seismicity related to the glacier of cotopaxi volcano ecuador 1 significant seismic activity is generally recorded on volcanoes covered by an icecap this work was carried out in order to quantify the role of the glaciers in the generation of seismicity for cotopaxi volcano we compared the seismic activity registered on the glacier and on the rock near the snout of the north flank glacier we focused on the analysis of low frequency events 5 hz similar to volcanic lp events when recorded on rock base the particle motion analysis helps to estimate source locations which are distributed in crevasses areas high incident angles suggest a superficial origin these events are interpreted as icequakes for which we propose as source mechanism a fluid driven crack model triggered by ice cracking or hydraulic transients the low quality factor values estimated are consistent with the resonance of an ice crack filled with water this work shows that low frequency icequakes can be confusingly taken as volcanic lp events

volcano geodesy and magma dynamics in iceland abstract here we review the achievements of volcano geodesy in iceland during the last 15 years extensive measurements of crustal deformation have been conducted using a variety of geodetic techniques including leveling electronic distance measurements campaign and continuous global positioning system gps geodesy and interferometric analysis of synthetic aperture radar images insar results from these measurements provide a comprehensive view of the behavior of icelandic volcanoes between inflation intrusion and eruption episodes volcanoes are likely to deflate or show no sign of seismic activity subsidence rates are often in the range of a few millimeters to a few centimeters a year reducing progressively with time since the last eruption or intrusion at the volcano subsidence can be caused by cooling and contraction of magma outflow of magma it can be related to plate spreading volcano subsidence or lack of deformation is often interrupted by episodic magma flow towards near surface locations such magma recharge has been observed geodetically at hengill hekla eyjafjallajokull katla grimsvotn and krafla volcanoes with inflow inferred to last from a few months up to two decades in the last 15 years five volcanic eruptions three intrusive events and two m6 earthquakes have occurred in recent years the grimsvotn and katla volcanoes have exhibited continuous inflation of a few centimeters per year which at grimsvotn culminated in an eruption on 1 november 2004 hekla and torfajokull volcanoes have inflated at rates an order of magnitude less subsidence is occurring presently at the askja and krafla volcanoes within the period of geodetic measurement signals consistent with no deformation are typical for most of the 35 active volcanoes in iceland

twin sources of high frequency volcanic tremor of izu oshima volcano japan the 1986 fissure eruption of izu oshima volcano was preceded and followed by strong volcanic tremor activities the post eruption tremor activity consists of an alternating sequence of a tremor episode lasting about 10 min and the subsequent quiescence of about 40 50 min the authors observed this post eruption activity by a 24 channel seismic array deployed on the caldera floor the semblance analysis of the recorded data revealed that high frequency 5 hz components of the tremor were radiated from two separated sources beneath the caldera the tremor first occurred at one source and then migrated to the other source in a transition time of about a few minutes during each tremor episode this transition suggests that the two sources are dynamically linked with each other in a magma filled crack or conduit

modes of bed load movement on a smooth rigid surface sediment grains transported as supply limited bed load on a rigid surface move either discretely or collectively as bed forms with significantly different effective grain speeds and active storage volumes the adopted mode has implications for sediment sorting and heavy mineral placer formation dispersal of grain associated pollutants and accumulation and flushing of sediment deposits in unlined canals and sewers the threshold condition between the two modes has been established for a smooth surface from flume experiments with different sediment types flow conditions and sediment supply rates this is expressed in terms of a relationship between the sediment movability number a dimensionless bed load parameter and a grain shear reynolds number

large explosive basaltic eruptions at katla volcano iceland fragmentation grain size and eruption dynamics abstract katla volcano in iceland produces hazardous large explosive basaltic eruptions on a regular basis but very little quantitative data for future hazard assessments exist here details on fragmentation mechanism and eruption dynamics are derived from a study of deposit stratigraphy with detailed granulometry and grain morphology analysis granulometric modeling componentry and the new quantitative regularity index model of fragmentation mechanism we show that magma water interaction is important in the ash generation process but to a variable extent by investigating the large explosive basaltic eruptions from 1755 and 1625 we document that eruptions of similar size and magma geochemistry can have very different fragmentation dynamics our models show that fragmentation in the 1755 eruption was a combination of magmatic degassing and magma water interaction with the most magma water interaction at the beginning of the eruption the fragmentation of the 1625 eruption was initially also a combination of both magmatic and phreatomagmatic processes but magma water interaction diminished progressively during the later stages of the eruption however intense magma water interaction was reintroduced during the final stages of the eruption dominating the fine fragmentation at the end this detailed study of fragmentation changes documents that subglacial eruptions have highly variable interaction with the melt water showing that the amount and access to melt water changes significantly during eruptions while it is often difficult to reconstruct the progression of eruptions that have no quantitative observational record this study shows that integrating field observations and granulometry with the new regularity index can form a coherent model of eruption evolution

saturated and subcooled hydrothermal boiling in groundwater flow channels as a source of harmonic tremor the potential of hydrothermal boiling in groundwater flow channels for generating harmonic tremor a relatively monochromatic ground vibration associated with volcanic activity is examined we use simple organ pipe theory of normal mode fluid vibration and fundamental energy considerations to develop a first order analytical model of a hydrothermal boiling source of harmonic tremor we use this model to estimate order of magnitude groundwater flow channel lengths and boiling heat transfer rates required to produce harmonic tremor with dominant frequencies in the range 0 5 5 hz and surface wave reduced displacements of up to 100 cm2 depending on groundwater sound speed flow channel lengths of the order of 1 1000 m are required to produce fluid vibration eigenfrequencies in the range 0 5 5 hz the boiling heat transfer rate required to produce tremor with a given surface wave reduced displacement depends on the tremor frequency and on whether saturated boiling or subcooled boiling is the cause of the tremor saturated boiling produces groundwater vibration via steam bubble growth whereas subcooled boiling produces groundwater vibration via steam bubble collapse we find that subcooled hydrothermal boiling is from 102 to 104 times more efficient than saturated boiling in converting boiling thermal power to seismic power for example the boiling heat transfer rates required to produce 1 hz tremor with reduced displacements of up to 100 cm2 via subcooled boiling are generally less than a few thousand megawatts for saturated boiling the required boiling heat transfer rates are several orders of magnitude larger than this the highest values of heat flow reported in the literature for volcanic crater lakes and terrestrial and ocean floor geothermal areas are of the order of 1000 mw taking this value as a first order estimate of an upper limit on possible boiling heat transfer rates in volcanic hydrothermal systems our results suggest that saturated hydrothermal boiling is capable of generating only low amplitude harmonic tremor with surface wave reduced displacements no higher than a few square centimeters however subcooled hydrothermal boiling could potentially generate high amplitude harmonic tremor with reduced displacements as large as several hundred square centimeters as a specific application of our model we evaluate the potential of hydrothermal boiling for generating harmonic tremor at recently active mount st helens and nevado del ruiz volcanoes we conclude that subcooled boiling likely could have produced the tremor episodes considered at both volcanoes saturated boiling also could explain the nevado del ruiz tremor but probably not the more powerful mount st helens tremor

locating tremor using stacked products of correlations we introduce a back projection method to locate tremor sources using products of cross correlation envelopes of time series between seismic stations for a given subset of n stations we calculate

evidence for gas influence on volcanic seismic signals recorded at stromboli abstract the meaning of the large variety of seismic waveforms showing different frequencies associated with volcanic activity is still uncertain no definitive model for source dynamics has been proposed yet at present seismic models explaining the origin of the spectral content of the seismic signal are mainly linked to geometrical features of the volcanic conduit and to resonant effects induced by pressure fluctuations in a fluid filled conduit such models assume the physical system to be in a steady state over a long interval of time at stromboli the seismicity produced by each of the three active vents is not stable and can suddenly change in time therefore the application of stable resonator models appears to be unwarranted on the basis of infrared image analyses atmospheric pressure and seismic wavefield signals we show that different frequency contents and different explosive styles occur at stromboli at the same time at different vents moreover we give evidence to support the idea that seismicity and explosivity are both controlled by a variable gas flow regime released during explosions at the top of the magma column we have recognized two main pressure regimes controlling the explositivity at stromboli one is impulsive short and possibly produced by a gas accumulation beneath a cap rock the other has an intermittent regime feature and lasts longer we demonstrate how the first one generates a monochromatic low frequency wavefield while the second shows a high frequency spectrum where the frequency content depends on pressure fluctuations and on pressure gradient we suggest different pressure growth and gas flow in the magma as the common source for both explosive style and seismic wavefield

seismo acoustic evidence for an avalanche driven phreatic eruption through a beheaded hydrothermal system an example from the 2012 tongariro eruption abstract the 6 august 2012 te maari eruption comprises a complex eruption sequence including multiple eruption pulses a debris avalanche that propagated 2 km from the vent and the formation of a 500 m long arcuate chasm located 300 m from the main eruption vent the eruption included 6 distinct impulses that were coherent across a local infrasound network marking the eruption onset at 11 52 18 all times utc an eruption energy release of 3 1012 j was calculated using a body wave equation for radiated seismic energy a similar calculation based on the infrasound record shows that 90 of the acoustic energy was released from three impulses at onset times 11 52 20 20 of total eruption energy 11 52 27 50 and 11 52 31 20 these energy impulses may coincide with eyewitness accounts describing an initial eastward directed blast followed by a westward directed blast and a final vertical blast pre eruption seismic activity includes numerous small unlocatable micro earthquakes that began at 11 46 50 two larger high frequency earthquakes were recorded at 11 49 06 and 11 49 21 followed directly by a third earthquake at 11 50 17 the first event was located within the scarp based on an arrival time location from good first p arrival times and probably represents the onset of the debris avalanche the third event was a tornillo characterised by a 0 8 hz single frequency resonance and has a resonator attenuation factor of q 40 consistent with a bubbly fluid filled resonator this contrasts with a similar tornillo event occurring 2 5 weeks earlier having q 250 1000 consistent with a dusty gas charged resonator we surmise from pre eruption seismicity and the observed attenuation change that the debris avalanche resulted from the influx of fluids into the hydrothermal system causing destabilisation and failure the beheaded hydrothermal system may have then caused depressurisation frothing of the remaining gas charged system leading to the onset of explosive activity

seismic and geodetic insights into magma accumulation at katla subglacial volcano iceland 1999 to 2005 katla is one of iceland s most active volcanoes with at least 20 eruptions in the last 1100 years the volcano is covered mostly by the m rdalsjokull ice cap consequently katla eruptions are phreato magmatic and are capable of producing jokulhlaups a jokulhlaup in july 1999 preceded by an episode of continuous seismic tremor was the first sign of renewed magma movement under the volcano since 1955 using seismic and geodetic observations and insights into geothermal activity from ice surface observations we analyze this period of unrest and assess the present state of katla volcano from 1999 to 2004 gps measurements on nunataks exposed on the caldera edge revealed steady inflation of the volcano our measurements show uplift and horizontal displacement of the nuntatak benchmarks at a rate of up to 2 cm a 1 together with horizontal displacement of far field stations 11 km at about 0 5 cm a 1 away from the caldera centre using a point source model these data place the center of the magma chamber at 4 9 km depth beneath the northern part of the caldera however this depth may be overestimated because of a progressive decrease in the mass of the overlying ice cap the depth may be only 2 3 km about 0 01 km3 of magma has accumulated between 1999 and 2004 this value is considerably less than the estimated 1 km3 of material erupted during the last eruption of katla in 1918 presently rates of crustal deformation and earthquake activity are considerably less than observed between 1999 and 2004 nonetheless the volcano remains in an agitated state

olivine diogenites the mantle of the eucrite parent body abstract two olivine rich antarctic diogenites alh a77256 and alh 84001 of the howardite eucritediogenite hed meteorite association have olivine pyroxene ratios similar to normative ratios in devolatilized ordinary chondrites based on chemical data and petrological analysis these meteorites represent the residuum of partial melting of the mantle in the eucrite parent body epb mineral assemblages in these olivine rich diogenites record a continuum in thermal histories from initial partial melting 1150 1200 c to subsolidus re equilibration 795 55 c the small number of olivine rich diogenites known hints that only the outer portion of the epb has been sampled

determination of planetary basalt parentage a simple technique using the electron microprobe many basaltic meteorites are being discovered in old and new meteorite suites including those from cold deserts e g antarctica and hot desert environments it is important to establish the specific planetary body source proven techniques for establishing planetary parentage include stable isotopic signatures especially oxygen certain elemental ratios in bulk samples and certain elemental ratios in specific minerals some of these techniques are expensive require considerable sample preparation and are adversely affected by weathering processes on the parent body or on earth we have been seeking key major and minor elemental ratios in pyroxene olivine and feldspar that can be measured by the electron microprobe on standard thin sections these ratios may be preserved in unweathered portions of mineral grains and thus see through weathering processes in addition if the sample is too small to provide a representative bulk composition it may still have key information recorded in individual minerals we have found that some of the most useful chemical parameters are fe mn atomic in olivine or pyroxene and the percent anorthite an in plagioclase solid solutions a plot of fe mn in pyroxene and or olivine verses an defines compositional fields that are significantly different for earth mars moon 4 vesta and the angrite parent body this method may be especially powerful when combined with oxygen isotope data

origin and implications of troilite orthopyroxene intergrowths in the brecciated diogenite northwest africa 7183 abstract troilite orthopyroxene intergrowths are present as a common material in the brecciated diogenite northwest africa nwa 7183 in this study we report on the petrographic mineralogical and rare earth element abundances of the troilite orthopyroxene intergrowths to constrain their origin and assess their implications for the diverse petrogenesis of diogenites two groups of troilite orthopyroxene intergrowths with various grain sizes and mineral chemistry have been observed in nwa 7183 one group of intergrowths contains fine grained

seismicity crisis at the katla volcano iceland signs of a cryptodome abstract katla one of the most active and hazardous icelandic volcanoes has shown signs of unrest since 1999 in july that year a small glacial flood lasting a few hours was observed accompanied by abnormal seismicity it was probably caused by a short lived shallow magma intrusion or possibly a small subglacial eruption in 2002 seismic activity increased dramatically particularly in the go abunga area west of the caldera and earthquakes have occurred continuously ever since a network of four portable seismometers was run at katla in the spring summer 2003 with one station directly at the locus of the go abunga activity these observations are combined with the data of the permanent icelandic digital seismograph network run by the icelandic meteorological office the earthquakes at go abunga are concentrated in a small area with a diameter of 3 to 4 km and the events are shallow mainly within the uppermost 2 km we propose that the unusual pattern of seismicity indicates an intruding hot and acidic cryptodome apparently this dome has been slowly rising for decades but its propagation towards the surface accelerated some time around 1999 possibly triggered by a basaltic intrusion this may lead to a silicic dome building eruption in the go abunga area which should be taken into consideration when estimating the eruption hazard at katla

crustal differentiation in the early solar system clues from the unique achondrite northwest africa 7325 nwa 7325 the unique achondrite nwa 7325 is an unusual olivine gabbro composed chiefly of calcic plagioclase an85 93 diopsidic pyroxene en50 1 54 0 wo44 8 49 3 fs0 6 1 3 and forsteritic olivine fo97 it is al and mg rich and fe and na poor and displays very low concentrations of incompatible trace elements much below 0 3 x ci abundances for many of them it is also characterized by huge eu and sr anomalies eu eu 65 srn cen 240 although the o isotopic composition of nwa 7325 and some ureilites those with olivine cores in the range fo75 to fo88 are similar a genetic relationship between them is unlikely due to the fe poor composition of nwa 7325 it is almost certainly derived from a distinct planetesimal not previously sampled by other achondrites the low na al ga al zn al ratios as well as the low k rb and cs shown by nwa 7325 suggest a volatile depleted parent body this unique gabbro is demonstrably a cumulate but the composition of its parental melt cannot be precisely assessed however the liquid from which nwa 7325 crystallized would have been very poor in incompatible trace elements yb in the range of 0 25 to 1 5 x ci abundance with a very large positive eu anomaly such a melt cannot be the product of the early magmatic activity on a small parent body instead we propose that the parental melt to nwa 7325 formed as a consequence of the total melting of an ancient gabbroic lithology possibly upon impact in agreement with the systematics of 26al 26mg based on recent dating the crustal material that was parental to nwa 7325 must have been older than 4562 8 ma and formed possibly 4566 ma ago if this scenario is correct nwa 7325 provides evidence of one of the earliest crusts on a differentiated body so far studied

multidisciplinary constraints of hydrothermal explosions based on the 2013 gengissig lake events kverkfjoll volcano iceland hydrothermal explosions frequently occur in geothermal areas showing various mechanisms and energies of explosivity their deposits though generally hardly recognised or badly preserved provide important insights to quantify the dynamics and energy of these poorly understood explosive events furthermore the host rock lithology of the geothermal system adds a control on the efficiency in the energy release during an explosion we present results from a detailed study of recent hydrothermal explosion deposits within an active geothermal area at kverkfjoll a central volcano at the northern edge of vatnajokull on august 15th 2013 a small jokulhlaup occurred when the gengissig ice dammed lake drained at kverkfjoll the lake level dropped by approximately 30 m decreasing pressure on the lake bed and triggering several hydrothermal explosions on the 16th here a multidisciplinary approach combining detailed field work laboratory studies and models of the energetics of explosions with information on duration and amplitudes of seismic signals has been used to analyse the mechanisms and characteristics of these hydrothermal explosions field and laboratory studies were also carried out to help constrain the sedimentary sequence involved in the event the explosions lasted for 40 50 s and involved the surficial part of an unconsolidated and hydrothermally altered glacio lacustrine deposit composed of pyroclasts lavas scoriaceous fragments and fine grained welded or loosely consolidated aggregates interbedded with clay rich levels several small fans of ejecta were formed reaching a distance of 1 km north of the lake and covering an area of approximately 0 3 km2 with a maximum thickness of 40 cm at the crater walls the material volume of approximately 104 m3 has been ejected by the expanding boiling fluid generated by a pressure failure affecting the surficial geothermal reservoir the maximum thermal craterisation and ejection energies calculated for the explosion areas are on the order of 1011 1010 and 109 j respectively comparison of these with those estimated by the volume of the ejecta and the crater sizes yields good agreement we estimate that approximately 30 of the available thermal energy was converted into mechanical energy during this event the residual energy was largely dissipated as heat while only a small portion was converted into seismic energy estimation of the amount of freshly fragmented clasts in the ejected material obtained from sem morphological analyses reveals that a low but significant energy consumption by fragmentation occurred decompression experiments were performed in the laboratory mimicking the conditions due to the drainage of the lake experimental results confirm that only a minor amount of energy is consumed by the creation of new surfaces in fragmentation whereas most of the fresh fragments derive from the disaggregation of aggregates furthermore ejection velocities of the particles 40 50 m s measured via high speed videos are consistent with those estimated from the field the multidisciplinary approach used here to investigate hydrothermal explosions has proven to be a valuable tool which can provide robust constraints on energy release and partitioning for such small size yet hazardous steam explosion events

a review of glacier outburst floods in iceland and greenland with a megafloods perspective the very largest glacier outburst floods have been termed megafloods given their volume and peak discharge that definition might be revised because those floods have become understood due to their distinctive and pervasive landscape impacts at least three floods in iceland can be categorized as megafloods since they produced impressive bedrock canyons and giant fluvially transported boulders glacier lake outburst floods glofs in greenland might also have megaflood type attributes given the enormous lake volumes drained we therefore here present the first review of glacier outburst floods in greenland sites isvand russell glacier kuannersuit glacier lake tininnilik two unnamed lakes near amitsulooq ice cap and iluliallup tasersua base camp lake lake hullett qorlortorssup tasia imaersartoq tordenso north midternaes and an outlet glacier of the a p olsen ice cap overall megaflood type landscape impacts in iceland tend to be best preserved and most easily identified inland although there has also been extensive offshore sedimentation there are very few reported impacts of glacier outburst floods in greenland in greenland ice dam failure causes frequent flooding compared to the volcanically triggered floods in iceland and this combined with the proximity of the greenland glacier lakes to the coast means that most proglacial channels in greenland are flood hardened and most landscape impact is likely to be offshore in estuaries and fjords future floods with megaflood type attributes will occur in iceland induced by volcanic activity in greenland they will be induced by extreme weather and rapid ice melt any potential landscape impact of these future floods remains open to question

interpretation of rayleigh wave ellipticity observed with multicomponent passive seismic interferometry at hekla volcano iceland the 2010 eruption of eyjafjallajokull has drawn increased attention to iceland s eastern volcanic zone evz due to the threat it poses to the heavily used air traffic corridors of the northern atlantic ocean within the evz hekla is historically one of the most active volcanoes and has exhibited a decadal eruption pattern for the past 40 years hekla most recently erupted in 2000 and is thus ripe for another decadal eruption because hekla is generally aseismic except for a brief time period hours leading up to an eruption monitoring has previously depended on precursory deformation signals linde et al 1993 as a result seismic tomography of the internal structure of the volcano using phase arrivals of local earthquakes is not possible motivated by hekla s practically aseismic behavior in inter eruptive periods we installed a temporary network of four broadband seismometers around the volcanic edifice in late august 2010 with the intention of investigating the applicability of passive seismic

source location of the 26 sec microseism from cross correlations of ambient seismic noise 1 very strong narrow band rayleigh wave arrivals peaking near 26 sec are observed in cross correlations of long time sequences of ambient noise records on us european and african stations with apparent arrival times that are typically smaller than expected for propagation along the great circle linking the stations use of these apparent travel times to locate the source of narrow band arrivals shows that the waves originate off the west african coast in the gulf of guinea and propagate with an average speed of about 3 5 km s i e close to the expected group speed of rayleigh waves at this period using data from different months demonstrate that the source location is temporally stable with amplitudes that maximize during the southern hemisphere winter a microseism with similar features but with a slightly broader spectral peak is observed at stations in east asia and in the western pacific and apparently originates in the north fiji basin the nearly antipodal location of the two source regions leads to the hypothesis that the 26 sec signals are excited by a single source located in the gulf of guinea the pacific inter station cross correlations may be for major arc propagation

the crustal magma chamber of the katla volcano in south iceland revealed by 2 d seismic undershooting summary results of a 2 d seismic undershooting experiment on the katla central volcano in south iceland are reported large localized traveltime anomalies 0 4 s are observed on an array within the katla caldera the traveltimes are forward modelled using a wavefront tracker developed in appendix a thus non linear effects encountered in traveltime tomography are avoided as well as common problems with ray tracing in the presence of strong lateral heterogeneity an extreme variation in compressional velocity is required to extend over a significant volume in order to model the data the resulting model is not unique but constraints on the allowable range of velocities 2 5 6 0 km s render the basic features well constrained a clear s wave shadow is closely associated with delays in traveltime due to a shallow slow anomaly low amplitude p waves go hand in hand with early arrivals due to thin structural features flanking the slow anomaly the model is interpreted in terms of a magma chamber containing extensively molten rock the magma chamber is shallow with a bottom at a depth of about 1 5 km below sea level 3 0 km below surface and measures about 5 km across the depth of the chamber is roughly at the level of buoyant equilibrium for basaltic melt in the crust owing to poor vertical resolution at shallow depths in the undershooting geometry the top of this shallow magma chamber is not well resolved on the other hand the bottom of the chamber is well resolved the chamber is underlain by rocks of average or high velocity for that depth the magma chamber is a persistent feature big enough 10 km3 to supply magma for large eruptions and to supply heat to permit remelting of hydrated basaltic crust to produce silicic magmas at shallow levels the chamber is fed by magma fracturing from below the model agrees with phenomenological models of magma chambers in iceland based on geological observations and provides a quantification of those models in terms of depth and size on the other hand it is fundamentally different from recent models of magma chambers at mid ocean ridges which may be more akin to the pervasive region of partial melt at depth beneath iceland this underlines the important effect of the icelandic hotspot on tectonics and volcanism in iceland and implies a substantially different crustal and thermal structure in iceland from that of normal mid ocean ridges

observations of volcanic tremor at mount st helens volcano digital recordings of ground motion during tremor episodes accompanying eruptions at mount st helens volcano in the state of washington on august 7 and october 16 18 1980 are studied the spectra of the vertical component waveforms contain at least two dominant peaks at 1 0 and 1 3 hz for all events recorded during both eruptions that were studied spectra of horizontal ground motion show peaks at 0 9 and 1 1 hz the relative amplitude of the two peaks changes between tremor episodes and during single tremor episodes and shows no consistent relation to amplitude of ground motion spectra of long period earthquakes are very similar to those of tremor events suggesting that tremor is composed of many long period earthquakes that occur over a period of time the unique waveform of tremor events observed at mount st helens must be due to a source effect since the relative amplitude of the two dominant peaks changes during tremor episodes the path effect on tremor waveforms is small since there are no peaks in the spectra of waveforms recorded during tectonic earthquakes occurring in the vicinity of mount st helens the consistency of the location of the spectral peaks for the wide range of tremor amplitudes means that there must be a physical length at the source that is constant independent of the amplitude of motion at the source variations in amplitude of motion generated during tremor events must be due to variations in the force driving the tremor amplitudes of ground motion varies between 0 11 and 4 7 m seismic moment rates during the two eruptions are calculated using the model of aki et al 1977 and found to vary between 6 1018 and 1 1020 dynes cm s 1 which are larger than values found by aki et al 1977 who studied amplitudes of shallow tremor events recorded during the october 1963 eruption of kilauea volcano in hawaii study of tremor amplitudes recorded at corvallis oregon leads to the conclusion that tremor accompanying the cataclysmic may 18 1980 eruption was at least one order of magnitude larger in amplitude than tremor during august and october

ordinary mesostasis and not so ordinary symplectites late stage assemblages in howardites abstract two categories of symplectites have been observed in howardites three phase composed of vermicular intergrowths of ferroan augite fayalitic olivine and silica and two phase composed of vermicular intergrowths of orthopyroxene and troilite three phase symplectites have been previously shown to represent the breakdown products of metastable pyroxene in howardites they appear to be genetically related to gabbroic eucrites in some cases and under yet to be specified conditions ferroan clinopyroxene in gabbroic eucrites may undergo only localized decomposition resulting in oriented exsolution like features breakdown phases in those cases are fayalitic olivine silica and depending on the mgo content of the system orthopyroxene as opposed to three phase symplectites two phase symplectites are most likely of diogenitic origin they probably formed via impact induced localized melting of diogenitic orthopyroxene in the presence of troilite grain boundary melting three phase symplectites in howardites occasionally contain accessory amounts of ilmenite troilite and or kamacite and are exclusively associated with medium grained feo rich pyroxene silica and plagioclase all minerals involved are late stage crystallites or mesostasis phases in general highly evolved eucritic lithologies constitute only a minor fraction of howardites however considering that three phase symplectites are generated in a low pressure i e near surface environment feo and cao rich eucritic rocks may be exposed locally on vesta s surface this in turn is highly relevant to the ongoing dawn mission

experimental flume study of the deposition of heavy minerals in a simulated witwatersrand sandstone unconformity the concentration of heavy minerals in a sedimentary deposit depends inter alia on the composition of the source material local hydraulic conditions during deposition sizes and densities of the sediment grains and sizes of the grains relative to the bed roughness effects of these factors have been investigated in a laboratory flume by depositing pure heavy mineral and mixed heavy and light mineral sediments on a stationary granular bed experiments with pure heavy minerals indicate that once a minimum mobility condition is exceeded deposits will be fairly extensive and uniform and only slightly affected by the flow condition in all experiments deposits were generally finer grained than the supply sediments and in some cases were bimodal the concentrations and total amounts of heavy mineral in the deposits were influenced by the concentrations in the supply mixtures and were strongly dependent on the sizes of the light mineral grains the results show that settling velocity is a poor indicator of hydraulic equivalence while critical shear velocity appears to be a good indicator

variations in tilt rate and harmonic tremor amplitude during the january august 1983 east rift eruptions of kilauea volcano hawaii abstract during january august 1983 a network of telemetered tiltmeters and seismometers recorded detailed temporal changes associated with seven major eruptive phases along the east rift of kilauea volcano hawaii each eruptive phase was accompanied by subsidence of the summit region and followed by reinflation of the summit to approximately the same level before renewal of eruptive activity the cyclic summit tilt pattern and the absence of measurable tilt changes near the eruptive site suggest that conditions in the summit region controlled the timing of the last six eruptive phases the rate of summit subsidence progressively increased from one eruptive phase to the next during the last six phases the amplitude of harmonic tremor increased during the last four phases the increases in subsidence rate and in tremor amplitude suggest that frequent periods of magma movement have reduced the flow resistance of the conduit system between the summit and the rift zone

characteristics of seismic waves composing hawaiian volcanic tremor and gas piston events observed by a near source array a correlation method specifically designed for describing the characteristics of a complex wave field is applied to volcanic tremor and gas piston events recorded by a semicircular array of geos instruments set at the foot of the puu oo crater on the east rift of kilauea volcano hawaii the spatial patterns of correlation coefficients obtained as functions of frequency for the three components of motion over the entire array are similar for gas piston events and tremor and clearly depict dispersive waves propagating across the array from the direction of puu oo the wave fields are composed of comparable amounts of rayleigh and love waves propagating with similar and extremely slow phase velocities ranging from 700 m s at 2 hz to 300 m s at 8 hz the highly cracked solidified lava flow on which the array was deployed and subjacent structure of alternating lava and ash layers formed during repeated eruptions of puu oo since 1983 appear to be responsible for the low velocities observed the results from puu oo stand in sharp contrast to those obtained in an experiment conducted in 1976 on the partially solidified lava lake of kilauea iki rayleigh waves were not observed in kilauea iki but well developed trains of love waves were seen to propagate there with velocities twice as high as those observed near puu oo these differences in the propagation characteristics of surface waves at the two sites may be attributed to the presence of a soft horizontal layer of molten rock in kilauea iki which may have lowered the phase velocity of rayleigh waves more drastically than that of love waves resulting in severe scattering of the rayleigh wave mode on the other hand the thin superficial pahoehoe flow under our array at puu oo may have favored the development of vertical columnar joints more extensively at this location than at kilauea iki which may have reduced the shear moduli controlling the love wave mode the average phase velocities in the frequency band from 2 to 5 hz found at puu oo are roughly similar to those determined for tremor at klyuchevskoy volcano kamchatka but the frequency dependence appears much stronger at puu oo

glacial long period seismic events at katla volcano iceland repeating long period lp earthquakes are commonly8 observed in volcanic regions worldwide they are usually9 explained in terms of a volcanic source effect or anomalous10 propagation through the

long period seismic events with strikingly regular temporal patterns on katla volcano s south flank iceland katla is a threatening volcano in iceland partly covered by the myrdalsjokull ice cap the volcano has a large caldera with several active geothermal areas a peculiar cluster of long period seism

joint relative location of earthquakes without a pre defined velocity model an example from a peculiar seismic cluster on katla volcano s south flank iceland relative location methods are commonly used to precisely locate earthquake clusters consisting of similar waveforms repeating waveforms are often recorded at volcanoes where however the crust s

hydrologic and geomorphic effects of temporary ice dammed lake formation during jokulhlaups glacial outburst oods jokulhlaups occur frequently in glaciated environments and the resultant ooding causes geomorphic change and in some instances damage to local infrastructure during some jokulhlaups oodwater is stored temporarily in ice marginal locations in july 1999 a linearly rising jokulhlaup burst from solheimajokull iceland during this remarkable event subglacial oodwater pooled transiently in two relict ice dammed lake basins before draining suddenly back into solheimajokull the signi cance of such rapid formation and attendant drainage of temporary ice dammed lakes during jokulhlaups has not been addressed consequently this paper i assesses the hydrologic and geomorphic effects of temporary ice dammed lake formation caused by lake basin retro lling and ii discusses the impact and signi cance of transient retro lling under jokulhlaup conditions pre and post ood eldwork at solheimajokull enabled the impact and signi cance of lake basin retro lling to be assessed field evidence demonstrates that the july 1999 jokulhlaup had an unusually rapid rise to peak discharge resulting in subglacial oodwater being purged to ice marginal locations the propensity for temporary retro lling was controlled by rapid expulsion of oodwater from solheimajokull coincident with locations suitable for oodwater storage floodwater inundated both ice marginal lake basins permitting signi cant volumes of sediment deposition coarse grained deltas prograding from the ice margin and boulders perched on scoured bedrock provide geomorphic records of sudden retro lling the depositional characteristics of lake basin deposits at solheimajokull are similar to jokulhlaup sediments documented in proglacial settings elsewhere however their depositional setting and association with ice marginal landforms is distinctive findings suggest that temporary ice dammed lake formation and drainage has the capacity to alter the shape of the ood hydrograph especially if drainage of a temporary lake is superimposed on the original jokulhlaup deposits associated with lake basin retro lling have a long term preservation potential that could help to identify temporary ice dammed lake formation in modern and ancient glacial environments copyright 2003 john wiley sons ltd

ash from the eyjafjallajokull eruption iceland fragmentation processes and aerodynamic behavior 1 the fragmentation process and aerodynamic behavior of ash from the eyjafjallajokull eruption of 2010 are investigated by combining grain size scanning electron microscopy sem and quantitative particle morphology ash samples were collected on land in iceland at 3 55 km distance from the volcanic vent and represent various phases of the pulsating eruption the grain size is fine even for deposits close to the vent suggesting that the parent particle population at fragmentation consisted of a substantial amount of fine ash sem investigation reveals that ash produced during the first phase of the eruption consists of juvenile glass particles showing key features of magma water interaction suggesting that phreatomagmatism played a major role in the fragmentation of a vesicle poor magma in the last phase of the eruption fragmentation was purely magmatic and resulted from stress induced reaction of a microvesicular fragile melt the shape of ash as determined by quantitative morphology analysis is highly irregular rendering the settling velocity quite low this makes transportation by wind much easier than for other more regularly shaped particles of sedimentary origin we conclude that the combination of magma s fine brittle fragmentation and irregular particle shape was the main factor in the extensive atmospheric circulation of ash from the mildly energetic eyjafjallajokull eruption

a double correlation tremor location method a double correlation method is introduced to locate tremor sources based on stacks of complex doubly correlated tremor records of multiple triplets of seismographs back projected to hypothetical s

trace element characteristics of different pyrite types in mesoarchaean to palaeoproterozoic placer deposits a comparative in situ la icp ms trace element study on pyrite from three different variably auriferous archaean to palaeoproterozoic palaeoplacer deposits in the ouro fino syncline quadrilatero ferrifero brazil the elliot lake area north of lake huron se canada and several deposits within the witwatersrand basin south africa revealed systematic differences between morphologically different pyrite types and between the various palaeoplacer deposits especially the ni and au concentrations as well as co ni and mo ni ratios were found to be systematically different in detrital compact detrital porous and post sedimentary hydrothermal pyrite grains from different source areas high co ni ratios and low au concentrations are typical of post sedimentary pyrite which is hydrothermal in origin in contrast relatively low co ni ratios and high au contents characterise detrital porous banded and concentric pyrite grains au 1 ppm which are syn sedimentary in origin in the elliot lake area and the witwatersrand basin detrital compact rounded pyrite is characterised by high co ni ratios which is in agreement with derivation from a hydrothermal source low au concentrations in this pyrite type support the contention of the gold and the pyrite in these deposits coming from different source rocks in contrast derivation from an originally diagenetic pyrite is suggested for the detrital compact pyrite in the ouro fino syncline because of low to intermediate co ni ratios high au contents may indicate a genetic relationship between pyrite and gold there systematic differences exist between the three areas with respect to au ni co mo and cu distributions in detrital pyrite which reflects differences in the provenance a predominantly mafic ultramafic source is indicated for the ouro fino a felsic source for the elliot lake and a mixed felsic mafic provenance for the witwatersrand pyrite populations independently of pyrite type the higher au endowment of the studied witwatersrand and ouro fino conglomerates are also reflected by an overall higher au concentration in the respective pyrite grains compared to the relatively au poor samples from elliot lake in general a strong positive correlation between au and pb levels in the various pyrite grains is noted analogous to pb which is well known for not being easily accommodated in the pyrite crystal lattice but occurring as discrete pbs phases au is considered to be present mainly in the form of discrete au phases in minute pores and interstices of the pyrite grains rather than within the pyrite lattice

the origin of eucrites diogenites and olivine diogenites magma ocean crystallization and shallow magma chamber processes on vesta the asteroid 4 vesta is one of the very few heavenly bodies to have been linked to samples on earth the howardite eucrite diogenite hed meteorite suite this large and diverse suite of meteorites provides a detailed picture of vesta s igneous and postigneous history we have used the range of igneous rock types and compositions in the hed suite to test a series of chemical models for solidification processes following peak melting magma ocean conditions on vesta fractional crystallization cannot have been a dominant early process in the magma ocean because it leads to excessive fe enrichment in the melt models that are dominated by equilibrium crystallization cannot produce orthopyroxene cumulates diogenites our best models invoke 60 70 equilibrium crystallization of a magma ocean followed by continuous extraction of the residual melt into shallow magma chambers fractional crystallization in these magma chambers combined with continuous or periodic addition of more melt from the slowly compacting crystal mush magmatic recharge can produce all of the igneous hed lithologies noncumulate and cumulate eucrites diogenites dunites harzburgites and olivine diogenites magmatic recharge can also explain the narrow range in eucrite compositions and the variability of incompatible trace element concentrations in diogenites we predict an internal structure for vesta that permits excavation of the heds during the formation of the rheasilvia basin while remaining consistent with observations from the dawn mission and most impact models

la icp ms elemental mapping of pyrite an application to the palaeoproterozoic atmosphere a hydrothermal origin has been advocated for the genesis of rounded and subhedral euhedral pyrite in some neoarchaean palaeoproterozoic clastic sedimentary rocks thereby limiting their value as proxies for the composition of the early atmosphere we present laser ablation inductively coupled plasma mass spectrometry la icp ms element maps of rounded and euhedral subhedral pyrite grains from the basal conglomerates of the palaeoproterozoic mississagi formation huronian supergroup canada these maps reveal the common existence of rounded detrital cores and isolated grains variably modified by hydrothermal overgrowth the detrital origin of pyrite grains is demonstrated by the rounding of isolated grains and the presence of cores in subhedral euhedral grains rounding and breakage of grains is implied to have occurred via physical abrasion during sediment transport furthermore trace element maps expose truncated cores of originally rounded detrital fragments that also indicate abrasive rather than accretional or dissolutional rounding finally we document a complex core that consists of multiple grains suggestive of various source materials that were co deposited in the original placer textural and geochemical evidence further suggests the detrital porous pyrite had a diagenetic origin prior to fluvial transport grain size and shape analysis suggests that the large porous pyrite cores and grains may have had a shorter transport distance than the on average smaller compact rounded grains transport was prolonged from tributaries into the main valley and the high energy setting implies well aerated palaeoproterozoic river water since pyrite is unstable under oxidising conditions the frequent survival of detrital pyrite in the fluvial mississagi formation after sustained transport in the catchment basin and alluvial valley as well as aerated palaeoproterozoic river waters therefore implies that the contemporary atmosphere was oxygen deficient the depositional age of the mississagi formation is between 2 45 ga thessalon fm and 2 31 ga gordon lake fm and the presence of the detrital pyrite therefore suggests that the atmosphere was devoid of any significant amount of free oxygen at the time immediately preceding the great oxygenation event c 2017 elsevier b v all rights reserved

kinematic parameters of the tremor wave field at mt etna sicily the tremor wave field at mt etna was recorded with an array of three 3 component broad band seismometers the analysis of its polarisation and dispersion properties leads to the conclusions that 1 the wave field consists mainly of surface waves and that 2 two of the observed spectral peaks are caused by a wave guide effect along the propagation path

ancient water on asteroid 4 vesta evidence from a quartz veinlet in the serra de mage eucrite meteorite abstract the meteorite serra de mage a eucrite inferred to be from the asteroid 4 vesta contains quartz veinlets they are identical to antitaxial or crack seal quartz veinlets in terrestrial rocks and are extraterrestrial and ancient because they pre date a 4 40 ga metamorphism the quartz was likely deposited from liquid water solutions as are terrestrial veins other potential solvents or transport mechanisms are inadequate or unlikely because there is no indication of internal magmatic water in the eucrite meteorites and thus in vesta the water from which the veinlet was deposited probably came from outside vesta by analogy with water ice deposits on the moon and mercury vesta and similar asteroids may have had or now have polar ice deposits possibly derived from comet impacts

geothermal activity in the subglacial katla caldera iceland 1999 2005 studied with radar altimetry the katla caldera is located under the myrdalsjokull ice cap and is one of the most hazardous volcanoes in iceland due to major jokulhlaups that accompany eruptions subglacial geothermal activity is manifested in several 10 50 m deep depressions ice cauldrons within and at the caldera rim and the total geothermal heat output is of the order of a few hundred megawatts a short lived but powerful pulse in geothermal heat output took place in 1999 probably including a minor subglacial eruption when new ice cauldrons formed in three places and an unexpected jokulhlaup occurred following these events a comprehensive monitoring program was set up for katla including ice surface elevation profiling from aircraft to monitor variations in geothermal heat and detect signs of subglacial water accumulation a radar altimeter coupled with a kinematic gps is used achieving an absolute elevation accuracy of 3 m and internal consistency of 1 2 m profiles across the caldera are flown twice a year an annual accumulation ablation cycle in surface elevation with amplitude of 5 10 m is observed by removing this cycle from the data changes due to subglacial geothermal activity are obtained after the events in 1999 a decline in geothermal activity was observed in 2001 03 some ice cauldrons expanded and deepened by 10 15 m indicating renewed increase in geothermal activity this trend is also apparent for 2003 05 the increase in geothermal power amounts to a few tens of megawatts it is likely that the increased thermal output is related to increased seismicity and caused by magma inflow

volcanic tremor location during the 2004 mount etna lava effusion 1 a lava emission started at mt etna italy on 7 september 2004 neither earthquake seismicity heralded or accompanied the opening of the fracture field from which the lava poured out nor volcanic tremor changed in amplitude and frequency content at the onset of the effusive activity to highlight long term changes we propose a method for the location of the tremor source based on a 3d grid search using the amplitude decay of the seismic signal from january to november 2004 we find the centroid of the tremor source within a zone close to and partially overlapped with the summit craters pre effusive phase which extended up to 2 km south of them effusive phase the depths are of between 1698 and 2387 m a s l we hypothesize the lava effusion stemmed from a degassed magma body although we find evidence of temporary magma overpressure conditions such as those documented on 25 september

long period seismicity reveals magma pathways above a laterally propagating dyke during the 2014 15 barðarbunga rifting event iceland abstract the 2014 15 bar arbunga holuhraun rifting event comprised the best monitored dyke intrusion to date and the largest eruption in iceland in 230 years a huge variety of seismicity was produced including over 30 000 volcano tectonic earthquakes vts associated with the dyke propagation at 6 km depth below sea level and large magnitude earthquakes accompanying the collapse of bar arbunga caldera we here study the long period seismicity associated with the rifting event we systematically detect and locate both long period events lps and tremor during the dyke propagation phase and the first week of the eruption we identify clusters of highly similar repetitive lps which have a peak frequency of 1 hz and clear p and s phases followed by a long duration coda the source mechanisms are remarkably consistent between clusters and also fundamentally different to those of the vts we accurately locate lp clusters near each of three ice cauldrons depressions formed by basal melting that were observed on the surface of dyngjujokull glacier above the path of the dyke most events are in the vicinity of the northernmost cauldron at shallower depth than the vts associated with lateral dyke propagation at the two northerly cauldrons periods of shallow seismic tremor following the clusters of lps are also observed given that the lps occur at 4 km depth and in swarms during times of dyke stalling we infer that they result from excitation of magmatic fluid filled cavities and indicate magma ascent we suggest that the tremor is the climax of the vertical melt movement arising from either rapid repeated excitation of the same lp cavities or sub glacial eruption processes this long period seismicity therefore represents magma pathways between the depth of the dyke vt earthquakes and the surface notably we do not detect tremor associated with each cauldron despite melt reaching the base of the overlying ice cap a concern for hazard monitoring

placer formation in gravel bedded rivers a review the literature on placer formation processes within fluvial systems is widespread and ranges between detailed laboratory studies of the hydrodynamic segregation processes through to the intuitive interpretation of the distribution of minerals within geological sections however there are few if any comprehensive reviews of the literature surprisingly given the economic importance of placers the theoretical framework relating to the hydrodynamics of physical grain sorting is not well developed and there are relatively few detailed laboratory hydraulic investigations to inform theory in this wide ranging review the history of the development of principles of placer formation is explored as far as possible in a non technical fashion a consideration is given to the hydrodynamics of physical grain sorting above lower stage and upper stage bedforms and the typical internal sedimentary structures associated with placer concentrations are detailed finally examples of the depositional environment of diamond tin and gold placers are considered

volcanic tremor wave field during quiescent and eruptive activity at mt etna sicily abstract this paper reports the results of an analysis of volcanic tremor at etna in the years 1987 to 1992 the data utilized were obtained from the osservatorio vesuviano s serra la nave permanent station and several seismic surveys carried out by means of portable digital seismic stations equipped with three component geophones the spatial temporal patterns of main parameters such as intensity spectral content polarization and wave composition of volcanic tremor in different phases of etna s activity were studied eruptive activity appears to be significantly correlated with volcanic tremor in particular it is worth pointing out that the magma upwelling in the terminal part of the conduit is characterized by a marked increase in low frequency components 3 4 hz of the spectrum of volcanic tremor hence volcanic tremor at etna can be considered as a short period precursor of eruptions an analysis of polarization and propagation velocity of volcanic tremor shows the presence of love waves overlapping other seismic phases

ice volcano interactions during the 2010 eyjafjallajokull eruption as revealed by airborne imaging radar 1 during the eruption of the ice covered eyjafjallajokull volcano a series of images from an airborne synthetic aperture radar sar were obtained by the icelandic coast guard cloud obscured the summit from view during the first three days of the eruption making the weather independent sar a valuable monitoring resource radar images revealed the development of ice cauldrons in a 200 m thick ice cover within the summit caldera as well as the formation of cauldrons to the immediate south of the caldera additionally radar images were used to document the subglacial and supraglacial passage of floodwater to the north and south of the eruption site the eruption breached the ice surface about four hours after its onset at about 01 30 utc on 14 april 2010 the first sar images obtained between 08 55 and 10 42 utc show signs of limited supraglacial drainage from the eruption site floodwater began to drain from the ice cap almost 5 5 h after the beginning of the eruption implying storage of meltwater at the eruption site due to initially constricted subglacial drainage from the caldera heat transfer rates from magma to ice during early stages of cauldron formation were about 1 mw m 2 in the radial direction and about 4 mw m 2 vertically meltwater release was characterized by accumulation and drainage with most of the volcanic material in the ice cauldrons being drained in hyperconcentrated floods after the third day of the eruption meltwater generation at the eruption site diminished due to an insulating lag of tephra

diogenites as polymict breccias composed of orthopyroxenite and harzburgite abstract a few relatively unbrecciated olivine rich diogenites consist of an equilibrium assemblage of olivine and magnesian orthopyroxene harzburgite more common diogenites with smaller amounts of olivine are breccias containing two distinct orthopyroxenes one magnesian and one ferroan these diogenites are mixtures of a harzburgite lithology that is more magnesian with the normal orthopyroxenite lithology that is ferroan and may contain small amounts of plagioclase both lithologies likely formed by fractional crystallization in multiple plutons emplaced within the crust of asteroid 4 vesta minor element trends in orthopyroxenes indicate that these plutons exhibited a range of compositions we propose a revised taxonomy for the hed howardites eucrites and diogenites suite where all ultramafic samples are referred to as diogenites within this group the prefixes dunitic harzburgitic and orthopyroxenitic are used to distinguish diogenites consisting of more than or equal to 90 olivine olivine orthopyroxene and more than or equal to 90 orthopyroxene respectively the prefix polymict is used to describe brecciated mixtures of any of these rock types the recognition that olivine is a significant phase in some diogenites is consistent with spectral interpretations of olivine in a deeply excavated crater on vesta and has important implications for the bulk composition and petrogenesis of that body

permanent tremor of masaya volcano nicaragua wave field analysis and source location the masaya volcano nicaragua is a basaltic caldera in a subduction zone the permanent source of the volcanic tremor was located inside santiago crater at the lava lake s position and 400 m below the ne rim and therefore corresponds to superficial magma activity we used two tripartite arrays 90 m side one semicircular array r 120 m in 1992 and two semicircular arrays r 60 m and a 2500 m long linear array radiating out from the source and on the flank of the crater in 1993 we used both a cross spectrum method and a correlation method to determine the wave delay time between the reference station and the other stations of an array and to quantify the wave field using the delays therefore by intersecting the back azimuth wave directions from the arrays we could pinpoint the source additionally the correlation coefficients obtained as functions of frequency for the three components of motion confirm the inferred position of the source of tremor the tremor s wave field is composed of comparable quantities of dispersed rayleigh and love surface waves whose phase velocities lie in the ranges 730 1240 m s at 2 hz and 330 550 m s at 6 hz the dispersive phase velocities were inverted to obtain crustal structures with a minimal number of layers the resulting velocity models are similar for the northern and southern parts of the volcano after geometrical spreading corrections q2hz 14 and q3hz 31 were determined along the northern linear array the typical low velocities and low q corresponding to the cone structure and are similar to those of other basaltic volcanoes like puu oo hawaii and klyuchevskoy kamchatka

composition of the rheasilvia basin a window into vesta s interior 1 the estimated excavation depth of the huge rheasilvia impact basin is nearly twice the likely thickness of the vestan basaltic crust so the mantle should be exposed spectral mapping by the dawn spacecraft reveals orthopyroxene rich materials similar to diogenite meteorites in the deepest parts of the basin and within its walls significant amounts of olivine are predicted for the mantles of bulk chondritic bodies like vesta and its occurrence is demonstrated by some diogenites that are harzburgite and dunite however olivine has so far escaped detection by dawn s instruments spectral detection of olivine in the presence of orthopyroxene is difficult in samples with 25 olivine and olivine in rheasilvia might have been diluted during impact mixing or covered by the collapse of basin walls the distribution of diogenite inferred from its exposures in and around rheasilvia provides a geologic context for the formation of these meteorites but does not clearly distinguish between a magmatic cumulate versus partial melting restite origin for diogenites the former is favored by geochemical arguments and crystallization in either a magma ocean or multiple plutons emplaced near the crust mantle boundary is permitted by dawn observations

frictional faulting model for harmonic tremor before redoubt volcano eruptions volcanic tremor can be caused by small earthquakes occurring within the volcano mechanical modelling of volcanic tremor generated at redoubt volcano alaska suggests that high frequency tremor is the result of stick slip motion in faults within the volcano conduit

the 2011 unrest at katla volcano characterization and interpretation of the tremor sources abstract a 23 hour tremor burst was recorded on july 8 9th 2011 at the katla subglacial volcano one of the most active and hazardous volcanoes in iceland this was associated with deepening of cauldrons on the ice cap and a glacial flood that caused damage to infrastructure increased earthquake activity within the caldera started a few days before and lasted for months afterwards and new seismic activity started on the southern flank no visible eruption broke the ice and the question arose as to whether this episode relates to a minor subglacial eruption with the tremor being generated by volcanic processes or by the flood the tremor signal consisted of bursts with varying amplitude and duration we have identified and described three different tremor phases based on amplitude and frequency features a tremor phase associated with the flood was recorded only at stations closest to the river that flooded correlating in time with rising water level observed at gauging stations using back projection of double cross correlations two other phases have been located near the active ice cauldrons and are interpreted to be caused by volcanic or hydrothermal processes the greatly increased seismicity and evidence of rapid melting of the glacier may be explained by a minor sub glacial eruption a less plausible interpretation is that the tremor was generated by hydrothermal boiling and or explosions with no magma involved this may have been induced by pressure drop triggered by the release of water when the glacial flood started all interpretations require an increase of heat released by the volcano

the dispersion of magnetite bedload tracer across a gravel point bar and the development of heavy mineral placers economic concentrations of heavy minerals are often associated with fluvial point bars but prospecting models identifying the heaviest concentrations are poorly developed consequently the dispersal and storage of a heavy mineral bedload tracer magnetite across a rapidly evolving point bar was studied using magnetic susceptibility as a surrogate measure of magnetite concentration the bar head was a preferential area for the development of a placer owing to a lag accumulation of magnetite over an armoured bed surface in contrast when viewed in plan the bar platform and bar tail were regions of tracer dilution owing to downstream dispersion and mixing with shale in the vertical as the bar top rapidly aggraded however in section false bottom placers developed along bedding planes were evident the latter consisted of thin layers of concentrated magnetite resulting from the passage of bedload sheets consisting of a mix of shale and magnetite moving repeatedly from the bar head to accrete over the bar tail differential density sorting of magnetite and shale occurred during transport and deposition such that the heavier magnetite tended to accumulate as a visible concentrated bed layer later to be over run by layers of shale sediment in which magnetite was present diffusely however the placer thickness was greater than that visible because finer fractions of magnetite from each concentrated layer infiltrated the interstices of the top of the shale bed below the placer thickness the infiltration potential of the sediment bed and the actual rate of infiltration of the tracer were determined by fitting a mathematical function to measured variation in magnetic susceptibility with depth in the sediment body finally a simple mathematical model described in the literature as reproducing the plan view of flow and topographic patterns in river bends was found to reproduce patterns of depth velocity shear stress and competence in the point bar environment which were in accordance with the interpretation of the field data it was concluded that such a model when linked to entrainment functions for sediments of mixed density might be suitable for prospecting for economic heavy minerals in the point bar environment

detection of new olivine rich locations on vesta abstract the discovery of olivine on vesta s surface by the vir imaging spectrometer onboard the dawn space mission has forced us to reconsider our views of vestan petrogenetic models olivines were expected to be present in the interior of vesta in the mantle of a vertically layered body as invoked by the magma ocean models or at the base or within the mantle crust boundary as proposed by fractionation models olivines have been detected by vir dawn in two wide areas near arruntia and bellicia regions located in the northern hemisphere interestingly these olivine rich terrains are far from the rheasilvia and the more ancient veneneia basins which are expected to have excavated the crust down to reach the mantle in this work we present our attempts to identify other undetected olivine rich areas on vesta by using spectral parameters sensitive to olivine such as the band area ratio bar and other specific parameters created for the detection of olivines on mars forsterite fayalite and a generic olivine index as a preliminary step we calibrated these parameters by means of vis ir spectra of different hed meteorite samples behaviors versus sample grain size and albedo were analyzed and discussed we selected the bar and the forsterite index as the best parameters that can be used on vesta a cross correlation analysis has been applied in order to detect olivine signature on the vir hyperspectral cubes these detections have then been confirmed by an anti correlation analysis between the bar and one of the olivine parameters independent of the first method applied in agreement with the recent discovery arruntia and bellicia were found to be as the most olivine rich areas i e where the parameter values are strongest in addition we detected 6 new regions all but one located in the vesta north hemisphere this result confirms again that the old petrogenetic models cannot be straightforwardly applied to vesta and should be reshaped in the view of these new detections an alternative and very recent option can be represented by the model according to which surface eruption of material from the mantle including olivine can reach the surface of vesta

array measurements and modeling of sources of shallow volcanic tremor at kilauea volcano hawaii we show that resonances in near surface layers path effects or a combination of near surface resonances and source resonances source effects could be responsible for the sharp spectral peaks found in the records of gas piston activity and volcanic tremor recorded near puu oo crater on kilauea volcano hawaii two types of sources are found to be compatible with observations and can not be distinguished using our data in one model impulsive explosion point sources are embedded in the puu oo structure in the other model impulsive point sources of pressure excite the resonances of a fluid filled crack embedded in that structure both models require shallow sources z 100 m and display a strong dependence of the radiated spectrum on source depth over a depth range comparable to the overall thickness of the surficial layers based on these results it may be possible to track changes in source depth through temporal changes in observed spectra a potentially useful tool for monitoring volcanic activity at this site we estimate the depth and spatial extent of volcanic tremor and gas piston activity using two dense arrays with respective apertures of 800 and 120 m located near puu oo measurements of slowness ray parameter and azimuth as a function of time clearly indicate that the sources of volcanic tremor and gas piston activity are located beneath or in close proximity to the puu oo crater at depths shallower than approximately 1 km based on slowness and particle motion analyses we find that the records of volcanic tremor and gas piston events at puu oo consist of a complex combination of body and surface waves

record of s rich vapors on asteroid 4 vesta sulfurization in the northwest africa 2339 eucrite in the northwest africa nwa 2339 eucrite a few high fe pigeonite fragments were partially replaced by fine grained troilite mg rich augite silica with minor ilmenite and mg rich ferrosilite the relict pigeonite has distinctly lower fe mn values 17 18 than those 30 of augite and mg rich ferrosilite in the fine grained replacement textures and other eucritic pyroxenes in nwa 2339 the few plagioclase grains associated with these fe rich pigeonite fragments contain high albite components ab17 31 similar replacement textures are also present in a lithic clast consisting of pyroxene and na rich plagioclase ab20 25 in this lithic clast high fe subcalcic augite was replaced by troilite mg rich hedenbergite silica and minor ilmenite whereas mg rich pigeonite remains intact troilite also occurs as tiny inclusions in porous regions of plagioclase moreover the porous regions of plagioclase are enriched in si and depleted in al ca and na compared to relict plagioclase these textures indicate that the formation of troilite rich mineral assemblages is related to the reaction between fesio3 component in pyroxene and s rich vapors whereas the formation of tiny troilite in porous regions of plagioclase is related to the reaction between fe2 in plagioclase and s rich vapors x ray mapping results reveal that during sulfurization of pyroxene and plagioclase lithophile elements mn al ca na and mg were removed to various extents very likely by the s rich vapors based on our observations the s rich vapors could be dry s o p vapors which most likely have been formed by volatilization of pre existing s p bearing materials due to impact heating on the surface of asteroid 4 vesta