geomorphological evidence for jokulhlaups from kverkfjoll volcano iceland abstract jokulhlaups glacial outburst floods are known to have drained along the jokulsa a fjollum river in iceland during the holocene however little is known about their number age source and flow characteristics this paper provides detailed geomorphological evidence for jokulhlaups that have routed from the kverkfjoll ice margin and hence into the jokulsa a fjollum erosional evidence of jokulhlaups from kverkfjoll includes gorges cataracts spillways subaerial lava steps and valley wide scoured surfaces depositional evidence includes wash limits boulder bars cataract fill mounds terraces slackwater deposits and outwash fans some of these landforms have been documented previously in association with jokulhlaups however subaerial lava surfaces that have been scoured of the upper clinker gorges within pillow hyaloclastite ridges gorges between pillow hyaloclastite ridges and subaerial lava flows subaerial lava lobe steps cataract fill mounds and boulder run ups are previously undocumented in the literature these landforms may therefore be diagnostic of jokulhlaups within an active volcanic rifting landscape the nature and spatial distribution of these landforms and their stratigraphic association with other landforms suggest that there have been at least two jokulhlaups through kverkfjallarani the biskupsfell eruption occurred between these two jokulhlaups kverkfjallarani jokulhlaups were very strongly influenced by topography geology and interevent processes that together determined the quantity and nature of sediment availability such controls have resulted in jokulhlaups that were probably fluidal turbulent and supercritical over large areas of the anastomosing channel bed kverkfjallarani jokulhlaups would have had highly variable hydraulic properties both spatially and temporally the knowledge of flow characteristics that can be gained from jokulhlaup impacts has implications for recognising jokulhlaups in the rock record and for hazard analysis and mitigation within similar landscapes and upon other glaciated volcanoes

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

formation of an a ā lava delta insights from time lapse multibeam bathymetry and direct observations during the stromboli 2007 eruption five consecutive multibeam bathymetries collected before during and after the 2007 stromboli eruption combined with visual inspections allowed us to document the morphological evolution of an a lava fed delta and to reconstruct the main processes acting during its submarine emplacement the 2007 stromboli delta extended down to 600 m water depth and covered an area of 420 103 m2 with a maximum thickness of 65 m and a total estimated volume of 7 106 m3 i e three times larger than its subaerial counterpart the lava delta grew mainly through the emplacement of discrete lobes about 50 150 m in size lobes were fed from point sources along the paleoshoreline and their subaqueous pathways seem to be mainly controlled by the submarine morphology with flows mostly filling in depressions left by previous lobes the main controlling factors on the lobe morphology and thickness are the effusion rates and the pre eruption morphology i e the geometry and gradients of the basal surface data also shows that sudden slope failure of portions of the submarine delta may occur simultaneously with accretion implying that a significant part of the delta material can be transported to greater depths by submarine gravity flows the present study is relevant for future monitoring and hazard assessment during the growth of active lava fed deltas as well as for a better interpretation of ancient volcaniclastic successions inland

special collection on the june 1993 volcanic eruption on the coaxial segment juan de fuca ridge the mid ocean ridge system is the primary site of oceanic crustal accretion and a major source of chemical thermal flux from the earth s interior to the hydrosphere although geological mapping geophysical exploration and hydrographie chemical surveys have provided important insights into accretionary processes until recently there has been no method of monitoring the dynamics of these systems over long periods and large areas insights into spreading center dynamics have depended on serendipitous discoveries of evidence of activity based on water column anomalies baker et al 1987 bathymetric differences fox et al 1992 or direct field observations haymon et al 1993 in situ instrumentation has been used to monitor dynamics at a few selected sites for long periods but these instruments are generally unable to telemeter data in real time

volcanic investigations of the puna ridge hawai i relations of lava flow morphologies and underlying slopes abstract previous investigators have demonstrated that submarine lava flow morphologies are the result of a complex interplay between lava rheology effusion rate and underlying slope here we specifically investigate the relation between underlying slope and submarine lava flow morphology along three study sites of the puna ridge kilauea volcano hawai i using electronic still camera esc images and detailed bathymetry collected by argo ii we can compare the lava morphology and the associated underlying slope our results indicate that rubble is most common on the steepest slopes 25 and that pillowed and lobate flows dominate on slopes 20 sheet flows were only seen on relatively shallow slopes 15 these observations disagree with the results obtained from previous laboratory analog experiments suggesting that the laboratory results are directly applicable for lavas emplaced on relatively low

nature of and controls on volcanism in the ca 2 32 2 06ga pretoria group transvaal supergroup kaapvaal craton south africa abstract the time of deposition of the pretoria group between 2 32 and 2 06 ga on south africa s kaapvaal craton was characterized by the first major increase in atmospheric oxygen it was accompanied by the extrusion of significant thicknesses of volcanic deposits namely the bushy bend lavas of the timeball hill formation the hekpoort formation and the machadodorp volcanic member of the silverton formation marking the three major volcanic events within the transvaal supergroup which are thought to be precursors to the succeeding bushveld complex magmatism the bushy bend lava member of the timeball hill formation is characterized by subaqueous basaltic andesitic fissure eruptions with fumarolic activity and probably minor subaerial explosive eruptions in the hinterland of the transvaal supergroup basin the subaerial volcanism of the hekpoort formation appears to have been dominated by fissure eruptions with a preponderance of lava flows and locally important pyroclastic material intermittent hiatuses in volcanism were marked by local lacustrine shale deposition finally the machadodorp lava member can be interpreted as the deposits of several seamounts aligned along a fissure probably within an extensional environment the geodynamic control inferred for the evolution of the pretoria group basin encompasses two cycles of prerift uplift subsequent mechanical rifting and long lived thermal subsidence the limited extent of the bushy bend lavas in the south of the pretoria group depository attests to the likelihood that volcanism accompanying the first rifting event was short lived in contrast the second rifting cycle postulated for the pretoria group basin has a strong association with widespread and large scale volcanism of the hekpoort ongeluk flood basalts which may have been plume related the scale of the second cycle volcanism and its importance in influencing the upper part of the pretoria group basin fill is underlined by the machadodorp volcanism probably related to hot spot volcanism as the ongeluk hekpoort plume waned

importance of surface crust strength during the flow of the 1988 1990 andesite lava of lonquimay volcano chile 1 the emplacement of the 1988 1990 andesite lava of lonquimay volcano chile is examined using theoretical expressions for the relevant dynamical flow regimes the surface crust regime where the flow is controlled by the growth of a surface crust rather than by the rheology of the fluid interior is found to predict accurately the entire propagation of the lonquimay lava flow this discovery offers the exciting prospect of being able to predict the propagation of future blocky lavas simply from early observations of both the volume erupted and the flow length as functions of time without the need to know anything about the rheology of the interior lava

emplacement of the rocche rosse rhyolite lava flow lipari aeolian islands the rocche rosse lava flow marks the most recent rhyolitic extrusion on lipari island italy and preserves evidence for a multi stage emplacement history due to the viscous nature of the advancing lava 108 to 1010 pa s indicators of complex emplacement processes are preserved in the final flow this study focuses on structural mapping of the flow to highlight the interplay of cooling crust formation and underlying slope in the development of rhyolitic lavas the flow is made up of two prominent lobes small 0 2 m scale folding and a channelled geometry foliations dip at 2 4 over the flatter topography close to the vent and up to 30 50 over steeper mid flow topography brittle faults tension gashes and conjugate fractures are also evident across flow heterogeneous deformation is evident through increasing fold asymmetry from the vent due to downflow cooling and stagnation a steeper underlying topography mid flow led to development of a channelled morphology and compression at topographic breaks resulted in fold superimposition in the channel we propose an emplacement history that involved the evolution through five stages each associated with the following flow regimes 1 initial extrusion crustal development and small scale folding 2 extensional strain stretching lineations and channel development over steeper topography 3 compression at topographic break autobrecciation lobe development and medium scale folding 4 progressive deformation with stagnation large scale folding and re folding and 5 brittle deformation following flow termination the complex array of structural elements observed within the rocche rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at the chilean volcanoes of chaiten and cordon caulle offering a fluid dynamic and structural framework within which to evaluate our data

shapes of venusian pancake domes imply episodic emplacement and silicic composition the main evidence available for constraining the composition of the large circular pancake domes on venus is their gross morphology laboratory simulations using polyethylene glycol show that the height to diameter aspect ratios of domes of a given total volume depend critically on whether their extrusion was continuous or episodic with more episodes leading to greater cooling and taller domes thus without observations of their emplacement the compositions of venusian domes cannot be uniquely constrained by their morphology however by considering a population of 51 venusian domes to represent a sampling of many stages during the growth of domes with comparable histories and by plotting aspect ratio versus total volume we find that the shapes of the domes are most consistent with episodic emplacement on earth this mode of dome growth is found almost exclusively in lavas of dacite to rhyolite composition strengthening earlier inferences about the presence of evolved magmas on venus

the lobes of lava flows on earth and olympus mons mars the lobate distal margins of lava flows provide a useful source of morphological information on the rheology of the lava if the lobes are assumed to represent the arrest of free flowing isothermal bingham fluids on a slope the widths of lobes are a more useful practical index than lobe thicknesses because they are about an order of magnitude larger and can be more accurately measured from aerial photographs and other remote images lobes do not suffer from the changes in morphology that channels undergo during the course of eruptions a terrestrial data set of flow lobe and ancillary measurements from lavas throughout the range alkali olivine basalt to rhyolite shows some features that are predicted by the isothermal bingham fluid model these are correlation of width and thickness over more than two orders of magnitude and essentially no correlation of aspect ratio with slope there is a positive correlation of lobe width with silica content of the lava from a data set of measurements on lava flow lobes from the martian volcano olympus mons the mean value of aspect ratio 0 07 was found to be significantly less than that for the terrestrial data set 0 19 higher general levels of effusion rate on olympus mons are probably the factor responsible after normalisation lobe widths on olympus mons are found to be largely equivalent to those expected for terrestrial flows with andesitic basaltic silica contents

a ā lava flows in the deccan volcanic province india and their significance for the nature of continental flood basalt eruptions newly identified a lava flows outcrop intermittently over an area of 110 km2 in the western deccan volcanic province dvp india they occur in the upper thakurvadi formation in the region south of sangamner the flows one of which is compound are 15 25 m thick and exhibit well developed basal and flow top breccias the lavas have microcrystalline groundmasses and are porphyritic or glomerocrystic and contain phenocrysts of olivine clinopyroxene or plagioclase feldspar they are chemically similar to compound p hoehoe flows at a similar stratigraphic horizon along the western ghats petrographic and geochemical differences between a flows at widely spaced outcrops at the same stratigraphic horizon suggest that they are the product of several eruptions potentially from different sources their presence in the dvp could suggest relative proximity to vents this discovery is significant because a lavas are generally scarce in large continental flood basalt provinces which typically consist of numerous inflated compound p hoehoe lobes and sheet lobes their scarcity is intriguing and may relate to either their occurrence only in poorly preserved or exposed proximal areas or to the flat plateau like topography of flood basalt provinces that may inhibit channelization and a formation or both in this context the a flow fields described here are inferred to be the products of eruptions that produced unusually high effusion rate lavas compared to typical flood basalt eruptions whether these phases were transitional to lower intensity sustained eruptions that fed extensive low effusion rate p hoehoe flow fields remains unclear

the role of seamount volcanism in crustal construction at the mid atlantic ridge 24 30 n an analysis of approximately 6000 km2 of sea beam swaths indicates that the floor of the median valley of the mid atlantic ridge mar between 24 30 n is strewn with near circular volcanoes we have identified 481 seamounts in the height range 50 650 m because many of the features which appear to be seamounts do not meet our criteria fully they have not been counted and our numbers are likely a minimum estimate of the population the large abundance of seamounts on the median valley floor indicates that seamount volcanism plays an important role in the accretionary processes at this section of the mar the summit height distribution of the mar seamount population is consistent with the exponential frequency size distribution model for off axis eastern pacific seamounts jordan et al 1983 smith and jordan 1987 the model parameters for the mar population yield an average of about 195 seamounts per one thousand square kilometers and a characteristic height of about 60 m shape statistics compiled from the 481 seamounts give parameters that are exactly the same or cover the same range in values as those obtained from a study of pacific seamounts in the height range 140 3800 m smith 1988 implying a universal control on seamount construction based on the volcanic morphology we identify 18 spreading segments along the ridge all except two contain a prominent axial volcanic ridge many of the seamounts identified are associated with the axial ridges from the sea beam swaths we infer that the ridges are composed of piled up seamounts and hummocky flows and interpret them to be the primary sites of crustal construction this style of volcanism contrasts strongly with that observed at the east pacific rise where seamounts are virtually absent at the spreading axis the construction of seamounts and hummocky flows may be directly related to the fact that the mar is fed by magma chambers that are limited in size and frequency we suggest that small magma pockets with slow eruption rates produce seamounts either from pipes or initial fissure eruptions that collapse to construct a single edifice small magma bodies with somewhat higher eruption rates produce hummocky fissure fed flows using buoyancy arguments the heights of the mar seamounts are related to the depth of the magma bodies we hypothesize that small magma bodies rise buoyantly to the base of the hydrothermally cooled brittle lid where they are trapped and then erupt if this hypothesis is correct the thickness of the brittle lid controls seamount height and the exponential distribution of seamount summit heights implies that the thickness of the brittle hd follows an exponential distribution in time and space with characteristic thickness 1 4 1 9 km if seamounts and hummocky flows are fed each from their own discrete magma body trapped at the brittle ductile transition then the lower crust of the mar will be made up of the products of a multitude of small plutons

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

triterpane and sterane biomarkers in the ya13 1 condensates from qiongdongnan basin south china sea triterpanes and steranes in condensates from the ya13 1 gas field qiongdongnan basin were monitored the ya13 1 condensates have unusual biomarker distributions dominated by terpanes and steranes derived from higher plants anomalously abundant 1 got oleanane and remarkably abundant bicadinanes are present in the ya13 1 condensates whereas the 17alpha hopane contents are extremely low taraxastane and significantly abundant 17alpha diahopanes occur in the condensates in addition a number of unknown c 29 and c 30 pentacyclic triterpanes including previously unreported compounds were detected in the condensates some of which are significantly abundant the unknown compounds may be terrestrial biomarkers c 29 homologues are relatively predominant among the regular and rearranged steranes the diasterane concentrations are markedly higher than those of regular steranes the maturity of the ya13 1 condensates is relatively high at the peak to late oil generation stage corresponding to 0 85 1 10 ro based on sterane and terpane and including bicadinane maturity parameters i e t t 1 r and 2t r bicadinane ratios the above maturity assessment result is different from that based on diamondoid maturity parameters ro 1 60 1 70 org geochem 25 1996 179 which can be explained by a contribution of hydrocarbons from two sources at different depths the ya13 1 condensates were probably generated from the yacheng and lingshui coal bearing source rocks buried both in the qiongdongnan basin 3400 5000 m and in the yinggehai basin 5000 m the possible contribution of lower maturity hydrocarbons from the yacheng and lingshui formations 3400 4100 m in the qiongdongnan basin to the ya13 1 gases and condensates should not be neglected c 2003 elsevier science b v all rights reserved

the east pacific rise near 21 n 13 n and 20 s inferences for along strike variability of axial processes of the mid ocean ridge abstract data obtained along various segments of the mid ocean ridge mor are used to construct an idealized model for crustal accretion the model seeks to predict the topographic volcanic tectonic and hydrothermal characteristics of any given spreading segment of the mor as a function of distance away from the bounding transform faults this model is based on a series of detailed mapping efforts carried out on segments of the mor having a broad range of spreading rates between 2 and 16 cm yr this paper includes the results of the french searise program carried out during the summer of 1980 aboard the n o jean charcot and two american cruises conducted in 1981 aboard the r v melville

a simplified two component model for the lateral growth of pahoehoe lobes unconfined pahoehoe lobes composed of networks of numerous pahoehoe toes often show a transverse profile with central thickening and crude bilateral symmetry the overall widths of individual lobes are often relatively constant compared to the large diversity in widths of individual toes these observations collectively suggest that there is a lateral self confinement mechanism at the scale of a lobe although previous correlated random walk models successfully address the nature of this mechanism the underlying physical processes are still not clearly understood here we propose a simplified two component model for the lateral self confinement mechanism the model assumes that the surface crust retains an inner hot core until its overpressure surpasses the strength of the crust it also assumes that fracturing of the crust occurs at the top of the flow where the crust has the weakest strength and then a breakout of the hot core spills out to form a new flow unit episodic fracturing and subsequent coalescence of multiple toes form a broad lobe which is then considered theoretically to behave as a single large flow unit although simplified the model can determine the inflated thickness necessary to fracture the crust and the width scale of the lateral spreading with a self confinement effect the model also provides theoretical support for the correlated random walk model for pahoehoe emplacement

effect of surface solidification on the emplacement of lava flows on a slope 1 the emplacement dynamics of lava flows on a slope is investigated using theoretical analyses and laboratory experiments for the case where a fixed volume of lava is rapidly released and propagates downhill as a two dimensional flow when the lava has no internal yield strength we identify four dynamical flow regimes that can arise an inertial slumping regime a horizontal viscous regime a sloping viscous regime and a crust yield strength regime that finally stops the flow when the lava has an internal yield strength it can also flow in a sloping viscoplastic regime which is accurately predicted by a simple box model that we derive our results are applied to predict the propagation downhill of various volumes of two typical lavas a hawaiian lava with no internal yield strength and a mount etna lava with an internal yield strength in particular we find that sloping flows of the mount etna lava are stopped by the surface crust strength rather than the internal yield strength

high resolution studies of the summit of axial volcano sea beam bathymetry sea marc i side scan 30 khz towed camera and submersible data from axial volcano juan de fuca ridge jdfr have been integrated to produce detailed maps of the volcano s summit region in order to elucidate its volcanic and tectonic evolution the proximity of axial volcano the youngest edifice of the cobb eickelberg seamount chain to the jdfr superposes a hotspot derived radial stress pattern onto the linear stress field of a mid ocean ridge spreading center the morphology of the summit of axial volcano reflects the differing eruptive styles produced from this superposition long rift zones begin at the edges of the caldera and extend as much as 75 km to the north and south axial volcano has a distinct summit plateau similar to those found on many other submarine volcanos the process by which summit plateaus are constructed is illustrated by the lava flows originating from the south rift zone which have partially filled the southern half of the caldera and have smoothed the flanks the summit plateau contains penetrative ne sw fracturing that is approximately parallel to the jdfr the unusual rectangular caldera is 3 8 km in size and its trend is about 160 three possible mechanisms are discussed for the caldera s formation 1 canary island type trapdoor formation 2 overlapping spreading center interaction and 3 magma source migration although none of these models is fully compatible with the present data base the overlapping spreading center model is preferred postcaldera volcanism probably began with the formation of the central caldera eruptive complex which was characterized by relatively low volume high viscosity flows the most recent volcanism has apparently taken place along the northern and southern rift zones which have erupted more fluid lavas resulting in areally extensive flows covering up to 60 of the caldera floor extensive low temperature venting and areas of high temperature venting near the northern and southern rift zones and caldera walls suggest a shallow magmatic source beneath the summit of axial volcano

methods of determining the rheological properties of magmas at sub liquidus temperatures non vesicular basaltic melts behave as newtonian fluids at temperatures above their liquidus and their viscosities can be calculated using a method developed by shaw 1972 and bottinga and weill 1972 because many igneous processes involve the flow of silicates at sub liquidus temperatures numerous attempts have been made to calculate the interactive effects of the crystal phase however current methods are appropriate only for relatively low crystal concentrations and they assume newtonian behaviour we argue that this assumption is invalid when bubble or crystal concentrations exceed 30 at higher concentrations factors other than concentration become increasingly important these include particle shape and size distribution a method which takes these factors into account is tested on a range of suspensions including magmas at sub liquidus temperatures and rheological properties calculated using this method agree closely with the measured values we also demonstrate that an equation which was introduced to explain large differences in measured apparent viscosities during the cooling and crystallisation of mount st helens dacite murase et al 1985 and which is currently used to calculate the rheological properties of crystallising lavas generates viscosities which may be in error by several orders of magnitude this difference is argued to be caused by a combination of factors including the ten orders of magnitude range in the strain rates utilised during the mount st helens measurements causing orders of magnitude difference in the resulting apparent viscosities rheological data on crystallising silicic melts are reinterpreted taking into account the non newtonian rheology of the magmas and changes in activation energy of flow during crystallisation

the influence of topographic roughness on lava flow emplacement a quantitative understanding of the factors controlling lava flow emplacement is critical for both hazard assessment and mitigation and for the interpretation of past flow emplacement conditions the influence of topography with a vertical amplitude smaller than flow thickness i e substrate roughness is currently not accounted for in most flow emplacement models and hazard estimates here we measure the effect of substrate roughness on flow emplacement through experiments using analog fluids and molten basalt complementing recent work on the interaction of lava flows with obstacles taller than flow thickness we present results from three sets of analog experiments in which corn syrup polyethylene glycol and molten basalt were each extruded onto a sloping plane covered with a series of beds of varying grain sizes we find that flow front advance rates are impacted by bed roughness for all materials with decreases in average velocities by up to 50 with increases of substrate grain sizes by 5 100 times ranges analogous with topographic variations found in nature these decreases in flow front advance velocities are equivalent to up to an order of magnitude increase in fluid viscosity we interpret this velocity decrease to be caused by the movement of material into void spaces between substrate grains and by enhanced cooling through heat conduction to the substrate due to increased surface contact area the difference in advance velocity with increasing grain size diminishes with time after initial emplacement as a basal boundary layer is established additionally the experimental flow geometry measured by the complexity of the flow external perimeter became increasingly complex with increasing substrate grain size this effect will act to both slow the forward advance of lava flows and to create irregular emplacement paths of flows moving over rough surfaces we propose that flow emplacement models should be modified possibly through a calibrated effective viscosity term to account for bed roughness to increase accuracy in flow prediction and hazard estimation models

solidification and morphology of submarine lavas a dependence on extrusion rate the results of recent laboratory experiments with wax extruded beneath relatively cold water may be extrapolated to predict the surface morphology of submarine lavas as a function of the extrusion rate and melt viscosity the experiments with solidifying wax indicated that the surface morphology was controlled by a single parameter the ratio of the time taken for the surface to solidify and a time scale for lateral flow for submarine basalts a solution of the cooling problem which is dominated by conduction in the lava but convective heat transfer in the water and estimates of lava viscosities place this parameter within the empirically determined pillowing regime over a wide range of extrusion rates this result is consistent with the observation that pillow basalts are the most common products of submarine eruptions smoother surfaces corresponding to the various types of submarine sheet flows are predicted for sufficiently rapid extrusions of basaltic magma still higher eruption rates in regions of low topographic relief may produce submarine lava lakes minimum emplacement times can be calculated for submarine volcanic constructs of a single lava flow type

lava flows from a mid 1980s submarine eruption on the cleft segment juan de fuca ridge a series of lava flows with a total volume of 0 05 km3 were erupted in the mid 1980s along 17 km of the northern cleft segment of the juan de fuca ridge observations from camera tows and submersible dives show that the new flows are all similar in appearance and consist entirely of pillow lava with a mixture of smooth and striated surface textures suggesting a relatively uniform eruption rate approaching 1 m3 s at point source vents the flows vary in size from small patches to large steep sided ridges and were probably erupted from a dike intruded along the ridge axis because they are aligned along a linear fissure graben system observations at north cleft show that the physical appearance of new flows changes more rapidly than previously realized and that earlier qualitative dating of young lavas based on sediment cover and glassy surface texture were probably overestimates by an order of magnitude sediment accumulation on the lavas is quite variable and locally surprisingly substantial mainly due to hydrothermal deposits that formed while the lava flows were cooling biological vent communities photographed on the new flows in 1989 show that vent animals can colonize new vent sites rapidly but that warm water was still venting only in a few places nonvent animals are much slower to colonize the new flows and rates of colonization observed at north cleft may be useful for making improved age estimates of young 10 years lava flows elsewhere the north cleft eruption represents about 2 of the estimated average annual volcanic output along the global mid ocean ridge implying that many other submarine eruptions are occurring undetected

quantification of extraterrestrial lava flow effusion rates through laboratory simulations we have used carefully controlled laboratory simulations to develop a model which relates lava flow morphology to effusion rate and rheology through comparisons with measured and estimated eruption rates on earth this approach allows us to constrain eruptive styles and compositions of extraterrestrial lava flows by applying this model to lava flows on the moon mars and venus we have determined that all the common flow morphologies domes folds and levees on these planets could have been produced by basalt like or andesite like lavas through either continuous or episodic emplacement the presence of more evolved magma compositions on other planets is not required to explain any of the observed lava flow morphologies

axial seamount an active ridge axis volcano on the central juan de fuca ridge axial seamount some of the manuscripts in this special section refer to the edifice with the more precise name of axial volcano a large ridge axis volcano is located on the central segment of the juan de fuca ridge approximately 250 nautical miles west of the washington oregon british columbia coast currently both volcanically and hydrothermally active axial lies directly at the intersection of the cobb eickelberg seamount chain and the juan de fuca ridge figure 1 the volcanic activity associated with the seamount formation strongly interacts with and is affected by the normal seafloor spreading processes at the intersection because of this unique geologic setting its proximity to west coast ports and oceanographie institutions and its shallow depth axial has become the focus of a large number of scientific investigations over the past decade

a laboratory analog study of the surface morphology of lava flows extruded from point and line sources abstract in laboratory experiments designed to model lava flow processes liquid polyethylene glycol wax is forced through either a small hole or a long narrow slit onto the base of a tank of cold water where it spreads laterally while cooling and solidifying at its surface we observe the surface structure of the flow and its dependence on the flow rate thermal conditions and basal roughness in each case solidification of a crust during spreading gives rise to a number of different surface morphologies each of which forms under a restricted range of conditions the dominant morphologies referred to as pillows rifts transverse folds and marginal levees correspond to features observed on natural lava flows results for radial spreading over a rough base and for spreading in two directions from the line source over both smooth and rough bases complement those reported earlier for radial spreading of solidifying wax from a point source on a smooth base together they indicate a robust dependence of morphology on the distance from the vent at which solid crust begins to form this distance is in turn determined by the extrusion rate the rheology of the liquid wax or magma the reduced gravity the magnitude of the surface heat flux and the amount of cooling required to solidify the flow surface the results also indicate factors influencing the distribution of crust and its deformation and may provide a means by which observations of surface morphology can be used to place constraints on the emplacement conditions of lava flows

a laboratory investigation into the effects of slope on lava flow morphology abstract in an attempt to model the effect of slope on the dynamics of lava flow emplacement four distinct morphologies were repeatedly produced in a series of laboratory simulations where polyethylene glycol peg was extruded at a constant rate beneath cold sucrose solution onto a uniform slope which could be varied from 1 through 60 the lowest extrusion rates and slopes and highest cooling rates produced flows that rapidly crusted over and advanced through bulbous toes or pillows similar to subaerial toey pahoehoe flows and to submarine pillowed flows as extrusion rate and slope increased and cooling rate decreased pillowed flows gave way to rifted flows linear zones of liquid wax separated by plates of solid crust similar to what is observed on the surface of convecting lava lakes then to folded flows with surface crusts buckled transversely to the flow direction and at the highest extrusion rates and slopes and lowest cooling rates to leveed flows which solidified only at their margins a dimensionless parameter primarily controlled by effusion rate cooling rate and flow viscosity quantifies these flow types increasing the underlying slope up to 30 allows the liquid wax to advance further before solidifying with an effect similar to that of increasing the effusion rate for example conditions that produce rifted flows on a 10 slope result in folded flows on a 30 slope for underlying slopes of 40 however this trend reverses slightly owing to increased gravitational forces relative to the strength of the solid wax because of its significant influence on heat advection and the disruption of a solid crust slope must be incorporated into any quantitative attempt to correlate eruption parameters and lava flow morphologies these experiments and subsequent scaling incorporate key physical parameters of both an extrusion and its environment allowing their results to be used to interpret lava flow morphologies on land on the sea floor and on other planets

systematics of modal phenocryst assemblages in submarine basalts petrologic implications phenocryst assemblages in ocean ridge basalts generally show an increasing proportion of plagioclase as the total amount of phenocrysts increases the variations in phase assemblages as well as most crystal liquid kd s are similar to variations equimodal trends predicted by low pressure laboratory experiments suggesting that many of these basalts have experienced varying degrees of low pressure cyrstallization prior to quenching with little sorting of crystals and liquid important exceptions include moderately to highly phyric basalts enriched either in plagioclase or olivine which lie well off the experimental trends in these basalts megacrysts and xenocrysts usually cited as evidence for magma mixing commonly represent a small proportion of the total crystalline phase assemblage however phase proportions for many of these basalts lie well outside the range that could be produced by simple mixing selective gravitative sorting either prior or subsequent to mixing appears to be the likely explanation for these phyric basalts a relation between spreading rate and phase proportions is neither supported nor refuted by the data which as yet do not adequately represent fast spreading ridges

downflow width behavior of martian and terrestrial lava flows examination of the downflow width behavior of 59 terrestrial lava flows at puu oo hawaii and glass mountain california and 86 martian flows at alba patera tyrrhena patera elysium and olympus mons was completed using aerial photographs topographic maps previously published flow maps and viking orbiter images the examined lava flows exhibit diverse width behavior from which information about flow processes and conditions was assessed for puu oo flows no significant correlation was found between the average width of a flow and flow length or average underlying slope a significant but weak relationship was found between average width and average flow thickness in analyses of the downflow width behavior of individual flows no consistent correlations were observed between width and thickness or underlying slope when width was analyzed as a function of distance from the source for all flows a variety of flow width behavioral trends were recognized and quantitatively classified the most common behavior observed on earth and mars involved variations of width sometimes significant about a mean without a significant downflow narrowing or widening trend the distributions of width behavior trends for the alba patera and puu oo flows examined were similar with this type of constant behavior dominating in contrast tyrrhena patera flows showed a tendency to widen with distance downflow and silicic flows at glass mountain were more likely to narrow flows were also subdivided by distance from the vent and the width behavior of each division classified subdivision of flows resulted in significant changes in the classification of width behavior while width behavior in the medial regions of flows was similar to that over entire flow lengths proximal regions show more variability possibly due to greater fluidity of lavas near the vent and distal regions tend to uniformly narrow possibly due to limited supply in certain cases classification and subdivision analysis can be used to link flow emplacement processes to the resulting morphology in particular width behavior can be correlated to the presence or absence of lateral levees

a ā lava emplacement and the significance of rafted pyroclastic material marcath volcano nevada usa lava emplacement at monogenetic volcanoes has been seldom documented when compared to persistently active volcanoes such as mt etna or kilauea to expand the scientific understanding of lava emplacement and to help assess the hazards posed by monogenetic systems and of lava flows in general we present an investigation of the lava field at marcath volcano 35 ka lunar crater volcanic field central nevada usa key data include lava surface characteristics as well as size and abundance data of rafted pyroclastic material derived from the source cone upon exiting the source crater lava initially ponded in an upland saddle between marcath and an older cone before breaking out to feed three lava lobes that spread out onto a flat valley floor below quantitative estimates based upon morphological parameters suggest time averaged discharge rates of 40 100 m3 s 1 emplacement duration of 5 20 days and bulk lava viscosities on the order of 106 to 107 pa s in the main lobes sizes and distributions of 1021 mapped pyroclastic rafts suggest that the early stages of the eruption produced much of the total raft volume the source of most of the raft material was likely the now missing western portion of an early marcath cone after the initial breaching of the cone the raft production rate likely kept pace with cone building over the eruption s duration such that once the cone was breached on one side it did not heal rafts were not always passive passengers on the lava they had an important impact on lava morphology in specific locations as they caused bifurcation of entire flow lobes and produced other flow features the common occurrence of rafts in monogenetic lava fields suggests that incorporation of raft lava interactions may be important in lava propagation models

new field and laboratory evidence for the origin of hyaloclastite flows on seamount summits new field observations with the submersible alvin and photographic evidence from a study of the summits of seamounts near the east pacific rise show that hyaloclastite deposits occur commonly hyaloclastite outcrops were found on six volcanoes at depths from 1240 to 2500 m these new observations plus laboratory study of new hyaloclastite specimens extend the results of previous studies most of the hyaloclastite samples are of hydrovolcanic eruptive origin but a few show evidence of a predominantly sedimentary origin primarily from morphology we identify several vent areas from which hyaloclastite presumably erupted the surface appearance of the hyaloclastite deposits varies with distance to these vents leading us to propose a facies model for deep sea hyaloclastites on seamount summits hyaloclastites of hydromagmatic origin exhibit weak normal grading and bedding parallel alignment of platy shards they consist of blocky sliver and fluidal basalt glass shards and lithics in a matrix that contains pelagic sediment the shards themselves are remarkably free of even the tiniest crystals and are usually chemically homogeneous we propose that the shards form mainly by cooling contraction granulation but cannot rule out the possibility of limited steam explosivity hyaloclastites are closely associated with submarine pahoehoe and we propose that a very rapid eruption rate promoting clastic dominated versus flow dominated eruptive behavior is the dominant control on hyaloclastite formation we propose that shard formation occurs during submarine lava fountaining gravitational instability of the resulting slurry of shards sea water and possibly steam causes gravity flow that carries the shards outward from the vent further field and modelling studies are needed to test these ideas and more quantitatively constrain the ascent mechanism eruption dynamics and deposition of deep sea hyaloclastites

news from the north a late middle palaeolithic site rich in handaxes on the drenthe frisian till plateau near assen the netherlands first results of a trial excavation abstract the first middle palaeolithic artefacts to turn up in situ in boulder sand erosional residue of glacial till were found in 2011 the open air site is located on the saalian till plateau in the northern netherlands not far from the city of assen the capital of the province of drenthe the finds from a trial excavation comprise flakes blades cores and retouched tools the latter category consists predominantly of handaxes but a few side scrapers and backed knives are also present apart from erratic baltic flint of which most artefacts are made raw materials include quartzitic sandstone quartzite and remarkably halleflinta rock flint the assemblage is exceptional because of the many handaxes that dominate the tool spectrum leading the authors to suggest that butchering activities played a major role in the formation of the assemblage one of the reasons for neanderthals to frequent this location which is situated near a stream valley close to the confluence with a small tributary might be the presence of relatively good quality flint nodules and fairly large slabs of halleflinta the site is one of the northernmost middle palaeolithic occurrences in the netherlands in europe as well and obviously postdates the saalian glaciation mis 6 assen most likely dates to mis 3 or mis 5a 5c of the weichselian the presence of many relatively small sub cordiform and sub triangular handaxes indicates a cultural affiliation with the mousterian of acheulian tradition type a the site is situated near the northern limit of the occupation range of middle palaeolithic hominins and the lithic assemblage is comparable to that from several other sites in the northern part of the north european plain

styles of eruptive activity on intraplate volcanoes in the society and austral hot spot regions bathymetry petrology and submersible observations submersible observations carried out in the society and austral hot spot regions south pacific during the teahitia ii cruise 1988 1989 enable us to propose a model relating the style of volcanism to the depth of eruption on large intraplate seamounts 1 the bases of volcanic edifices are characterized by broad flat flows formed during a high rate of discharge of a very fluid magma on the sea floor 2 the edifices flanks deeper than 500 m are mainly made up of bulbous tubular pillows and large drained lava tunnels occurring on slopes steeper than 60 70 these lava flows occur on lateral volcanic vents about 200 300 m high along linear rift zones which are formed on the flank of the major edifices 3 volcanic ejecta due to hydromagmatic eruptions occur at shallow depths 500 m in height are individual conical features built at a high rate of volcanic discharge localized along radial linear eruptive fissures called rift zones the slopes located between the rift zones are covered by talus material are limited and unimportant mass wasting sector collapse features were observed on the edifices the conical shaped features are the primary morphology of the intraplate volcanoes formed during edifice growth which is closely linked to the hydrostatic pressure of the magmatic column the mean values of the slopes 11 17 of intraplate seamounts are the same as those of subaerial intraplate shield volcanoes when the seawater hydrostatic pressure is taken into account

rapid emplacement of a mid ocean ridge lava flow on the east pacific rise at 9 46 51 n in april 1991 during a submersible diving expedition to the east pacific rise epr crest at 9 46 51 n a new volcanic eruption on the sea floor was discovered here we report results from numerical modeling of that eruption which indicate that 4 106 6 106 m3 of lava was emplaced in 1 2 h with an average eruption rate of 103 106 m3 s 1 comparable to rates observed in hawaii at kilauea s east rift zone if the rapid emplacement of the 1991 epr lava and its short eruption duration are typical of volcanic events at fast spreading mid ocean ridge crests these characteristics have broad implications for our ability to detect monitor and understand the evolution of magmatic and volcanic processes within the axial zone

volatiles in basaltic glasses from the east pacific rise at 21 n implications for morb sources and submarine lava flow morphology pillow rim glasses from a suite of moderately evolved lavas erupted along the axis of the east pacific rise epr at 21 n were analyzed by high temperature mass spectrometry for volatile content concentrations of h2o f and cl in the 21 n glasses are low and correlate inversely with mg yielding well defined trends these and other geochemical data indicate derivation of the 21 n glasses from similar parental magmas produced from a highly depleted nearly homogeneous source 1 total volatile h2o f and s contents are lower and co2 content is somewhat higher in these samples than in previously analyzed mid atlantic ridge mar glasses 21 n glasses are similar in volatile content to glasses from the galapagos spreading center gsc at 95 w except in cl lower and co2 higher unlike most mar and gsc glasses co2 is the dominant volatile in all of the 21 n glasses with mg 62 all of the epr and gsc glasses contain reduced carbon species co and ch4 unlike most previously analyzed mar samples these data indicate that sources for mid ocean ridge basalts are extremely volatile poor 0 10 wt and are probably dominantly reduced below quartz fayalite magnetite buffer sheet flow and pillow basalts contain identical volatile contents thus volatile abundance is not a factor controlling flow morphology extrusion rate and or surface topography are probably the most important factors influencing flow morphology in submarine basalts h2o release patterns are however related to flow morphology mass pyrograms for sheet flow and pillow basalt glasses both show bimodal h2o release behavior at the same temperatures 800 c and1000 c 50 c however the dominant h2o release peak for sheet flow glasses is at the lower temperature for pillow rim glasses it is at the higher temperature infrared spectroscopic studies indicate that h2o in these glasses is present only as hydroxyl groups thus the cause of differences in the bimodal h2o release and how it is related to flow morphology is unclear

along axis variations in seafloor spreading in the mark area recent investigations with the manned submersible alvin and the angus deep towed camera sled greatly extended the known range of variations in the style of seafloor spreading along the axis of the mid atlantic ridge five transects of the spreading centre at intervals of10 20 km south of the kane fracture zone at 24 n latitude demonstrate dramatic changes in the style and magnitude of tectonic extension development of the neovolcanic zone expression of hydrothermal venting types oflithologic exposures and morphology of the median valley

structure and organization of submarine basaltic flows sheet flow transformation into pillow lavas in shallow submarine environments distal pillows occur associated with a sheet flow and megapillows in the menakoz outcrops of the basque cantabrian basin n spain basaltic volcanic rocks are interbedded with turonian sediments and depict typical features of shallow submarine emissions an exceptional basaltic flow displays four types of morphology 1 sheet lava with columnar jointing 2 welded columnar breccia 3 megapillows and 4 pillow lavas with sparse megapillows the field data from menakoz combined with experimental and field data from the literature for similar volcanic facies can be integrated into a new propagation model for the transition from sheet flows to pillow lavas in underwater environments at near vent high emission rates lava flows develop a thin crust immediately after its emplacement and break at the front under the magma pressure allowing for the massive propagation of lava as a sheet flow increased cooling promotes thickening of the lava outer crust far from the vent while continuous supply of fresh magma increases the pressure onto the thick crust until its rupture the lava emitted in small volumes from the flow front promotes the formation of megapillows and pillow lavas that are later on covered by the advancing sheet flow the lava flow freezes progressively toward more distal parts gradually increasing its viscosity until it stops the crust temporarily holds the residual melt pressure increasing the volume of the flow distal section by inflation finally the internal magma pressure breaks the crust and liberates lava at moderate to low flow rates producing pillows while lava drainage inside the inflated sheet flow produces lava tunnels and gravitational collapse of the roofs by hydrostatic pressure to form breccias nurtured by columnar lava fragments

automated display and statistical analysis of interpreted deep sea bottom photographs abstract an automated system for interpreting and displaying deep sea bottom photographs has been developed which allows rapid compilation and analysis of geological information initially collected photographs are classified using a scheme similar to those applied to deep sea volcanic and hydrothermal terrains by other workers towed camera positions from a transponder navigation system are smoothed using a cubic spline technique to obtain a more accurate model of the tow vehicle track line scan recorded data of the camera s height above the seafloor and camera lens characteristics are used to calculate the field of view for each photograph these data sources are integrated to produce a graphic output which combines the location orientation field of view geological and biological information for all photographs in a single color display an illustration of the technique is presented for a photographic data set collected within the caldera of axial seamount 45 57 n 130 03 w a site of active high and low temperature hydrothermal venting on the central juan de fuca ridge results confirm the existence and pinpoint the locations of several areas of known hydrothermal activity within the caldera quantitative analyses of the data base indicate statistical associations between various geological and hydrothermal parameters in particular rigorous statistical testing indicates that hydrothermal activity is associated with regions dominated by sheet flow lavas and fracturing

quantification of submarine lava flow morphology through analog experiments we developed a technique for determining paleoeffusion rates and emplacement times for submarine lava flows using observations of flow morphology and estimates of eruption volume eruption temperature lava viscosity and preflow topography using laboratory simulations and correlating these results with sea floor observations four submarine lava flow morphologies are considered to be diagnostic of specific effusion rates jumbled folded and lineated sheets and striated pillows we applied this approach to the coaxial flow emplaced in less than 14 days on the juan de fuca ridge in early summer 1993 and we calculated an effusion rate of 100 m3 s giving an emplacement time of 10 days

estimates of rheologic properties for flows on the martian volcano ascraeus mons morphological measurements on six well defined volcanic flows near the summit of the martian volcano ascraeus mons were used to calculate the yield strength and viscosity of the lavas the yield strength estimates range from 3 3 104 to 8 3 104 pa n m 2 with an average value of 2 1 104 these values are similar to yield strengths calculated for other flows on martian and terrestrial shield volcanoes but they are an order of magnitude less than the value for terrestrial andesite flows and two orders of magnitude greater than values for lunar flood basalts lengths of the ascraeus mons flows indicate lower limits on the effusion rate of 18 60 m3 s 1 with an average value of 35 effusion rate and yield strength are used to calculate upper limits on the lava viscosity of 6 4 105 to 2 1 108 pa s with an average value of 2 3 107 equivalent to 2 3 108 poise ridges on one flow indicate a viscosity lower limit of 1 1 108 pa s for a ridge growth time of one hour the estimated rheologic properties of the ascraeus mons flows are most consistent with basaltic or basaltic andesite lavas but some individual flows may consist of more highly evolved lavas

paving the seafloor volcanic emplacement processes during the 2005 2006 eruptions at the fast spreading east pacific rise 9 50 n 1 the 2005 2006 eruptions near 9 50 n at the east pacific rise epr marked the first observed repeat eruption at a mid ocean ridge and provided a unique opportunity to deduce the emplacement dynamics of submarine lava flows since these new flows were documented in april 2006 a total of 40 deep towed imaging surveys have been conducted with the woods hole oceanographic institution s whoi towcam system more than 60 000 digital color images and high resolution bathymetric profiles of the 2005 2006 flows from the towcam surveys were analyzed for lava flow morphology and for the presence of kipukas collapse features faults and fissures we use these data to quantify the spatial distributions of lava flow surface morphologies and to investigate how they relate to the physical characteristics of the ridge crest such as seafloor slope and inferred dynamics of flow emplacement we conclude that lava effusion rate was the dominant factor controlling the observed morphological variations in the 2005 2006 flows we also show that effusion rates were higher than in previously studied eruptions at this site and varied systematically along the length of the eruptive fissure this is the first well documented study in which variations in seafloor lava morphology can be directly related to a well documented ridge crest eruption where effusion rate varied significantly

the evolution of craters and calderas on young seamounts insights from sea marc i and sea beam sonar surveys of a small seamount group near the axis of the east pacific rise at 10 n a northwest trending group of seamounts located just west of the east pacific rise epr axis has been mapped using high resolution sea marc i side scan sonar and sea beam multibeam bathymetry these seamounts have 9 13 km basal diameters and the shapes of the volcanos change from conical domes near the epr axis to truncated cones and larger elliptical truncated cones farther away from the rise axis the detailed resolution of constructional volcanic features on these seamounts and the progressive development of summit depressions craters to large complex calderas and summit plateaus suggest to us a succession of evolutionary stages through which seamounts grow our evolutionary scheme for constructing these volcanos calls for the development of satellite extrusive centers around the base of a growing seamount which serve to drain off magmas and precipitate summit collapse the creation of a summit depression on a seamount will structurally constrain the style of eruptive volcanism to be principally along ring fractures which localize vents around the margin of a crater or caldera the concentration and channelization of volcanic eruptions around the top of the volcano lead to a progradation of the summit area and the establishment of a summit plateau the steep sides of a seamount reflect growth of the summit area out over the upper flanks of the volcano caused by continued eruption of lavas around the margin of the caldera the steep constructional slopes are sites for vigorous mass wasting that shapes and modifies flank terrain as a seamount evolves the crestal topography is the product of many volcanic cycles characterized by filling and subsequent draining of the caldera and expansion of caldera area through progressive collapse and migration of primary magmatic conduits the final phase of volcanism may be a calderafilling episode that builds a rough conical mount over the summit plateau

komatiites i eruption and flow because of their high eruption temperatures and ultrabasic composition komatiite lavas had low viscosities which typically ranged from 0 1 to 10 pa s a major consequence of this low viscosity is that most lavas erupted as turbulent flows an analysis of their ascent through the lithosphere suggests ascent velocities in the range of 1 to over 10ms 1 and reynolds numbers much greater than the critical value of 2000 the lavas would have remained turbulent for most or all of their subsequent flow and emplacement typical horizontal flow rates are estimated to range from 0 5 to 100 m2 s per unit width of flow such turbulent lava flows would have lost their heat by convection to the surroundings at rates which are orders of magnitude greater than the rates for laminar flows which cool by conduction a quantitative analysis of the cooling of komatiites indicates cooling rates from over 1000 c hr to a few c hr 1 while the flows remained turbulent these rates are in an appropriate range to cause phenomena such as high nucleation rates strong supersaturation of the lava delayed nucleation of olivine and skeletal or dendritic crystal morphologies komatiites often flowed over ground composed of rocks with lower melting temperatures it is proposed that the turbulent lavas melted the ground to form deep thermal erosion channels melting rates at the lava source are calculated at several metres per day and deep troughs with depths of several metres to hundreds of metres and lengths of several kilometres probably formed laboratory experiments performed to simulate thermal erosion show qualitative agreement with the theory with channel depth decreasing downstream the experiments also revealed that the channel margins become undercut during thermal erosion to form overhanging sides of the channel some sinuous rilles observed in the mare regions of the moon are thought to have formed by thermal erosion hulme 1973 they provide analogues of the channels postulated to form in komatiite eruptions where conditions were in fact more favourable for thermal erosion an assessment of the role of olivine crystals precipitated in the cooling turbulent flows indicates that they will remain in suspension until the lava has come to rest contamination of komatiite lava by underlying rock can be as much as 10 per cent some illustrative calculations show how the major element and trace element compositions of residual melts can be significantly modified by combined assimilation and fractional crystallization in a moving flow assimilation of tholeiitic basalt into a komatiite can cause incompatible trace element ratios such as ti zr and y zr and the rare earth patterns of derivative lavas to vary substantially some of the variations in such geochemical parameters which are often ascribed to mantle heterogeneity also could have resulted from assimilation of the ground assimilation could have modified the isotope geochemistry of lava suites and led to apparent ages which differ from the true eruption age the thermal erosion model also provides an explanation of the formation of some nickel sulphide ores found at the bottom of thick komatiite flows it is proposed that ores can form by assimilation of sulphur rich sediment which combines with ni from the komatiite to form an immiscible liquid

role of heat advection in a channeled lava flow with power law temperature dependent rheology 1 the cooling of a lava flow both in the transient and the steady state is investigated considering that lava rheology is pseudoplastic and dependent on temperature lava exits from the vent with constant velocity and flows down a slope under the effect of gravity force inside a channel of rectangular cross section we consider that cooling of lava is caused by thermal radiation into the atmosphere and thermal conduction at the channel walls and at the ground the heat equation is solved numerically in a 3 d computational domain and the solution is tested to evaluate the numerical errors we study the steady state and the initial transient period of lava cooling results indicate that the advective heat transport significantly modifies the cooling rate of lava slowing down the cooling process since the lava velocity depends on temperature the cooling rate depends on the effusion temperature velocity profiles are modified during cooling showing two marginal static zones where the crust can form and remain stable the fraction of crust coverage is calculated under the assumption that the solid lava is a plastic body with temperature dependent yield strength we numerically confirm that heat advection cannot be neglected in the mechanism of formation of lava tubes

rheology and topography control the path of a lava flow insight from numerical simulations over a preexisting topography 1 determination of flow path is strongly controlled by both the preexisting topography and rheology of the lava flow using the okmok 1997 eruption as an example lava flow we perform numerical simulations of bingham fluids flowing over preexisting topography and find that flow rheology determines whether or not new lobe formation or bifurcation occurs from the main flow at a topographic divide or remains confined by local topography therefore lobe or branch length may increase for higher viscosity flows when considering the effect of topographic control also even one order of magnitude difference in the rheological properties allows lava flows to move in completely different paths which may suggest that flow bifurcation due to topographic control provides insight to the local rheological properties of a lava flow the effect reported here should be taken into account in risk assessments of future volcanic hazards

the 1998 eruption of axial seamount new insights on submarine lava flow emplacement from high resolution mapping 1 axial seamount an active submarine volcano on the juan de fuca ridge at 46 n 130 w erupted in january 1998 along 11 km of its upper south rift zone we use ship based multibeam sonar high resolution 1 m bathymetry sidescan sonar imagery and submersible dive observations to map four separate 1998 lava flows that were fed from 11 eruptive fissures these new mapping results give an eruption volume of 31 106 m3 70 of which was in the northern most flow 23 in the southern most flow and 7 in two smaller flows in between we introduce the concept of map scale submarine lava flow morphology observed at a scale of hundreds of meters as revealed by the high resolution bathymetry and an interpretive model in which two map scale morphologies are produced by high effusion rate eruptions inflated lobate flows are formed near eruptive vents and where they drain downslope more than 0 5 1 0 km they transition to inflated pillow flows these two morphologies are observed on the 1998 lava flows at axial a third map scale flow morphology that was not produced during this eruption pillow mounds is formed by low effusion rate eruptions in which pillow lava piles up directly over the eruptive vents axial seamount erupted again in april 2011 and there are remarkable similarities between the 1998 and 2011 eruptions particularly the locations of eruptive vents and lava flow morphologies because the 2011 eruption reused most of the same eruptive fissures 58 of the area of the 1998 lava flows is now covered by 2011 lava

the influence of cross sectional channel geometry on rheology and flux estimates for active lava flows lava rheology and effusion rate are critical factors in determining the evolution of lava flows however direct and accurate field measurements are difficult to carry out and estimates are usually based on measurements of the flow s surface velocity and assumptions of sub surface geometry using numerical flow models we show that the potential for error due to geometry uncertainty is minimized if a semi elliptical cross sectional channel shape is assumed flow is simulated for isothermal newtonian temperature dependent newtonian and isothermal power law rheology lavas for isothermal newtonian lava we find that the error in channel shape alone can make apparent viscosity estimates 3 5 times too large e g for inappropriate use of the jeffreys equation on a narrow semi elliptical channel for a temperature dependent rheology using an analytical approximation for newtonian flow in a semi elliptical geometry yields apparent viscosity and flux values that are more accurate than estimates which assume a rectangular geometry for all channel shapes considered including rectangular channels viscosity calculations for real channels on mauna loa and mount etna show that for a newtonian rheology a semi elliptical analytical solution gives an approximation three times closer to the actual viscosity than a rectangle with the same depth while if the lava is shear thinning power law exponent m 0 6 a rectangular approximation is 15 more accurate our results can be used to bracket possible viscosity and flux estimates when channel topography is poorly constrained

the morphology of lava flows in planetary environments predictions from analog experiments the rates of surface cooling and lateral spreading are evaluated for lava flows on the surface of earth venus mars the moon and io differences between the flow morphologies expected in these environments are then predicted under the assumption that the results of recent laboratory simulations of lavas using wax extruded beneath cold water fink and griffiths 1990 can be carried over these experiments involved the spreading of viscous liquid under gravity in the presence of a solidifying surface crust and revealed a set of four distinct surface morphologies transitions from one morphology to the next occurred in a well defined sequence when the relative rates of surface solidification and lateral spreading were varied in comparison with subaerial flows on earth the surface of lavas solidifies faster on venus where the dense atmosphere provides additional convective heat transfer lateral flow of lava is much slower under the smaller gravity of the moon hence for a given extrusion rate and viscosity solid crust is predicted to form closer to the vent on both the moon and venus than on earth equivalently faster extrusion rates than those on earth are required on the moon io and venus in order to produce a given surface morphology a comparison of observed structure flow rates and estimated viscosities for some well documented terrestrial lava flows shows reasonable agreement with the predictions of the model extrapolation to extraterrestrial lavas is then illustrated by constraining the effusion rate for a martian lava flow whose composition is assumed spectral information on the chemical composition of martian flows to be sought by the thermal emission spectrometer on the mars observer mission in conjunction with detailed morphologic observations from the mars observer camera could allow much more accurate estimates of effusion rates for martian lavas

formation of channelized lava flows on an unconfined slope 1 the formation of channelized lava flows on a wide uniform slope is investigated both theoretically and experimentally when a lava is released at a constant flow rate from a point source we predict that it flows both down and across the slope at the same rate in a early time regime before undergoing a transition to a long time regime where down slope flow is faster than lateral flow eventually the lateral flow is stopped by the strength of the growing surface crust and the flow then travels down slope in a channel of constant width using scaling analysis we derive expressions for the final channel width in both flow regimes as a function of the flow rate the slope the density difference driving the flow the lava viscosity the thermal diffusivity and the yield strength of the crust we also find a dimensionless flow morphology parameter that controls whether the subsequent channel flow occurs in a mobile crust regime or in a tube regime these theoretical predictions are in good agreement with laboratory experiments in which polyethylene glycol wax flows down a wide uniform slope under cold water the theory is also applied to the understanding of the formation of a basaltic sheet flow lobe in hawaii which had an estimated crust yield strength of order 6 104 pa