late quaternary tephrochronology of sweden a review abstract studies of late quaternary sediments in south and central sweden have yielded a detailed tephrochronology for the last glacial interglacial transition lgit ca 15 000 10 000 cal yr bp and the holocene more than ten tephra layers have been detected and geochemically characterised the most widespread tephra from the lgit is the rhyolitic phase of the vedde ash ca 12 000 cal yr bp which has been found in lacustrine sediments and marine clays south of the younger dryas moraines in south sweden other horizons from the lgit identified to date include the borrobol tephra ca 14 400 cal yr bp the hasseldalen tephra ca 11 500 cal yr bp the 10 ka askja tephra ca 11 300 cal yr bp and the hogstorpsmossen tephra ca 10 200 cal yr bp the most significant holocene isochrones are hekla 4 ca 4260 cal yr bp hekla selsund kebister ca 3750 cal yr bp hekla 3 ca 3000 cal yr bp and askja 1875 two new late holocene tephra horizons the stomyren tephra ca 2100 cal yr bp and the gullbergby tephra ca 2700 cal yr bp were identified in single sites and are so far less valuable as marker horizons but are potentially important for the future

geothermal control on flow patterns in the last glacial maximum ice sheet of iceland because it is located both on the mid atlantic ridge and on a mantle plume iceland is a region of intense tectonics and volcanism during the last glaciation the island was covered by an ice sheet approximately 1000 m thick a reconstruction of the ice flow lines based on glacial directional features shows that the ice sheet was partly drained through fast flowing streams fast flow of the ice streams has been recorded in megascale lineations and flutes visible on the currently deglaciated bedrock and is confirmed by simple mass balance considerations locations of the major drainage routes correlate with locations of geothermal anomalies suggesting that ice stream activity was favoured by lubrication of the bed by meltwater produced in regions of high geothermal heat flux similar control of ice flow by geothermal activity is expected in ice sheets currently covering tectonically and volcanically active area such as the west antarctic ice sheet copyright 2000 john wiley sons ltd

modelling the macroscopic behavior of strombolian explosions at erebus volcano abstract we analyze seismic signals associated with the strombolian explosion quakes at erebus volcano antarctica examining the high frequency 0 5 hz portion of the spectrum we consider recordings relative to two time periods during the years 2005 and 2006 cross correlation analysis allows us to distinguish three classes of events spectral properties and polarization analysis provide evidence of a very complex volcanic structure we conduct analyses to elucidate the macroscopic dynamic system associated with the explosions the distribution of the times between successive explosion quakes is exponential implying a poissonian process as observed at stromboli volcano but on a different time scale the sequence of the occurrence of the explosions can be described by classical intermittency a coalescence chandrasekar landau mean field model reproduces gas bubble sizes comparable with those observed at the lava lake surface finally the classical equation for the ascent of gas bubbles is generalized by adding a diffusive process this model provides ascent velocities depending on the bubble radius for gas bubbles greater than a few centimeters variation in ascent velocity due to diffusion becomes negligible and the ascent velocity appears to be governed primarily by buoyancy

influence of cone morphology on dykes stromboli italy abstract the island of stromboli represents the emerged part of a 2 6 km high composite volcano elongated in a ne direction over the period 100 13 ka bp the morphological evolution of the volcano was characterised by a series of summit caldera collapses between major building phases from 13 ka bp onward a series of large lateral collapses occurred northwestwards in one sector of the cone the results of the field study of the total 94 dyke population is discussed in this paper they show that during the last 100 ka the majority of dykes were injected with a nnegssw to ene wsw strike along a ne sw weakness zone crossing the volcano summit this is interpreted as a volcanic rift the geometry of which is controlled by regional tectonic stresses dykes injected prior to 13 ka bp at lower altitudes are generally steeper than those injected at higher elevations after 13 ka bp dykes were injected along the ne sw weakness zone and parallel and close to the margins of the earliest sector collapse at dips of 20 80 inclined towards the collapse depression i suggest that this is linked to unbuttressing of the collapse depression or to seaward gravity instability of the depression infill deposits extensive emplacement of long dykes along the ne sw weakness zone occurred only when the volcano regained a conical shape some of the dykes emplaced close to the original surface of the cone bent to assume a dip direction parallel to the local slope i propose that this local change of dyke geometry can be explained by the direct influence of the free surface of the cone leading to a rotation of the least principal stress which assumes an orientation perpendicular to the slope

multi method dating comparison for mid pleistocene rangitawa tephra new zealand abstract the rangitawa tephra a widespread mid pleistocene marker in the new zealand region is dated by fission track thermoluminescence tl infrared stimulated luminescence irsl k ar and single crystal laser fusion sclf 40 ar 39 ar methods as well as by matching to the astronomical timescale via oxygen isotope stratigraphy in deep sea cores fifty one independent numerical age estimates for rangitawa tephra range from 173 to 456 ka however only 15 of these results are considered to be reliable five zircon fission track results four isothermal plateau fission track itpft age estimates on glass shards four sclf 40 ar 39 ar results and two astronomically calibrated age estimates from deep sea cores the weighted mean of the nine reliable fission track age determinations is 345 12 ka in excellent agreement with the weighted mean of 340 7 ka for the two reliable astronomically calibrated age estimates the weighted mean of the four reliable 40 ar 39 ar results 302 8 ka is significantly younger and further ar ar dating is recommended to investigate this difference since the tl and irsl dating methods are experimental for sediments beyond 200 ka we have excluded these from the group of reliable age results tl and irsl results on dunesand appear to be systematically younger than tl results on loess and loess results depend upon analytical procedures

plio pleistocene megacycles record of climate and tectonics abstract paleoclimatic records from the deep sea floor show that in the last 3 m y more than 100 oscillations of mild and cool global climate took place with a larger amplitude than any experienced during the holocene variations of dry and wet climates in the chinese loess plateau and in the loess belt of central europe have similar frequency it has been convincingly proved that the periodicity of the past gross climate changes agrees with that of the earth s orbital perturbations however while the amplitude of the orbital cycles and of the oceanic oxygen isotope variations is relatively uniform several of the cold climate episodes recorded on land appear more severe than the remainder they correspond to chinese loess units l1 l2 l5 l6 and l9 correlating with central european loess of cycles b c f h and j these units correspond to oxygen isotope stages 2 6 12 16 and 22 and to the weichselian saalian and elsterian ice advances in addition chinese loess layers l13 l15 wl1 wl2 wl3 and wl4 appear to represent exceptionally dry and cold episodes apparently correlative with the inter bavelian cooling and with menapian eburonian and praetiglian glacials of the rhine delta based on this observation we propose to distinguish within the last 2 5 m y ten megacycles describe them in the chinese loess sequences and name them in the order of increasing age mc1 mc10 each megacycle starts with an unusually thick loess unit interpreted as a deposit of an exceptionally severe glaciation and terminates with a cluster of well developed soils indicative of warm humid climates interrupted by relatively mild glacials the megacycles of the last 2 5 m y lasted between 200 and 340 millennia each with an average duration of 255 thousand years when correlated with the stratigraphic record of the chinese loess plateau the wurm terrace as well as the saale glacier advances the eem marine transgression the weichsel ice advance and the holocene correspond to a still incomplete megacycle mc1 the riss terrace the elster ice advance holstein transgression and subsequent mild and cool intervals ending with the schoningen interglacial sensu urban 1992 belong to the megacycle mc2 recognition of four megacycles within brunhes resolves the long standing discrepancy between the limited number of classical continental glacial and interglacial units and the frequent climate oscillations recorded in the deep sea sediments and the loess sequences only in the holsteinian and eemian interglacials was the crustal rebound delayed enough to permit oceanic transgressions reaching deep inland there is no apparent astronomic reason for the exceptional intensity and deep southward penetration of continental ice sheets during only some of the cold intervals since the differences are much more pronounced on land than in the ocean and since the major ice advances are closely linked with terraces it seems that the megacycles were preconditioned by tectonic movements intermittent pulses of rapid uplift of mountain ranges could have impacted climate worldwide by deflecting atmospheric circulation in the sense of ruddiman and raymo 1988 it is also probable that the tectonically changing shape of the sea floor sills reoriented the oceanic circulation which then could have affected plio pleistocene climates world wide the loess covered terraces in the lanzhou area demonstrate that the tectonic movements in the northern part of the tibet plateau correlate closely with the advances of continental ice in europe suggesting that the uplift of the tibet plateau significantly contributed to the gradual climate deterioration of the last million years

an adaptive finite volume solver for ice sheets and glaciers 1 we have developed a new adaptive finite volume scheme for numerical simulations of ice sheets and glaciers the mathematical basis of the adaptive solver is represented by the finite volume method and irregular voronoi cell grids evaluation of spatial derivatives are obtained at cell edges from approximating the ice surface elevation locally by second order polynomials following a least squares approach the proposed scheme includes a simple and accurate method for handling discontinuities in ice thickness gradients along ice margins the flexibility of the voronoi cell structure allows for local mesh refinement in selected areas we show how increased mesh density along a steep ice margin may considerably increase overall numerical accuracy of an ice sheet simulation although the numerical scheme is not restricted to ice sheet representations using the shallow ice approximation sia we here use analytical sia solutions to test the accuracy of the method

controlling factors on earthquake swarms associated with magmatic intrusions constraints from iceland abstract the currently two most important surveying tools in volcano monitoring are observations of seismicity and surface deformation magma migration within the earth s crust is frequently associated with seismic activity often occurring as distinct earthquake swarms understanding the exact nature and significance of these swarms is important when evaluating volcanic crisis situations there seems however to be no general correlation between the amount of seismic energy release and the rate and volume of magma on the move which may complicate an immediate risk evaluation it has previously been shown that stressing rate appears as the controlling factor on the occurrence of seismicity during intrusion however in this paper we emphasize that this is only true under specific circumstances other factors influence the evolution and resulting seismic energy release and each intrusion scenario needs to be evaluated separately three icelandic cases where seismic swarms have been confirmed through deformation measurements to be related to magmatic movements were selected we show how the relationship between volume change and resulting seismicity varies greatly between cases and suggest that in a general approach the most important factor governing the level of seismic energy release is the background stress state tectonic setting regional stresses and tectonic history are therefore all of great importance when evaluating a magmatically induced seismic crisis the stressing rate only plays the dominant role when either a stress in the intruded area is close to the yield strength before intrusion or possibly b when the intrusion is extraordinarily voluminous and rapid

a level set method for modeling the evolution of glacier geometry a level set method is proposed for modeling the evolution of a glacier surface subject to a prescribed mass balance this leads to a simple and versatile approach for computing the evolution of glaciers the description of vertical fronts and overriding phenomena presents no difficulties topological changes are handled naturally and steady state solutions can be calculated without integration over time a numerical algorithm is put forth as a means of solving the proposed model of glacier surface evolution it is evaluated by comparing different numerical solutions of the model with analytical and published numerical solutions the level set method appears to be a reliable approach for dealing with different glaciological problems

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

off rift and rift zone palaeostresses in northwest iceland abstract the vestfirdir peninsula of northwest iceland consists mainly of gently dipping basaltic lava flows 8 14 ma old detailed studies of its principal tectonic elements basaltic dykes normal faults and minor faults and observations of the trends of the major fjords and valleys make it possible to reconstruct the evolution of the associated stress field the results show that a kink shaped curved rift zone existed in this area until about 5 ma ago in the northern part of the peninsula the rift zone trended nne but ene in the southern part it is proposed that the tectonic elements of the vestfirdir peninsula were generated in two stress fields one operating inside the rift zone the other operating outside it the rift zone stress field was responsible for the formation of most normal faults dykes and the main extension direction inferred from the minor faults conversely the off rift stress field was responsible for the formation of several holocene normal faults in the southern part of the peninsula the direction of the secondary extension inferred from the minor faults as well as for most major fjords and valleys in the area boundary element studies suggest that the off rift stress field generated on the concave side of a curved rift zone is different from that generated on its convex side absolute tensile stresses that encourage the formation of valleys and fjords concentrate very near to or at the convex margin but at a considerable distance from the concave margin applying these model results to iceland as a whole it is concluded that the valley formation in northwest iceland occurred at a large distance form the associated rift zone whereas in east iceland the valleys formed near to the margin of the rift zone furthermore the model predicts that zones of relative tension may propagate radially from the convex side of the rift zone and act as magma channels for volcanoes the location and orientation of major fjords and valleys in east and northwest iceland as well as the existence of several major off rift holocene volcanoes support the model predictions

quaternary erosion in the sognefjord drainage basin western norway abstract the preglacial paleic landscape configuration in the sognefjord drainage basin of western norway is reconstructed and the total quaternary erosion is quantitatively determined to 7610 km 3 by subtracting the present topography from the reconstructed preglacial surface with an average erosion of 610 m during the suggested time span of 600 000 yr when scandinavian ice sheets reached the continental shelf off western norway mean quaternary erosion rates are calculated to ca 1 02 mm yr using the average relief of 2000 m along the fjord however the rate of glacial erosion was 3 3 mm yr taking into account the selective nature of glacial erosion by ice streams along the fjord an estimate of 2 0 5 mm yr is likely limited to the east by the main watershed a rough estimate of the total quaternary glacial erosion in the fjord region of western norway is calculated to about 35 000 km 3 of rock with a soft sediment porosity of 30 50 this corresponds to about 45 500 52 500 km 3 of continental shelf deep sea sediments

flow to fracture transition in a volcanic mush plug may govern normal eruptions at stromboli stromboli is a model volcano for studying eruptions driven by degassing the current paradigm posits that strombolian eruptions represent the bursting of gas slugs ascending through melt filled conduits but petrological observations show that magma at shallow depth is crystalline enough to form a three phase plug consisting of crystals bubbles and melt we combine a 1d model of gas flushing a crystalline mush with a 3d stress model our results suggest that localized gas segregation establishes hot conduits of mobile magma within a stagnant plug the plug is prone to tensile failure controlled by gas over pressure and tectonic stress with failure most likely beneath the observed vent locations we hence argue that strombolian eruptions are related to plug failure rather than flow our proposed three phase model of the shallow plumbing system may provide a promising framework for integrating geophysical petrological and morphological observations at stromboli and in open system volcanism more generally

growth of an intermittent ice sheet in iceland during the late pliocene and early pleistocene abstract deep sea paleoclimatic records show that the quaternary climate around iceland was and probably still is very sensitive to rapid shifts in north atlantic oceanic circulation studies of several key sections in iceland indicate that similar oscillations are reflected in the late pliocene and early pleistocene terrestrial stratigraphy correlations between six rock sequences in western northern eastern and southern iceland show a fairly distinct trend during the pliocene pleistocene transition indicating the progressive growth of an ice sheet from southeast toward the north and west the correlations are based on k ar dates and paleomagnetic studies a total of 11 glacial horizons are recorded in a stratigraphic column from eastern iceland extending back 6 5 myr in western iceland 7 glacial horizons are preserved in a rock section dated from 7 0 to 1 8 myr and in northern iceland 14 glacial horizons are identified in a section that extends back to 9 0 myr well over 20 glacial horizons have been identified in the stratigraphic column in iceland full scale glacial interglacial cyclicity with regional ice cover is indicated at approximately 2 6 myr a further amplification leading to islandwide glaciations is identified at 2 2 2 1 myr these results show that changes in the ice cover in iceland correlate with the deep sea oxygen isotope records from benthic and planktonic foraminifera as well as ird studies from the north atlantic

magma dynamics during the 2007 stromboli eruption aeolian islands italy mineralogical geochemical and isotopic data abstract after the 6 month long effusive event of 2002 2003 a new lava effusion occurred at stromboli between 27 february and 2 april 2007 despite the different durations approximately the same volume of magma was emitted in both eruptions in the order of 107 m3 a paroxysmal eruption occurred at the summit craters in both the 2002 2003 and 2007 episodes during which a significant amount of low porphyritic lp volatile rich magma was erupted in both cases the paroxysm did not interrupt the lava emission here we present compositional data including texture mineralogy chemistry and sr and nd isotope ratios of bulk rock groundmass and separated minerals of lavas erupted in 2007 together with chemistry and sr and nd isotope composition of the pumices emitted during the 15 march paroxysm as a whole the lavas have the same texture and chemistry that characterize the highly porphyritic hp products usually erupted at stromboli during normal strombolian activity and effusive events compared to the previous hp products the 2007 lavas show minor but systematic mineralogical and isotopic variations which are consistent with a modest increase of the magma supply rate of the volcano compositional variations during the entire duration of the event are very modest glass chemistry changes in lavas erupted in the second half of march can be explained by the minor mixing between the volatile rich lp magma rising through the shallow magmatic system during the 15 march paroxysm and the degassed residing hp magma a first conclusion of this study is that there is no compositional evidence supporting major changes in the magma dynamics of the volcano accompanying the effusive activity as also suggested for the 2002 2003 event the activity of stromboli is controlled by a steady state feeding system in which refilling mixing degassing and crystallization at shallow level continuously operate with modest oscillations in the magma supply rate switching between normal strombolian and effusive activity is related to periods of relatively more vigorous refilling of the shallow system leading to progressive pressure increase in the upper conduits associated with only minor compositional variations in the erupted products

coupled thermal oscillations in explosive activity at different craters of stromboli volcano 1 thermal infrared thermometers deployed 250 m from stromboli s active craters can detect thermal emissions during strombolian explosions explosions appear as spikes in thermal time series with variations in the mass erupted during each event revealed by pulses in the time series during may 2001 stromboli s ne and sw craters showed consistently different thermal signatures sw crater events were characterized by long lasting 10 s higher amplitude thermal signals with significant fluctuations whereas the ne crater was characterized by short 5 s impulsive lower amplitude signatures the two craters showed well correlated variations in thermal amplitude evolving over periods of several hours and providing strong evidence for linkage of the craters to a common feeding system affected by cyclic processes that drive steady variations in the style of emission

late warming and early cooling of the sea surface in the nordic seas during mis 5e eemian interglacial abstract geochemical identification of a tephra layer found in two cores from the ne atlantic ocean and the se norwegian sea respectively and dated to 127 ka bp has enabled us to obtain a precise correlation across the iceland scotland ridge at the marine isotope stage mis 6 5 transition the direct distance between the two cores is only about 200 km south of the iceland scotland ridge sea surface temperatures rose abruptly at 130 ka bp at the onset of mis 5e and at least 2 3000 years earlier than north of the ridge maximum sea surface temperatures south of the ridge occurred during this initial phase of mis 5e when temperatures in the nordic seas were still low north of the ridge the sea surface warmed rapidly at 127 ka bp correlations between the north atlantic records and the eemian of northwest europe tentatively indicate that the initial phase of mis 5e correlates with the early part of the eemian characterised by a warm continental type of climate the period after the warming of the nordic seas corresponds to the slightly cooler and more oceanic middle eemian interval in europe the sea surface temperatures fell gradually north of the ridge during the later part of mis 5e and they were low during mis 5d 5a south of the ridge the temperatures remained relatively high the data shows that there was no outflow of deep water from the norwegian sea during the later part of mis 6 outflow began at the mis 6 5 transition simultaneous with the sea surface warming south of the ridge

evolving pliocene pleistocene climate a north pacific perspective abstract siliceous microfauna in sediments from north pacific deep sea drilling project sites record the response of the regional surface and near surface waters to global climate change over the past 3 0 ma during the late pliocene 2 7 3 0 ma the northern subtropical and subpolar pacific experienced warmer climate conditions than those of today the first predominant polar assemblage maximum occurs in the north pacific at 2 45 ma signifying this region s response to the initiation of significant northern hemisphere glaciation north pacific faunal data show that late pliocene 1 8 2 5 ma glacial maxima were only about half to two thirds as severe as those which occurred during the late pleistocene low faunal assemblage variability during a 200 ka interval in the latest pliocene 1 6 1 82 ma in the north pacific indicates minimal variations in the surface water properties and climate conditions most like those which existed just prior to 2 5 ma a distinct change in faunal assemblage registered in sediments from site 580 between 1 2 and 1 2 ma marks the first cooling in the north pacific comparable in intensity to those of the late pleistocene since 1 26 ma high amplitude high frequency variations in the north pacific polar assemblage have continued to occur providing further evidence that the interglacial glacial extremes that characterize the late pleistocene have persisted since this time the frequency distribution of north pacific winter sea surface temperature time series for the late pliocene and early pleistocene includes major concentrations of variance power centered at a frequency corresponding to a 41 ka period with variance dominance of the temperature time series for the last 800 ka shifting to lower frequencies 110 ka period

seven tephra isochrones in scotland this paper reports the presence and geochemical characteristics of seven separate tephras in scotland that fell in ad 1510 and about 450 bp 2100 bp 3600 bp 3830 bp 5600 bp and around 6000 bp the results come from 14 peat bogs spread throughout the highlands and islands where 26 tephra deposits have been characterized using over 400 grain discrete electron probe micro analysis firstly tephras are identified and defined by major element characteristics at a reference site secondly tephras are linked between sites on the basis of geochemistry and dated informal names based on british sites are suggested for tephras not yet linked to precise sources in iceland despite some apparent variation in colour all analysed grains in these seven deposits are silicic or intermediate in composition sio2 57 this phenomenon does not appear to be an artifact of preservation for two reasons first small 40 m basic glass shards in peat bogs in northern iceland are found to have undergone minimal alte

on estimating length fluctuations of glaciers caused by changes in climatic forcing the reaction of alpine glaciers to shifts in the equilibrium line altitude ela is calculated by using a two dimensional numerical model to solve the full equations for the velocity and stress fields full system model in the absence of basal motion rates of advance and retreat of the snout of typically sized alpine glaciers are found to be insensitive to the details of the flow at the snout even when the glaciers are far from steady state a comparison of results obtained with a full system model and a shallow ice approximation sia model yields no significant differences in advance or retreat rates this assumption has been implicitly made in numerous previous climatic studies and is here shown to be well justified using a realistic mass balance altitude feedback only slight model dependent changes in steady state lengths are found the relative importance of mass balance and glacier dynamics for the transient response of alpine glaciers to changes in the ela is given a precise meaning by determining the model dependent additional shifts in ela needed for the sia and the full system models to produce identical changes in length for alpine glaciers these additional shifts in ela are on the order of 10 m which is within the error range of ela estimates it follows that at least in the absence of significant basal motion there is no need to include the effects of horizontal stresses when calculating the reaction of alpine glaciers to climatic changes attention should focus on accurate determination of the mass balance distribution and model tuning to give realistic ice thickness distributions

point counting technique for fission track dating of tephra glass shards and its relative standard error fission track dating of glass is potentially an efficient technique for tephrochronological studies however most glasses from quaternary tephra have very low spontaneous track densities and track counting is laborious the point counting technique is a simplified procedure for evaluating fission track areal densities in a glass shard population that allows the analyst to count larger numbers of tracks in significantly shorter times a field of view is coded as 1 if its center is on glass and is 0 otherwise and the total area of glass is estimated by counting the number of 1 s under simple assumptions the binomial distribution appears to provide a reasonable evaluation of the additional experimental error in a fission track density determination by this technique glass shard populations have been simulated assuming that glass areas are random samples from distributions analogous to real ones the effect of variation in glass area on the relative standard error of the estimated track density is found to be small the point counting technique significantly enhances the potential of fission track dating especially for very low track densities typical of most quaternary tephra as the additional error associated with its use is largely counterbalanced by the greater number of tracks that can be counted

statistical analysis of the volcano seismicity during the 2007 crisis of stromboli italy 1 we analyze the volcano seismicity recorded during the pre and co eruptive regimes of the 2007 effusive crisis at stromboli volcano italy data set is composed of the continuous recordings of a three component broad band seismometer and of a sacks evertson strainmeter starting from the characterization of the non effusive phase as a stationary state of equilibrium we investigate the effusive phase as a non equilibrium state a statistical analysis reveals that the explosion occurrence is always driven by a nearly poissonian process as for the standard activity even during the effusive phase with the only difference in shortening the inter times explosion quake amplitudes are lognormally distributed until the effusive phase becoming then broader this indicates that many scales are involved a slightly different process can be advocated for the swarms of the explosions occurring during the effusive phase this suggests that the dynamics of the exsolution and or aggregation of the gas slugs should differ from the nucleation mechanism responsible of the standard strombolian activity the pre eruptive regime is characterized by a very long deformative signal that appears as a transient oscillating signal with a period of about three days that modulates the explosion amplitudes in a conceptual vibrating cavities model it is related to a chocking phenomenon induced by magma injection which in turn leads to the effusion

a record of pliocene and pleistocene glaciations and climatic changes in the north atlantic based on variations in volcanic and sedimentary facies in iceland abstract the location of iceland directly below the arctic circle and on the north atlantic plate boundary gives the island a characteristic record of interbedded lavas glacial deposits and other sediments opening a window on the geological and climatic history of the north atlantic frequently extruded lava flows tend to shield underlying sediments from subsequent erosion explosive volcanism keeps the sedimentation rate high and produces extensive time markers continuing studies of diamictites interbedded within basaltic lava suites of cainozoic age in iceland deal specifically with the problem of differentiating between glacial and non glacial sediments that have very similar attributes a multifaceted approach has been taken in order to differentiate these deposits this includes both lateral and vertical lithofacies description and clast fabric studies based on extensive field work a comparison with modern analogues and detailed laboratory work textural studies on thin sections and palaeomagnetic studies the results suggest that both the nature and extent of late pliocene and early pleistocene glaciations can be inferred from the preserved record the rock sequence offers excellent opportunities for pinning down the age of each event through palaeomagnetic correlation and radiometric dating of the lava flows the oldest tillite along the north coast of iceland has been bracketed down to approximately 2 1 ma and in inland mid western iceland to approximately 2 6 ma it is anticipated that continuing work elsewhere in iceland can further define the trends of pliocene glaciation in the north atlantic the significance of the frequency of identified glacial deposits in the icelandic sections may be tested through comparison with the latest deep sea record of glacial interglacial cycles

quantification of the gas mass emitted during single explosions on stromboli with the so2 imaging camera we performed measurements using an so2 imaging camera of the so2 gas mass emitted during five discrete explosive events on stromboli volcano on 3 october 2006 the so2 gas mass released during discrete explosions was 15 40 kg per explosion producing 3 8 of the total daily so2 gas emission demonstrating that in terms of gas flux strombolian explosions are a second order phenomenon compared with quiescent degassing using the typical gas composition measured with op ftir allows us to determine the total gas mass released during an explosion as 360 960 kg with a volume of 1500 4100 m 3 at 1 bar at the probable source pressure of gas slug formation of 75 mpa this gas amount would occupy a volume equivalent to a sphere with a radius of 0 8 1 m comparable with estimates of stromboli s conduit geometry c 2009 elsevier b v all rights reserved

early to middle holocene silicic tephra horizons from the katla volcanic system iceland new results from the faroe islands comparatively few icelandic tephra horizons dated to the early part of the holocene have so far been detected outside iceland here i present several tephra horizons that have been recorded in a holocene peat sequence on the faroe islands geochemical analyses show that at least two dacitic and one rhyolitic tephra layers were erupted from the katla volcanic system on southern iceland between ca 8000 and 5900 cal yr bp the upper two layers can be correlated with the silk tephras described from southern iceland whereas the third dated to ca 8000 cal yr bp has a geochemistry virtually identical to the rhyolitic component of the vedde ash the results suggest that the late weichselian and early holocene eruption history of the katla volcano was probably more complex than inferred from iceland a new early holocene rhyolitic tephra dated to ca 10 500 cal yr bp probably originates in the snaefellsnes volcanic centre in western iceland these new findings may play an important role in developing a holocene tephra framework for northwest europe copyright 2002 john wiley sons ltd

so2 flux from stromboli during the 2007 eruption results from the flame network and traverse measurements abstract so 2 fluxes emitted by stromboli during the 27th february 2nd april 2007 effusive eruption were regularly measured both by an automatic network of scanning ultraviolet spectrometers and by traverse measurements conducted by boat and helicopter the results from both methodologies agree reasonably well providing a validation for the automatic flux calculations produced by the network approximately 22 000 t of so 2 were degassed during the course of the 35 day eruption at an average rate of 620 t per day such a degassing rate is much higher than that normally observed 150 200 t d because the cross sectional area occupied by ascending degassed magma is much greater than normal during the effusion as descending degassed magma that would normally occupy a large volume of the conduit is absent we propose that the hydrostatically controlled magma level within stromboli s conduit is the main control on eruptive activity and that a high effusion rate led to the depressurisation of an intermediate magma reservoir creating a decrease in the magma level until it dropped beneath the eruptive fissure causing the rapid end of the eruption a significant decrease in so 2 flux was observed prior to a paroxysm on 15th march 2007 suggesting that choking of the gas flowing in the conduit may have induced a coalescence event and consequent rapid ascent of gas and magma that produced the explosion

geochemistry of historical age silicic tephras in iceland the major element chemistry of nine silicic tephras of historical age from iceland is assessed as a key step in the development of the recent tephrochronology of the north atlantic region the tephras include the largest such layers produced by each of the five central volcanoes hekla o raefajokull eyjafjallajokull torfajokull and askja since the ninth century ad h 1104 o1362 e 1821 landnam tephra c 870 a 1875 and four other tephras h 1158 h 1510 h 1947 o1727 the determination of grain discrete major element chemistry of the glass fraction is a fundamental stage in the identification and correlation of tephra and allows links to be made between icelandic source areas with precise dating evidence and distal deposits elsewhere in the north atlantic region although major element data can be used to discriminate between tephra layers produced by the different central volcanoes on its own it cannot be used to identify all the holocene layers produc

calendar year ages of three mid holocene tephra layers identified in varved lake sediments in west central sweden three intermediate to rhyolitic icelandic holocene tephra horizons hekla 3 kebister and hekla 4 have been identified in annually laminated varved lake sediments in the province of varmland west central sweden calendar year ages were obtained from varve counts and are supported by additional c 14 dating based on terrestrial plant macrofossils the varve ages of the three tephras are 3295 95 cal bp hekla 3 4030 103 cal bp kebister and 4390 107 cal bp hekla 4 the varve age of hekla 3 refines the former calibrated 14 c age based on studies in the british isles and germany considering the age error estimates associated with the varve chronology and calibrated c 14 ages the ages of kebister and hekla 4 are in agreement with former studies thus the age difference between kebister and hekla 4 is estimated to be ca 400 40 varve years formally estimated to ca 200 c 14 years between hekla 3 and hekla 4 to ca 1135 55 varve years formally estimated to ca 1100 calibrated c 14 years and between hekla 3 and kebister 708 20 varve years less

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

lava effusion a slow fuse for paroxysms at stromboli volcano questo lavoro ha analizzato i risultati del monitoraggio termico delle eruzioni di stromboli del 2002 2003 e 2007 ed ha mostrato come prima di ogni parossisma il volume di lava eruttato nel corso dell attivita effusiva sia stato confrontabile questa osservazione ha fatto ipotizzare l esistenza di una decompressione critica nel sistema di alimentazione superficiale del vulcano raggiungibile anche lentamente che innesca la veloce risalita del magma ricco in gas responsabile dei parossismi durante l attivita effusiva a questa decompressione critica e associabile una soglia di volume di magma emesso che diventa la misura discriminante per valutare la fase critica del vulcano e predire il parossisma

temporal changes in holocene δ18o records from the northwest and central north iceland shelf the region of north iceland is highly sensitive climatically owing to its location with respect to atmospheric and oceanographic fronts in this study we present total carbonate and 18o records of benthic and planktic foraminifera from nine sediment cores from the north iceland shelf the results of this work indicate that the deglaciation of the vestfirdir peninsula was completed by 10 200 cal yr bp the 8200 cal yr bp cold event is present only as a minor isotopic event and seems not to have had much of a cooling effect on the bottom waters of the northwest iceland shelf the holocene maximum warmth attributed to a stronger north icelandic irminger current occurred between ca 7800 and 6200 cal yr bp over the past 4500 cal yr bp a general cooling trend has occurred on the north iceland shelf and superimposed on this overall cooling trend are a number of oscillations between periods when relatively warmer and cooler waters occupied the shelf relatively cooler waters were present at 4200 4000 cal yr bp 3200 2900 cal yr bp 2500 2350 cal yr bp and 600 200 cal yr bp whereas relatively warmer waters were present on the shelf at 3750 3450 cal yr bp 2800 2600 cal yr bp and 1700 1000 cal yr bp copyright 2004 john wiley sons ltd

evidence for a change in the periodicity of tropical climate cycles at 2 4 myr from whole core magnetic susceptibility measurements the earth s orbit about the sun is influenced by gravitational interactions with the moon and other planets the resulting orbital perturbations give rise to cyclical variations in orbital eccentricity obliquity and precession with periods of 100 41 19 and 23 kyr respectively1 these variations are climatically important because they affect the seasonal and latitudinal distribution of solar radiation magnetic susceptibility measurements in deep sea sediment cores can be used as a sensitive indicator of temporal variations in the concentration of terrigenous material supplied to the sea bed here we use this approach to study the evolution of cycles of terrigenous sedimentation at ocean drilling program sites in the arabian sea and the eastern tropical atlantic we show from spectral analyses of the two susceptibility time series spanning the past 3 2 3 5 myr that the records are driven strongly by orbital forcing before 2 4 myr before present bp both records are strongly influenced by the 23 and 19 kyr periodicities but after 2 4 myr they are both significantly influenced by the 41 kyr periodicity this shift coincides with the beginning of major northern hemisphere glaciation which indicates for the indian ocean site that the supply of terrigenous sediment carried by monsoonal winds has responded to the rapid increase in ice cover at this time we cannot however exclude possible effects of changes in bottom water circulation on the susceptibility record of the atlantic site

thermal seismic and infrasonic evidences of variable degassing rates at stromboli volcano abstract during june 1999 we measured the amplitude and rate number of events per second at which gas exited the vent at stromboli volcano as discrete gas bursts or puffs this allowed us to identify two styles of gas burst puffing activity the first is characterized by frequent rapidly rising puffs the second by less frequent slowly rising puffs each style persisted over 5 40 min long durations and was associated with a high and low number of strombolian explosions per hour respectively each period was also associated with characteristic delay times between the arrival of the infrasonic and thermal signals during strombolian explosions the delays were longer during vigorous puffing periods to explain our observations we propose a model in which the degassing process cycles between vigorous and weak degassing phases during vigorous degassing phases bubble layers ascend the conduit at a frequency of 0 5 1 0 s 1 this high degassing level reflects a gas rich magma column and leads to an increased rate in the formation of shallow foams and hence an increase in puffing and explosive activity as well as a higher free surface level and or gas jet velocity during weak phases bubble layers ascend the conduit at a reduced frequency of 0 2 0 3 s 1 during such times the magma column is poor in gas this leads to a decreased rate of foam layer formation and hence a reduction in puffing and explosive activity as well as a lower free surface level and or gas jet velocity variations in puffing activity can thus be used to track changes in the rate at which the shallow system is supplied by fresh gas rich magma our observations indicate that the two degassing styles last from 5 to 40 min and that the switch from one to the other occurs over a matter of minutes

late pliocene glaciation and landscape evolution of vestfirðir northwest iceland abstract vestfir ir northwest iceland has been extensively modified by glacial activity but the timing and landscape impact of pre last glacial maximum lgm glacial activity is not well known we present new geochemical and chronological data from two tephras o oli and hjallanes which constrain the age of high altitude ice dammed lake sediments near the plateau surface of skagafjall located on the outer westernmost fjords of vestfir ir our findings provide the first dated evidence of late pliocene glaciation on vestfir ir the 2 26 0 11 ma fission track age of the airfall rhyolitic o oli tephra is compatible with reversed palaeomagnetic polarity data and suggests an ice dammed lake existed on skagafjall at broadly the same time as a major and well documented late pliocene downturn in global climate we assess the likely impact of late pliocene and subsequent glacial activity on vestfir ir landscapes and propose that 1 geomorphological features and sedimentary deposits on or near the skagafjall plateau surface could have survived beneath relatively low basal velocity areas and or relatively non erosive areas of glacial maxima ice sheets on vestfir ir at glacial maxima and 2 the heavily incised fjord network the principal macroscale landscape feature of vestfir ir existed in the late pliocene

the polarization of volcanic seismic signals medium or source abstract with the proliferation of three component seismometers on volcanoes the temptation is great to use polarization analysis as we do in earthquake seismology to determine propagation direction and or wavetype in order to locate and characterize the wave s source in volcano seismology there are two impediments to such a procedure the complexity of the volcano s structure and the often long lasting volcanic seismic signals i develop a simple model of acoustic scattering and apply it to three simple theoretical source signals which represent the classes of signals encountered at volcanoes when the medium is strongly scattering the polarization at a receiver location for impulsive sinusoidal or square wave sources mimics the characteristics for volcanic shocks tornillos with a single frequency and multichromatic tremor or tornillos the polarization observed for the square wave source resembles that observed for multichromatic tremor at lascar volcano chile and multichromatic tornillos at galeras volcano colombia at low frequencies the particle motion is fairly linear and nearly constant but cannot necessarily be used directly to indicate the direction to the source at all frequencies the particle motion exhibits some characteristics of rayleigh waves namely ellipticity of varying degrees and an rz product that oscillates with twice the frequency of the mode if this model is correct the lack of change of fundamental wavefield parameters such as the polarization for low frequencies during any given tornillo and from one tornillo to the next implies that the location of the source is stable to within a resolution of about 200 m

low frequency submarine volcanic swarms at the southwestern end of the okinawa trough 1 a low frequency lf submarine volcanic swarm has been first observed at the southwestern end of the okinawa trough where some submarine volcanoes have recently been identified a swarm of more than 24 earthquakes was recorded at land seismic stations in taiwan between september 1st and september 4th 2006 these earthquakes without clear s arrivals were substantially different from other abundant tectonic earthquakes in the area the dominant frequency of around 1 or 2 hz recorded at all stations shows that the lf seismograms were generated by neither path nor site effects but directly from the source these lf earthquakes can be characterized as b type volcanic earthquakes which have been observed in some active volcanoes before significant eruptions the observations of these lf volcanic earthquakes beneath submarine volcanic cones and seamounts are strong indicator that some submarine volcanoes are still active at the southwestern end of the okinawa trough

isothermal plateau fission track ages of hydrated glass shards from silicic tephra beds abstract the age of silicic tephra beds that have experienced a simple thermal history can be accurately and precisely determined by application of the isothermal plateau fission track technique to hydrated glass shards age estimates obtained by this means compare very well with those based on co existing mineral phases using the k ar 40ar 39ar external detector fission track and thermoluminescence techniques this concordance contradicts the popular belief that hydrated glass shards give unreliable ages distal tephra beds many of which are difficult to date because of their fine grainsize low abundance of crystals and common presence of detrital grains are readily dated by the isothermal plateau glass fission track method this new advance should greatly facilitate the development of detailed chronologies of tephra bearing sedimentary sequences located far from volcanic centres

dynamics of volcanic systems in iceland example of tectonism and volcanism at juxtaposed hot spot and mid ocean ridge systems volcanic systems are swarms of tectonic fractures and basalt volcanoes formed as a result of plate pull as the plates are pulled apart associated with the mid ocean ridges and the magma dynamics of the iceland mantle plume most systems are 40 150 km long 5 20 km wide and develop a central volcano they supply magma to all eruptions in iceland data obtained in the last few years have greatly improved our knowledge of their volcanotectonic environment as a result the geometry of the plume is better constrained and the crust previously considered thin 10 km is now modeled as thick 20 40 km depending on the location of the volcanic systems their activity either decreases or increases faulting in the two main seismic zones from this we can infer that emplacement of the feeder dike to the largest historical eruption in iceland that of laki in 1783 increased shear stress in the south iceland seismic zone and almost certainly triggered the largest m 7 1 in 1784 historical earthquake in ic

seven million years of glaciation in greenland glacial till glaciomarine diamictites and ice rafted detritus found in marine cores collected off the shore of southeast greenland record multiple late cenozoic glaciations beginning in the late miocene distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast greenland margin glaciers advanced to the sea during several intervals in the pliocene and pleistocene north atlantic glaciation may have nucleated in southern greenland rather than further north because of the high mountains and the high levels of precipitation in this region

origin of the sound generated by strombolian explosions during strombolian eruptions large bubbles break at the surface of the lava column and produce sound acoustic pressure recorded during several explosions on the eastern vent of stromboli volcano shows a pattern consistent between explosions the well marked oscillation contains only very low frequencies around 7 hz and is followed by a signal containing now both higher frequencies and lower frequency less than 4 hz the generation of sound is explained by the vibration 7 hz and bursting higher frequencies of large bubbles followed by the drainage of magma down in the conduit less than 4 hz the interpretation suggests that 1 the bubble vibrates before bursting and 2 the vibration prior to bursting yields more energy than the bursting itself the radius of bubbles responsible for explosions is determined to be close to 1 meter in agreement with observations of a few conduit sizes

explosion swarms at stromboli volcano a proxy for nonequilibrium conditions in the shallow plumbing system 1 in this paper we look at changes of the statistics of the stationary explosive process at a basaltic volcano as a proxy for departures from thermodynamic equilibrium conditions in the shallow plumbing system specifically we investigate the explosion process of stromboli volcano that occurred during 2002 2003 2006 2007 and 2010 2011 the first two periods were characterized by eruptions with significant lava effusion and strong paroxysmal events while the last one shows persistent explosive activity accompanied by minor episodes of lava flow we use three component seismic data recorded by broadband stations operating on the volcano and for 2007 and 2010 2011 cases strainmeter data from a sacks evertson borehole dilatometer for each time interval we study the explosive process by looking at the inter occurrence times and at the amplitude distribution moreover we analyze its waveforms spectral content and polarization properties in all three cases we find sharp increases of the explosion rate associated with swarms swarms are characterized by quasi monochromatic seismic events with frequency peak close to about 3 hz higher amplitude than the usual explosions and variability coefficient of the inter occurrence times close to 0 5 in correspondence to the swarms we also observe negative variations in the strain signals which indicate a depressurization in the shallow plumbing system this depressurization emerges clearly from the data collected during 2010 2011 whereas it is less sharp for the 2007 episode and has been estimated in about 105 pa from the polarization analysis we infer that this depressurization affects the upper 0 3 0 8 km of the plumbing system

north atlantic deep sea sedimentation of late quaternary tephra from the iceland hotspot piston cores recovered from the north atlantic were used to study the sedimentation of holocene and pleistocene volcanic ash in the irminger and iceland basins ash zones 1 11 100 yr b p 2 55 000 yr b p and 3 305 000 yr b p were identified from their major element glass composition the silicic and alkalic ash zones 1 and 2 originate from the southeastern volcanic zone of iceland where they correlate with the solheimar ignimbrite from katla volcano and the thorsmork ignimbrite from tindfjallajokull volcano respectively the low alkali composition of silicic ash zone 3 indicates a source from one of the silicic centers in the active rift system ash zones 2 and 3 occur in the irminger basin as dispersed glass shards over a depth interval of several tens of centimeters their compositional and granulometric characteristics reflect an initial fallout on pack ice north of iceland followed by ice rafting sedimentation in the denmark strait prior to bioturbation 18o stratigraphy of foraminifera in the cores indicates that the ash zones were deposited during a cold interval at the time when seas north of iceland were ice covered sedimentary features indicate that turbidity currents were also involved in the dispersal of ash zones 1 and 2 south of iceland the initiation of these gravity currents from the shelf can be attributed to either glacier bursts jokulhlaups carrying tephra or the entrance of pyroclastic flows into the ocean

subevents of long period seismicity implications for hydrothermal dynamics during the 2004 2008 eruption of mount st helens 1 one of the most striking aspects of seismicity during the 2004 2008 eruption of mount st helens msh was the precise regularity in occurrence of repetitive long period lp or drumbeat events over sustained time periods however this precise regularity was not always observed and at times the temporal occurrence of lp events became more random in addition accompanying the dominant lp class of events during the 2004 2008 msh eruption there was a near continuous randomly occurring series of smaller seismic events these subevents are not always simply small amplitude versions of the dominant lp class of events but appear instead to result from a separate random process only loosely coupled to the main lp source mechanism we present an analysis of the interevent time and amplitude distributions of the subevents using waveform cross correlation to separate lp events from the subevents we also discuss seismic tremor that accompanied the 8 march 2005 phreatic explosion event at msh this tremor consists of a rapid succession of lps and subevents triggered during the explosion in addition to broadband noise from the sustained degassing immediately afterward seismicity returned to the pre explosion occurrence pattern this triggering in relation to the rapid ejection of steam from the system and subsequent return to pre explosion seismicity suggests that both seismic event types originated in a region of the subsurface hydrothermal system that was 1 in contact with the reservoir feeding the 8 march 2005 phreatic explosion but 2 not destroyed or drained by the explosion event finally we discuss possible thermodynamic conditions in a pressurized hydrothermal crack that could give rise to seismicity pressure drop estimates for typical lp events are not generally large enough to perturb pure water in a shallow hydrothermal crack into an unstable state however dissolved volatiles such as co2 may lead to a more unstable system increasing the seismogenic potential of a hydrothermal crack subject to rapid heat flux the interaction of hydrothermal and magmatic systems beneath msh in 2004 2008 thus appears able to explain a wide range of observed phenomena including subevents lp events larger md 2 events and phreatic explosions

seismic and acoustic observations at mount erebus volcano ross island antarctica 1994 1998 volcanic activity at mount erebus is dominated by eruptive activity within a phonolitic summit lava lake common eruption styles range from passive degassing to strombolian explosions which typically occur several times daily and occasionally in swarms of up to 900 per day shallow explosions although generally the result of steady exsolution of volatiles from depth can be triggered by surficial input of h 2o through mass wasting of rock snow and ice from the crater walls broadband observations of strombolian explosions document very long period vlp signals with strong spectral peaks near 20 12 and 7 s which are polarized in the vertical radial plane these signals precede lava lake surface explosions by 1 5 s are highly repeatable and persist for up to 200 s first motions indicate a deflationary source with any precursory inflation being below the 30 s passband of our instruments particle motions suggest a vlp source residing up to 800 m below the lava lake surface however this depth could be exaggerated by near field radial tilt seismic and acoustic signals associated with lava lake explosions commonly show evidence for multiple bubble bursts in corresponding complexity features resulting from varying time delays and relative sizes of superimposed bursts a systematic decrease in seismic acoustic ratio for smaller surface explosions suggests that either the seismic energy from the smallest shallowest bubble bursts experiences much greater seismic attenuation than energy arising from larger events which may involve a deeper less attenuative portion of the magma column and or that the shallowest layer is seismically isolated from deeper parts of a stratified magma column which are not excited by the smallest explosions due to sharp impedance contrasts across distinct layers tremor at erebus is uncommon with only a few isolated instances identified in five years of monitoring some tremor events are nearly monochromatic and some exhibit numerous gliding harmonic spectral lines q 2000 elsevier science b v all rights reserved

extending the limits of the borrobol tephra to scandinavia and detection of new early holocene tephras analyses of two infilled lakes in blekinge southeast sweden indicate the presence of at least three tephra horizons of termination 1 and early holocene age geochemical analyses confirm the presence of the borrobol tephra the askja tephra 10 000 14c yr b p and one previously unreported tephra of icelandic origin extending the limits of the borrobol tephra to scandinavia illustrates that this ash is far more widespread than previously realized and is therefore an important marker horizon for determining the rate and timing of the initial warming at the start of greenland interstade 1 gi 1 within europe the relatively unknown askja tephra and the newly discovered hasseldalen tephra are stratigraphically placed at the younger dryas preboreal transition this paper demonstrates the suitability and success associated with the extraction techniques for tracing microtephra horizons in areas distal to volcanic sources

swarms of similar long period earthquakes in the mantle beneath mauna loa volcano abstract we present analyses of two swarms of long period lp earthquakes at 30 km depth that accompanied the geodetically observed 2002 2005 mauna loa intrusion the first lp earthquake swarm in 2002 consisted of 31 events that were precursory and preceded the start of mauna loa inflation the second lp swarm of two thousand events occurred from 2004 2005 the rate of lp earthquakes slowed significantly coincident with the occurrence of the december 26 2004 m w 9 3 sumatra earthquake suggesting that the seismic waves from this great earthquake may have had a dynamic triggering effect on the behavior of mauna loa s deep magma system using waveform cross correlation and double difference relocation we find that a large number of earthquakes in each swarm are weakly similar and can be classified into two families the relocated hypocenters for each family collapse to compact point source regions almost directly beneath the mauna loa intrusion we suggest that the observed waveform characteristics are compatible with each family being associated with the resonance of a single fluid filled vertical crack of fixed geometry with differences in waveforms between events being produced by slight variations in the trigger mechanism if these lp earthquakes are part of the primary magma system that fed the 2002 2005 intrusion as indicated by the spatial and temporal associations between mantle seismicity and surface deformation then our results raise the possibility that this magma system may be quite focused at these depths as opposed to being a diffuse network it is likely that only a few locations of mauna loa s deep magma system met the geometric and fluid dynamic conditions for generating lp earthquakes that were large enough to be recorded at the surface and that much of the deep magma transfer associated with the 2002 2005 intrusion occurred aseismically

rhyolitic tephra horizons in northwestern europe and iceland from the ad 700s 800s a potential alternative for dating first human impact the distribution and geochemistry of four rhyolitic tephra horizons from iceland dated to the ad 700s 800s is assessed these include the rhyolitic phase of the landnam tephra ad 870s the ad 860

flow dynamics of tidewater glaciers a numerical modelling approach the dynamics of grounded tidewater glaciers is investigated with a time dependent numerical flow model which solves the full equations for the stress and velocity fields and includes a water pressure dependent sliding law the calving criterion implemented in the model shifts the calving front at each time step to the position where the frontal ice thickness exceeds flotation height by a prescribed value with this model the linear relation between calving rate and water depth proposed on empirical grounds is qualitatively reproduced for the situation of a slowly retreating or advancing terminus but not for situations of rapid changes length changes of tidewater glaciers i e especially rapid changes are dominantly controlled by the bed topography and are to a minor degree a direct reaction to a mass balance change thus accurate information on the near terminus bed topography is required for reliable prediction of the terminus changes due to climate changes the results also confirm the suggested cycles of slow advance and rapid retreat through a basal depression rapid changes in terminus positions preferably occur in places where the bed slopes upwards in the ice flow direction

vedde ash layer discovered in a small lake basin on the scottish mainland a thin layer of micro tephra particles has been discovered in a lake sediment sequence from sutherland scotland the tephra is attributed to the vedde ash on the basis of ash geochemistry the vedde ash which has been dated to c 10 300 radiocarbon years bp and which was thus deposited during the younger dryas chronozone has previously been reported from lake sequences in norway from sediment cores from the ne north atlantic and from greenland ice cores but this is the first reported record from the british mainland it is likely that this ash layer also occurs in other lake sediment sequences in northern britain thus providing the potential for more precise correlations of younger dryas sequences than has hitherto been the case the way in which correlation by tephrochronology may revolutionize approaches to reconstructing the sequence of events in thene atlantic region during the last glacial interglacial transition is briefly considered

were there two borrobol tephras during the early lateglacial period implications for tephrochronology abstract a series of ams radiocarbon measurements of terrestrial plant macrofossil remains are presented from a lake sequence in southernmost sweden in an attempt to constrain the age of the borrobol tephra this recently identified ash layer has been frequently suggested as a potentially significant marker horizon for assessing the precise timing of the initial warming in different parts of europe at the start of greenland interstadial 1 gi 1 two different methods are adopted in order to derive a calendar age estimate for this event an age of ca 13 900 cariaco varve yrs bp is derived from a visual wiggle match of the age series to the cariaco basin data set the second approach is based on bayesian probability analysis and constrains the age of the borrobol tephra in southern sweden to between 13 800 14 450 and 13 667 14 331 cal yrs bp 95 confidence using the cariaco and lake suigetsu records as calibration data sets respectively these new age depth models together with the pollen stratigraphy suggest that the borrobol tephra as found in southern sweden falls within the late older dryas gi 1d or the early allerod gi 1c whereas other european sequences indicate that this tephra falls close to the gs 2 gi 1 transition whether or not this indicates that the different occurrences of the bt in northern europe are coeval is discussed and the implications that arise for the application of tephrochronology during this period are outlined

magma flow instabilities in a volcanic conduit implications for long period seismicity silicic volcanic eruptions are typically accompanied by repetitive long period lp seismicity that originates from a small region of the upper conduit these signals have the capability to advance eruption prediction since they commonly precede a change in the eruption vigour shear bands forming along the conduit wall where the shear stresses are highest have been linked to providing the seismic trigger however existing computational models are unable to generate shear bands at the depths where the lp signals originate using simple magma strength models presented here is a model in which the magma strength is determined from a constitutive relationship dependent upon crystallinity and pressure this results in a depth dependent magma strength analogous to planetary lithospheres hence in shallow highly crystalline regions a macroscopically discontinuous brittle type of deformation will prevail whilst in deeper crystal poor regions there will be a macroscopically continuous plastic deformation mechanism this will result in a depth where the brittle ductile transition occurs and here shear bands disconnected from the free surface may develop we utilise the finite element method and use axi symmetric coordinates to model magma flow as a viscoplastic material simulating quasi static shear bands along the walls of a volcanic conduit model results constrained to the soufriere hills volcano montserrat show the generation of two types of shear bands upper conduit shear bands that form between the free surface to a few 100 m below it and discrete shear bands that form at the depths where lp seismicity is measured to occur corresponding to the brittle ductile transition and the plastic shear region it is beyond the limitation of the model to simulate a seismic event although the modelled viscosity within the discrete shear bands suggests a failure and healing cycle time that supports the observed lp seismicity repeat times however due to the paucity of data and large parameter space available these results can only be considered to be qualitative rather than quantitative at this stage c 2007 elsevier b v all fights reserved

extending the known distribution of the younger dryas vedde ash into northwestern russia the known distribution of wind blown vedde ash ca 10 3 ka bp has been extended to the karelian isthmus in northwestern russia this has been possible as the result of a density separation technique that separates the rhyolitic vedde ash shards from the minerogenic host sediment the vedde ash occurs in the middle of a pollen zone with high percentages of for example artemisia and chenopodiaceae suggesting that the younger dryas or gs i in the grip ice core event stratigraphy was cold and dry throughout its duration this is in agreement with sites in south sweden where the vedde ash also occurs in the middle of a pollen zone dominated by artemisia chenopodiaceae and cyperaceae copyright 2000 john wiley sons ltd

new tephra horizons from oxygen isotope stage 5 in the north atlantic correlation potential for terrestrial marine and ice core archives abstract tephra horizons of oxygen isotope stage ois 5 age from two cores in the north atlantic have been analysed geochemically the results show that several discrete tephra horizons are present which have an icelandic provenance tephras of basaltic geochemistry dominate the sequences correlation of the cores is based on the occurrence of a basaltic tephra near the base of ois 5e a rhyolitic tephra has been discovered within ois 5e sediments in a core from the se norwegian sea which is geochemically identical to the middle eemian tephra found in several cores from the nordic seas this tephra is probably widespread and thus the potential exists for its wider detection in terrestrial sequences on mainland europe and the greenland ice cores

the correlation between reduction in fission track diameter and areal track density in volcanic glass shards and its application in dating tephra beds abstract the relationship between the reduction in fission track diameter and the reduction in areal track density in hydrated glass shards has been investigated under varying annealing and etching conditions a near 1 1 relation is observed for adequately etched tracks following laboratory heating of induced tracks the partially reduced areal track density was renormalized with error

long period seismicity at shishaldin volcano alaska in 2003 2004 indications of an upward migration of the source before a minor eruption abstract we have analyzed the long period lp seismic activity at shishaldin volcano aleutians islands alaska in the period october 2003 july 2004 during which a minor eruption took place in may 2004 with ash and steam emissions thermal anomalies volcanic tremor and small explosions we have focused the attention on the time evolution of lp rate size spectra and polarization dip angle along the dataset we find an evolution toward more shallow dip angles in the polarization of the waveforms during the sequence the dip angle is a manifestation of the source location because the lp seismic sources are presumed to reflect the aggregation of gas slug or pockets within the melt we use the polarization dip at the lp onset as a proxy for the nucleation depth of the seismic events within the conduit we refer to this parameter as the nucleation dip and the position along the conduit of the gas aggregation as nucleation depth the nucleation dip changes throughout the dataset it shows a sharp decrease between the end of december 2003 and the end of january 2004 followed by a gradual increase until the onset of the eruption at the same time a general increase of the lp rate occurs we have associated the dip evolution with a sinking and a subsequent decrease of the nucleation depth which would quickly migrate up to about 8 km below the crater rim followed by a slow depth decrease which culminates in the eruption the change in the nucleation depth reflects either a pressure variation within the plumbing system which would affect the confining pressure experienced by the gas aggregations we have imputed such a pressure change to the intrusion of batches of magma from a deeper magma chamber 5 km for a cylindric conduit with rigid walls this leads to a volume of the injected new magma of 10 5 10 7 m 3 compatible with estimates in other areas suggesting that the lp process can be considered a good proxy of the thermodynamical conditions of the shallow plumbing system

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

a statistical study of the stromboli volcano explosion quakes before and during 2002 2003 eruptive crisis 1 we study the seismic wavefield and the statistical properties of the stromboli volcano explosions preceding and during the 2002 2003 crisis we analyze the recordings of a three component seismometer operating since 23 may 2002 to 30 january 2003 including the first 34 days of the crisis before the crisis we recognize three bell shaped classes of spectra with maxima falling in the range 1 5 hz spectral content has two main changes the most prominent one occurring at the crisis onset when the frequency peak at 0 3 hz increases in amplitude independent component analysis extracts three time stable independent oscillations that peaked at 1 1 1 8 and 2 5 hz with radial and shallow polarization indicating a stable source mechanism energy of the explosions is lognormally distributed except during a 2 month time interval before the crisis when it also shows a higher mean value the interoccurrence time distributions display an homogeneous poissonian behavior with a mean intertime of 250 s without changes at the crisis onset only swarms of explosions are not ruled by a poisson process and display higher occurrence rates and higher energies finally we depict a scheme of the crisis a modification of the equilibrium is induced by rising magma that produces a change in the boundary conditions of the plumbing system the escape from the equilibrium produces at first variations in the usual statistics of the explosions then it leads to the lava effusion and to a pressure drop in the plumbing system that induces a deep gas slug nucleation and the excitation of low frequencies

late quaternary glacial and deglacial history of eastern vestfirdir iceland using cosmogenic isotope 36cl exposure ages and marine cores the late glacial and deglacial history of vestfirdir nw iceland is interpreted from terrestrial field based evidence and compared with marine cores and seismic studies understanding the timing of deglaciation is complicated by a lack of dateable organic material on land uncertainties associated with interpretation of diamictons and ambiguities in radiocarbon dating new 36cl exposure ages of boulders and bedrock surfaces suggest that at least part of the coastal uplands were ice free by approximately 20 ka deglaciation of the valleys followed boulders from the crest of an end moraine in the sela river valley have a mean 36cl age of 14 6 ka 0 8 ka n 4 and the outermost moraine in the valley adjacent to kaldalonjokull has a mean 36cl age of 11 7 ka 0 9 ka n 2 tephrochronology provides a link between the terrestrial and marine sequences around vestfirdir the vedde ash ca 12 k cal yr bp is present in some offshore cores but it is absent from terrestrial sites suggesting that its distribution provides a constraint on ice extent during the younger dryas the saksunarvatn ash 10 2 0 6 k cal yr bp confirmed by geochemical analyses and radiocarbon dating is present in at least three terrestrial locations on eastern vestfirdir and in many cores from the fjords and shelf which constrains early holocene ice extent copyright 2006 john wiley sons ltd

preglacial surface remnants and quaternary glacial regimes in northwestern sweden abstract we present a detailed map of the distribution of preglacial surface remnants in the kebnekaise region of northwestern sweden in this mountain area we discern four important large scale geomorphological units each representing a specific set of erosional agents and formative conditions these are i intact preglacial surface remnants characterized by gentle slopes round summits wide shallow valleys and an absence of rock basins ii preglacial surface remnants showing signs of minor glacial erosion and deposition iii glacially scoured surfaces including glacial troughs iv deep fluvial valleys cut into the preglacial surface the pattern of glacial erosion is explained as the result of three specific modes of glaciation known to have existed during the last 120 000 years and inferred to have repeatedly prevailed during the last 2 75 million years cirque glaciation mountain ice sheets and fennoscandian ice sheets a deep ocean oxygen isotope record of foraminifera from the north atlantic dsdp 607 was used to infer the temporal extent of these modes of glaciation during the last 2 75 million years we interpret the preglacial landscape preservation and the pattern of glacial erosion in terms of the configuration the basal thermal regime and the duration of such glaciation events the average subglacial thermal regime of both ice sheet types was frozen on the uplands and melting in the main valleys where outlet glaciers and ice streams formed the pre glacial landscape is best preserved at intermediate elevations low enough not to have been covered by cirque glaciers and apparently high enough not to have experienced melted bed conditions and subglacial erosion during ice sheet overriding events in a narrow high relief zone along the elevation axis interglacial fluvial erosion was morphologically important the absence of glacial erosion on uplands in this zone allowed fluvial erosion to commence on the same locations during each ice free interval in contrast no persistent fluvial valley pattern could develop in zones subjected to repeated glacial scouring and hence derangement of fluvial patterns

passive margin uplift around the north atlantic region and its role in northern hemisphere late cenozoic glaciation tectonic climatic models of late cenozoic global cooling emphasize the importance of middle latitude uplifts e g tibetan plateau and the american west but ignore widespread tectonic events on the margins of the north atlantic ocean pleistocene glaciations after 2 5 ma are characterized by circum north atlantic continental ice sheets that formed by the coalescence of perennial snow fields on extensive plateau surfaces in eastern canada northwest britain and scandinavia plateaus record cenozoic uplift of peneplains in response to semisynchronous magmatic underplating and thermal buoyancy of rifted continental margins high standing plateaus are very sensitive to small reductions in summer temperature as late cenozoic climate cooling proceeded driven by uplift in regions external to the north atlantic region elevated plateaus became sites for extensive snow fields and ultimately ice sheets circum atlantic uplift took place in the key latitudinal belt that is most sensitive to orbitally forced changes in solar irradiation this together with albedo effects from large snow fields could have amplified the relatively weak milankovitch signal

stability of the seismic source during effusive and explosive activity at stromboli volcano 1 in december 2002 stromboli volcano erupted triggering a sector collapse and a tsunami during the 7 month long effusive eruption the typical persistent and moderate explosive activity of stromboli ceased however very long period vlp seismic events typically associated with the explosions at stromboli were recorded during the effusive eruption these were clustered mainly in two groups with stable waveforms this suggests that strombolian activity never ceased but was confined deep within the magma conduit a location method based on the seismic directivity recorded with an asynchronous seismic deployment positioned the two clusters 60 m apart from each other at 510 m a s l and 180 m nw from the summit craters however seismic polarization reveals a 50 m upward migration of the vlp source at the end of the eruption when volcanic activity moved from the effusive style to more typical strombolian activity

preservation of landforms under ice sheets and ice caps abstract this article addresses the question of whether or not distinct glacial and non glacial landforms can survive beneath ice sheets and ice caps with little or no morphological alteration a review of recent work documents the existence of pre last stadial landforms and landscapes in areas covered by the fennoscandian and laurentide ice sheets a substantial number of independent works indicate that landforms such as eskers drainage channels and boulder fields have escaped destruction despite complete ice overriding during several tens of millenia full preservation of former ground surfaces or delicate landforms probably is linked to areas where the ice sheet base was continuously frozen to its bed larger robust landforms such as large drumlins appear to have been preserved even under wet based conditions in glaciated areas patches preserved under dry cold based conditions provide important windows towards the past showing landscapes that were destroyed in surrounding areas affected by wet based and eroding ice some consequences for the research fields of non glacial geomorphology archaeology and botany include the possibility of subglacial museums and refugia a time space model describes geomorphological access to information from older events in glaciated areas

polarisation analysis of the independent components of low frequency events at stromboli volcano eolian islands italy abstract independent component analysis ica applied on low frequency lf events recorded at stromboli volcano reveals that these signals are composed of three independent components in three different frequency bands approximately 0 8 1 2 2 4 3 0 3 2 4 5 hz respectively the first two frequency ranges are mainly composed of body waves coming from a direction in a range of 30 30 around the crater area this result is a clear indication that the entire signal in these frequency bands comes from the source area in fact any scattered wave should have different back azimuth propagation due to the random distribution of scatterers location however the last independent component is dominated by other kinds of waves coming from many different directions

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

limited modification of mid latitude landscapes by ice sheets the case of northeast scotland the paper uses a case study in scotland to examine the amount and processes of landscape modification by quaternary ice sheets there is an inverse correlation between the distribution of landforms of glacial erosion and pre glacial landscape remnants in northeast scotland the implication is that in places ice sheets can preserve a pre glacial landscape unscathed while elsewhere they remove the pre glacial weathered rock the location of glacial protection or erosion is strongly influenced by the topography and its influence on former ice sheet flow and basal thermal regime the classic glacially eroded landscape of areal scouring can be produced by the removal of only 10 50 m of weathered rock furthermore rock basins often regarded as the hallmark of glacial erosion may be directly inherited from the pre glacial pattern of deep weathering

image processing of explosive activity at stromboli abstract a new way to study the dynamics of explosive behaviour at different vents of stromboli volcano is proposed the method is based on computer processing of images taken by an infrared film camera at a rate of 4 pictures per second each picture has been digitized by use of an image scanner with a 75 d p i dots per inch resolution and 256 levels of gray then processed and the total mass of the ejected material has been calculated for each photograph with this procedure the flux of ejected matter throughout every single explosive event has been reconstructed the analysis of trajectories made on adequate samples of ejecta has allowed us to evaluate the ejection velocity the mode of the mass flux distribution and the mean value of the velocities calculated for individual particles quantify the kinetic energy of an explosion vents nos 1 and 3 which remained active after the last effusive eruption of 1985 1986 show several explosive patterns the energy of which is measured the observed flux distributions have been checked both numerically and experimentally by modelling impulsive events the computer simulations of the mass distributions have allowed us to speculate on the possible explosive dynamisms two different models have been used a single impulse model confirms the behaviour actually shown by one of the two vents while the behaviour of the other is better depicted by a cumulative trend of successive impulses in rhythmic sequence moreover through the experimental approach we have had the opportunity to test the overall resolution of the method the observed matter flux distribution has then been associated to the seismic signals in order to correlate the dynamics involved in the explosions with the seismic source mechanisms

effusive to explosive transition during the 2003 eruption of stromboli volcano the persistent explosive activity of stromboli volcano italy ceased in december 2002 and correlated with the onset of a seven month long effusive eruption on the volcano flank from new vents that opened just below the summit craters we intensively monitored this effusive event collecting and interpreting in real time an extensive multiparametric geophysical data set the resulting data synergy allowed detailed insights into the conduit dynamics that drove the eruption and the transition back to the typical strombolian activity we present a direct link between gas flux magma volume flux and seismicity supporting a gas driven model whereby the balance between gas flux and gas overpressure determines whether the system will support effusive or explosive activity this insight enabled us to monitor the migration of the magma column up the conduit and to explain the onset of explosive activity

ground deformation associated with the march 1996 earthquake swarm at akutan volcano alaska revealed by satellite radar interferometry in march 1996 an intense swarm of volcano tectonic earthquakes 3000 felt by local residents mmax 5 1 cumulative moment of 2 7 1018 n m beneath akutan island in the aleutian volcanic arc alaska produced extensive ground cracks but no eruption of akutan volcano synthetic aperture radar interferograms that span the time of the swarm reveal complex island wide deformation the western part of the island including akutan volcano moved upward while the eastern part moved downward the axis of the deformation approximately aligns with new ground cracks on the western part of the island and with holocene normal faults that were reactivated during the swarm on the eastern part of the island the axis is also roughly parallel to the direction of greatest compressional stress in the region no ground movements greater than 2 83 cm were observed outside the volcano s summit caldera for periods of 4 years before or 2 years after the swarm we modeled the deformation primarily as the emplacement of a shallow east west trending north dipping dike plus inflation of a deep mogi type magma body beneath the volcano the pattern of subsidence on the eastern part of the island is poorly constrained it might have been produced by extensional tectonic strain that both reactivated preexisting faults on the eastern part of the island and facilitated magma movement beneath the western part alternatively magma intrusion beneath the volcano might have been the cause of extension and subsidence in the eastern part of the island we attribute localized subsidence in an area of active fumaroles within the akutan caldera by as much as 10 cm during 1992 1993 and 1996 1998 to fluid withdrawal or depressurization of the shallow hydrothermal system

multifractal dimension and b value analysis of the 1998 1999 quito swarm related to guagua pichincha volcano activity ecuador 1 temporal variations of spatial multifractal dimensions of quito swarm seismicity ecuador are related to the august 1998 to december 1999 guagua pichincha volcanic activity multifractal dimensions decrease a few days before the five main seismic energy peaks and increase again before or just after these peaks this behavior reveals a self organization of earthquakes that precedes main seismic energy peaks the quito swarm is also characterized by a bimodal gutenberg richter law with two b values b1 0 95 0 15 and b2 1 48 0 15 this bimodality may reveal the superposition of two different processes one related to a classical elastic rupture and the other related to hydraulic fracture leading to high b values resulting from magma and overpressurized groundwater movements groundwater expulsion may be driven by heat released from deeper upgoing magma and manifested on the surface by the occurrence of phreatic explosions beginning 7 august 1998 and by the formation of eight dacitic lava domes beginning 25 september 1999