a compositional tipping point governing the mobilization and eruption style of rhyolitic magma measurements of the composition dependent viscosity of rhyolitic magma reveal a tipping point that changes the physical properties of the melt and controls the transition between effusive and explosive eruptions calcalkaline rhyolites produce the largest explosive volcanic eruptions but these eruptions can switch repeatedly between being effusive and explosive this is difficult to attribute to the rheological effects of magma water content or crystallinity danilo di genova and co authors report the viscosity of a series of melts spanning the compositional range of the yellowstone rhyolitic volcanic system they find that within a narrow compositional zone melt viscosity increases by up to two orders of magnitude which they propose to be the consequence of melt structure reorganization the authors confirm that such a compositional tipping point exists in the global geochemical record of rhyolites which separates effusive from explosive deposits they conclude that the anhydrous water free composition of calcalkaline rhyolites is decisive in determining mobilization and eruption dynamics of the earth s largest volcanic systems the most viscous volcanic melts and the largest explosive eruptions1 on our planet consist of calcalkaline rhyolites2 3 these eruptions have the potential to influence global climate4 the eruptive products are commonly very crystal poor and highly degassed yet the magma is mostly stored as crystal mushes containing small amounts of interstitial melt with elevated water content5 it is unclear how magma mushes are mobilized to create large batches of eruptible crystal free magma further rhyolitic eruptions6 7 8 can switch repeatedly between effusive and explosive eruption styles and this transition is difficult to attribute to the rheological effects of water content or crystallinity9 10 here we measure the viscosity of a series of melts spanning the compositional range of the yellowstone volcanic system and find that in a narrow compositional zone melt viscosity increases by up to two orders of magnitude these viscosity variations are not predicted by current viscosity models11 12 and result from melt structure reorganization as confirmed by raman spectroscopy we identify a critical compositional tipping point independently documented in the global geochemical record of rhyolites at which rhyolitic melts fluidize or stiffen and that clearly separates effusive from explosive deposits worldwide this correlation between melt structure viscosity and eruptive behaviour holds despite the variable water content and other parameters such as temperature that are inherent in natural eruptions thermodynamic modelling demonstrates how the observed subtle compositional changes that result in fluidization or stiffening of the melt can be induced by crystal growth from the melt or variation in oxygen fugacity however the rheological effects of water and crystal content alone cannot explain the correlation between composition and eruptive style we conclude that the composition of calcalkaline rhyolites is decisive in determining the mobilization and eruption dynamics of earth s largest volcanic systems resulting in a better understanding of how the melt structure controls volcanic processes

ice nucleation and overseeding of ice in volcanic clouds 1 water is the dominant component of volcanic gas emissions and water phase transformations including the formation of ice can be significant in the dynamics of volcanic clouds the effectiveness of volcanic ash particles as ice forming nuclei in is poorly understood and the sparse data that exist for volcanic ash in have been interpreted in the context of meteorological rather than volcanic clouds in this study single particle freezing experiments were carried out to investigate the effect of ash particle composition and surface area on water drop freezing temperature measured freezing temperatures show only weak correlations with ash in composition and surface area our measurements together with a review of previous volcanic ash in measurements suggest that fine ash particles equivalent diameters between approximately 1 and 1000 m from the majority of volcanoes will exhibit an onset of freezing between 250 260 k in the context of explosive eruptions where super micron particles are plentiful this result implies that volcanic clouds are in rich relative to meteorological clouds which typically are in limited and therefore should exhibit distinct microphysics we can expect that such overseeded volcanic clouds will exhibit enhanced ice crystal concentrations and smaller average ice crystal size relative to dynamically similar meteorological clouds and that glaciation will tend to occur over a relatively narrow altitude range

holocene tephrochronology of the hualaihue region andean southern volcanic zone 42 s southern chile late glacial and holocene soils and sediments in southern chile contain an important record of explosive volcanic activity since the end of the last glaciation and have considerable potential for

vegetation and climate change fire regime shifts and volcanic disturbance in chiloe continental 43 s during the last 10 000 years abstract disentangling the roles of paleofires and explosive volcanism from climatic drivers of past vegetation change is a subject insufficiently addressed in the paleoecological literature the coastal region of the chiloe continental sector of northwestern patagonia is ideal in this regard considering its proximity to active eruptive centers and the possibility of establishing comparisons with more distal upwind sites where volcanic influence is minimal here we present a fine resolution pollen and macroscopic charcoal record from lago teo with the aim of documenting the local vegetation and climate history and assessing the role of disturbance regimes as drivers of vegetation change during the last 10 000 years the lago teo record shows a conspicuous warm dry interval between 7500 and 10 000 cal yrs bp followed by a cooling trend and increase in precipitation that has persisted until the present in agreement with previous studies in the region and interpretations of past southern westerly wind activity at multi millennial scales the presence of 26 tephras throughout the record allows examination of the relationship between explosive volcanism and vegetation change under contrasting climatic states of the holocene we found consistent statistically significant increases in tepualia stipularis after tephra deposition over the last 10 000 years in eucryphia caldcluvia between 7500 and 10 000 cal yrs bp and in hydrangea over the last 7500 years our results indicate a primary role of climate change as driver of long term vegetation change and as a modulator of vegetation responses to volcanic disturbance at multidecadal and centennial timescales

geodetic measurements of plate motions across the central gulf of california 1982 1986 a trilateration network was set up in early 1982 by a team of french and mexican institutions across the central part of the gulf of california in order to study the plate boundary related movements in this transition area between the san andreas fault system and the east pacific rise the reobservation of this network in march 1986 provides a first set of data on the present day deformations in this area both surveys used aga8 laser geodimeter measurements between 11 stations located on elevated points of baja california and sonora and on the islands between the peninsula and mainland coasts deformation patterns during the 1982 1986 interval obtained through three different methods indicate mainly a right lateral shear movement in the gulf axis direction n46 w between baja california peninsula and angel de la guarda island 17 4 cm of dextral slip occurred between the coast of sonora and the central islands of the gulf the mean displacement amount to about 23 12 cm in the southwestern part of the network weaker movements seem to have occurred and are smaller than estimated errors this may indicate either that the boundary is locked in this part or is deflected towards the ese these results which give an estimation of the relative plate velocity of 8 3 cm a are consistent with the generally accepted relative movement between north american and pacific plates about 6 cm a

holocene explosive activity of hudson volcano southern andes fallout deposits in the vicinity of the southern andean hudson volcano record at least 12 explosive holocene eruptions including that of august 1991 which produced 4 km3 of pyroclastic material medial isopachs of compacted fallout deposits for two of the prehistoric hudson eruptions dated at approximately 3600 and 6700 bp enclose areas at least twice that of equivalent isopachs for both the 1991 hudson and the 1932 quizapu eruptions the two largest in the andes this century however lack of information for either the proximal or distal tephra deposits from these two prehistoric eruptions of hudson precludes accurate volume estimates andesitic pyroclastic material produced by the 6700 bp event including a 1 10 cm thick layer of compacted tephra that constitutes a secondary thickness maximum over 900 km to the south in tierra del fuego was dispersed in a more southerly direction than that of the 1991 hudson eruption the products of the 6700 bp event consist of a large proportion of fine pumiceous ash and accretionary lapilli indicating a violent phreatomagmatic eruption this eruption which is considered to be the largest for hudson and possibly for any volcano in the southern andes during the holocene may have created hudson s 10 km diameter summit caldera but the age of the caldera has not been dated independently

the 1963 1964 eruption of agung volcano bali indonesia the february 1963 to january 1964 eruption of gunung agung indonesia s largest and most devastating eruption of the twentieth century was a multi phase explosive and effusive event that produced both basaltic andesite tephra and andesite lava a rather unusual eruption sequence with an early lava flow followed by two explosive phases and the presence of two related but distinctly different magma types is best explained by successive magma injections and mixing in the conduit or high level magma chamber the 7 5 km long blocky surfaced andesite lava flow of 0 1 km3 volume was emplaced in the first 26 days of activity beginning on 19 february on 17 march 1963 a major moderate intensity 4 107 kg s 1 explosive phase occurred with an 3 5 h long climax this phase produced an eruption column estimated to have reached heights of 19 to 26 km above sea level and deposited a scoria lapilli to fine ash fall unit up to 0 2 km3 dense rock equivalent dre in volume with plinian dispersal characteristics and small but devastating scoria and ash flow deposits on 16 may a second intense 4 h long explosive phase 2 3 107 kg s 1 occurred that produced an 20 km high eruption column and deposited up to 0 1 km3 dre volume of similar ash fall and pyroclastic flow deposits the latter of which were more widespread than in the march phase the two magma types porphyritic basaltic andesite and andesite are found as distinct juvenile scoria populations this indicates magma mixing prior to the onset of the 1963 eruption and successive injections of the more mafic magma may have modulated the pulsatory style of the eruption sequence even though a total of only 0 4 km3 dre volume of lava scoria and ash fall and scoria and ash pyroclastic flow deposits were produced by the 1963 eruption there was considerable local damage caused mainly by a combination of pyroclastic flows and lahars that formed from the flow deposits in the saturated drainages around agung minor explosive activity and lahar generation by rainfall persisted into early 1964 the climactic events of 17 march and 16 may 1963 managed to inject ash and sulfur rich gases into the tropical stratosphere

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr

three dimensional volcanic aerosol dispersal a comparison between multiangle imaging spectroradiometer misr data and numerical simulations 1 the three dimensional reconstruction of volcanic plumes is a central goal to enhance our understanding on dispersal processes in this paper we use data from the multiangle imaging spectroradiometer misr on board nasa s terra spacecraft combined with a stereo matching retrieval procedure we show the potential of misr in capturing important features of volcanic plumes like column height optical depth type and shape of the finest particles of two highly explosive eruptions occurring on mount etna in 2001 and 2002 this work tests how tephra dispersal models reconstruct the 3 d shape of volcanic clouds we compare misr data with fall3d an eulerian model for the transport and deposition of volcanic ash and aerosols coupled with the weather research and forecasting mesoscale meteorological model agreement between simulations and misr data is good regarding both events although it could be improved by increasing the accuracy of the meteorological data a better constraint on volcanological input parameters like the height of the eruptive column and improving our understanding of processes such as aggregation phenomena and volcanic cloud microphysics

regional horizontal deformation associated with the march 2 1987 edgecumbe earthquake new zealand following the march 2 1987 edgecumbe earthquake magnitude ml 6 3 angle and distance measurements were made from 4 previously observed survey stations to a further 10 stations to determine the regional horizontal deformation associated with the event the surface faulting associated with the earthquake was largely confined to the rangitaiki plain a low lying flood plain on which four of the survey stations are located these stations show large relative displacements which imply local compression of at least 100ppm the stations off the plain show a more consistent pattern of behaviour which may be characterised as the stations to the nw of the plain having moved about 0 7m in direction n20 w with respect to the stations to the se the displacements can be modelled by a 28km long by 2 3km wide rectangular fault striking at n40 e with a 39 dip to the nw and with the top at depth 3km on which 1 4m right lateral strike slip and 5 4m normal dip slip movement occurred though the model fault plane is unrealistically narrow its extrapolation is consistent with the hypocentre location aftershock distribution and focal mechanism observed for the event

deformation in the yakataga seismic gap southern alaska 1980 1986 a 60 by 40 km trilateration network in the yakataga seismic gap was surveyed in 1980 1982 1984 and 1986 with precise electro optical distance measuring equipment to measure strain accumulation the overall deformation is roughly approximated by a 0 24 0 03 strain yr n32 w 2 4 uniaxial contraction that is uniform in time however the spatial distribution of deformation shows some concentration of convergence in the neighborhood of the chugach st elias fault and of right lateral shear across the contact fault a simple dislocation model of the plate interaction in the yakataga gap fits the observed deformation reasonably well but seems to require that the motion of the pacific plate relative to the north american plate be directed more nearly n36 w than n15 w the generally accepted direction of relative motion for this location however the direction of plate motion inferred from the dislocation model depends upon details of the interaction at the plate boundary that may not have been modeled accurately a nearby but smaller trilateration network at icy bay was surveyed in 1982 1984 and 1986 this network spans the southwest corner of the rupture zone of the 1979 st elias earthquake the deformation at icy bay consists of left lateral shear across a northeast trending zone the relation of this deformation to strain accumulation in the yakataga gap postseismic relaxation associated with the 1979 earthquake or rebound from the unloading associated with the rapid recession of the guyot glacier is not understood

strain accumulation at yucca mountain nevada 1983 1998 a 14 station 50 km aperture geodetic array centered on the proposed radioactive waste disposal site at yucca mountain nevada was surveyed in 1983 1984 1993 and 1998 to determine the rate of strain accumulation there the coseismic effects of the 1992 ms 5 4 little skull mountain earthquake which occurred within the array were calculated from a dislocation model and removed from the data the measured principal strain accumulation rates determined over the 1983 1998 interval are e1 2 12 nanostrain yr n87 w 12 and e2 22 12 nanostrain yr n03 e 12 extension reckoned positive and quoted uncertainties are standard deviations the n65 w extension rate is 2 12 nanostrain yr significantly less than the 1991 1997 n65 w rate of 50 9 nanostrain yr reported by wernicke et al 1998 the implied maximum right lateral engineering shear strain accumulation rate is e1 e2 23 10 nanostrain yr a marginally significant rate almost half e1 6 nanostrain yr n90 w e2 6 nanostrain yr n00 e and 12 nanostrain yr of the measured strain rate can be attributed to strain accumulation on the death valley furnace creek 50 km distant and hunter mountain panamint valley 90 km distant faults the residual strain rate after the removal of those fault contributions is not significant at the 95 confidence level

deposition of the 2011 2012 cordon caulle tephra chile 40 s in lake sediments implications for tephrochronology and volcanology tephras preserved in lake sediments are commonly used to synchronize sedimentary archives of climate and environmental change and to correlate them with terrestrial environments they also provide opportunities to reconstruct volcanic explosive activity e g eruption frequency and tephra dispersal although sedimentary processes may affect the record of tephras in lakes lake sediments are generally considered as one of the best archives of tephra stratigraphy the 2011 2012 eruption of cordon caulle volcano chile 40 degrees s offered an ideal opportunity to study the processes affecting tephra deposition in lakes although the prevailing westerlies transported the erupted pyroclastic material away from nearby puyehue lake the tephra was identified within this relatively large lake with a thickness ranging from 1 to 10cm this is in contrast with smaller lakes where tephra thickness was in agreement with ashfall distribution maps geomorphological observations and sedimentological analyses provide evidence that the tephra deposited in puyehue lake entirely consists of material reworked from the upper watershed transported by rivers and distributed by lake currents according to particle size and density our results have important implications for tephrochronology and volcanology they suggest that 1 lakes do not act as passive tephra traps 2 lakes with large watersheds record more eruptions than smaller lakes which only register direct ashfalls affecting conclusions regarding the recurrence of volcanic eruptions and 3 using lakes with large watersheds for isopach mapping systematically leads to an overestimation of erupted tephra volumes smaller lakes with limited drainage basins are generally better suited for volcanological studies

iron deficiency limits phytoplankton growth in antarctic waters enrichment experiments were performed in the ross sea to test the hypothesis that iron deficiency is responsible for the phytoplankton s failure to use up the luxuriant major nutrient supplies found in these and all other offshore antarctic ocean waters nitrate uptake rates in the controls without added trace elements ranged from 0 58 to 1 22 mol kg 1 d 1 the addition of 1 to 5 nmol of unchelated fe per liter resulted in rates that were 2 to 10 times higher 2 54 to 6 00 mol no3 kg 1 d 1 rates in bottles with 2 nmol mn added were identical to those in the controls 0 57 to 1 04 mol no3 kg 1 d 1 total decreases in no3 were balanced by increases in particulate organic n these results suggest that fe deficiency is the primary reason that the present day southern ocean biological pump is shut off in contrast iron was 50 times more abundant during the last glacial maximum greater fe availability may have stimulated the biological pump and contributed to the ice age drawdown of atmospheric c02 these results also imply that large scale southern ocean fe fertilization is feasible at least in terms of the total amounts of fe required i e 100 000 to 500 000 tons yr 1

the determination of displacement fields from geodetic data along a strike slip fault observations of angles or distances between stations of a geodetic network are commonly used to infer information about the movement of the surface of the earth the absence of any observations external to the network leads to an ambiguous displacement field existing techniques for eliminating this ambiguity are all unsatisfactory in some respect the best technique an inner coordinate solution is not appropriate for networks located in a strike slip fault environment the inner coordinate solution zeros the rotation of all stations about their center of mass along a strike slip fault like the san andreas however motion normal to the fault is less likely than motion parallel to the fault the solution presented here an outer coordinate solution finds the rotation of the network that minimizes the components of displacement normal to the fault since motion along a strike slip fault is generally expected to be parallel to the fault the displacements obtained with the outer coordinate solution are more reasonable than those obtained with other techniques examination of a trilateration network near san francisco bay demonstrates the large effect that the choice of adjustment technique can have on the inferred relative motion of the two sides of the fault the inner coordinate solution gave a rate of about 1 mm yr whereas the preferred outer coordinate solution rate was 36 mm yr

the respiratory health hazards of volcanic ash a review for volcanic risk mitigation studies of the respiratory health effects of different types of volcanic ash have been undertaken only in the last 40 years and mostly since the eruption of mt st helens in 1980 this review of all published clinical epidemiological and toxicological studies and other work known to the authors up to and including 2005 highlights the sparseness of studies on acute health effects after eruptions and the complexity of evaluating the long term health risk silicosis non specific pneumoconiosis and chronic obstructive pulmonary disease in populations from prolonged exposure to ash due to persistent eruptive activity the acute and chronic health effects of volcanic ash depend upon particle size particularly the proportion of respirable sized material mineralogical composition including the crystalline silica content and the physico chemical properties of the surfaces of the ash particles all of which vary between volcanoes and even eruptions of the same volcano but adequate information on these key characteristics is not reported for most eruptions the incidence of acute respiratory symptoms e g asthma bronchitis varies greatly after ashfalls from very few if any reported cases to population outbreaks of asthma the studies are inadequate for excluding increases in acute respiratory mortality after eruptions individuals with pre existing lung disease including asthma can be at increased risk of their symptoms being exacerbated after falls of fine ash a comprehensive risk assessment including toxicological studies to determine the long term risk of silicosis from chronic exposure to volcanic ash has been undertaken only in the eruptions of mt st helens 1980 usa and soufriere hills montserrat 1995 onwards in the soufriere hills eruption a long term silicosis hazard has been identified and sufficient exposure and toxicological information obtained to make a probabilistic risk assessment for the development of silicosis in outdoor workers and the general population a more systematic approach to multi disciplinary studies in future eruptions is recommended including establishing an archive of ash samples and a website containing health advice for the public together with scientific and medical study guidelines for volcanologists and health care workers

mid latitude trans pacific reconstructions and comparisons of coupled glacial interglacial climate cycles based on soil stratigraphy of cover beds abstract south westland new zealand and southern chile are two narrow continental corridors effectively confined between the pacific ocean in the west and high mountain ranges in the east which impart significant influence over regional climate vegetation and soils in both these southern mid latitude regions evidence for extensive and repeated glaciations during cold phases of the quaternary is manifested by arrays of successively older glacial drift deposits with corresponding outwash plain remnants in south westland these variably aged glacial landforms are mantled by layered multisequal soils characterised by slow loess accretion and pedogenesis in an extreme leaching and weathering environment these cover bed successions have undergone repeated coupled phases of topdown and upbuilding soil formation that have been related to fluctuating cycles of interglacial warm and glacial cold climate during the quaternary in this study we recognise multisequal soils overlying glacial landforms in southern continental chile but unlike the spodic podzolic soil sequences of south westland these are of dominantly volcanigenic andic provenance and are very similar to multisequal soils of andic provenance that predominate in and adjacent to areas of rhyolitic to andesitic volcanism in north island new zealand here we develop a soil stratigraphic model to explain the observed occurrence of multisequal soils mantling dominantly glacial landforms of southern continental chile based on proxy data from southern chile we propose that persistent vegetation cover and high precipitation on the western side of the andes during colder than present episodes tended to suppress the widespread production of glacially derived loessial materials despite the pervasive occurrence of glacial and glacio fluvial deposits that have frequently inundated large tracts of this landscape during the quaternary given the lack of loess cover beds that have traditionally assisted in the relative dating of glacial episodes prior to the late quaternary surface exposure dating techniques could provide another chronological alternative to address this issue however there have been two main obstacles to successfully apply this dating technique in patagonia first minimum exposure ages may be obtained on moraines older than the last glacial cycle due to erosion although dating outwash plains is more robust second on the wet western side adjacent to the andes persistent vegetation cover during both glacial and post glacial times as well as widespread inundation by volcanic mass flows appear preventive we make a case that soil genesis within this region appears to be dominated by a constant flux of intermittently erupted andean sourced tephra which has continued to upbuild soils at the ground surface separated by intervals where topdown weathering processes are intensified as already demonstrated by new zealand studies multisequal soil successions have a clear implied connection to coupled glacial and interglacial climate cycles of the quaternary on this basis similar sequences in northwest patagonia provide a relatively untapped archive to enable quaternary glacial and environmental changes in this pervasively glaciated volcanic region to be constructed

eruption dynamics of the 22 23 april 2015 calbuco volcano southern chile analyses of tephra fall deposits abstract after 54 years since its last major eruption in 1961 calbuco volcano ensenada southern chile reawakened with few hours of warning on 22 april 2015 at 18 05 local time the main explosive eruption consisted of two eruption pulses lasting 1 5 and 6 h each one on 22 and 23 april producing stratospheric 15 km height eruption columns the erupted materials correspond to porphyritic basaltic andesite 55 wt of sio2 the tephra fall affected mainly the area northeast of the volcano and the finest ash was deposited over southern chile and patagonia argentina we studied the tephra fall deposits of both pulses in terms of stratigraphy distribution volume emplacement dynamics and eruption source parameters here we show field observations that have been made 5 470 km downwind and distinguish five layers layers a b b1 c and d representing different stages of the eruption evolution eruption onset layer a pulse 1 followed by the first paroxysmal event layer b pulse 1 in some places interbedded by layer b1 tentatively representing the sedimentation of a secondary plume during the end of pulse 1 we recognized a second paroxysm layer c pulse 2 followed by the waning of the eruption layer d pulse 2 the total calculated bulk tephra fall deposit volume is 0 27 0 007 km3 0 11 0 13 km3 dense rock equivalent 38 of which was erupted during the first phase and 62 during the second pulse this eruption was a magnitude 4 45 event vei 4 eruption of subplinian type

the spatial extent of tephra deposition and environmental impacts from the 1912 novarupta eruption the eruption of novarupta within the katmai volcanic cluster south west alaska in june 1912 was the most voluminous eruption of the twentieth century but the distal distribution of tephra deposition is inadequately quantified we present new syntheses of published tephrostratigraphic studies and a large quantity of previously un investigated historical records for the first time we apply a geostatistical technique indicator kriging to integrate and interpolate such data our results show evidence for tephra deposition across much of alaska yukon the northern pacific western british columbia and northwestern washington the most distal tephra deposition was observed around 2 500 km downwind from the volcano associated with tephra deposition are many accounts of acid deposition and consequent impacts on vegetation and human health kriging offers several advantages as a means to integrate and present such data future eruptions of a scale similar to the 1912 event have the potential to cause widespread disruption historical records of tephra deposition extend far beyond the limit of deposition constrained by tephrostratigraphic records the distal portion of tephra fallout deposits is rarely adequately mapped by tephrostratigraphy alone contemporaneous reports of fallout can provide important constraints on the extent of impacts following large explosive eruptions

a past millennium maximum in postglacial activity from volcan chaiten southern chile volcan chaiten southern chile 43 s initiated an historically unprecedented eruption in a d 2008 surprising the local inhabitants chilean and argentine authorities and the geologic community available data at the time indicated an absence of explosive eruptions from this rhyolitic volcano since a large magnitude eruptive event dated at ca 10 500 yr b p we present lake sediment data from lago teo a small closed basin lake located in the immediate vicinity of both chaiten township and the volcano that spans the past 10 000 yr and contains 26 pyroclastic fallout deposits glass shard electron microprobe analyses revealed ten rhyolitic tephras indistinguishable in composition from the 2008 volcan chaiten eruption and ten others potentially derived from the michinmahuida volcanic complex among the rhyolites we detected three closely spaced tephras deposited between ca 9460 and 9680 yr b p followed by two thick tephras dated at ca 7700 and ca 5080 yr b p three other closely spaced tephras occur between ca 600 and 850 yr b p the most recent prehistoric event at ca 420 yr b p and a 3 cm thick tephra deposited during the 2008 event we calculate a median recurrence of 310 yr between eruptive events from all sources over the past 10 000 yr and 200 yr between volcan chaiten events over the past millennium our results not only challenge the notion of an 10 500 yr long quiescence for volcan chaiten activity but also suggest that the 2008 eruption was an overdue phenomenon in the context of its postglacial eruptive history illustrating the advantage and absolute necessity of utilizing lake sediment archives for developing continuous well dated time series inventories of explosive volcanic events

baroclinic developments in jet entrances and exits i linear normal modes this study examines the effect of the ageostrophic circulations associated with jet entrance and exit regions on the structure and growth rates of baroclinic normal modes a linearized gcm is used to find the most unstable normal mode disturbances for a zonally symmetric basic state consisting of a zonal jet and meridional circulation normal mode growth rates are reduced by up to 20 for realistic strengths of meridional overturning and normal mode structures are significantly affected for example the normal mode poleward tilt with height varies affecting the conversion of basic state available energy a mechanism for the change in poleward tilt is proposed ageostrophic meridional circulations may play a significant role in determining the magnitude and length of mid latitude storm tracks

extraordinary sediment delivery and rapid geomorphic response following the 2008 2009 eruption of chaiten volcano chile u s geological survey volcano science center sernageomin s programa de riesgos volcanicos conicyt fondecyt grants 1110609 1141064 11130671 conicyt fondap 15090013 vamos research centre

strain effects near palmdale associated with the san fernando earthquake 1971 abstract field data from the southeast palmdale network in california are the basis for a practical strain analysis with triangulation data available for the year 1938 and 1958 and trilateration data at 1 year intervals from 1971 to date a uniform although small strain accumulation over the last forty years appears to be evident from this data set a possible soceismic strain jump of 2 strain in both shearing strain components related to the 1971 san fernando earthquake may be postulated in the observations however it was already pointed out previously that this coseismic strain jump needs further qualifications due to the corrupting influence of uncertainties in the network height differences this particular situation arises because triangular data have to be compared with trilateration data for the computation of the coseismic strain changes to clarify this situation the height differences of the southeast palmdale network were determined by trigonometric levelling in spring 1981 the effect of this new height data on the interpretation of the coseismic strain change is discussed in detail a comparison of this result with strain model calculations is presented

measurements of the complex refractive index of volcanic ash at 450 546 7 and 650 nm the detection and quantification of volcanic ash is extremely important to the aviation industry civil defense organizations and those in peril from volcanic ashfall to exploit the remote sensing techniques that are used to monitor a volcanic cloud and return information on its properties the effective complex refractive index of the volcanic ash is required this paper presents the complex refractive index determined in the laboratory at 450 0 nm 546 7 nm and 650 0 nm for volcanic ash samples from eruptions of aso japan grimsvotn iceland chaiten chile etna italy eyjafjallajokull iceland tongariro new zealand askja iceland nisyros greece okmok alaska augustine alaska and spurr alaska the becke line method was used to measure the real part of the refractive index with an accuracy of 0 01 the values measured differed between eruptions and were in the range 1 51 1 63 at 450 0 nm 1 50 1 61 at 546 7 nm and 1 50 1 59 at 650 0 nm a novel method is introduced to derive the imaginary part of the refractive index from the attenuation of light by ash the method has a precision in the range 10 3 10 4 the values for the ash imaginary refractive index ranged 0 22 1 70 10 3 at 450 0 nm 0 16 1 93 10 3 at 546 7 nm and 0 15 2 08 10 3 at 650 0 nm the accuracy of becke and attenuation methods was assessed by measuring the complex refractive index of hoya neutral density glass and found to have an accuracy of 0 01 and 2 10 5 for the real and imaginary parts of the refractive index respectively

characterization of the recent ash emissions at popocatepetl volcano mexico abstract nine representative ash emissions from 1994 1997 were studied to characterize the recent activity and the eruptive process at popocatepetl a series of tephra eruptions began on december 21 1994 and intermittent activity continues to present the first eruptions were phreatomagmatic but in mid march 1996 they turned magmatic cumulative volumes 529 1810 10 3 m 3 were determined for the first eruptions however when eruptions grew larger more widely spaced and magmatic the volumes were then calculated individually 22 1107 10 3 m 3 both using the simpson rule and based on 244 sampling sites this numerical integration method is more precise than other methods especially since sub mm isopachs are neglected in most cases dominant winds carried ash mainly to the east january through april 1995 and april 1996 except for the summer months when ash fell on mexico city to the northwest october 28 1996 and june 30 1997 in march 1996 changing wind direction produced ash fall to the southwest as well during the first year volume calculations indicated that emission rate was higher at the beginning of the eruptions and then declined and stopped activity resumed the following year with a similar pattern until larger amounts of magma ascended detailed studies of the ashfall provided constraints on the dynamics of the volcanic plumbing system tephra emission was related with clearing december 1994 to march 1995 and clogging of the vent may 1995 to february 1996 until a larger new ascending batch was able to clear its way to the surface march 1996 after april 1996 dome formation and explosive destruction were related to individual small ascending magma batches tephra from december 1994 to early march 1996 was made up mostly of andesitic lithic clasts and plagioclase and pyroxene crystals with minor amounts of accidental and accessory minerals in march 1996 prior to dome formation glass was also detected afterwards ash components were mostly dome lithics and scoria with minor amounts of plagioclase pyroxene and olivine crystals from the incoming magma batches

identifying potentially active volcanoes in the andes radiometric evidence for late pleistocene early holocene eruptions at volcan imbabura ecuador abstract recent eruptions from volcanoes with no previously known historical activity in chile and indonesia have raised the importance of the early identification of potentially active centers for the purpose of hazard assessment here we bring radiometric evidence 14 c 39ar 40ar of previously unrecognized but significant magmatic activity at partly eroded imbabura volcano ecuador in late pleistocene to early holocene times on whose perimeter live more than 300 000 persons following an effusive stage from 50 to 30 ka with the emplacement of andesitic lava flows on different flanks of its edifice the activity became explosive with the generation of andesitic block and ash flows on its eastern side beginning at 35 ka cal bp subsequently a flank collapse associated with a volcanic blast occurred on the volcano s sw flank at 30 ka cal bp the resulting debris avalanche and blast breccias cover an area now heavily populated around san pablo lake and its source was later concealed by successive dome building episodes at huarmi which produced 2 8 km3 of silicic andesite renewed dome activity at the edifice s taita summit occurred at 17 ka cal bp and continued intermittently into early holocene times as indicated by pyroclastic flow deposits overlying a palaeosoil dated at 9 ka cal bp in summary this study reveals an eruptive behavior characterized by a low recurrence rate but with quite large eruptions a pattern which is also observed at other silicic volcanoes of ecuador s western cordillera it is now imperative to reconsider the origin and source of the many tephra layers catalogued in holocene lacustrine sediments in the imbabura area tephra and lava volume estimates for imbabura volcano converted to dense rock equivalent values yield a minimum magmatic output rate of 0 13 km3 ka in the past 35 000 years which argues for sustained magma production for this volcano in recent geological times the imbabura example thus raises the question of how to improve population preparedness for volcanoes with infrequent eruptions and how to guide authorities decisions concerning the development of urban areas and infrastructures near presently inactive but potentially highly dangerous volcanoes

sedimentological analysis of the tephra from the 12 15 august 1991 eruption of hudson volcano the tephra fallout from the 12 15 august 1991 explosive eruption of hudson volcano cordillera de los andes 45 54 s 72 58 w chile was dispersed on a narrow elongated ese sector of patagonia covering an area on land of more than 100 000 km2 the elongated shape of the deposit together with the relatively coarse mean and median values of the particles at a considerable distance from the vent were the result of strong winds blowing to the southeast during the eruption the thickness of the fall deposit decreases up to 250 km ese from hudson volcano where it begins to thicken again secondary maxima are well developed at approximately 500 km from the vent secondary maxima together with grainsize bimodality in individual layers and in the bulk deposit suggest that particle aggregation played an important role in tephra sedimentation the fallout deposit is well stratified with alternating fine grained and coarsegrained layers which is probably a result of strong eruptive pulses followed by relatively calm periods and or changes in the eruptive style from plinian to phreatoplinian the tephra is mostly composed of juvenile material the coarse mode mostly pumice shifts to finer sizes with distance from the volcano the fine mode mostly glass shards is always about 5 6 phi glass shards and pumice are mostly light gray to colorless however considerable amounts of dark poorly vesiculated blocky shards suggest a hydromagmatic component in the eruption a land based tephra volume of 4 35 km3 was estimated and a total volume of 7 6 km3 arose from an extrapolation which took into account the probable volume sedimented in the sea bulk density ranges from 0 9 to 1 10 gr cm3 beyond 110 km from the vent rather uniform density values measured in crushed samples 2 45 2 50 gr cm3 at all distances from the vent reveal a relatively homogeneous composition mean and median sizes decrease rapidly up to 270 km from the vent beyond that point they are more or less constant whereas the maximum size 1 phi shows a steady decrease up to 550 km a concomitant improvement in sorting is observed this is attributed to sorting due to wind transport combined with particle aggregation at different times and distances from the vent the hudson tephra fallout shares some strikingly similar features with the mount st helens 18 may 1980 and quizapu 1932 eruptions

soluble iron inputs to the southern ocean through recent andesitic to rhyolitic volcanic ash eruptions from the patagonian andes patagonia due to its geographic position and the dominance of westerly winds is a key area that contributes to the supply of nutrients to the southern ocean both through mineral dust and through the periodic deposits of volcanic ash here we evaluate the characteristics of fe dissolved into soluble and colloidal species from volcanic ash for three recent southern andes volcanic eruptions having contrasting features and chemical compositions contact between cloud waters wet deposition and end members of andesitic hudson volcano and rhyolitic chaiten volcano materials was simulated results indicate higher fe release and faster liberation rates in the andesitic material fe release during particle seawater interaction dry deposition has higher rates in rhyolitic type ashes rhyolitic ashes under acidic conditions release fe in higher amounts and at a slower rate while in those samples containing mostly glass shards fe release was lower and faster the 2011 puyehue eruption was observed by a dust monitoring station puyehue type eruptions can contribute soluble fe to the ocean via dry or wet deposition nearly reaching the limit required for phytoplankton growth in contrast the input of fe after processing by an acidic eruption plume could raise the amount of dissolved fe in surface ocean waters several times above the threshold required to initiate phytoplankton blooms a single eruption like the puyehue one represents more than half of the yearly fe flux contributed by dust

strain accumulation in owens valley california 1974 to 1988 strain accumulation observed over the 1974 to 1988 interval in a 25 by 100 km aperture trilateration network spanning owens valley is adequately described by a strain rate that is uniform in space and time the tensor strain rate components referred to a coordinate system with the 2 axis directed n18 w parallel to the trend of the valley and the 1 axis n72 e are 11 0 042 0 014 strain yr 12 0 058 0 007 strain yr and 22 0 002 0 014 strain yr quoted uncertainties are standard deviations and extension is reckoned positive across the 25 km breadth of the network this amounts to 1 0 0 3 mm yr extension normal to the axis of the valley 2 9 0 4 mm yr right lateral shear across the axis and no extension parallel to the axis if the measured strain accumulation is attributed to slip on the deeper section of the owens valley fault with the uppermost 10 km of the fault locked the observed right lateral deformation would imply about 7 mm yr right lateral slip on the buried fault much greater than the geologic estimate of 2 0 5 mm yr right lateral secular slip beanland and clark 1994 nor is the observed uplift profile across the valley consistent with continuing normal slip on just the deep segment of the owens valley fault normal slip at depth on the sierra frontal fault also seems to be required the observed deformation across owens valley apparently implies processes more complicated than those represented by the conventional model of strain accumulation along a throughgoing fault

geochemical relationships in cretaceous bentonites as inferred from linear discriminant analysis abstract bentonites serve as an important stratigraphic tool for facies correlation due to their instantaneous deposition and preservation across multiple depositional environments correlating one bed to another can be a complex issue limited by the 3 dimensional availability of outcrops and core this process is reliant on the assumption that the geochemical signatures of ash beds do not vary enough to statistically alter the correlation coefficients that tie one ash fall to another this assumption may be faulty however and the problem compounds as bentonite bed thickness increases because the chemical composition varies through an eruption due to stratification of the magma chamber and through physical transport linear discriminant analysis lda can significantly aid with this issue allowing for the utilization of a multivariate dataset to statistically separate chemically similar groups here we present a statistical approach to assessing the primary discriminatory variables on a suite of 87 cretaceous bentonites deposited in the bighorn basin wyoming usa that span five geologic stages and seven formations from the cloverly formation 110 ma to the meeteetse formation 70 ma and includes nine named ash beds using lda bentonites were sorted into groups based on geologic stage formation and unique beds using key elemental concentrations and radiogenic isotopes e g 87sr 86sr tio2 sc na and th additionally distinct similarities in the discrimination pattern between formations reveal two periods of magmatism the development of the idaho batholith and the migration and development of the boulder batholith and surrounding related plutons with well preserved temporally constrained ash lda can correlate ancient tephra deposits while also shedding light on the cyclical nature of geochemical trends in a migrating subduction zone

simulations of tephra dispersal from the 1991 explosive eruptions of hudson volcano chile abstract the 1991 explosive eruptions of hudson volcano in southern chile produced 2 7 km 3 dense rock equivalent of basalt and trachyandesite tephra during the period august 8 15 the initial basaltic phase phase i august 8 9 produced a maximum column height of 12 km above sea level asl and tephra fallout was directed to the north and northeast by the prevailing winds the paroxysmal trachyandesitic phase phase ii august 12 15 involved at least three separate events with a maximum 18 km high asl eruption column inferred from satellite temperature data during the initial 24 h of this phase the plume was advected almost directly south before swinging towards the east as the wind changed direction the plume was ultimately directed to the southeast and stayed relatively fixed at this bearing for the remainder of the eruption these temporal variations in the main dispersal direction during the earlier stages of the phase ii eruption produced a much wider overall deposit than would be expected from a plume with a relatively fixed transport direction e g latter stages of phase ii the lagrangian ash tracking model puff was utilized to simulate the 1991 explosive eruptions and was able to successfully reproduce the aerial distribution and temporal evolution of the plumes the optimal agreement between the observed and simulated plumes occurs when the highest concentration of ash particles coincides with the tropopause a height that is typically lower than the maximum observed column heights for the 1991 eruptions gravitational settling of the laterally spreading umbrella region e g pinatubo 1991 may result in the concentration of ash at this level this may account for differences in column height estimates between ground or satellite based and lithic based models the plume associated with the paroxysmal phase august 12 15 1991 produced a multilayered deposit composed of alternating layers of fine ash and pumice lapilli the highly stratified nature of the fall deposit is likely the result of multiple eruptive events coupled with a time varying wind field a strongly changing wind direction that occurred during the earlier stages of the paroxysmal eruption could have produced variations in the dominant grain size being deposited between fine ash and pumice lapilli during individual eruptive sequences

sedimentation from turbulent jets and plumes theoretical models are developed for the sedimentation from the margins of a particle laden axisymmetric turbulent buoyant plume in a still environment and for an axisymmetric turbulent momentum jet the models assume that the mass of each individual size fraction of sediment carried in a parcel of fluid decreases exponentially with time for relatively coarse particles the fallout models predict that the sediment deposition beyond a distance r on the ground expressed in log units should decay linearly with distance away from the vent for the momentum jet and should decrease with r1 3 for the buoyant plume the exponential decay constant j is proportional to the terminal fall velocity vt of the particles in both cases and inversely proportional to the square root of the initial momentum flux m0 for the jet fallout jj vtmo 1 2 and to the third power of the initial buoyancy flux fo for the plume fallout jp vtfo 1 3 smaller particles are affected by reentrainment caused by the turbulent eddies sweeping ambient fluid back into the plume or jet and thus reincorporating some particles that were released from the flow at greater heights this is taken into account by introducing a reentrainment coefficient into the theoretical models with the assumption that the coefficient has a constant value for a plume of given strength in new experiments fallout occurs from the margins of particle laden fresh water buoyant jets and plumes in a tank of salty water and sedimentation is measured on the tank floor two experiments were weakly affected by reentrainment and show excellent agreement with the simple theory for smaller particles and increasingly buoyant plumes and strong jets particle reentrainment is important the experimental data are fitted by the new reentrainment theory confirming that values of the reentrainment coefficient are approximately constant for a given flow a settling number is defined as the ratio of the characteristic velocity of the jet or plume to the particle settling velocity for 1 reentrainment seems to reach an equilibrium state for which the reentrainment coefficient is a constant of value 0 1 for jets and 0 4 for plumes irrespective of flow strength or particle size the plume experiments indicate that the value of the reentrainment coefficient is strongly dependent on plume strength and particle size for slightly less than 1 the general principles of sedimentation from turbulent plumes and jets are applied to the fallout of pumice from volcanic eruption columns and of metalliferous particles from black smokers on the ocean floor for volcanic eruptions the results provide an explanation for the near vent overthickening of tephra fall deposits and imply that lithic and pumice fragments from small lapilli up to at least 1 m diameter blocks are efficiently reentrained into eruption columns the size of particles reentrained in hydrothermal plumes is predicted to vary from less than 100 m in weakly buoyant plumes up to over 1000 m in megaplumes

late quaternary tephrostratigraphy of southern chile and argentina abstract the southern and austral volcanic zones of the andes comprise 74 volcanic centres with known post glacial activity at least 21 of these have had one or more large explosive eruptions in the late quaternary dispersing tephra over vast areas these tephra layers therefore have great potential as tephrochronological marker horizons in palaeoenvironmental studies in southern chile and argentina a region that is particularly useful to study climate dynamics of the southern hemisphere however to date tephrochronology has rarely been fully utilised in this region as a correlation and dating tool here we review the existing post glacial tephrostratigraphic record of the southern and austral volcanic zones and compile a database of known occurrences of tephra from these volcanoes in ice and lacustrine marine peat and cave sediment records we address the inconsistencies in and revisions of the tephrostratigraphies presented in prior literature and discuss the challenges in correlating tephras and the limitations of the tephrostratigraphic record in this area this study highlights the many gaps that still exist in our knowledge of the eruptive histories of these volcanoes but also reveals the largely under utilised potential of tephra as a correlation tool in this region this is exemplified by the severe lack of adequate geochemical analysis of tephra layers preserved in many lacustrine and peat sediment sections which are particularly important tephrostratigraphic records in southern chile and argentina due to the paucity of surface preservation

the 1992 m 7 cape mendocino california earthquake coseismic deformation at the south end of the cascadia megathrust we invert geodetic measurements of coseismic surface displacements to determine a dislocation model for the april 25 1992 m 7 cape mendocino california earthquake the orientation of the model slip vector which nearly parallels north america juan de fuca relative plate convergence and the location and orientation of the model fault relative to the offshore cascadia megathrust suggest that the 1992 cape mendocino earthquake is the first well recorded event to relieve strain associated with the cascadia subduction zone we use data from three geodetic techniques 1 the horizontal and vertical displacements of 13 monuments surveyed with the global positioning system corrected for observed horizontal interseismic strain accumulation 2 88 section elevation differences between leveling monuments and 3 the uplift of 12 coastal sites observed from the die off of intertidal marine organisms maximum observed displacements are 0 4 m of horizontal movement and 1 5 m of uplift along the coast we use monte carlo techniques to estimate an optimal uniform slip rectangular fault geometry and its uncertainties the optimal model using all the data resolves 4 9 m of slip on a 14 by 15 km fault that dips 28 se the fault extends from 1 5 to 8 7 km in depth and the main shock hypocenter is close to the downdip projection of the fault the shallowly dipping fault plane is consistent with the observed aftershock locations and the estimated geodetic moment is 3 1 1019 n m 70 of the seismic moment other models that exclude leveling data collected in 1935 and 1942 are more consistent with seismological estimates of the fault geometry if the earthquake is characteristic for this segment the estimated horizontal slip vector compared with plate convergence rates suggests a recurrence interval of 140 years with a 95 confidence range of 100 670 years the coseismic uplift occurred in a region that also has high quaternary uplift rates determined from marine terrace studies if repeated ruptures of this southernmost segment of the cascadia megathrust are responsible for the quaternary uplift a comparison of the coseismic uplift with coastal uplift rates suggests a recurrence interval of 200 400 years thus comparing horizontal and vertical coseismic to long term deformation suggests a recurrence interval of about 100 300 years for m 7 events at the south end of the cascadia megathrust

andesitic plinian eruptions at mt ruapehu quantifying the uppermost limits of eruptive parameters new tephro stratigraphic studies of the tongariro volcanic centre tgvc on the north island new zealand allowed reconstruction of some of the largest andesitic explosive eruptions of mt ruapehu large eruptions were common in the late pleistocene before a transition to strombolian vulcanian and phreatomagmatic eruptive styles that have predominated over the past 10 000 years considering this is the most active volcano in north island of new zealand and the uppermost hazard limits are unknown we identified and mapped the pyroclastic deposits corresponding to the five largest eruptions since 27 ka the selected eruptive units are also characterised by distinctive lithofacies associations correlated to different behaviours of the eruptive column in addition we clarify the source of the 10 9 7 ka pahoka tephra identified by previous authors as the product of one of the largest eruptions of the tgvc the most common explosive eruptions taking place between 13 6 and 10 ka cal years bp involved strongly oscillating partially collapsing eruptive columns up to 37 km high at mass discharge rates up to 6 108 kg s and magnitudes of 4 9 ejecting minimum estimated volumes of 0 6 km3 our results indicate that this volcano as well as the neighbouring andesitic mt tongariro can generate plinian eruptions similar in magnitude to the chaiten 2008 and askja 1875 events such eruptions would mainly produce pyroclastic fallout covering a minimum area of 1 700 km2 ese of the volcano where important touristic agricultural and military activities are based as for the 1995 1996 eruption our field data indicate that complex wind patterns were critical in controlling the dispersion of the eruptive clouds developing sheared commonly bilobate plumes

first seismic record for intra arc strike slip tectonics along the liquine ofqui fault zone at the obliquely convergent plate margin of the southern andes a temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike slip liquine ofqui fault zone lofz in southern chile seventy five shallow crustal events with magnitudes up to m tief w 3 8 and depths shallower than 25 km were observed in an 11 month period mainly occurring in different clusters those clusters are spatially related to the lofz to the volcanoes chaiten michinmahuida and corcovado and to active faulting on secondary faults further activity along the lofz is indicated by individual events located in direct vicinity of the surface expression of the lofz focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike slip mechanisms indicating a ne sw direction of the p axis for the lofz at this latitude the seismic activity reveals the present day activity of the fault zone the recent m tief w 6 2 event near puerto aysen southern chile at 45 4 s on april 21 2007 shows that the lofz is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region

bromine as indicator of source of lacustrine sedimentary organic matter in paleolimnological studies bromine br to organic matter om concentration ratio is studied in lake sediment sequences to provide information on environmental changes modifying om production the sequences studied were extracted from shallow lakes morenito el trebol escondido and portezuelo and deep lakes futalaufquen moreno and traful north patagonia andean range lake morenito a former lake moreno bay until its closure in ad 1960 showed a decrease in br om ratios from 1 38 to 0 74 after lake closure associated with an increase of primary autochthonous productivity attributable to the development of submerged and emerging macrophytes sedimentary sequences from lakes escondido portezuelo and el trebol with large participation of macrophytes in primary productivity and from lakes moreno futalaufquen and traful with little development of littoral macrophytes showed br om ratios consistent with the lake morenito pattern consistently the morphometric parameters mean depth and shoreline development correlate with br om ratios therefore br om ratios can be associated with the composition of primary autochthonous productivity with values of about 0 7 associated to significant macrophyte contributions and higher values associated with more pelagic contributions accordingly br om variations along a sedimentary sequence can be associated with modifications on the composition of the primary autochthonous productivity of the water body providing information on environmental changes

discussion on displacement analysis detection of crustal deformation in using geodetic networks to detect crustal motion there is always a question about what to use as a reference if the stations in a subset of the network can be shown to remain fixed relative to one another then this subset can be used as a reference for determining the motion of the remaining stations in the network we derive such a solution for the displacement of a geodetic network referred to as a stationary station solution the advantage of this technique over other solutions to the same problem is that it neither depends on a single station nor makes assumptions about the movement of all the stations of the network application of the technique to a geodetic network near hollister california indicates that stations between the faults are stationary although for the block between the calaveras and san andreas faults the stations are only marginally stationary relative to one another the technique is then extended to give the total block motion between the faults

kinematics and deformation of central and southwestern greece from historical triangulation data and implications for the active tectonics of the aegean abstract changes in the coordinates of 38 stations 32 of which were common to three historical triangulation surveys 1889 1905 1927 1930 and 1950 1970 in central greece were computed based on conventional adjustment techniques and the assumption of a nearly fixed baseline length some of the calculated coordinate changes are significant against the a posteriori network adjustment errors and are likely to indicate tectonic motions consistent with those deduced from geological and geophysical data and other geodetic studies comparison of the first survey network with gps data more explicitly the historical geodetic data confirm the rotational character of the deformation in the area but they show that the strain pattern is likely to have changed after 1930 between 1890 and 1930 strain was changing smoothly as if no strain discontinuities existed while the peloponnesus was under contraction from the northeast probably reflecting accommodation of strain from the arc significant left lateral shear in the gulf of corinth and n s extension in the whole of the study area were observed only after 1930 estimates of strain are consistent with those deduced from comparison of historical triangulation and gps data corrected for the scale error that exists in the terrestrial geodetic data in greece and estimates of strain from seismological data the change in the kinematic pattern after 1930 seems to be confirmed by changes in the shear strain computed directly from changes in observed angles between stations and from changes in the seismicity rates such changes although not unusual in the geological record are not easy to explain but may reflect elastic rebound effects in area with an extremely complicated tectonic fabric or hysteresis in the accommodation of e w compression from the arc by n s stretching

fallout and distribution of volcanic ash over argentina following the may 2008 explosive eruption of chaiten chile 1 the major explosive eruption of chaiten volcano chile in may 2008 provided a rare opportunity to track the long range dispersal and deposition of fine volcanic ash the eruption followed 10 000 years of quiescence was the largest explosive eruption globally since hudson chile in 1991 and was the first explosive rhyolitic eruption since novarupta alaska in 1912 field examination of distal ashfall indicates that 1 6 1011 kg of ash dense rock equivalent volume of 0 07 km3 was deposited over 2 105 km2 of argentina during the first week of eruption the minimum eruption magnitude estimated from the mass of the tephra deposit is 4 2 several discrete ashfall units are identifiable from their distribution and grain size characteristics with more energetic phases showing a bimodal size distribution and evidence of cloud aggregation processes ash chemistry was uniform throughout the early stages of eruption and is consistent with magma storage prior to eruption at depths of 3 6 km deposition of ash over a continental region allowed the tracking of eruption development and demonstrates the potential complexity of tephra dispersal from a single eruption which in this case comprised several phases over a week long period of intense activity

a uniform isotopic and chemical signature of dust exported from patagonia rock sources and occurrence in southern environments patagonia is considered to be the most important source of dust from south america that is deposited in surrounding areas and we present here a systematic sr and nd isotopic study of sediment currently being exported eolian and suspended riverine sediments from patagonia have a homogeneous chemical and isotopic composition that results from the mixing of by products from explosive andean volcanism derived from the extensive jurassic silicic province of chon aike and pyroclastic materials from the basic to intermediate southern andean quaternary arc which are easily denudated and dispersed the main andean uplift and the glaciations that began in the late tertiary account for the extensive distribution of these sediments in the extra andean region the present geochemical signature of patagonian sediments was produced during the pleistocene along with the onset of the southern andean explosive arc volcanism previously published compositions of sediments from other southern south american source regions assumed to be representative of patagonia are distinct from our data considering the alleged importance of patagonia as a dust source for different depositional environments in southern latitudes it is surprising to verify that the chemical and isotopic signatures of patagonian sourced sediments are different from those of sediments from the southern ocean the pampean region or the antarctic ice sediments from these areas have a crustal like geochemical signature reflecting a mixed origin with sediment from other southern south american sources whereas patagonian sediments likely represent the basic to intermediate end member composition

the immediate environmental effects of tephra emission the earth s history is punctuated by large explosive eruptions that eject large quantities of magma and silicate rock fragments into the atmosphere these tephra particles can sometimes be dispersed across millions of square kilometres or even entire continents the interaction of tephra with or in receiving environments may induce an array of physical chemical and biological effects the consequences for affected systems and any dependent communities may be chronic and localised in the event of frequent small eruptions while larger and rarer events may have acute regional scale impacts it is therefore necessary to document the range of possible impacts that tephra may induce in receiving environments and any resulting effects in interconnected systems we collate results from many studies to offer a detailed multidisciplinary and interdisciplinary review of the immediate post eruptive effects of tephra emission into the atmosphere onto vegetation soil or ice snow surfaces and in aquatic systems we further consider the repercussions that may be induced in the weeks to years afterwards in the atmosphere tephra can influence cloud properties and air chemistry by acting as ice nuclei in or by offering sites for heterogeneous reactions respectively tephra on vegetation causes physical damage and sustained coverage may elicit longer term physiological responses tephra deposits on soils may alter their capacity to exchange gas water and heat with the atmosphere or may have a specific chemical effect such as nutrient input or acidification on sensitive soils tephra deposition onto snow or ice may affect ablation rates rivers and lakes may experience turbidity increases and changes in their morphology as a result of fallout and prolonged months or years erosion from the tephra covered catchment in the first weeks after deposition tephra leaching may affect river chemistry the abundance and speciation of phytoplankton populations in lakes may be altered by tephra induced changes in water chemistry or sediment water nutrient cycling in the oceans tephra deposition may fertilise fe limited waters with potential impacts on the global carbon cycle embracing the full complexity of environmental effects caused by tephra fall demands a renewed investigative effort drawing on interdisciplinary field and laboratory studies combined with consideration of the interconnectivity of induced impacts within and between different receiving environments

multivariate hypothesis tests for detecting recent crustal movements abstract for detecting recent crustal movements repeated geodetic measurements are often observed in a net of control points these data are evaluated in a multivariate statistical analysis in order to separate the set of control points into two disjunctive sets the set of fixed points and the set of variable points the coordinates of the control points are introduced as unknown parameters for the analysis of the observations at different time epochs however the geodetic measurements often do not contain any information about the translation the rotation or the scale of the coordinate system so that restrictions have to be introduced to obtain estimable quantities as shown these restrictions must be formulated for all fixed points in order to obtain a location of the control net which is optimal with respect to the detection of movements but the fixed points have to be found first by means of univariate and multivariate hypothesis tests this problem is solved by a successive estimation and test procedure which can be automated so that in a single analysis of the data the variable points are separated from the fixed points as shown by an example the univariate and multivariate test procedures enable the detection of horizontal movements in the order of magnitude of the lengths of the axes of the 95 confidence ellipses

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

principal component analysis of geodetically measured deformation in long valley caldera eastern california 1983 1987 typical geodetic measurements of deformation consist of repeated surveys of a particular geodetic network such deformation data can be interpreted as a consequence of one or more self coherent sources by means of principal component analysis a self coherent source is defined as any source that produces deformation that is time and space separable principal component analysis then gives the time and space factors that characterize the deformation attributed to each self coherent source geodetic measurements of deformation at long valley caldera provide two examples of the application of principal component analysis a 40 line trilateration network surrounding the caldera was surveyed in midsummer 1983 1984 1985 1986 and 1987 principal component analysis indicates that the observed deformation can be represented by a single coherent source the time dependence for that source displays a rapid rate of deformation in 1983 1984 followed by less rapid but uniform rate in the 1984 1987 interval the spatial factor seems consistent with expansion of a magma chamber beneath the caldera plus some shallow right lateral slip on a vertical fault in the south moat of the caldera an independent principal component analysis of the 1982 1983 1984 1985 1986 and 1987 leveling across the caldera requires two self coherent sources to explain the deformation the deformation pattern produced by the larger of these two sources appears to be roughly consistent with that found from the trilateration data the deformation due to the second source is a nearly uniform tilt in the uplift profile presumably that tilt is simply an artifact of systematic error in the leveling

tephra stratigraphy and eruptive volume of the may 2008 chaiten eruption chile on may 1st 2008 mount chaiten southern chile interrupted a long period of quiescence generating a sequence of explosive eruptions and causing the evacuation of chaiten town located a few kilometers south of the volcano the activity was characterized by several explosive events each associated with plumes which reached up to about 19 km above sea level the products were dispersed across a wide area with the finest ash reaching the atlantic coast of argentina our field observations in the proximal medial area 3 25 km from the vent indicate that the may 2008 tephra deposit consists of numerous layers most of which can be correlated with individual eruptive events these layers vary from extremely fine grained ash to layers of lapilli and blocks composed of both juvenile and lithic material here we describe the stratigraphy and physical characteristics of the may 2008 deposits and propose a reconstruction of the timing of the may 2008 events the deposits are mainly associated with the three main explosive phases which occurred on 1st 2nd may 3rd 5th may and 6th may with an estimated bulk tephra volume of 0 5 1 0 km3 integration of both exponential and power law fitting for the 6th may event represented by a layer composed mainly of lithic lapilli and blocks 2 mm an isopleth map was compiled from which a 19 km plume height was determined which is in good agreement with satellite observations

compositional variations and magma mixing in the 1991 eruptions of hudson volcano chile the august 1991 eruptions of hudson volcano produced 2 7 km3 dense rock equivalent dre of basaltic to trachyandesitic pyroclastic deposits making it one of the largest historical eruptions in south america phase 1 of the eruption p1 april 8 involved both lava flows and a phreatomagmatic eruption from a fissure located in the nw corner of the caldera the paroxysmal phase p2 began several days later april 12 with a plinian style eruption from a different vent 4 km to the south southeast tephra from the 1991 eruption ranges in composition from basalt phase 1 to trachyandesite phase 2 with a distinct gap between the two erupted phases from 54 60 wt sio2 a trend of decreasing sio2 is evident from the earliest part of the phase 2 eruption unit a 63 65 wt sio2 to the end unit d 60 63 wt sio2 melt inclusion data and textures suggest that mixing occurred in magmas from both eruptive phases the basaltic and trachyandesitic magmas can be genetically related through both magma mixing and fractional crystallization processes a combination of observed phase assemblages inferred water content crystallinity and geothermometry estimates suggest pre eruptive storage of the phase 2 trachyandesite at pressures between 50 100 megapascal mpa at 972 26 c under water saturated conditions log fo2 10 33 0 2 it is proposed that rising p1 basaltic magma intersected the lower part of the p2 magma storage region between 2 and 3 km depth subsequent mixing between the two magmas preferentially hybridized the lower part of the chamber basaltic magma continued advancing towards the surface as a dyke to eventually be erupted in the northwestern part of the hudson caldera the presence of tachylite in the p1 products suggests that some of the magma was stalled close to the surface 0 5 km prior to eruption seismicity related to magma movement and the p1 eruption combined with chamber overpressure associated with basalt injection may have created a pathway to the surface for the trachyandesite magma and subsequent p2 eruption at a different vent 4 km to the south southeast

influence of particle aggregation on deposition of distal tephra from the may 18 1980 eruption of mount st helens volcano the may 18 1980 eruption of mount st helens msh produced an extensive ashfall deposit in washington idaho and montana with a minumum volume of 0 55 km3 tephra an unusual feature of the deposit is the occurrence of a second thickness maximum 325 km ene of msh near ritzville washington grain size and component abundance analysis of samples along the main dispersal axis indicates that ash in this region is very fine grained mean size 22 m poorly sorted polymodal and rich in glass shards and pumice fragments a computer simulation of ash fallout from an atmospherically dispersed eruption plume was developed to evaluate various hypotheses for the origin of the distal ash characteristics particularly the thickness versus distance relationship the model was constrained by observations of the eruption column height elevation of major ash transport lateral spreading of the eruption plume and atmospheric wind structure in the vicinity of msh results of different simulations indicate that the second thickness maximum cannot be attributed to either decreased wind velocities over central washington or injection of fine ash above the horizontal wind velocity maximum near the tropopause for the model to fit the observed characteristics of the deposit significant particle aggregation of ash finer than 63 m must be invoked the best fit occurs when ash less than 63 m is aggregated into particles several hundred microns in diameter with a settling velocity of 0 35 m s support for this process comes from the observation and collection of fragile ash clusters of similar size which fell at pullman washington during the may 18 eruption sorem 1982 the premature fallout of fine ash as particle aggregates is a fundamental process in the origin of the grain size characteristics variations in component abundances and thickness versus distance relationship of the may 18 msh ash fall deposit

ash production and dispersal from sustained low intensity mono inyo eruptions recent rhyolitic volcanism has demonstrated that prolonged low intensity ash venting may accompany effusive dome formation we examine the possibility and some consequences of episodes of extended weak ash venting at the rhyolitic mono inyo chain in eastern california we describe ash filled cracks within one of the youngest domes panum crater which provide a textural record of ash venting during dome effusion we use synchrotron based x ray computed tomography to characterize the particles in these tuffisites particle sizes in well sorted tuffisite layers agree well with grain size distributions observed during weak ash venting at soufriere hills volcano montserrat and yield approximate upper and lower bounds on gas velocity and mass flux during the formation of those layers we simulate ash dispersal with ash3d to assess the consequences of long lived mono inyo ash venting for ash deposition and the accompanying volcanic hazards our results highlight the sensitivity of large scale outcomes of volcanic eruptions to small scale processes

an example of enhanced tephra deposition driven by topographically induced atmospheric turbulence spatial variations in the thickness and grain size characteristics of tephra fall deposits imply that tephra depositional processes cannot be fully captured by models of single particle sedimentation from the base of the eruption plume here we document a secondary thickness maximum in a 9 75 ka tephra fall deposit from chaiten volcano chile cha1 eruption this secondary thickness maximum is notably coarser grained than documented historical examples being dominated by medium grained ash and an origin via particle aggregation is therefore unlikely in the region of secondary thickening we propose that high levels of atmospheric turbulence accelerated particles held within the mid to lower troposphere 0 to 6 km towards the ground surface we suggest that this enhancement in vertical atmospheric mixing was driven by the breaking of lee waves generated by winds passing over elevated topography beneath the eruption plume lower atmospheric circulation patterns may exert a significant control on the dispersal and deposition of tephra from eruption plumes across all spatial scales particularly in areas of complex topography

bimodal grain size distribution and secondary thickening in air fall ash layers investigation of the ashfall deposit from the 1980 mount st helens eruption reveals that the deposit is bimodal the finer population maintaining a uniform grain size distribution away from source and that the deposit exhibits secondary thickening beyond the 1 cm isopach grain size distribution shows that at least 64 of the deposit is finer than 63 m far more than is generally supposed for plinian eruptions an investigation of other ashfall deposits reveals similar grain size bimodality features which are interpreted as evidence of aggregation of fine particles in the eruption cloud our data suggest that aggregation may be a common process during ash fallout from explosive eruptions and that secondary thickening may often occur providing that other conditions are met

interpretations of a middle miocene and late quaternary steady dextral transpression in sw japan and the opening tectonics for the japan sea abstract an internal rotation hypothesis for the deformation of sw japan for middle miocene and recent times is studied rotations are known to have occurred from paleomagnetic data for the earlier case two geodetic flow field estimates as well as another tectonic study suggest that the rotations are also taking place at present a further examination of the geodetic flow models suggests that the rotations contained in these flow models are intrinsic to the deformation of sw japan which occurs in an e w dextral transpressive simultaneous pure and simple shear tectonic regime maps of rotation rates one half of vorticity and shear gradients the n s variation of the e w velocity field constructed from the geodetic flow models resemble one another in pattern the estimates of the directions of the principal strain rates from the geodetic models are on the whole n s contractional and or e w extensional which match the geodetic reference coordinate system used in the adjustment of the geodetic data these observations suggest that the vortical flow contained in the geodetic flow models is a frame independent shear induced vorticity as the material is rotating with respect to the principal directions of the strain rates and that the oblique motion of the philippine sea plate is partitioned between shear and arc normal convergence components the rotation rate is 10 12 ma furthermore the kinematical vorticity number estimates from the geodetic data correlate well with the first order tectonic fabric patterns in sw japan super simple shear deformation for large parts of sw japan where the median tectonic line and other large strike slip faults are found is also indicated in the internal kinematical vorticity number estimates a new model for the formation of the japan sea is proposed extrusion of japan due to the okhotsk eurasia collision this model agrees with the fundamental observations of the early middle miocene deformation in the region the application of an indentation extrusion model to the okhotsk eurasia collision results in a better agreement between the predicted and observed structures and leads to simpler more reasonable and coherent interpretations for the origin and development of the structures compared with the achievements of the previous models the nne trending early middle miocene rifts lying along the continental margin of western hokkaido formed as pull apart basins along a sinistral fault related to the collision of the okhotsk plate which segmented in a left handed sense because the collision was oblique the n s trending rifts and the normal faults found in the back arc domain of the ne honshu arc formed by eastward extrusion under the influence of the mariana type subduction in the japan trench these rift basins were subsequently left laterally displaced by movement along nw trending sinistral strike slip faults the shikoku basin opened from the east toward the west and dextral shear was imparted to the sw margin from the nankai trough leading to clockwise rotations in the middle miocene in sw japan the paleomagnetic rotations are accommodated as fully internal structural rotations in the new model for the origin of the japan sea the current episode of deformation in sw japan began 1 5 million years ago after a hiatus during a 15 5 ma interval and is likely a continuation of the middle miocene style of tectonics

deformation from 1973 to 1987 in the epicentral area of the 1959 hebgen lake montana earthquake ms 7 5 a 40 km aperture trilateration network centered on the 1959 hebgen lake earthquake epicenter has been surveyed in 1973 1974 1976 1978 1981 1984 and 1987 the deformation inferred from those surveys is described roughly by a uniaxial 0 266 0 014 strain yr n15 e 1 extension that is uniform in both time and space that extension is orthogonal to the strike n78 w 5 of the 1959 rupture plane inferred from focal mechanism solutions the absence of strain accumulation in the n75 w direction suggests that the source of deformation must be greatly elongated in that direction looked at in greater detail the deformation is found to be concentrated in the northern part of the network the zone of concentrated deformation coincides with a part of a well defined trend in seismicity that extends at least 100 km n75 w from the sour creek resurgent dome in the yellowstone caldera extension perpendicular to that trend is indicated by focal mechanism solutions thus the zone of rifting identified within the hebgen lake network apparently extends east southeast to the yellowstone caldera about 8 mm yr extension is observed across a 20 km width within the zone

distal enhanced sedimentation from volcanic plumes insights from the secondary mass maxima in the 1992 mount spurr fallout deposits some tephra fallout deposits show an increase of mass and thickness at distances from the source 100 km areas of secondary mass maximum asmm which demonstrates distal enhanced sedimentation from volcanic plumes we explore development of the asmms during the 1992 august and september mount spurr eruptions usa by combining eld data on the spatial distribution of mass and grain size with 1 simulations of individual particle settling through a homogeneous and horizontally strati ed atmosphere and 2 mesoscale models of the three dimensional wind eld that include the effect of the underlying topography the crosswind and downwind variations of deposit characteristics indicate that the increase of sedimentation at the asmms is not formed solely because of preferential settling of small ash particles 125 m as commonly assumed in aggregation models instead asmm grain sizes correspond to the ne modes of the bimodal total grain size distributions there also appears to be a link between the asmm and the topography the mass local minima occur across the windward ank of 2 km high mountain ranges while the asmms spread on the leeward ank mesoscale models of the three dimensional wind eld show vertical oscillations in the wind over mountainous regions which may enhance mechanisms of en masse sedimentation aggregation hydrometeor formation and particle boundary layers as well as strong spatial variations of the horizontal wind eld in the lower troposphere our study demonstrates the importance of using grain size as well as mass data to constrain the complex processes responsible for particle sedimentation from volcanic plumes

the 600 yr eruptive history of villarrica volcano chile revealed by annually laminated lake sediments lake sediments contain valuable information about past volcanic and seismic events that have affected the lake catchment and they provide unique records of the recurrence interval and magnitude of such events this study uses a multilake and multiproxy analytical approach to obtain reliable and high resolution records of past natural catastrophes from 600 yr old annually laminated varved lake sediment sequences extracted from two lakes villarrica and calafquen in the volcanically and seismically active chilean lake district using a combination of micro x ray fl uorescence xrf scanning microfacies analysis grain size analysis color analysis and magnetic susceptibility measurements we detect and characterize four different types of event deposits lacustrine turbidites tephra fall layers runoff cryptotephras and lahar deposits and produce a revised eruption record for villarrica volcano which is unprecedented in its continuity and temporal resolution glass geochemistry and mineralogy also reveal deposits of eruptions from the more remote carran los venados volcanic complex quetrupillan volcano and the huanquihue group in the studied lake sediments time series analysis shows 112 eruptions with a volcanic explosivity index vei 2 from villarrica volcano in the last 600 yr of which at least 22 also produced lahars this signifi cantly expands our knowledge of the eruptive frequency of the volcano in this time window compared to the previously known eruptive history from historical records the last vei 2 eruption of villarrica volcano occurred in 1991 based on the last 500 yr for which we have a complete record from both lakes we estimate the probability of the occurrence of future eruptions from villarrica volcano and statistically demonstrate that the probability of a 22 yr repose period anno 2013 without vei 2 eruptions is 1 7 this new perspective on the recurrence interval of eruptions and historical lahar activity will help improve volcanic hazard assessments for this rapidly expanding tourist region and it highlights how lake records can be used to signifi cantly improve historical eruption records in areas that were previously uninhabited

strain accumulation across the wasatch fault near ogden utah deformation of a 70 by 40 km trilateration network spanning the north trending wasatch fault near ogden utah has been monitored from 1972 through 1990 all but nine of the 200 measurements are consistent with deformation that is linear in time we presume that those nine observations are contaminated by some blunder in making the measurements and that deformation is linear in time the strain rate over the 1972 1990 interval across a 40 km wide zone west of the wasatch fault hanging wall block is adequately approximated by a 0 04 0 01 strain yr n85 e 5 uniaxial extension adequate coverage of the footwall block is available only over the 1981 1990 interval and the strain rate across a 30 km wide zone there is approximated by a 0 07 0 03 strain yr n20 e 12 uniaxial extension the observed extension of the hanging wall block in the direction normal to fault strike suggests that the wasatch fault may be listric a planar fault would produce a zone of contraction normal to the fault at the surface of the hanging wall block the component of extension parallel to fault strike observed on the footwall block is unexplained

quantification of volcanic cloud top heights and thicknesses using a train observations for the 2008 chaiten eruption new evidence of vertically thin 10 km ash clouds from the may 2008 chaiten eruption in southern chile is presented a train remote sensors were used to measure high resolution volcanic cloud top heights vcths during the explosive phase 2 10 may 2008 of the eruption ash clouds were identified using a reverse absorption technique applied to hyperspectral measurements taken by the atmospheric infrared sounder once identified heights and thicknesses were derived from the cloud aerosol lidar with orthogonal polarization caliop instrument as these two instruments are part of the same constellation of satellites coincident retrievals are routinely possible collocation of the data allowed for detection of volcanic ash within caliop profiles using a simple thresholding algorithm vcth and thickness were derived from the caliop profiles a total of 12 vcth measurements ranging from 3 7 to 16 6 km have been derived back trajectories from the hybrid single particle lagrangian integrated trajectory dispersion model were used as a check on volcanic origin of the detected ash clouds ensemble forward trajectories were generated to demonstrate how the new data could be used to improve volcanic ash advisory center operations the findings reported here demonstrate several cases where low level ash was not recorded previously and include observations of thin ash clouds at large distances 4000 km from the volcano

horizontal and vertical crustal movements from three dimensional very long baseline interferometry kinematic reference frame implication for the reversal timescale revision three dimensional kinematic reference frame of geodetic very long baseline interferometry vlbi stations tied to a geologic plate motion model was established using the glb907 solution by first selecting globally distributed stable plate interior stations and then applying a small translation and a rotation for the entire network in a three dimensional space so that the differences in the horizontal velocities between the vlbi observations and the model predictions are minimized since the vlbi network is global we only assume that the horizontal movements of technically stable stations obey a plate motion model we need not introduce any unwarranted constraints to the vertical velocities of specific stations to realize the frame a suggestive correlation was found between the estimated vertical velocities of north american stations and those predicted by a postglacial rebound model the revision of the magnetic polarity timescale mpts causes a uniform increase or decrease of the predicted velocities which could be detected as the small difference between the measured and the predicted relative plate velocities direct estimation of the correction suggests that the vlbi data fit best to the model when the nuvel1 model is corrected by 3 4 1 2 which differs significantly from the 4 5 deduced from the astronomical mpts calibration this was further confirmed by estimating the rotation rates for individual plate pairs

volcanic particle aggregation in explosive eruption columns part i parameterization of the microphysics of hydrometeors and ash abstract the aggregation of volcanic ash particles within the eruption column of explosive eruptions has been observed at many volcanoes it influences the residence time of ash in the atmosphere and the radiative properties of the umbrella cloud however the information on the processes leading to aggregate formation are still either lacking or very incomplete we examine the fate of ash particles through numerical experiments with the plume model atham active tracer high resolution atmospheric model in order to determine the conditions that promote ash particle aggregation in this paper we describe the microphysics and parameterization of ash and hydrometeors in a companion paper this issue we use this information in a series of numerical experiments the parameterization includes the condensation of water vapor in the rising eruption column the formation of liquid and solid hydrometeors and the effect of latent heat release on the eruption column dynamics are considered the interactions of hydrometeors and volcanic ash within the eruption column that lead to aggregate formation are simulated for the first time within a rising eruption column the microphysical parameterization follows a modal approach the hydrometeors are described by two size classes each of which is divided into a liquid and a frozen category by analogy with the hydrometeor classification we specify four categories of volcanic ash particles we imply that volcanic particles are active as condensation nuclei for water and ice formation ash can be contained in all categories of hydrometeors thus forming mixed particles of any composition reaching from mud rain to accretionary lapilli collisions are caused by gravitational capture of particles with different fall velocity coalescence of hydrometeor ash aggregates is assumed to be a function of the hydrometeor mass fraction within the mixed particles the parameterization also includes simplified descriptions of electrostatics and salinity effects

implications for paleomobility studies of the effects of quaternary volcanism on bioavailable strontium a test case in north patagonia argentina abstract strontium isotopes 87sr 86sr are used as geochemical tracers for paleomobility studies because they display predictable and stable patterns in ecosystems primarily controlled by the underlying geological regimes while bedrock geology is stable over thousands of years geomorphological processes can influence the 87sr 86sr in ecosystems over archeologically relevant timescales among these geomorphological processes the deposition and reworking of volcanic sediments over quaternary timescales are little studied but could be an important control of 87sr 86sr variations in many archeological regions north patagonia is a key archeological region to address animal and human movements and an ideal location to test the influence of quaternary volcanism on 87sr 86sr variation as it is located downwind of major volcanic centers in this study we aim to assess the main environmental and geological controls of bioavailable 87sr 86sr and to build a high resolution isoscape using a machine learning regression framework for forthcoming paleomobility studies we sampled several locations and analyzed different types of samples n 94 the ratios show a limited range of variation which is not related to the bedrock geology rather bioavailable 87sr 86sr variations display a progressive increase going eastward away from the andes following dust aerosol deposition and elevation variations r2 0 71 rmse 0 00041 we argue that this trend relates to the deposition and reworking of unradiogenic volcanic sediments by aeolian fluvial and glacial erosion during the quaternary as most of this sediment reworking occurred during glacial periods the current bioavailable 87sr 86sr variations across the study area likely represent a long term average that varied little during the holocene consequently our isoscape provides a solid base for holocene paleomobility studies in north patagonia and underlines the importance of quaternary volcanism processes for interpreting 87sr 86sr data in paleomobility studies in volcanic regions

construction of volcanic records from marine sediment cores a review and case study montserrat west indies detailed knowledge of the past history of an active volcano is crucial for the prediction of the timing frequency and style of future eruptions and for the identification of potentially at risk areas subaerial volcanic stratigraphies are often incomplete due to a lack of exposure or burial and erosion from subsequent eruptions however many volcanic eruptions produce widely dispersed explosive products that are frequently deposited as tephra layers in the sea cores of marine sediment therefore have the potential to provide more complete volcanic stratigraphies at least for explosive eruptions nevertheless problems such as bioturbation and dispersal by currents affect the preservation and subsequent detection of marine tephra deposits consequently cryptotephras in which tephra grains are not sufficiently concentrated to form layers that are visible to the naked eye may be the only record of many explosive eruptions additionally thin reworked deposits of volcanic clasts transported by floods and landslides or during pyroclastic density currents may be incorrectly interpreted as tephra fallout layers leading to the construction of inaccurate records of volcanism this work uses samples from the volcanic island of montserrat as a case study to test different techniques for generating volcanic eruption records from marine sediment cores with a particular relevance to cores sampled in relatively proximal settings i e tens of kilometres from the volcanic source where volcaniclastic material may form a pervasive component of the sedimentary sequence visible volcaniclastic deposits identified by sedimentological logging were used to test the effectiveness of potential alternative volcaniclastic deposit detection techniques including point counting of grain types component analysis glass or mineral chemistry colour spectrophotometry grain size measurements xrf core scanning magnetic susceptibility and x radiography this study demonstrates that a set of time efficient non destructive and high spatial resolution analyses e g xrf core scanning and magnetic susceptibility can be used effectively to detect potential cryptotephra horizons in marine sediment cores once these horizons have been sampled microscope image analysis of volcaniclastic grains can be used successfully to discriminate between tephra fallout deposits and other volcaniclastic deposits by using specific criteria related to clast morphology and sorting standard practice should be employed when analysing marine sediment cores to accurately identify both visible tephra and cryptotephra deposits and to distinguish fallout deposits from other volcaniclastic deposits

atmospheric distribution and removal of volcanic ash after the eruption of kasatochi volcano a regional model study 1 in august 2008 kasatochi volcano on the aleutian islands erupted without much advance warning volcanic ash released during this eruption quickly settled out of the atmosphere mainly into the ne pacific ocean the amount of volcanic ash as well as the ash fall area and volume into the ne pacific ocean remains speculative as only a limited number of measurements is available we used a three dimensional atmosphere chemistry aerosol model to determine the atmospheric distribution of so2 and volcanic ash and its fallout after the eruption of kasatochi volcano in a first step modeled atmospheric so2 distributions are compared with satellite data thereby evaluating the model capabilities to reasonably reproduce atmospheric transport patterns for modeled volcanic ash mass a considerable reduction of the atmospheric content already occurred by 10 august the second day after the eruption in accordance with satellite observations gravitational settling is the most efficient removal process for volcanic ash mass exceeding dry and wet deposition by far assuming an ash volume of 0 3 km3 released during the eruption of kasatochi volcano and a median ash particle diameter of 4 m the mass of volcanic ash removed at ground within the 0 1 mm isopach covers an area of 7 6 105 km2 over the ne pacific ocean and makes up 49 of the removed material out of the atmosphere the amount of ash and that of iron attached to it is sufficient to explain measured seawater co2 decrease at the ocean station papa in august 2008 induced by iron fertilization and subsequent phytoplankton production

ascent driven crystallisation of dacite magmas at mount st helens 1980 1986 we introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system qz ab or h2o in order to relate variations in volcanic glass chemistry to changing pressure p and temperature t conditions in the sub volcanic magma system by this means an important distinction can be made between ascent driven and cooling driven crystallisation under water saturated or undersaturated conditions in samples containing feldspar and a silica phase quartz or tridymite quantitative p t estimates of the conditions of last equilibrium between crystals and melt can be made formation of highly silicic melts i e 77 wt sio2 is a simple consequence of the contraction of the silica phase volume with decreasing pressure such that high silica glasses can only form by crystallisation at low pressure resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation groundmass and inclusion glasses in dacites from the 1980 1986 eruption of mount st helens volcano wa span a wide range in sio2 68 80 wt anhydrous the compositions of the least evolved sio2 poor inclusions in amphibole phenocrysts record entrapment of silicic liquids with 5 4 wt water corresponding to a water saturation pressure of 200 mpa at 900 c the compositions of more evolved higher sio2 plagioclase hosted inclusions and groundmass glasses are consistent with extensive ascent driven fractional crystallisation of plagioclase oxide and orthopyroxene phenocrysts and microlites to low pressures during this polybaric crystallisation plagioclase phenocrysts trapped melts with a wide range of dissolved water contents 3 5 5 7 wt magmas erupted during the plinian phase of the 18 may 1980 eruption were derived from a large reservoir at depths of 6 km subsequent magmas ascended to varying depths within the sub volcanic system prior to extraction from glass chemistry and groundmass texture two arrest levels have been identified at depths of 0 5 1 and 2 4 km a single dome sample from february 1983 contains groundmass plagioclase tridymite and quartz testifying to temperatures of at least 885 c at 11 mpa these shallow storage conditions are comparable to those in the cryptodome formed during spring 1980 the corresponding thermal gradient 0 2 c mpa 1 is consistent with near adiabatic magma ascent from 8 km we argue that the crystallisation history of mount st helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation this challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980 1986 eruption because the crystallisation process is both polybaric and fractional it cannot be simulated directly using isobaric equilibrium crystallisation experiments however calculation of the phase proportions in water saturated 910 15 c experiments by rutherford et al 1985 over the pressure range 220 125 mpa reproduces the crystallisation sequence and phenocryst modes of mount st helens dacites from 18 may 1980 by allowing for the effects of fractional versus equilibrium crystallisation entrained residual source material and small temperature differences between nature and experiment phase compositions can also be matched to the natural samples we conclude that decompression of water saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres

late pleistocene and holocene tephrostratigraphy of interior alaska and yukon key beds and chronologies over the past 30 000 years abstract the aleutian arc alaska peninsula and wrangell volcanic field are the main source areas for tephra deposits found across alaska and northern canada and increasingly tephra from these eruptions have been found further afield in north america greenland and europe however there have been no broad scale reviews of the late pleistocene and holocene tephrostratigraphy for this region since the 1980s and this lack of data is hindering progress in identifying these tephra both locally and regionally to address this gap and the variable quality of associated geochemical and chronological data we undertake a detailed review of the latest pleistocene to holocene tephra found in interior alaska and yukon this paper discusses nineteen tephra that have distributions beyond southwest alaska and that have the potential to become or already are important regional markers this includes three modern events from the 20th century ten with limited data availability but potentially broad distributions and six that are widely reported in interior alaska and yukon each tephra is assessed in terms of chronology geochemistry and distribution with new bayesian age estimates and geochemical data when possible this includes new major element geochemical data for crater peak 1992 redoubt 1989 90 and two andesitic tephra from st michael island tephra d as well as revised age estimates for dawson tephra oshetna hayes set h aniakchak cfe ii and the white river ashes northern and eastern lobes

tectonic stress state in ne japan as part of the okhotsk plate abstract an existing geodetic flow velocity model obtained by using an internal free network adjustment technique is used to derive estimates for various strain rates parameters in ne japan the greatest shortening rates of the principal strains trending e w are located in regions where much steady internal frame invariant plastic flow deformation is observed to be taking place the internal geodetic adjustment technique yielded the internal deformation in the tohoku arc most of the intraplate deformations including the much folding deformations observed in the inner zone are produced from within an interseismic transient elastic loading at a strongly coupled locked japan trench would not be needed the observed ongoing extensive ductile folding deformation in the inner zone of tohoku may mean that the geodetic strain rates causing shortening at 2 3 cm yr probably reflect the more correct level of the deformation which is steady permanent in ne japan as compared with seismic faulting data which indicate 0 5 cm yr shortening the calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework the tectonic stress state in ne japan as part of the okhotsk plate could mostly be influenced by the okhotsk plate which is extruding southward to lessen the significant accumulated contractional deformation in ne asia in the verkhoyansk cherskii mountains the principal strain rates are n s extensional essentially everywhere in ne japan as a result of the southerly extrusion except in its southernmost leading edge in the uetsu fossa magna province where the japan alps rampart rises in front of the extrusion here an e w compressional stress state prevails a second e w contractional zone is found in north central tohoku extending from the sanriku province in the outer zone to the inner zone in the japan sea side being more prevalent in the latter zone the calculated rotation rates from the geodetic flow model are clockwise cw in both of the e w contractional regions ne japan extruding southward faces buttresses in 1 the oga ojika line ool and or a crustal weakness zone between the northern and the southern halves of tohoku approx at 38 5 n latitude and especially 2 the japanese alps rampart these obstacles cause the northern and southernmost tohoku to veer to its right and rotate cw thereby setting up the e w trending compressional deformation in their respective inner zones between the ool or the 38 5 n boundary and the kanto tectonic line ktl the sense of the differential rotations is counterclockwise ccw towards the ocean to the se the northern tohoku north of the ool and the southernmost tohoku south of the ktl cannot rotate ccw towards the ocean because of the izu block s collision in the south and the relatively strong coupling along the subduction interface beneath the japan trench in the north off sanriku the relatively stronger long term coupling between the northern tohoku and the pacific plate at the sanriku coast with respect to that in off fukushima is due to a flatter subduction of the pacific slab there increasing the plates interface contact area the flattening of the subduction dip angle was caused by ccw rotation and shifting of the northern tohoku along the dextral honjo matsushima line roughly corresponding to the ool towards the pacific and overriding of the subduction zone during the formation of the japan sea

strain accumulation near yucca mountain nevada 1983 1993 over the decade 1983 1993 the u s geological survey has measured the deformation of a 50 km aperture trilateration network centered on yucca mountain the proposed disposal site for high level nuclear waste in the united states the network was surveyed in 1983 1984 and 1993 the average annual principal strain rates are 0 010 0 020 strain yr n90 w 24 and 0 009 0 021 strain yr n00 e 24 indicating no significant strain accumulation the southeast corner of the network was disturbed on june 29 1992 by the little skull mountain earthquake ms 5 4 the epicenter of which is about 20 km southeast of the yucca mountain site using the seismically determined fault plane dip 54 s55 e we find that 0 580 0 075 m of normal slip on a 5 km square rupture surface at a depth of about 8 km provides a good fit to the observed deformation in the southeast corner of the network the inferred seismic moment is 4 4 0 6 1017 n m which compares well with the observed seismic moment of 4 1 1017 n m

contemporary plate motion and crustal deformation the measurement of relative plate velocities during the past few years is a signal accomplishment in earth science leading to refinement of the precepts of steady motion of plate interiors and cyclic deformation along plate margins regrettably deformation premonitory to an earthquake has yet to be detected with confidence delineation of the spatial and temporal buildup of strain between earthquakes however has put limits on models of the earthquake cycle a diverse set of fault structures and crustal rheologic conditions can explain the pattern of surface strain accumulation and release along strike slip faults in contrast the geometry of thrusts and normal faults revealed by earthquake deformation has been found to differ markedly from expectations geodetic observations have proved vital to monitor the ascent of magma through the earth s crust and to predict volcanic eruptions at the earth s surface episodic vertical and horizontal deformation in southern california remains a subject of dispute if anything it is less certain than it once seemed

palaeoenvironmental response to the 74 ka toba ash fall in the jurreru and middle son valleys in southern and north central india distal deposits of rhyolitic volcanic ash from the 74 ka supervolcanic eruption of toba in northern sumatra are preserved in numerous river valleys across peninsular india the toba eruption is hypothesized to have resulted in climate change and the devastation of ecosystems and hominin populations this study reports the results of the analysis of sediments and stratigraphical sequences from sites in the jurreru and middle son valleys in southern and north central india the aim of the study is to determine the extent of palaeoenvironmental change in both valleys as a result of the ash fall inferences based on evidence from the jurreru valley are more detailed where pre and post toba palaeoenvironmental changes are divided into seven phases the results indicate that ash fall deposits in both valleys underwent several phases of reworking that possibly lasted for several years indicating that ash was mobile in the landscape for a considerable period of time prior to burial this could have enhanced and lengthened the detrimental effects of the ash on vegetation and water sources as well as animal and hominin populations