the surface the maar crater in turn reacts to the underlying subsidence processes and also grows both in depth and diameter thermohydraulic explosions which fragment both magma and the surrounding country rocks mostly occur within the bottom part of the root zone violent explosions in small pipes may clear the overlying diatreme for a short period of time before tephra fall and collapse of the walls of the new crater refill the small initial diatreme in larger pipes via expansion of the mixture of highly pressurized water vapor juvenile gas phases and explosively produced tephra the confined and expanding eruption cloud has to pierce through the diatreme fill in a feeder conduit in order to erupt diatreme clearing events in large pipes are difficult or impossible to maintain since the explosive force in the root zone is only in exceptional instances strong enough to lift or entrain the entire diatreme tephra knowledge of the genetic relationships between root zones and diatremes is critical to understand pipe growth processes the combination of such processes can lead to substantial variation in volcanic behavior and thus produce fundamentally different volcano and rock types it is the purpose of this paper to outline important features of root zones and suggest their significance for the genesis and evolution of maar diatreme and related volcanoes

infrasonic monitoring at stromboli volcano during the 2003 effusive eruption insights on the explosive and degassing process of an open conduit system 1 stromboli is an open conduit volcano characterized by persistent conduit degassing and explosive dynamics during the 2003 effusive eruption we monitored this activity with a five element array deployed at 450 m from the active craters the array allows us to track in real time changes of explosive activity in terms of source position and excess pressure release infrasonic monitoring located the new active vents in the same preeruptive position revealing that the collapse of the crater terrace has not changed the geometry of the shallow feeding system elevation of the infrasonic source is stable at 750 m above sea level coincident with the elevation of the crater terrace this suggests a shallow position of the magma column or if the source is embedded in the conduit diffraction at the crater rim at the end of the eruption back azimuth analysis indicates that explosive activity was progressively reestablished at all of the craters following a ne toward sw direction along the collapsed trench the array detected significant small amplitude 1 pa infrasonic activity occurring at a rate of approximately one pulse every 2 s and generally located in only one vent at a time this persistent activity is not related to strombolian explosion but we infer it is reflecting the overpressurized degassing of the magma column amplitude distribution of 7 million infrasonic signals shows that this degassing is 1 order of magnitude more energetic than the explosions besides infrasonic amplitude distribution presents a decay with a double slope indicating that explosions and degassing are driven by conduit dynamics acting at two different rates

metal remobilization at a spreading centre studied using lead isotopes the metalliferous sediment deposits of the atlantis ii deep in the red sea are an example of submarine hydrothermal deposits at a spreading centre the brine salinities 270 for the atlantis ii lower brine originate from leaching of the miocene evaporites the mantle is considered as a possible source of metal by analogy with east pacific rise deposits during the hydrotherm cruise may 1985 on rv marion dufresne two cores numbered 683 and 684 were collected from the sw and w basins respectively of the atlantis ii deep fig 1 these two cores reached the basaltic basement and therefore allowed full and representative sampling of the metalliferous sediment series as well as of the underlying basalt our lead isotope results suggest that the metals in the sediments are not derived from a basaltic source we show that lead in the metalliferous sediments was derived both from the recent biogenic terrigenous sediments and another unknown sedimentary source the variations in the lead isotopic composition of atlantis ii deep sediments suggest a discontinuous brine supply

experiments on vertical basement fault reactivation below volcanoes scaled modeling has been conducted to study the role played by the reactivation of vertical basement faults in the destabilization process of overlying volcanoes results show that basement fault reactivation induces the formation of faults within the volcanic edifice these faults delimite a central block which is extruded from between the two undeformed lateral parts of the edifice collapse of this central block can occur when heterogeneous cones are used in experiments revealing that mechanical interfaces are of paramount importance in triggering rockslide avalanches collapse structures may display horseshoe shapes in map view and are then surprisingly similar to avalanche scars resulting from failure created by magmatic intrusions in natural volcanoes large scale destabilisation of half the surface of the cone may also occur in a single event depending on the position of the reactivated basement fault below the edifice it is emphasized that the process under consideration may occur on a dormant volcano as well provided that a fault is reactivated below it

consequences of volcano sector collapse on magmatic storage zones insights from numerical modeling abstract major volcano flank collapses strongly affect the underlying magmatic plumbing system here we consider the magma storage zone as a liquid pocket embedded in an elastic medium and we perform numerical simulations in two dimensional axisymmetric geometry as well as in three dimensions in order to evaluate the consequences of a major collapse event we quantify the pressure decrease induced within and around a magma reservoir by a volcano flank collapse this pressure reduction is expected to favor replenishment with less evolved magma from deeper sources we also estimate the impact of the magma pressure decrease together with the stress field variations around the reservoir on the eruptive event associated with the edifice failure we show that for a given magma reservoir geometry the collapse of a large strato volcano tends to reduce the volume of the simultaneous eruption destabilization of large edifices may even suppress magma emission resulting in phreatic eruptions instead this effect is greater for shallow reservoirs and is more pronounced for spherical reservoirs than for vertically elongated ones it is reduced for compressible magmas containing a large amount of volatiles over a longer time scale the modification of pressure conditions for dyke initiation at the chamber wall may also explain an increase in eruption rate as well as an apparent change of magma storage location

cyclic formation of debris avalanches at mount st augustine volcano volcanic debris avalanches have been seen at many volcanoes since the 1980 eruption of mount st helens but typically only one or two avalanche deposits are identified at each eruptive centre suggesting that catastrophic slope failures are rare or even unique events in the lifetime of a volcano1 4 here we present a series of radiocarbon dates from volcanic deposits showing that the summit edifice of mount st augustine a 1 220 m high active volcano on augustine island in the cook inlet area of south central alaska has repeatedly collapsed and regenerated averaging 150 200 years per cycle during the past 2 000 years the unprecedented frequency of summit edifice failure was made possible by sustained lava effusion rates over 10 times greater than is typical of plate margin volcanoes

preeruptive inflation and surface interferometric coherence characteristics revealed by satellite radar interferometry at makushin volcano alaska 1993 2000 1 pilot reports in january 1995 and geologic field observations from the summer of 1996 indicate that a relatively small explosive eruption of makushin one of the more frequently active volcanoes in the aleutian arc of alaska occurred on 30 january 1995 several independent radar interferograms that each span the time period from october 1993 to september 1995 show evidence of 7 cm of uplift centered on the volcano s east flank which we interpret as preeruptive inflation of a 7 km deep magma source v 0 022 km3 subsequent interferograms for 1995 2000 a period that included no reported eruptive activity show no evidence of additional ground deformation interferometric coherence at c band is found to persist for 3 years or more on lava flow and other rocky surfaces covered with short grass and sparsely distributed tall grass and for at least 1 year on most pyroclastic deposits on lava flow and rocky surfaces with dense tall grass and on alluvium coherence lasts for a few months snow and ice surfaces lose coherence within a few days this extended timeframe of coherence over a variety of surface materials makes c band radar interferometry an effective tool for studying volcano deformation in alaska and other similar high latitude regions

geochemical precursors of the activity of an open conduit volcano the stromboli 2002 2003 eruptive events 1 marked increases of co2 h2 and he dissolved in thermal waters and changes in the dissolved carbon isotopic composition were observed at stromboli before the 28 december 2002 eruption and before a violent explosive paroxysm occurred on 5 april 2003 high anomalous co2 flux values were recorded at the crater rim since a week before the eruption onset the first anomalies in the thermal waters dissolved co2 amount appeared some months before the eruption when magma column rose at a very high level in the conduit high peaks of dissolved h2 and he were recorded a few days before the paroxysm carbon isotopic composition indicates a magmatic origin of the dissolved co2 whose increase together with those of h2 and he is attributed to an increasing output of deep gases likely produced by depressurization of a rising batch of a deep gas rich magma whose fragments have been emitted during the explosion

mechanisms for ground surface fracturing and incipient slope failure associated with the 2001 eruption of mt etna italy analysis of ephemeral field data abstract during the july august 2001 eruption of mt etna development of extensional fractures faults and grabens accompanied magma intrusion and subsequent volcanic activity during the first days of the eruption we performed an analysis of attitude displacement and propagation of fractures and faults exposed on the ground surface in two sites torre del filosofo and valle del leone located along the same fracture system in the region surrounding the valle del bove depression on the eastern flank of mt etna fractures and faults formed as the consequence of a shallow intruding dyke system that fed the several volcanic centres developed along the fracture system the investigated sites differ in slope attitude and in geometrical relationships between fractures and slopes in particular the fracture system propagated parallel to the gentle slope

deposits of the 30 march 1956 directed blast at bezymianny volcano kamchatka russia on 30 march 1956 a catastrophic directed blast took place at bezymianny volcano it was caused by the failure of 0 5 km3 portion of the volcanic edifice the blast was generated by decompression of intra crater dome and cryptodome that had formed during the preclimactic stage of the eruption a violent pyroclastic surge formed as a result of the blast and spread in an easterly direction effecting an area of 500 km2 on the lower flank of the volcano the thickness of the deposits although variable decreases with distance from the volcano from 2 5 m to 4 cm the volume of the deposit is calculated to be 0 2 0 4 km3 on average the deposits are 84 juvenile material andesite of which 55 is dense andesite and 29 vesicular andesite on a plot of sorting vs median diameter inman coefficients the deposits occupy the area between the fall and flow fields in the proximal zone less than 19 km from the volcano three layers can be distinguished in the deposits the lower one layer a is distributed all over the proximal area is very poorly sorted enriched in fragments of dense juvenile andesite and contains an admixture of soil and uncharred plant remains the middle layer layer b is distributed in patches tens to hundreds of metres across on the surface of layer a layer b is relatively well sorted as a result of a very low content of fine fractions and it contains rare charred plant remains the uppermost layer layer c forms still smaller patches on the surface of layer b layer c is characterized by intermediate sorting is enriched in vesicular juvenile andesitic fragments and contains a high percentage of the fine fraction and very rare plant remains which are thoroughly charred maximum clast size decreases from layer a to layer c the absence of internal cross bedding is a characteristic of all three layers in the distal zone more than 19 km from the volcano stratigraphy changes abruptly deposit here consists of one layer 26 to 4 cm in thickness is composed of wavy laminated sand with a touch of gravel is well sorted and contains uncharred plant remains the bezymianny blast deposits are not analogous with known types of pyroclastic surges with the exception of the directed blast deposits of the mount st helens eruption of 18 may 1980 the peculiarities of deposits from these two eruptions allow them to be separated into a special type blast surge this type of surge is formed when failure of volcanic edifice relieves the pressure from an inter crater dome and or cryptodome a model is proposed to explain the peculiarities of the formation transportation and emplacement of the bezymianny blast surge deposits

geology of a complex kimberlite pipe k2 pipe venetia mine south africa insights into conduit processes during explosive ultrabasic eruptions k2 is a steep sided kimberlite pipe with a complex internal geology geological mapping logging of drillcore and petrographic studies indicate that it comprises layered breccias and pyroclastic rocks of various grain sizes lithic contents and internal structures the pipe comprises two geologically distinct parts k2 west is a layered sequence of juvenile and lithic rich breccias which dip 20 45 inwards and k2 east consists of a steep sided pipe like body filled with massive volcaniclastic kimberlite nested within the k2 pipe the layered sequence in k2 west is present to 900 m below present surface and is interpreted as a sequence of pyroclastic rocks generated by explosive eruptions and mass wasting breccias generated by rock fall and sector collapse of the pipe walls both processes occurred in tandem during the infill of the pipe several breccia lobes extend across the pipe and are truncated by the steep contact with k2 east dense pyroclastic rocks within the layered sequence are interpreted as welded deposits k2 east represents a conduit that was blasted through the layered breccia sequence at a late stage in the eruption this phase may have involved fluidisation of trapped pyroclasts with loss of fine particles and comminution of coarse clasts we conclude that the k2 kimberlite pipe was emplaced in several distinct stages that consisted of an initial explosive enlargement followed by alternating phases of accumulation and ejection

through the high rock and beyond placing the last supper cave and parman paleoindian lithic assemblages into a regional context based on source provenance data derived from paleoindian artifacts in the great basin most researchers agree that early groups were mobile and far ranging however current explanations of the behavior reflected by those data differ some models portray paleoindians as residentially mobile foragers while others portray them as wetland tethered collectors reliant upon logistical forays we consider the types of hunter gatherer behavior that could produce trends in the x ray fluorescence data from three paleoindian assemblages in northwest nevada where abundant high quality obsidian essentially allows us to hold the effects of raw material availability constant between sites we conclude that while it is difficult to differentiate between residential and logistical mobility using technological and sourcing data alone we can nevertheless begin to understand the relative time averaged importance of particular locations on the landscape and why such places attracted paleoindians

ore related breccias in volcanoplutonic arcs an overview of breccias related to a variety of base metal precious metal and lithophile element deposits in volcanoplutonic arcs permits definition of six possible mechanisms for subsurface brecciation 1 release of magmatic hydrothermal fluids from high level hydrous magma chambers during second boiling and subsequent decompression generates a spectrum of breccia types in which fragments may suffer collapse and or ascent single or multiple intrusion related breccia pipes and pre and intermineral breccias in porphyry copper deposits provide widespread examples 2 magmatic heating and expansion of meteoric pore fluids may lead to brecciation commonly of late or postmineral age and including pebble dikes in porphyry type and related deposits magmatic heating of rocks saturated with seawater may cause submarine hydrothermal eruptions late in the emplacement histories of kuroko type massive sulfide deposits many of the resultant breccias underwent limited sedimentary transport overpressuring of heated fluids beneath semipermeable partly self sealed cap rocks may lead to brecciation and subaerial hydrothermal eruptions in shallow epithermal precious metal settings magmatic heating or tectonic disturbance may have triggered brecciation 3 interaction of cool ground waters with subsurface magma can generate phreatomagmatic explosions postmineral phreatomagmatic diatremes associated with porphyry systems and premineral diatremes with epithermal precious or base metal deposits were generated in this manner these attained the palcosurface to produce pyroclastic base surge and fall deposits that accumulated as tuff rings around maar craters 4 magmatic hydrothermal brecciation may lead to disruption of rocks through to the paleosurface decompression and fragmentation and eruption of the top part of an underlying magma chamber pre and postmineral magmatic diatremes of this sort are inferred to accompany a few porphyry type and other base and precious metal systems they were manifested at the palcosurface by accumulations of pyroclastic fall and flow deposits 5 breccias may result from mechanical disruption of wall rocks during subsurface movement of magma any intrusion related deposit may include such intrusion breccias 6 tectonic breccias resulting from fault displacement may accompany any type of ore deposit a continuum exists between many of these breccia types and it is difficult to identify unique criteria for their unambiguous distinction

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

observations of physical effects from tsunamis of december 30 2002 at stromboli volcano southern italy on december 30 2002 following an intense period of activity of stromboli volcano south tyrrhenian sea italy complex mass failures occurred on the northwest slope of the mountain which also involved the underwater portion of the volcanic edifice for a total volume of about 2 3 107 m3 two main landslides occurred within a time separation of 7 min and both set tsunami waves in motion that hit the coasts of stromboli causing injuries to three people and severe damage to buildings and structures the tsunamis also caused damage on the island of panarea some 20 km to the sse from the source they were observed all over the aeolian archipelago at the island of ustica to the west along the northern sicily coasts to the south as well as along the tyrrhenian coasts of calabria to the east and in campania to the north this paper presents field observations that were made in the days and weeks immediately following the events the results of the quantitative investigations undertaken in the most affected places namely along the coasts of stromboli and on the island of panarea are reported in order to highlight the dynamics of the attacking waves and their impact on the physical environment on the coastal structures and on the coastal residential zone in stromboli the tsunami waves were most violent along the northern and northeastern coastal belt between punta frontone and the village of scari with maximum runup heights of about 11 m measured on the beach of spiaggia longa measured runups were observed to decay rapidly with distance from the source typical of tsunami waves generated by limited area sources such as landslides

textural analysis of a late palaeozoic coherent pyroclastic rhyolitic dyke system near burkersdorf erzgebirge saxony germany

the taupo eruption new zealand i general aspects the ca a d 186 taupo eruption was the latest eruption at the taupo volcanic centre occurring from a vent at horomatangi reefs now submerged beneath lake taupo in the central north island of new zealand minor initial phreatomagmatic activity was followed by the dry vent 6 km 3 hatepe plinian outburst large amounts of water then entered the vent during the 2 5 km 3 hatepe phreatoplinian ash phase eventually stopping the eruption though large amounts of water continued to be ejected from the vent area causing gullying of the ash deposits after a break of several hours to weeks phreatoplinian activity resumed generating the 1 3 km 3 rotongaio ash notable for its fine grainsize and for containing significant quantities of non or poorly vesicular juvenile material the vent area then became dry again and eruption rates and power markedly increased into the 23 km 3 taupo ultraplinian phase which is the most powerful plinian outburst yet documented synchronous with this ultraplinian activity lesser volumes of non to partially welded ignimbrite were generated by diversion of ejecta from or partial collapse of the eruption column the rapid rate of magma withdraw al during this phase removed support from the vent area to trigger local vent collapse and initiate the catastrophic eruption of the ca 30 km 3 taupo ignimbrite finally after some years lava was extruded on to the floor of the reformed lake taupo and floating fragments derived from the lava carapace were driven ashore the known eruption volume is more than 65 km 3 while additional volumes are represented by primary material now beneath lake taupo and layer 3 to the ignim brite phases a total volume of more than 105 km 3 is likely equivalent to more than 35 km 3 of magma plus more than 3 km 3 of lithic debris airfall deposits more than 10 cm thick blanketed 30000 km 2 of land east of the vent while ignimbrite covers a near circular area of 20000 km 2 widespread and locally severe ground shaking occurred during but mostly after the eruption associated with subsidence in the lake taupo basin secondary deposits are abundant above and extending beyond the taupo ignimbrite consisting of the products of surface water interacting with the still hot ignimbrite and subsequent water reworking of the light pumiceous materials the complexity and size of this eruption preclude accurate forecasting of the size nature and return period of the inevitable next eruption from the taupo volcanic centre

investigating collapse structures in oceanic islands using magnetotelluric surveys the case of fogo island in cape verde abstract one of the most remarkable natural events on earth are the large lateral flank collapses of oceanic volcanoes involving volumes of rock exceeding tens of km3 these collapses are relatively frequent in recent geological times as supported by evidence found in the geomorphology of volcanic island edifices and associated debris flows deposited on the proximal ocean floor the island of fogo in the cape verde archipelago is one of the most active and prominent oceanic volcanoes on earth the island has an average diameter of 25 km and reaches a maximum elevation of 2829 m above sea level m a s l at pico do fogo a young stratovolcano located within a summit depression open eastward due to a large lateral flank collapse the sudden collapse of the eastern flank of fogo island produced a megatsunami 73 ky ago the limits of the flank collapse were deduced as well from geomorphologic markers within the island the headwall of the collapse scar is interpreted as either being located beneath the post collapse volcanic infill of the summit depression or located further west corresponding to the bordeira wall that partially surrounds it the magnetotelluric mt method provides a depth distribution of the ground resistivity obtained by the simultaneous measurement of the natural variations of the electric and magnetic field of the earth two n s magnetotelluric profiles were acquired across the collapsed area to determine its geometry and boundaries the acquired mt data allowed the determination of the limits of the collapsed area more accurately as well as its morphology at depth and thickness of the post collapse infill according to the newly obtained mt data and the bathymetry of the eastern submarine flank of fogo the volume involved in the flank collapse is estimated in 110 km3 this volume the first calculated onshore stands between the previously published more conservative and excessive calculations offshore that were exclusively based in geomorphic evidence the model for the summit depression proposing two caldera collapses preceding the collapse of the eastern flank of fogo is supported by the mt data

understanding shallow magma emplacement at volcanoes orthogonal feeder dikes during the 2002 2003 stromboli italy eruption 1 understanding how shallow magma is emplaced within volcanoes is crucial for hazard assessment the 2002 2003 stromboli eruption provides the opportunity to investigate shallow magma emplacement resulting from orthogonal feeder dikes and its possible effects stromboli erupted in 2002 2003 when effusive activity replaced strombolian activity on december 28 a ne sw fissure propagated from the lava filled northernmost summit crater on december 29 a nw se fissure propagated north of the craters feeding nw se aligned vents on december 30 this area collapsed reaching the sea and generating a tsunami in mid february 2003 the nw se fissure became inactive while the ne sw effusive fissure continued until july a model for shallow magma emplacement is proposed the lateral propagation of a ne sw dike from the northernmost crater was triggered below a nw se dike propagating from the magma filled ne tip of the ne sw elongated conduit fed the nw se aligned vents in february the conduit periphery became solidified freezing the nw se dike and the transport of magma was limited to the central part focusing its rise below the craters this fed the ne sw fissure until the supply decreased further july returning to the ordinary level sustaining strombolian activity orthogonal dike emplacement followed the trajectories of the maximum gravitational stress 1 partly controlled by the irregular topography of the uppermost edifice the emplacement of orthogonal dikes in a limited area is feasible at non perfectly conical active volcanoes where the maximum gravitational stress may show variations from a purely radial path

volcanic edifice stability during cryptodome intrusion limit equilibrium analyses were applied to the 1980 mount st helens and 1956 bezymianny failures in order to examine the influence on stability of structural deformation produced by cryptodome emplacement weakening structures associated with the cryptodome include outward dipping normal faults bounding a summit graben and a flat shear zone at the base of the bulged flank generated by lateral push of the magma together with the head of the magmatic body itself these structures serve directly to localize failure along a critical surface with low stability deep within the interior of the edifice this critical surface with the safety coefficient reduced by 25 30 is then very sensitive to stability condition variation in particular to the pore pressure ratio ru and seismicity coefficient n for ru 0 3 or n 0 2 the deep surface suffers catastrophic failure removing a large volume of the edifice flank in the case of mount st helens failure occurred within a material with angle of friction 40 cohesion in the range 105 106 pa and probably significant water pore pressure on 18 may 1980 detachment of slide block i occurred along a newly formed rupture surface passing through the crest of the bulge although sliding of block i may have been helped by the basal shear zone significant pore pressure and a triggering earthquake were required ru 0 3 and n 0 2 detachment of the second block was guided by the summit normal fault the front of the cryptodome and the basal shear zone this occurred along a deep critical surface which was on the verge of failure even before the 18 may 1980 earthquake the stability of equivalent surfaces at bezymianny volcano appears significantly higher thus although magma had already reached the surface weaker materials or higher pore pressure and or seismic conditions were probably required to reach the rupture threshold from our analysis we find that deep seated sector collapses formed by removing the edifice summit cannot generally result from a single slide cryptodome induced deformation does however provide a deep potential slip surface as previously thought it may assist deep seated sector collapse because it favors multiple retrogressive slides this leads to explosive depressurization of the magmatic and hydrothermal systems which undermines the edifice summit and produces secondary collapses and explosive blasts