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

correlations between topography and intraflow width behavior in martian and terrestrial lava flows local correlations between topography and width behavior within lava flows at puu oo mount etna glass mountain cerro bayo alba patera tyrrhena patera elysium mons and olympus mons were investigated for each flow width and slope data were both referenced via downflow distance as a sequence of points the data were then divided into collections of adjacent three point features and two point segments four discrete types of analyses were conducted 1 three point analysis examined positional correlations between width and slope features 2 two point analysis did the same for flow segments 3 mean slope analysis included segment slope comparisons and 4 sudden width behavior analysis measured abruptness of width changes the distribution of types of correlations compared to random combinations of features and segments does not suggest a significant correlation between flow widths and local underlying slopes and indicates that for these flows at least other factors have more influence on changes in width than changes in underlying topography mean slopes underlying narrowing widening and constant flow width segments were calculated an inverse correlation between slope and width was found only at mount etna where slopes underlying narrowing segments were greater than those underlying widening in 62 of the examined flows for the majority of flows at mount etna puu oo and olympus mons slopes were actually greatest under constant width segments this may imply a topographically dependent resistance to width changes the rate of change of width was also examined sudden width changes are relatively common at puu oo mount etna elysium mons and tyrrhena patera and relatively rare at glass mountain cerro bayo olympus mons and alba patera after correction for mapping scale puu oo mount etna olympus mons and alba patera appear to fall on the same trend glass mount exhibits unusually small amounts of sudden width behavior and tyrrhena patera exhibits a relatively large number of sudden width behavior occurrences

detailed volcanic geology of the marnok area mid atlantic ridge north of kane transform we present the results of a detailed study of the volcanic geology of the median valley floor of the mid atlantic ridge in two adjacent but contrasting spreading segments immediately north of the kane transform fault based on a high resolution deep towed sidescan sonar tobi survey near bottom photographic traverses and geochemical analyses from 28 precisely sited sets of dredge samples this has allowed us to assess the relative importance of small intersegment and large transform boundaries on magmatic processes at slow spreading ridges we find that the petrological effect of the transform so called transform fault effect is minor compared to the manifestation of the second order segmentation the southern narrowgate type segment has a poorly developed neovolcanic zone which tapers towards its bathymetric centre where continuous faulting causes rapid dismemberment flat topped seamounts are preferentially located at the ends of the segment particularly near the non transform offset there is a striking variation in the degree of fractionation along the length of this segment primitive lavas were sampled at the centre while more fractionated basalts showing a greater range of parental compositions form discrete volcanic edifices at the ends in contrast the northern segment has a wider inner valley and syn magmatic faults extend up to 15 km along the crest of its robust axial volcanic ridge the along segment trend of increasing mgo towards the bathymetric crest of the axial volcanic ridge is similar to but less well defined than that for the southern segment there is no variation in the bulk degree of melting along the segments as determined from the major element geochemistry hence melt migration is favoured over focused mantle upwelling as the main cause of the crustal thickness variations which define second order segmentation radigenic isotopes show only very small variations with no systematic pattern emerging within or between the ridge segments the isotopic irregularities are not related to the variations in incompatible elements implying that the latter result from dynamic melting processes rather than from long lived source heterogeneity a model is developed which relates the volcanology tectonic style and the geochemical trends to the episodicity of magma supply and eruption

long submarine lava flows observations and results from numerical modeling long 100 km lava flows are relatively common on mars and venus and have been identified on the moon but they are rarely documented on earth however although 75 of the earth s surface is covered by water only a small percentage of the ocean floor has been investigated at a resolution sufficient to unequivocally identify the boundaries of long submarine lava flows even so basaltic lava flows as long as 110 km have been identified on the deep 1500 m seafloor near hawaii and the east pacific rise ambient conditions on the deep ocean floor may favor the development of long lava flows for the following reasons first high pressures 15 mpa keep volatiles dissolved in basaltic lavas preventing viscosity increases associated with exsolution and vesiculation second seawater rapidly quenches the surface of submarine basalt flows so that an insulating glass layer 1 5 cm thick encases submarine flows within seconds after their emplacement this glass rind effectively insulates the molten flow interior from additional heat loss making submarine basalt flows behave as well insulated subaerial tube fed flows thus for identical basalt flows emplaced on the deep seafloor and subaerially a submarine flow could advance farther before stopping results of numerical modeling indicate that thin 1 m submarine basalt flows behave similarly to identical subaerial flows but thicker submarine flows may advance significantly farther than their subaerial counterparts

formation of venusian canali considerations of lava types and their thermal behaviors because liquid water is unstable at present venusian surface conditions the discovery of channels termed canali on venus thousands of kilometers long was not predicted low viscosity lavas that remain fluid for several thousand kilometers are considered to be the canali forming agents possible compositions of venusian canali forming lavas include komatiite and high fe ti lunar type basalts results of analytical and numerical models of these lavas reveal that total cooling is more efficient on venus than on earth suggesting that venusian lavas rapidly form insulating crusts and thus that the canali lavas were essentially tube fed the models also reveal that thermal erosion should be less efficient on venus than on earth suggesting that venusian channels are either the product of mechanical rather than thermal erosion or constructional processes

axial summit trough of the east pacific rice 9 10 n geological characteristics and evolution of the axial zone on fast spreading mid ocean ridge the nature and morphological characteristics of axial summit troughs on fast 90 130 mm yr 1 full spreading rate and superfast spreading 130 mm yr 1 mid ocean ridge crests reflect the time integrated effects of long term magmatic cycles short term volcanic episodicity and the tensional stress regime imposed on young ocean crust two principal types of axial trough morphology have been identified and associated with distinct volcanic and tectonic processes occurring at fast and superfast spreading mid ocean ridge crests 1 narrow axial troughs 300 2000 m wide and 30 100 m deep on the east pacific rise crest are classified as axial summit graben the dimensions of axial summit graben as well as the morphological and structural character of their walls and floors suggest a primary tectonic origin an axial summit graben may contain a nested axial summit collapse trough implying that processes responsible for these endemic features may be linked near bottom side looking sonar and observational data collected using the towed vehicle argo i and submersible alvin have been used to characterize the axial summit trough of the fast spreading east pacific rise between 9 and 10 n a four stage model is presented for the evolution of this axial summit collapse trough as well as for other well studied portions of the east pacific rise crest from 21 n to 20 s we propose that the transition from a narrow surface collapse dominated axial trough to a broader fault bounded graben is controlled by the relative importance of diking volcanism hydrothermal cooling and tectonism along a ridge segment over time periods 104 years

the submarine volcanic system of the errigoiti formation albian santonian of the basque cantabrian basin northern spain stratigraphic framework facies and sequences abstract the errigoiti formation located in the central domain of the basque cantabrian basin is an albian to santonian bathyal submarine volcanic system of alkali basaltic character these volcanics occurred in an extensional geodynamic context generated by the drifting of the iberian plate with respect to the european plate stratigraphic analyses reveal the facies distribution and depositional architecture of a longitudinal cross section of the errigoiti volcanic system four facies groups were distinguished sheet lavas sl derived from low viscosity lava flows at high magma discharge rate pillow lavas pl derived from intermediate viscosity lava flows at moderate discharge rate pillow breccias pb derived either from in situ fragmentation of lavas pb1 or rock falling from pillow lava slopes pb2 and stratified volcaniclastites vc derived from volcaniclast resedimentation through gravity flows either by early remobilization vc1 or post volcanic reworking vc2 the facies groups occur in a predictable repetitive succession essentially from base to top an sl pl pb vc stacking pattern this is interpreted to reflect an upward waning in the magma discharge rate five major volcanic sequences make up the errigoiti formation each comprises packages tens to hundreds of meters thick deposited during short time spans of volcanic activity separated by long time intervals of volcanic inactivity consequently boundaries between sequences are associated with marked hiatuses reworked volcaniclasts and or turbidite pelagic sedimentation analysis of lateral and vertical facies evolution enabled us to propose a depositional model consisting of three depositional environments from proximal to distal settings these are amalgamated pillow volcanoes scattered pillow volcanoes and volcanic fringe basically responding to a proximal to distal pl pb pl vc and sl vc evolution of facies associations contemporaneous fossiliferous turbidite pelagic sequences that surround the volcanic succession allow paleobathymetry to be estimated on the basis of biofacies sites with the highest rate of volcanic emission correspond to an average depth of 900 m sites with thinner volcanic pile accumulated at a minimum depth of 1100 m the facies sequence established in this work and the processes involved in its formation are comparable with the sequences and processes described in other submarine basic volcanic systems consequently the depositional model for the errigoiti formation can perhaps serve as a reference model for this type of volcanic system

volcanic evolution of the submarine super volcano tamu massif of shatsky rise new insights from formation microscanner logging imagery tamu massif the southernmost plateau of shatsky rise is recently reported as the largest single volcano known on earth this work seeks to understand the type of volcanism necessary to form such an anomalously large single volcano by integrating core and high resolution wireline logging data in particular resistivity imagery obtained by the formation microscanner in integrated ocean drilling program hole u1347a located on the eastern flank of tamu massif was used to construct a logging based volcanostratigraphy this model revealed two different volcanic stages formed tamu massif i the core part of the massif s basaltic basement was formed by a construction phase of volcanism with cyclic eruption events from a steady state magma supply and ii the very topmost basaltic section was formed by a depositional phase of volcanism during which long traveling lava flows were deposited from a distant eruption center

significance of widespread low effusion rate eruptions over the past two million years for delivery of magma to the overlapping spreading centers at 9 n east pacific rise abstract ever since the discovery that the mid ocean ridge axis deepens at most axial discontinuities there has been vigorous debate about whether ridge axis depth and shape reflect magma supply here we report evidence from one of the most thoroughly studied ridge discontinuities on a fast spreading mid ocean ridge that volcanic eruption effusion rates have been low relative to nearby segment centers throughout its two million year history this pattern of low volcanic effusion rates is inferred from the fields of constructional volcanic mounds on the seafloor which are much more abundant in the off axis discordant zone of the east pacific rise epr 9 n overlapping spreading centers osc than on typical epr seafloor detailed seafloor mapping in 2007 shows that these mound fields consist of concentrations of large pillow mounds that formed within the current osc basin and ridge tips rather than off axis pillow lava erupted at approximately an order of magnitude lower effusion rate than lobate or sheet flows primarily builds mounds on the seafloor crustal thickness a proxy for long term magma supply does not decrease in spite of the decreased lava effusion rates implied by widespread pillow eruptions to resolve the problem of achieving the same magma emplacement rate with lower effusion rates without violating our observations by requiring drastically increased eruption frequency or unreasonably long eruption durations we propose that eruptions occur across the entire osc basin the current configuration of mid crustal melt sills within the osc as resolved by multichannel seismic reflection surveys have neither the correct location nor appropriate size to deliver magma to these eruptive vents in the osc basin via vertically propagating dikes instead we propose that magma delivery to eruptions occurs via laterally propagating dikes from robust mid crustal melt sills outside of the overlap zone

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

grain size dependent paleointensity results from very recent mid oceanic ridge basalts 1 we report paleointensity analyses on a suite of four samples from two axial zero age mid oceanic ridge basalt flows from the east pacific rise paleointensity experiments have been performed on several profiles each consisting of a batch of small millimeter scale subsamples going from the rapidly cooled glassy margin to the interior the coe version of the thellier double heating procedure was used with back checks performed after every other heating step most of the samples show very good behavior i e constant ratio between the lost and acquired magnetization through a large temperature range quality factor usually above 10 and positive checks which lead to unambiguous paleointensity determinations paleointensities obtained on glasses reported here and in a previously published study are very consistent and reproducible and in agreement with expected in situ values of earth s magnetic field intensity however results found within the crystalline part of the samples show values that are considerably up to 50 higher than expected these variations seem to be correlated with the cooling history of the samples and appear to be universal since all samples exhibit the same intriguing pattern an extensive study of magnetic properties allows us to link this incongruent behavior to 1 the presence of multidomain effects and 2 the cooling rate difference between laboratory experiments and in situ cooling

direct video and hydrophone observations of submarine explosive eruptions at nw rota 1 volcano mariana arc 1 extraordinary video and hydrophone observations of a submarine explosive eruption were made with a remotely operated vehicle in april 2006 at a depth of 550 560 m on nw rota 1 volcano in the mariana arc the observed eruption evolved from effusive to explosive while the eruption rate increased from near zero to 10 100 m3 h during the peak in activity cyclic explosive bursts 2 6 min long were separated by shorter non eruptive pauses lasting 10 100 s the size of the ejecta increased with the vigor of the explosions a portable hydrophone deployed near the vent recorded sounds correlated with the explosive bursts the highest amplitudes were 50 db higher than ambient noise at frequencies between 10 and 50 hz the acoustic data allow us to quantify the durations amplitudes and evolution of the eruptive events over time the low eruption rate high gas lava ratio and rhythmic eruptive behavior at nw rota 1 are most consistent with a strombolian eruptive style we interpret that the eruption was primarily driven by the venting of magmatic gases which was also the primary source of the sound recorded during the explosive bursts the rhythmic nature of the bursts can be explained by partial gas segregation in the conduit and upward migration in a transitional regime between bubbly flow and fully developed slug flow the strongest explosive bursts were accompanied by flashes of red glow and oscillating eruption plumes in the vent apparently caused by magma seawater interaction and rapid steam formation and condensation this is the first time submarine explosive eruptions have been witnessed with simultaneous near field acoustic recordings

morphological evolution of a new volcanic islet sustained by compound lava flows we investigated the creation of a volcanic islet and emplacement of lava flows in the sea by analyzing data from the island forming eruption at nishinoshima japan that has been continuing since november 2013 aerial observations and satellite images were used to perform a quantitative analysis of the eruption processes the most intriguing characteristic of the lava flows is the development of lobes and tubes from breakouts and bifurcations of andesitic a type lava flows internal pathways that fed lava to the active flow front were eventually developed by crust solidification and dominated the lava transport the average discharge was 2 10 5 m 3 day and the total volume of erupted material reached 0 1 km 3 at the end of february 2015 fractal analysis of the lava flow margins suggests that the growth pattern is self similar with a fractal dimension d of 1 08 1 18 which is within the range of subaerial basaltic lava flows the morphological evolution of nishinoshima is controlled primarily by effusion of lava with an apparent viscosity of 10 4 10 6 pa s average discharge of 2 3 m 3 s and eruption duration lasting 2 yr our data and analyses suggest that the effect of lava coming in contact with seawater as well as the variations in the lava discharge rate on local and overall scales are important factors affecting the development of crust and the lava transport system

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

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

spatial analysis of an intra plate basaltic volcanic field in a compressional tectonic setting south eastern australia abstract the newer volcanics province nvp is a pliocene to recent intra plate basaltic volcanic field bvf that has formed in a compressive tectonic setting v

three dimensional seismic imaging of ancient submarine lava flows an example from the southern australian margin this work comprises a part of the great australian bight deepwater marine program gabdmp for funding this project the gabdmp is a csiro research program sponsored by chevron australia the results of which will be made publicly available 3d seismic data was gratefully provided by tgs ihs are thanked for access to seismic interpretation software spectral decomposition was carried out using foster findlay associates geoteric software sverre planke and tracy gregg are thanked for constructive reviews

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

geomorphological variations at hydrothermal sites in the southern mariana trough relationship between hydrothermal activity and topographic characteristics abstract this study presents the first detailed geomorphological characterization of field scale geological features associated with hydrothermal systems in the southern mariana trough using near bottom swath mapping data collected by the autonomous underwater vehicle auv urashima during cruise yk09 08 and dive observation data acquired by the submersible shinkai6500 during cruise yk10 11 the motivation of this study is to examine the relationship between geomorphological characteristics and hydrothermal activity and to examine the nature of tectonic and volcanic controls on the hydrothermal system in this area two of the hydrothermal sites in the study area near 12 57 n 143 37 e are located on the active backarc spreading axis the snail and yamanaka sites one is located at the eastern foot of the axial high the archean site and two are located on an off axis knoll about 5 km from the spreading axis the pika and urashima sites the on axis area is divided into tectonically dominant and volcanically dominant zones volcanically dominant zones are characterized by mounds height 5 30 m diameter 250 320 m cut by fissures the snail and yamanaka sites are located adjacent to these fissures and are possibly represented local activity associated with a 4th order segment scale diking event on the basis of comparisons with previously studied cases on the east pacific rise with similar on axis geological characteristics in contrast to the on axis sites the off axis sites show no evidence of faulting the archean site at the foot of the axial high is characterized by a single mound height 50 100 diameter 250 300 m pronounced off axis lava flows and the presence of high amplitude rugged seafloor features the site is located at the top of the mound numerous ridge lines height mainly 2 6 m extend radially from the top of the mound and several chimney like structures up to approximately 6 m high occur on the top and slopes of the mound the pika site is located on the western peak of an off axis knoll and the newly discovered urashima site is located at the northern foot of the western peak of the same knoll the western peak is characterized by bumpy seabed textures formed by numerous smaller scale mounds and ridge lines however the eastern peak has a very smooth top and slope and shows no signs of hydrothermal activity numerous mounds heights 5 75 m diameters 50 350 m are developed on the comparatively gentle slope of the knoll in contrast to the numerous ridge lines height mainly 1 6 m developed on the relatively steep slopes of the knoll on the basis of the associated geomorphological features the three off axis sites archean pika and urashima were identified as localities created by relatively long term large scale hydrothermal activity as compared with sites in the on axis area the sustained activity at off axis sites appears closely related to an off axis upwelling magma system the three off axis hydrothermal sites are composed mainly of breccia assemblages that probably originated from hydrothermal activity with black smoker venting these areas are characterized by numerous ridge lines conical mounds and bumpy seabed texture whereas the on axis sites are characterized by the absence of ridge lines and the presence of white smoker and shimmering observed on dome shaped pillow mounds hence the distribution of ridge lines mound morphology and bumpy seabed texture is likely to correlate with hydrothermal activity

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

east pacific rise at 21 n the volcanic tectonic and hydrothermal processes of the central axis abstract photographs obtained by the angus survey system at 21 n reveal many similarities to the geological processes delineated at other spreading centers and in particular those observed in the galapagos rift at 86 w the region of recent volcanism is restricted to a narrow zone zone 1 approximately 1 km wide this suggests that the width of the magma chamber feeding these flows is also narrow at the top variations in sediment cover are used to subdivide the flows within zone 1 into three sheet flow pillow flow pairs the youngest pair appears to have erupted form a linear fissure 8 km long running parallel to the valley axis this fissure is part of a larger en echelon pattern of eruptive fissures active hydrothermal vents associated with the youngest flows are situated directly above the apparent eruptive fissure the high 350 c temperature for some of the fluids exiting from the vents suggests a highly restricted circulation system involving at times little to no mixing with cold seawater the lava terrain in the remainder of zone 1 and bordering regions is characterized by extensive fracturing further suggesting a narrow upper dimension to the magma chamber and also that subsurface hydrothermal deposition of massive sulfides may lead to a reduction in the mixing processes

effects of regional slope on viscous flows a preliminary study of lava terrace emplacement at submarine volcanic rift zones to understand how large submarine lava terraces form and why they are not commonly observed on land we developed an isoviscous gravity flow model on an inclined surface to simulate the evolution and emplacement of lava flows under submarine conditions by solving this preliminary model using a finite difference method we are able to quantify how lava viscosity pre existing topographic slope effusion rate and lava volume affect meso scale lava morphology our simulations show that in general high lava viscosity gentle regional slope and low effusion rate favor the formation of large terraces but environmental conditions also play an important role a gravity flow spreads more slowly underwater than subaerially we also conclude that for low viscosity basaltic lava the cooling of the lava body is one of the most critical factors that affect its shape this study shows that the isoviscous model though oversimplified provides a quantitative tool to relate lava morphology to eruption characteristics to gain a better understanding of the controls on submarine lava terrace formation future models must take into account the temporal and spatial variation of lava viscosity especially the effects of a brittle outer shell

eruptive hummocks building blocks of the upper ocean crust the spreading axis at many slow spreading mid ocean ridges is marked by an axial volcanic ridge in this study we use a combination of high resolution remote sensing methods to elucidate the detailed nature of volcanoes in such a ridge we find that the hummocks described in previous sidescan sonar studies are dome or cone shaped edifices 5 150 m high with diameters of 30 330 m we estimate they form quickly in single eruptions each of which may produce several hummocks hummock collapse is common and hummocks of all heights are prone to failure collapses generally occur down the regional seafloor slope suggesting control by local topography approximately 33 of hummocks lose 40 of their volume by collapse so 12 of all material erupted on the axial volcanic ridge is rapidly converted to talus the higher porosity of these deposits may increase average upper crustal porosity by several percent contributing 0 5 km s 1 to seismic velocity decrease in the upper oceanic crust and may be one of the dominant mechanisms for increasing porosity in upper slow spreading oceanic crust

submarine basaltic fountain eruptions in a back arc basin during the opening of the japan sea abstract basaltic rock generated during the middle miocene opening of the japan sea is widely distributed on the back arc side of the japanese archipelago few studies have investigated on submarine volcanism related to opening of the japan sea the present study aimed to reconstruct details of the subaqueous volcanism that formed the back arc basin basalts babb during this event and to discuss the relationship between volcanism and the tectonics of back arc opening using facies analyses based on field investigation the study area of the southern dewa hills contains well exposed basalt related to the opening of the japan sea five types of basaltic rock facies are recognized 1 coherent basalt 2 massive platy basalt 3 jigsaw fit monomictic basaltic breccia 4 massive or stratified coarse monomictic basaltic breccia with fluidal clasts and 5 massive or stratified fine monomictic basaltic breccia the basaltic rocks are mainly hyaloclastite based on facies distributions we infer that volcanism occurred along fissures developed mainly at the center of the study area given that the rocks contain many fluidal clasts submarine lava fountaining is inferred to have been the dominant eruption style the basaltic rocks are interpreted as the products of back arc volcanism that occurred by tensional stress related to opening of the japan sea which drove strong tectonic subsidence and active lava fountain volcanism

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

volcanic evolution of oceanic crust in a late ordovician back arc basin the solund stavfjord ophiolite complex west norway 1 the stratigraphy of the well preserved solund stavfjord ophiolite complex in the west norwegian caledonides documents the volcanic evolution of a spreading center in a late ordovician back arc basin basaltic sheet flows pillow lavas and volcanic breccias are the main components of the 470 800 m thick extrusive sequence and are organized stratigraphically in a cyclic manner cyclic units vary in thickness from 5 m to 225 m and are typically composed of basal sheet flows or lava flows with large pillows that are succeeded by flows with progressively smaller pillows and volcanic breccias thick independent breccia units also occur in the stratigraphy in sheet flow dominated parts of the sequence the cyclic units are thicker average 85 m than in pillow dominated parts average 20 m detailed logging of closely spaced profiles 1 km or less apart shows that the proportions of sheet flows pillow lavas and volcanic breccias varies laterally along an axial segment of less than 10 km the volcanic products change from predominantly sheet flows reflecting robust volcanic centers to pillow lavas to volcanic breccias sheet flow dominated volcanic centers seem to be spaced at intervals of 25 30 km and we tentatively interpret their regularity as an expression of volcanic segmentation at an intermediate to fast spreading center observations of modern ocean crust suggest that sheet flows dominate at fast spreading ridges while pillow lavas dominate at slow spreading ridges volcanic breccias are apparently rare in both of these environments these features contrast with the stratigraphy of the solund stavfjord ophiolite complex where the proportion of different volcanic products varies laterally and volcanic breccias are common we emphasize the importance of detailed studies of the volcanic stratigraphy of ophiolites as complements to those of in situ oceanic crust in order to provide a more complete picture of volcanic evolution of oceanic crust in different spreading regimes

eruption styles of basalt in oceanic spreading ridges and seamounts effect of magma temperature and viscosity basalts erupted along oceanic zones of spreading and on intraplate seamounts at depths where hydroexplosions are not likely follow various styles of eruption quiet eruptions produce a variety of forms including lava lakes and sheet pillow and pavingstone lavas reactive eruptions occur instead when the lava is thermally shattered as in the formation of hyaloclastites the stresses induced in a rapidly cooling lava flow are important in determining the different lava forms with lava lakes and sheet flows resulting from low stresses pillows from higher stresses and hyaloclastites from even higher stresses which cause rupture calculations show that if we consider basaltic lavas of the same composition the intensity of the stresses induced in the cooling lava increases proportionally to the initial viscosity and inversely to the temperature and rate of discharge of the lava at eruption the viscosity is strongly dependent on the crystal liquid ratio of the magma at eruption the temperature and viscosity of the lava at eruption are related ultimately to the thermal regime of the lithosphere below viscosity tends to increase going from fast to slow spreading ridges and to intraplate seamounts within a given ridge segment temperature tends to decrease and viscosity to increase approaching a transform or overlapping boundary thus the model predicts that going from fast to slow spreading ridges i e from east pacific rise to mid atlantic ridge the probability of forming lava lakes and sheet flows decreases and the probability of forming pillow flows increases moreover within a given ridge segment the areal sheet to pillow ratio should decrease as a transform or overlapping boundary is approached sheet flows should be significant only in the earliest stages of the growth of large intraplate seamounts pillows and hyaloclastites in later stages the probability of forming hyaloclastites should be low in spreading ridges higher in intraplate seamounts recent high resolution observations on the east pacific rise the galapagos rift the mid atlantic ridge and the red sea are consistent with the model because they show that 1 the areal ratio of lava lakes and sheet flows over pillows decreases going from fast to slow spreading ridges 2 within a given ridge segment it decreases approaching a transform and 3 hyaloclastites are important on seamounts only

reconstructing lava flow emplacement processes at the hot spot affected galapagos spreading center 95 w and 92 w 1 volcanic eruptions at mid ocean ridges mors control the permeability internal structure and architecture of oceanic crust thus establishing the foundation for the evolution of the ocean basins to better understand the emplacement of submarine lava flows at mors we have integrated submersible based geologic mapping with remote sensing techniques to characterize the lava flow morphology within previously mapped lava flow fields produced during single eruptive episodes at the galapagos spreading center gsc detailed attributes describing the surface geometry and texture of the lava flows have been extracted from high resolution sonar data and combined with georeferenced visual observations from submersible dives and camera tows based on signatures contained in these data a fuzzy logic based classification algorithm categorized lava flow morphology as pillows lobates or sheets the resulting digital thematic maps offer an unprecedented view of gsc lava morphology collectively covering 77 km2 of ridge axis terrain at a resolution of 2 m 2 m error assessments with independent visual reference data indicate approximately 90 agreement comparable to subaerial classification studies the digital lava morphology maps enable quantitative spatially comprehensive measurements of the abundance and distribution of lava morphologies over large areas of seafloor and within individual eruptive units a comparison of lava flow fields mapped at lower and higher magma supply settings 95 and 92 w respectively indicates that effusion rates increase along with magma supply and independent of spreading rate at the gsc although a complete range of eruptive behavior exists at each setting

facies architecture and origin of a submarine rhyolitic lava flow dome complex ponza italy the islands of ponza and gavi western pontine archipelago italy preserve parts of a subaqueously emplaced high silica 75 77 sio2 rhyolitic lava flow that overlies the margins of three older domes exposures of the lava alone cover 24 km2 and with a thickness of 150 m exposed in the cliffs the preserved volume of the lava flow is 3 6 km3 and the original volume is likely to have exceeded 7 km3 the lava flow consists of coherent obsidian and several hyaloclastite facies including in situ and clast rotated breccias and sandstones which all exhibit gradational relationships the coherent obsidian occurs as separate domains and is often flow banded although flow folds occur the banding is generally subhorizontal dipping gently to the nne the hyaloclastite representing 90 of the lava by volume has a diffuse layering varying from 0 5 to 2 m in thickness this layering also dips gently to the nne and is marked in places by alternation of some coherent horizons coarse and finely fragmented in situ hyaloclastite pumiceous hyaloclastite and clast rotated hyaloclastite the layering is laterally continuous and consistent in orientation over most of the 13 km length of ponza the subhorizontal orientation of the flow banding and presence of resedimented deposits in the upper parts of the sequence indicate that the unit is a lava flow the resedimented deposits comprise both proximal and distal deposits of debris flows and turbidity currents initiated by gravitational instability of the upper and marginal parts of the lava flow and include stratified monomictic obsidian breccias and bedded vitric siltstones and sandstones the lava flow has been intruded and crosscut by rhyolitic bodies of various ages including discordant coherent to internally fractured contemporaneous rhyolite bodies and late penecontemporaneous dikes with glassy margins and alteration haloes

mesozoic adakitic rocks from the xuzhou suzhou area eastern china evidence for partial melting of delaminated lower continental crust abstract adakitic rocks in the xuzhou suzhou area eastern china consist of dioritic and monzodioritic porphyries and were dated at 131 132 ma by the shrimp u pb zircon method these rocks have high mgo content 1 47 5 73 high mg values 0 49 0 61 and high la yb and sr y ratios these features are similar to rocks derived from partial melting of a subducted oceanic slab however their high initial 87sr 86sr 0 7053 0 7075 and low end t values 4 43 to 13 14 are inconsistent with the origin from slab melting these rocks often contain garnet residual crystals and eclogite garnet clinopyroxenite and garnet amphibolite xenoliths petrographical characteristics and estimated p t conditions of these xenoliths indicate that they were once deeply subducted and subsequently underwent rapid exhumation in the early mesozoic garnet residual crystals from the porphyries show similar chemical compositions to garnets from garnet clinopyroxenite and garnet amphibolite xenoliths ages of the inherited zircons of the xenoliths and their host rocks likely indicate that sources for the adakitic magma and protoliths of the eclogite and garnet clinopyroxenite xenoliths in the study area were from precambrian basement of the north china craton the data also suggest that the lower continental crust in the eastern north china craton was thickened during the early mesozoic and delaminated in the early cretaceous the high mg adakitic magma resulted from partial melting of this delaminated lower continental crust and its subsequent interaction with the mantle during upward transport leaving garnet as the residual phase

volcanic mound fields on the east pacific rise 16 19 s low effusion rate eruptions at overlapping spreading centers for the past 1 myr 1 volcanic mound fields identified on seamarc ii and hmr1 12 khz side scan data from the southern east pacific rise sepr occur near overlapping spreading centers oscs and migration traces of oscs the volcanic mound fields appear as a distinctive hummocky seafloor fabric due to side scan backscatter reflections from clusters of mound shaped reflectors the lack of growth of the mound fields away from the ridge axis and their occurrence in association with osc traces suggests that mound fields form along the ridge crest near oscs volcanic mound fields are found where 120 khz side scan and visual observations find fields of pillow mounds since pillow mounds are constructed by low effusion rate eruptions the volcanic mound fields found near the oscs and in their migration traces indicate that volcanic effusion rates tend to be lower near ridge discontinuities than midsegment regions this tendency for low effusion rate eruptions at oscs is documented for the past 1 myr three independent measurements of ridge segmentation 1 volcanic segment boundaries marked by the low effusion rate eruptions 2 tectonic segments defined by oscs and 3 magmatic segment boundaries based on continuity of parental magma composition all coincide in the study area high backscatter off axis lava fields not associated with seamounts are found on seafloor younger than 0 2 ma the 0 2 ma corridor corroborates previous results from the distribution of small isolated volcanoes that indicates randomly distributed off axis eruptions mainly occur on crust younger than 0 2 ma

high resolution remotely operated vehicle rov mapping of a slow spreading ridge mid atlantic ridge 45 n abstract 1 axial volcanic ridges avrs are found on most slow spreading mid ocean ridges and are thought to be the main locus of volcanism there in this study we present high resolution mapping of a typical well defined avr on the mid atlantic ridge at 45 n the avr is characterized by hummocky terrain composed typically of hummocks with pillowed or elongate pillowed flanks with pillowed or lobate lava flow summits often with small haystacks sitting on their highest points the avr is surrounded by several areas of flat seafloor composed of lobate and sheet lava flows the spatial and morphological differences between these areas indicate different eruption processes operating on and off the avr volcanic fissures are found all around and on the avr although those with the greatest horizontal displacement are found on the ridge crest and flat seafloor clusters of fissures may represent volcanic vents extremely detailed comparisons of sediment coverage and examination of contact relations around the avr suggest that many of the areas of flat seafloor are of a similar age or younger than the hummocky terrain of the avr additionally all the lavas surveyed have similar degrees of sediment cover suggesting that the avr was either built or resurfaced in the same 50 ka time frame as the flat seafloor

evolution of an englacial volcanic ridge pillow ridge tindar mount edziza volcanic complex ncvp british columbia canada abstract glaciovolcanic deposits are critical for documenting the presence and thickness of terrestrial ice sheets and for testing hypotheses about inferred terrestrial ice volumes based on the marine record deposits formed by the coincidence of volcanism and ice at the mount edziza volcanic complex mevc in northern british columbia canada preserve an important record for documenting local and possibly regional ice dynamics pillow ridge located at the northwestern end of the mevc formed by ice confined fissure fed eruptions it comprises predominantly pillow lavas and volcanic breccias of alkaline basalt composition with subordinate finer grained volcaniclastic deposits and dykes the ridge is presently 4 km long 1000 m in maximum width and 600 m high fifteen syn and post eruptive lithofacies are recognized in excellent exposures along the glacially dissected western side of the ridge we recognize five lithofacies associations 1 poorly sorted tuff breccia and dykes 2 proximal pillow lava dykes and tuff breccia 3 distal pillow lava poorly sorted conglomerate and well sorted volcanic sandstone 4 interbedded tuff lapilli tuff and tuff breccia units and 5 heterolithic volcanogenic conglomerate and sandstone given the abundance of pillow lavas and the lack of surrounding topographic barriers capable of impounding water we agree with souther souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp that the bulk of the edifice formed while confined by ice but have found evidence for a more complex and variable eruption history than that which he proposed preliminary estimates of water ice depths derived from ftir analyses of h2o give ranges of 300 to 680 m assuming 0 ppm co2 and 857 to 1297 m assuming 25 ppm co2 variations in depth estimates among samples may indicate that water ice depths changed during the evolution of the ridge which is consistent with our interpretations for the origins of different lithofacies associations given that the age of the units are likely to be ca 0 9 ma souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp pillow ridge may be the best documentation of a regional high stand of the cordilleran ice sheet cis in the middle pleistocene and an excellent example of the lithofacies and stratigraphic complexities produced by variations in water levels during a prolonged glaciovolcanic eruption

internal strain within lava flows from analogue modelling internal strain within lava flows can be measured in the field from deformed bubbles or vesicle foliations preferred crystal orientation or ams studies these measurements have important implications for the determination of vertical velocity profiles and flow directions recent field studies show very contrasting strain patterns especially in vertical profiles an experimental study was conducted to relate variations in internal strain to different boundary conditions during flow results show that viscous flow in a straight channel along a basal slope produces three successive stretch trajectories in vertical flow planes these trajectories are related to the distribution with time of a simple shear component and a pure shear component viscous flow in a straight channel along a horizontal base reveals convex stretch trajectories in the vertical flow plane radial spreading at the mouth of a straight channel reveals concentric stretching perpendicular to the radial direction of displacement in the upper part of the flow strain components deduced from experiments may also explain fold formation during motion these experimental results provide a few end member strain patterns which may facilitate the interpretation of strain measurements in natural lava flows in terms of emplacement mechanisms

evidence for volcanic eruption on the southern juan de fuca ridge between 1981 and 1987 the formation of new ocean crust at mid ocean ridges is known to be a discontinuous process in both space and time but little is known about the frequency and duration of eruptions along an active ridge segment here we present evidence from sea beam surveys and underwater photography for the eruption of lavas along a segment of the juan de fuca ridge between 1981 and 1987 although previous studies have inferred volcanic activity on ridges in areas where recent seismicity or young lava flows have been observed1 4 none has yet had direct evidence to date such a recent submarine eruption the temporal coincidence between this eruptive episode and the megaplumes huge sudden emissions of hot mineral laden water observed over this part of the ridge5 6 in 1986 and 1987 supports previous suggestions5 10 that megaplumes are caused by sea floor spreading events

kinetics of crystallization of igneous rocks the geochemistry of igneous rocks is discussed with the primary objectives of bringing together the theories underlying the kinetics of crystallization of igneous rocks and illustrating the use of these theories in understanding experimental and observational data the primary purpose of the chapter is to introduce current thinking about the kinetics of igneous rocks and to provide a basis for understanding other work a basic assumption made in the discussion is that the rate of any chemical reaction including the crystallization of igneous rocks is zero at equilibrium and proceeds at a finite rate only at a finite deviation from equilibrium as such an understanding of the processes operating in igneous rocks requires an understanding of how deviation from equilibrium affects the rates and mechanisms of the processes occurring during crystallization these processes are detailed with special emphasis given to nucleation and crystal growth jmt

direct observation of a submarine volcanic eruption from a sea floor instrument caught in a lava flow our understanding of submarine volcanic eruptions has improved substantially in the past decade owing to the recent ability to remotely detect such events and to then respond rapidly with synoptic surveys and sampling at the eruption site but these data are necessarily limited to observations after the event in contrast the 1998 eruption of axial volcano on the juan de fuca ridge was monitored by in situ sea floor instruments one of these instruments which measured bottom pressure as a proxy for vertical deformation of the sea floor was overrun and entrapped by the 1998 lava flow the instrument survived being insulated from the molten lava by the solidified crust and was later recovered the data serendipitously recorded by this instrument reveal the duration character and effusion rate of a sheet flow eruption on a mid ocean ridge and document over three metres of lava flow inflation and subsequent drain back after the brief two hour eruption the instrument also measured gradual subsidence of 1 4 metres over the next several days reflecting deflation of the entire volcano summit as magma moved into the adjacent rift zone these findings are consistent with our understanding of submarine lava effusion as previously inferred from seafloor observations terrestrial analogues and laboratory simulations

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

stratigraphy sedimentology and physical volcanology of the henik group central ennadai rankin greenstone belt northwest territories canada late archean paleogeography of the hearne province and tectonic implications abstract extensive areas of the hearne and rae provinces are underlain by archean metavolcanic and metasedimentary rocks in the rae province supracrustal sequences with prominent continental to shallow water quartz arenites have been interpreted by others as rift and passive margin deposits in the hearne province to the southeast the ennadai rankin greenstone belt is exposed in an area ca 700 200 km forming the second largest greenstone belt in canada it comprises mainly greenschist facies grade mafic and felsic volcanic siliciclastic chemogenic and volcaniclastic rocks stratigraphic sedimentologic and physical volcanologic data based on 1 50 000 scale mapping in the central part of the belt indicate deposition in a subaqueous mafic volcanic plateau slope basin system that was well removed from a continental influence water depth was below storm wave base as indicated by preservation of delicate lamination in pelitic and iron formation units absence of features suggestive of subaerial exposure oscillatory flow or tidal currents and lack of interfingering rocks that could represent laterally adjacent shelf coastal or continental environments reconnaissance level regional geologic and geochronologic data indicate an overall pattern of supracrustal deposition in the hearne province consisting of a large mafic volcanic plain isolated felsic volcanic centres with lenses and belts of deep water sedimentary rocks at least two speculative yet testable tectonic models are consistent with the inferred paleogeography for both the rae province is considered to be the western continental hinterland to the ensimatic hearne province the rae and hearne provinces may record late archean continental extension sea floor spreading oceanic volcanic arc growth diachronous back arc spreading and collapse and arc continent collision with thrusting of oceanic rocks on to attenuated rae crust alternatively the hearne province may represent northwestward accretion of multiple volcanic arc trench pairs

basaltic pillow mounds in the vinalhaven intrusion maine the vinalhaven intrusion is a dominantly granitic pluton of probable devonian age located on vinalhaven island and adjacent islands maine it consists of four main units coarse grained granite fine grained granite a gabbro diorite unit consisting of interlayered mafic hybrid and granitic rocks and a heterogeneous granitic unit the gabbro diorite unit occurs along the south and east coast of the island as a sheet like body hundreds of meters to more than 1 km thick that dips beneath the central granitic units and rests on heterogeneous granitic rocks that form the base of the intrusion and are exposed on islands to the southeast load cast and pipe structures at the bases of mafic sheets indicate that the gabbro diorite unit represents a sequence of basaltic injections that ponded on crystal rich mush at the base of a silicic magma chamber and variably interacted with overlying crystal poor granitic magma the pluton therefore represents a fossilized silicic magma chamber that was periodically replenished by basaltic magma near the base of the gabbro diorite unit some basaltic injections produced large mounds up to more than 10 m high and 100 m wide of tightly packed meter scale chilled basaltic pillows tubes and sheets in a granitic matrix the mounds appear to represent flow fronts of basaltic injections that entered and ponded on the floor of a silicic magma chamber although physical conditions differ significantly these plutonic pillow mounds appear to share many characteristics with submarine pillow basalts and lava flows

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

morphology and emplacement of a long channeled lava flow near ascraeus mons volcano mars 1 channeled lava flows hundreds of kilometers long are common on the lower flanks of the tharsis montes on mars our analysis of a 690 km long lava flow along the southwest perimeter of ascraeus mons shows that it was emplaced on low local slopes 100 km in length but the maximum effusion rates necessary on earth are essentially the minimum for martian flows on the basis of our calculated effusion rates the eruption duration was 3 to 7 earth months assuming a constant effusion rate and continuous eruption the morphology of the ascraeus mons flow shows similarities to terrestrial and simulated channeled flows downstream changes in morphology resemble those observed in the 1907 flow mauna loa volcano hawaii and channeled polyethylene glycol peg flows braided sections of the channel in the ascraeus mons flow contain islands which are hundreds of meters across and resemble features observed in the 1907 and 1984 flows on mauna loa volcano crosscutting relationships suggest islands in the proximal section were shaped by thermal and mechanical erosion whereas islands in the medial section are inferred to be material rafted by surges of lava through the channel overall understanding the morphology of long lava flows on mars is essential to the interpretation of their emplacement and constraining eruption conditions in the saddle regions of the tharsis volcanoes

high resolution bathymetric surveys using scanning sonars lava flow morphology hydrothermal vents and geologic structure at recent eruption sites on the juan de fuca ridge the coaxial and cleft segments of the juan de fuca ridge have isolated chronic high temperature and focused hydrothermal vent sites both segments also have experienced recent volcanic eruptions which produced extensive ephemeral low temperature and diffuse hydrothermal venting to study the geologic setting of these sites high resolution bathymetric surveys at eight locations on the coaxial and cleft segments were collected between 1993 and 1999 two 675 khz scanning sonar systems were used mesotech on the submersible alvin and imagenex on the remotely operated vehicle jason the bathymetry from these surveys can be gridded at a scale of 2 4 m and contoured at 1 m and thus can resolve many fine scale features on the seafloor that are indistinguishable in multibeam bathymetry collected at the sea surface bathymetric data at this resolution are particularly useful for identifying geologic features related to diking faulting and lava flow emplacement for example the high resolution bathymetric maps show that submarine fissure eruptions that form pillow lavas last long enough to become localized and to produce point source constructs along their length and their extrusion rate is low enough that no significant drainback occurs in contrast lobate sheet flows are formed by short lived high effusion rate eruptions in which no localization of output occurs along the eruptive fissure and inflation is quickly followed by drainback resulting in extensive collapse features however if the process of submarine lava flow inflation occurs at a slower rate and over a longer period of time it can create lava rises up to 25 m high with distinctive structure and morphology the scanning sonar data also show that fissures and grabens have formed or reactivated where dikes approach the surface adjacent to recent eruptive sites the fine scale bathymetry establishes that all the hydrothermal vent sites studied at the coaxial and cleft segments are located along prominent volcanic or tectonic extensional structures which provide the physical pathway for fluids from the subsurface to the seafloor furthermore the fine scale morphology of recent lava flows can be used as a qualitative indication of eruption duration

quantitative constraints on the growth of submarine lava pillars from a monitoring instrument that was caught in a lava flow 1 lava pillars are hollow vertical chimneys of solid basaltic lava that are common features within the collapsed interiors of submarine sheet flows on intermediate and fast spreading mid ocean ridges they are morphologically similar to lava trees that form on land when lava overruns forested areas but the sides of lava pillars are covered with distinctive evenly spaced thin horizontal lava crusts referred to hereafter as lava shelves lava stalactites up to 5 cm long on the undersides of these shelves are evidence that cavities filled with a hot vapor phase existed temporarily beneath each crust during the submarine eruption of axial volcano in 1998 on the juan de fuca ridge a monitoring instrument called vsm2 became embedded in the upper crust of a lava flow that produced 3 to 5 m high lava pillars a pressure sensor in the instrument showed that the 1998 lobate sheet flow inflated 3 5 m and then drained out again in only 2 5 hours these data provide the first quantitative constraints on the timescale of lava pillar formation and the rates of submarine lava flow inflation and drainback they also allow comparisons to lava flow inflation rates observed on land to theoretical models of crust formation on submarine lava and to previous models of pillar formation a new model is presented for the rhythmic formation of alternating lava crusts and vapor cavities to explain how stacks of lava shelves are formed on the sides of lava pillars during continuous lava drainback each vapor cavity is created between a stranded crust and the subsiding lava surface a hot vapor phase forms within each cavity as seawater is syringed through tiny cracks in the stranded crust above eventually the subsiding lava causes the crust above to fail quenching the hot cavity and forming the next lava crust during the 1998 eruption at axial volcano this process repeated itself about every 2 min during the 81 min long drainback phase of the eruption based on the thickness and spacing of the lava shelves the vsm2 data show that lava pillars are formed during short lived eruptions in which inflation and drainback follow each other in rapid succession and that pillars record physical evidence that can be used to interpret the dynamics of seafloor eruptions

cooling rates of hyaloclastites applications of relaxation geospeedometry to undersea volcanic deposits glass fragments from three different hyaloclastites have been used to evaluate the range of cooling rates experienced by undersea volcanic deposits we found that the glass fragments retain structures with a range of apparent quench rates from 25 to 0 15 k min 1 the most rapid cooling rates are interpreted to be those resulting from cooling of the lava near the water interface simple conductive cooling models produce a range of quench rates comparable to those of the more rapidly cooled samples the very slow apparent quench rates are unlikely to result from simple linear cooling through the glass transition because of the onset of crystallization instead they are indicators of a more complex thermal history that involves the annealing of glasses at temperatures within the glass transition interval for a dwell time sufficient to allow the relaxation of the glass to lower temperature structures the thermal history recorded in these samples illustrates the complexity of eruptive processes and demonstrates that quench rates for natural glasses retain information relevant to more complex cooling models

constraints on the formation of submarine lava flows from numerical model calculations abstract to constrain life time and flow rates in a submarine lava tube pillow 3d finite element calculations were carried out for a simplified fixed geometry model tube the principal parameters included into the model are a temperature dependent newtonian viscosity of the lava whereby viscosity is also dependent on composition temperature and crystallinity of the lava cooling by seawater and the release of latent heat of crystallization time dependent model runs suggest the longevity of the tube flow is constrained by the competition of advective heat flow along the tube axis and the conduction of heat towards the margins of the flow in order to keep the lava flowing a minimum critical pressure gradient along the tube is required otherwise the amount of thermal energy brought in by the influx of hot lava is less than the amount lost at the outer boundaries and the tube will solidify providing an exponentially decaying driving pressure at the tube inlet this critical pressure gradient has been calculated for different tube lengths and diameters and is compared to critical pressure values resulting from a more simplistic solution assuming constant viscosity and pure conductive or convective cooling an analysis of the difference between pressure gradients obtained through the numerical and simplified model is used to derive an appropriate power law for the critical pressure gradient in bodies cooled by convection and conduction including the effect of temperature dependent viscosity that gradient scales with the tube radius r as r3 85 this law is valid for tube style lava flows and lava viscosities in the basaltic range

the 1991 eruption of hekla iceland the eruption that started in the hekla volcano in south iceland on 17 january 1991 and came to an end on 11 march produced mainly andesitic lava this lava covers 23 km2 and has an estimated volume of 0 15 km3 this is the third eruption in only 20 years whereas the average repose period since 1104 is 55 years earthquakes as well as a strain pulse recorded by borehole strainmeters occurred less than half an hour before the start of the eruption the initial plinian phase was very short lived producing a total of only 0 02 km3 of tephra the eruption cloud attained 11 5 km in height in only 10 min but it became detached from the volcano a few hours later several fissures were active during the first day of the eruption including a part of the summit fissure by the second day however the activity was already essentially limited to that segment of the principal fissure where the main crater subsequently formed the average effusion rate during the first two days of the eruption was about 800 m3 s 1 after this peak the effusion rate declined rapidly to 10 20 m3 s 1 then more slowly to 1 m3 s 1 and remained at 1 12 m3 s 1 until the end of the eruption site observations near the main crater suggest that the intensity of the volcanic tremor varied directly with the force of the eruption a notable rise in the fluorine concentration of riverwater in the vicinity of the eruptive fissures occurred on the 5th day of the eruption but it levelled off on the 6th day and then remained essentially constant the volume and initial silica content of the lava and tephra the explosivity and effusion rate during the earliest stage of the eruption as well as the magnitude attained by the associated earthquakes support earlier suggestions that these parameters are positively related to the length of the preceeding repose period the chemical difference between the eruptive material of hekla itself and the lavas erupted in its vicinity can be explained in terms of a density stratified magma reservoir located at the bottom of the crust we propose that the shape of this reservoir its location at the west margin of a propagating rift and its association with a crustal weakness all contribute to the high eruption frequency of hekla

using submarine lava pillars to record mid ocean ridge eruption dynamics abstract submarine lava pillars are hollow glass lined basaltic cylinders that occur at the axis of the mid ocean ridge and within the summit calderas of some seamounts typically pillars are 1 20 m tall and 0 25 2 0 m in diameter with subhorizontal to horizontal glassy selvages on their exterior walls lava pillars form gradually during a single eruption and are composed of lava emplaced at the eruption onset as well as the last lava remaining after the lava pond has drained on the deep sea floor the surface of a basaltic lava flow quenches to glass within 1 s thereby preserving information about eruption dynamics as well as chemical and physical properties of lava within a single eruption investigation of different lava pillars collected from a single eruption allows us to distinguish surficial lava pond or lava lake geochemical processes from those operating in the magma chamber morphologic major element petrographic and helium analyses were performed on portions of three lava pillars formed during the april 1991 eruption near 9 50 n at the axis of the east pacific rise modeling results indicate that the collected portions of pillars formed in 2 5 h suggesting a total eruption duration of 8 20 h these values are consistent with observed homogeneity in the glass helium concentrations and helium diffusion rates major element compositions of most pillar glasses are homogeneous and identical to the 1991 flow but slight chemical variations measured in the outermost portions of some pillars may reflect post eruptive processes rather than those occurring in subaxial magma bodies because lava pillars are common at mid ocean ridges mors the concepts and techniques we present here may have important application to the study of mor eruptions thereby providing a basis for quantitative comparisons of volcanic eruptions in geographically and tectonically diverse settings more research is needed to thoroughly test the hypotheses presented here

an experimental study of the surface thermal signature of hot subaerial isoviscous gravity currents implications for thermal monitoring of lava flows and domes received 22 july 2011 revised 23 november 2011 accepted 23 november 2011 published 7 february 2012 1 management of eruptions requires a knowledge of lava effusion rates for which a safe thermal proxy is often used however this thermal proxy does not take into account the flow dynamics and is basically time independent in order to establish a more robust framework that can link eruption rates and surface thermal signals of lavas measured remotely we investigate the spreading of a hot isoviscous axisymmetric subaerial gravity current injected at constant rate from a point source onto a horizontal substrate we performed laboratory experiments and found that the surface thermal structure became steady after an initial transient we develop a theoretical model for a spreading fluid cooled by radiation and convection at its surface that also predicts a steady thermal regime we show that despite the model s simplicity relative to lava flows it yields the correct order of magnitude for the effusion rate required to produce the radiant flux measured on natural lava flows for typical thermal lava properties and an effusion rate between 0 1 and 10 m 3 s 1 the model predicts a steady radiated heat flux ranging from 10 8 to 10 10 w the assessed effusion rate varies quasi linearly with the steady heat flux with much weaker dependence on the flow viscosity this relationship is valid only after a transient time which scales as the diffusive time ranging from a few days for small basaltic flows to several years for lava domes the thermal proxy appears thus less reliable to follow sharp variations of the effusion rate during an eruption

polygonal feeder tubes filled with hydroclasts a new volcanic lithofacies marking shoreline subaerial submarine transition this paper describes for the first time a new lithofacies that formed in the passage zone during the construction of pahoehoe lava fed deltas in the north and ne coastal areas of gran canaria canary islands atlantic ocean these lava fed deltas which are pliocene in age present similar lithofacies associations to those previously described in the literature except for two distinct features low abundance of hyaloclastites and a new lithofacies in the passage zone this new lithofacies which we propose to name polygonal feeder tubes filled with hydroclasts comprises metre scale lava feeder tubes with decimetre scale coherent poorly vesicular and aphanitic rinds of polygonal morphology filled with closely packed hydroclasts generated in situ it represents the first stage in the interaction between seawater and thick lava flows entering the sea under the influence of a tidal regime thus marking sea level this lithofacies should be easily recognizable in ancient successions and thus represents a useful marker of palaeoshorelines supplementary material sample preparation and sample geochemistry are available at http www geolsoc org uk sup18785

geology of the alarcon rise southern gulf of california author s clague da caress dw dreyer bm lundsten l paduan jb portner ra spelz madero r bowles ja castillo pr guardado france r le saout m martin jf santa rosa del rio ma zierenberg ra abstract 2018 the authors meter scale auv bathymetric mapping and rov sampling of the entire 47 km long alarcon rise between the pescadero and tamayo transforms show that the shallowest inflated portion of the segment hosts all four active hydrothermal vent fields and the youngest hottest and highest effusion rate lava flows this shallowest inflated part is located 1 3 of the way between the tamayo and pescadero transforms and is paved by a 16 km2 channelized flow that erupted from 9 km of en echelon fissures and is larger than historic flows on the east pacific rise or on the gorda and juan de fuca ridges starting 5 km south of the pescadero transform 6 5 km of the alarcon rise is characterized by faulted ridges and domes of fractionated lavas ranging from basaltic andesite to rhyolite with up to 77 3 wt sio2 these are the first known rhyolites from the submarine global mid ocean ridge system silicic lavas range from g11 7 ka to as young as 1 1 ka a basalt to basaltic andesite sequence and an andesite to dacite to rhyolite sequence are consistent with crystal fractionation but some intermediate basaltic andesite and andesite formed by mixing basalt with dacite or rhyolite magmatism occurred along the bounding tamayo and pescadero transforms as extensive channelized flows the flows erupted from ring faults surrounding uplifted sediment hills inferred to overlie sills the transforms are transtensional to accommodate magma migration from the adjacent alarcon rise

fluidal clast breccia generated by submarine fire fountaining trooper creek formation queensland australia abstract a distinctive monomictic breccia composed of fluidal and blocky basaltic andesite clasts occurs in a cambro ordovician submarine volcanic succession in northern queensland australia associated with this fluvial clast buccia facies are coherent facies and coarse and fine breccia facies of the same composition the fluidal clast breccia facies is internally massive and 250 m thick varying only in the ratio of fluidal clasts to blocky clasts fluidal clasts range in size from 2 cm to 170 cm and have moderately to highly vesicular cores and thick up to 1 cm non vesicular formerly glassy rims blocky clasts are highly vesicular to non vesicular subaqueous fire fountain breccias are distinguished from subaerial fire fountain breccias by thick glassy margins on fluidal clasts the lack of welding and agglutination and the distinctive association of highly vesicular fluidal clasts with non vesicular angular blocky clasts recognition of submarine fire fountain breccias in volcanic successions constrains the eruption style proximity tens of metres to source and environment of deposition

a comparison between subaerial and submarine eruptions at kilauea volcano hawaii implications for the thermal viability of lateral feeder dikes eruption styles on the subaerial east rift zone erz of kilauea volcano are reviewed and a classification scheme for the different types of eruption is proposed the various eruption types are produced by differing thermal and driving pressure behaviour in the feeder dikes existing evidence is reviewed and new evidence presented of the types and volumes of eruptions on the puna ridge which is the submarine extension of the erz eruptions on the puna ridge fall into the same five classes as and are of comparable volume to those on the subaerial erz evidence is presented which suggests that feeder dikes for puna ridge eruptions are more thermally viable than those feeding subaerial eruptions and this difference causes long lived large volume eruptions to be more common on the puna ridge than on the subaerial erz this systematic variation in thermal viability may be due to increased dike width for puna ridge dikes or increased pressure gradients driving magma flow lateral dike emplacement is common to many basaltic systems including on other hawaiian volcanoes in iceland and at mid ocean ridges the systematic trend inferred for the erz of kilauea implies that in the other systems large volume eruptions may also be more common at great distances than they are close to the magma centre

basaltic subglacial sheet like sequences evidence for two types with different implications for the inferred thickness of associated ice abstract subglacially erupted volcanic sequences provide proxies for a unique range of palaeo ice parameters and they are potentially highly useful archives of palaeoenvironmental information particularly for pre quaternary periods they can thus be incorporated by climate and ice sheet modellers in the same way as other environmental proxies yet they remain largely under utilised basaltic volcanic sequences erupted subglacially consist empirically of two major types corresponding to eruptions under thick and thin ice respectively the latter are called subglacial sheet like sequences and only one generic type of sequence has been described so far however there is now evidence that there are at least two generic types with significantly different implications for interpretations of associated palaeo ice sheet thicknesses one type which is relatively well described is believed to be a diagnostic product of eruptions associated with a relatively thin glacial cover 1000 m eruptions that form the dalsheidi type of sequence commence with the injection and inflation of a sill along the ice bedrock interface such interface sills were predicted theoretically but had no known geological example until now subsequent evolution commonly involves floating of the ice cover catastrophic meltwater drainage and emplacement of widespread sheets of hyaloclastite as cohesionless mass flows and hyperconcentrated flows the water saturated hyaloclastite is characteristically intruded by apophyses sourced in the underlying interface sill eruptions are commonly not explosive until their later stages dalsheidi type deposits are outflow sequences probably linked to subglacial pillow volcanoes which in iceland were erupted along fissures they only provide an indication of minimum thicknesses of the associated overlying ice although theoretical considerations suggest substantial ice thicknesses in excess of 1000 m however they are likely to be characteristic products of eruptions under the thick west antarctic ice sheet but are currently inaccessible such eruptions may be capable of destabilising that ice sheet

formation of submarine flat topped volcanic cones in hawai i high resolution bathymetric mapping has shown that submarine flat topped volcanic cones morphologically similar to ones on the deep sea floor and near mid ocean ridges are common on or near submarine rift zones of kilauea kohala or mauna kea mahukona and haleakala volcanoes four flat topped cones on kohala were explored and sampled with the pisces v submersible in october 1998 samples show that flat topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage similarly shaped flat topped cones on the northwest submarine flank of ni ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage submarine postshield stage eruptions on hilo ridge mahukona hana ridge and offshore ni ihau form pointed cones of alkalic basalt and hawaiite the shield stage flat topped cones have steep 25 sides remarkably flat horizontal tops basal diameters of 1 3 km and heights 300 m the flat tops commonly have either a low mound or a deep crater in the center the rejuvenated stage flat topped cones have the same shape with steep sides and flat horizontal tops but are much larger with basal diameters up to 5 5 km and heights commonly greater than 200 m the flat tops have a central low mound shallow crater or levees that surrounded lava ponds as large as 1 km across most of the rejuvenated stage flat topped cones formed on slopes 10 and formed adjacent semicircular steps down the flank of ni ihau rather than circular structures all the flat topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades these and other submarine volcanic cones of similar size and shape apparently form as continuously overflowing submarine lava ponds a lava pond surrounded by a levee forms above a sea floor vent as lava continues to flow into the pond the lava flow surface rises and overflows the lowest point on the levee forming elongate pillow lava flows that simultaneously build the rim outward and upward but also dam and fill in the low point on the rim the process repeats at the new lowest point forming a circular structure with a flat horizontal top and steep pillowed margins there is a delicate balance between lava heat supply to the pond and cooling and thickening of the floating crust factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents moderate to high confining pressure at moderate to great ocean depth long lived steady eruption years to decades moderate effusion rates probably ca 0 1 km3 year and low but not necessarily flat slopes with higher effusion rates sheet flows flood the slope with lower effusion rates pillow mounds form hawaiian shield stage eruptions begin as fissure eruptions if the eruption is too brief it will not consolidate activity at a point and fissure fed flows will form a pond with irregular levees the pond will solidify between eruptive pulses if the eruption is not steady lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones as occurs during the post shield stage the steady effusion of lava on land constructs lava shields which are probably the subaerial analogs to submarine flat topped cones but formed under different cooling conditions

preeruptive flow focussing in dikes feeding historical pillow ridges on the juan de fuca and gorda ridges linear hummocky pillow mound volcanism dominates at slow and intermediate spreading rate mid ocean ridges volcanic hummocks are thought to be formed by low effusion rates or as a result of flow focussing during effusive fissure style eruptions in which the initial dike intercepts the seafloor and erupts along its entire length in this study high resolution autonomous underwater vehicle auv bathymetry is used to accurately map the extents of four historical fissure eruptions of the juan de fuca and gorda ridges on the north gorda north cleft and coaxial ridge segments the four mapped eruptions take the form of pillow mounds which are similar in both lithology and dimension to hummocks on the mid atlantic ridge pillow mounds may be isolated or coalesce to form composite mounds aligned as ridges or as clustered groups in three of the four mapped sites the eruptions were discontinuous along their lengths with pillow mounds and composite mounds commonly separated by areas of older seafloor this style of discontinuous eruption is inconsistent with typical en echelon fissure eruptions and is probably due to a mildly overpressured fingering dike intersecting the seafloor along parts of its length

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

evolution of a subglacial basaltic lava flow field tennena volcanic center mount edziza volcanic complex british columbia canada abstract studies of terrestrial glaciovolcanic deposits have elucidated the utility of these deposits as tools to constrain ice conditions at the time of their emplacement very few studies however have documented the emplacement of effusion dominated basaltic glaciovolcanic eruptions the tennena volcanic center tvc located at 57 40 57 705 n 130 39 43 138 w on the western flank of mount edziza volcanic complex mevc in northwestern british columbia canada preserves a detailed record of interactions between coherent basaltic lavas and a local regional ice sheet inferred to be associated with the last glacial maximum lgm here we describe the field characteristics of five primary volcanic lithofacies and five associated glaciogenic lithofacies and discuss their spatial distribution within the volcanic center we find that 1 the distribution of primary hydrovolcanic clastic deposits tuff breccias and lapilli tuffs is confined to tennena cone 2 pillow lavas are present throughout the extent of the surrounding lava field with morphologies that include distinctive structures comprising vertically oriented distended pillows 3 multiple lobes of massive non pillowed lavas that represent high initial magma discharge rates are confined to medial distances from the cone and 4 associated glaciogenic facies that underlie or onlap the tvc lavas indicate a variable sediment water ratio during subglacial meltwater drainage at the time of the eruption or shortly afterwards analyses of h 2 o co 2 in pillow rim samples give broad constraints for emplacement pressures equivalent to 500 1400 m of overlying ice no subaerial lava morphologies are found on the cone or in the proximal medial and distal lithofacies and the sequence is interpreted as documenting an eruption of basaltic lava flows beneath either the lgm cordilleran ice sheet or a younger dryas expansion of the still extant edziza ice cap the tvc lavas especially medial and distal ones display excellent examples of textures and morphologies that can be used to 1 help identify other terrestrial and martian basaltic lava flows emplaced beneath ice and 2 further our understanding on how sub ice lava flows are emplaced

recognizing distinct portions of seamounts using volcanic facies analysis examples from the archean slave province nwt canada abstract archean volcanic rocks in the mafic dominated ca 2 66 2 69 ga point lake and beaulieu river belts slave province northwest territories are significant in demonstrating the facies that characterize specific portions of pillow volcanoes or seamounts irrespective of tectonic setting three distinct localities mapped in detail display facies consistent with 1 proximal deep water 2 medial to distal deep water and 3 medial shallow water seamount settings the proximal facies in the point lake belt include a 55 m thick non vesicular pillowed sequence cut by numerous mafic dykes and sills dykes contain multiple chilled margins indicating successive magma pulses which contributed to edifice construction abundant feeder conduits in addition to the absence of fragmental facies and vesicles are typical of the central deep water portion of seamounts where growth is initiated the medial to distal deep water facies in the point lake belt are represented by a 30 80 m thick assemblage of disorganized pillow breccia and pillowed and massive flows with 5 27 vesicularity massive non vesicular hyaloclastite intermingled with sedimentary material fluidal peperite in addition to thin shale units interstratified with pillow breccia and hyaloclastite indicate that sedimentation and volcanism were contemporaneous an increase in fragmental units and vesicularity relative to the proximal deep water facies is suggestive of the medial to distal part of a seamount in shallower water bedded tuffs laterally along strike with massive flows are the results of turbidity current deposition immediately following localized subaqueous eruptions a medial shallow water seamount setting is represented in the beaulieu river belt by a 5 85 m thick sequence of vesicular lobate pillowed and massive flows stratified pillow breccia and hyaloclastite and mafic dykes vesicularity ranges from 21 49 in pillowed flows 5 40 in massive flows and 20 35 in pillow breccia and hyaloclastite stratified pillow breccia developed along steep flow fronts in shallow water whereas bedded hyaloclastite formed during reworking and redeposition of autoclastic hyaloclastite on seamount flanks in shallow water the volcanic facies associations in the study areas are analogous to those of modern seamounts associated with the mid atlantic ridge and east pacific rise as well as mesozoic cenozoic seamounts in the canary islands fiji southwest japan the sea of japan and cyprus volcanological studies in the point lake and beaulieu river volcanic belts and subsequent comparisons with phanerozoic analogues demonstrate the manner in which distinct portions of ancient seamounts can be recognized in similar archean terranes

time dependent profiles of lava flows this work investigates the combined effects of a time dependent effusion rate and a spatially varying viscosity on the thickness profile of a flowing lava we formulate relatively simple governing equations as a primitive dynamical model for these two influences on lava flow morphology free boundary solutions for the profile of the flow and its extent are presented and analyzed for different boundary conditions at the source of the flow and several models for the spatial dependence of the viscosity the results presented here suggest that time dependence in the flow depth at the source and the form of the viscosity variation are significant influences on the morphology and dimensions of lava flows moreover this analysis implies that time dependent source conditions may contribute to the scatter in plots of eruption rate versus flow length and disparities between field and laboratory estimates of lava viscosity

submarine explosive volcanism in the southeastern terceira rift sao miguel region azores abstract morphologic studies with sonar data and in situ observations of modern eruptions have revealed some information suggesting how submarine volcanic cones develop but the information only addresses the modern surfaces of these features here we describe a study combining morphological data with high resolution seismic reflection data collected over cones within the southeastern terceira rift a succession of deep basins volcanic bathymetric highs and islands e g sao miguel representing the westernmost part of the eurasian nubian plate boundary the cones 252 are distributed in depths down to 3200 m and exhibit an average diameter of 743 m an average slope of 20 and heights mainly between 50 and 200 m the cones are here classified into three different categories by physiographic or tectonic setting we find no particular morphometric differences in cone shapes between these areas first numerous cones located at the submarine flanks of sao miguel s sete cidades and fogo volcano are considered to be parasitic structures second in the southeast of the island they form a superstructure possibly reflecting an early submarine stadium of a posterior subaerial stratovolcano third some cones are controlled by faults mostly in a graben system southwest of the island high resolution multichannel seismic data indicates that the graben cones evolved synchronously with the graben formation bottom currents then probably removed the surficial fine grain size fraction leaving rough surface textures of the cones which backscatter sonar signals strongly in the data recorded here however a young cone investigated in detail is characterized by a smooth surface a marked increase of internal stratification with increasing distance from the summit and upwards concave flanks others exhibit central craters suggesting an explosive than an effusive evolution of these structures the morphological characteristics of these submarine cones show that they have similar sizes and shapes to cinder cones onshore sao miguel

on lava dome growth with application to the 1979 lava extrusion of the soufriere of st vincent abstract a theoretical analysis is presented for the spread of a viscous liquid flowing under its own hydrostatic pressure on a horizontal surface in order to model lava dome formation two situations are considered in detail the spreading of a constant volume of liquid and the case where the amount of liquid is continually increased experiments with silicone liquids show close agreement with theory the formation of a basaltic andesite lava extrusion in 1979 on the crater floor of the soufriere of st vincent west indies provided the motivation for and an application of the model the extrusion reached a diameter of 868 m and a height of 133 m over a period of 150 days over the first 90 days the growth relationships were consistent with those predicted by theory application of the theory to the soufriere dome suggests an effective viscosity of 2 x 10 12 poise for the basaltic andesite lava the large effective viscosity calculated for the lava may be attributed to the dominant influence of a high viscosity skin which forms at the margins of the flow as it cools after 70 days the rate of growth of the extrusion markedly decreased because a substantial collar of rubble accumulated at the flow front due to this collar the growth of the extrusion ceased after 150 days from approximately two weeks after the initiation of the extrusion the discharge rate of lava decreased approximately linearly with increasing dome height this observation suggests that the lava ascended under a decreasing hydrostatic driving pressure and that extrusion ceased when the lava column reached hydrostatic equilibrium

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

detailed geological mapping of two contrasting second order segments of the mid atlantic ridge between oceanographer and hayes fracture zones 33 30 n 35 n we present detailed geological mapping of the axial valley floor and ridge flanks of two neighboring but contrasting spreading segments oh1 and oh3 of the mid atlantic ridge between oceanographer and hayes fracture zones new in situ observations from the submersible nautile correlated with swath bathymetry and acoustic backscattering data from these segments reveal that the along and across axis volcanic tectonic variability within second order segments is larger than commonly acknowledged segment oh1 is a long and robust segment with a narrow and shallow axial valley the most intense magmatic activity is found at the segment center where the thickest crust has been imaged suggesting focused magma supply away from this part of the segment faulting and sedimentary cover predominate in contrast the center of segment oh3 is dominated by extensive sedimentary cover fissuring and faulting furthermore the most recent constructional volcanism is located away from the segment center in a region of greater depth and thinner crust this relocation of volcanism suggests either a recent shift in the magmatic source or the last vestige of a centrally located source fed by lateral dike injection segment tip magmatic oscillations are suggested by the distribution of rock types at both segment ends serpentinized peridotites and associated dolerites are exposed at the massifs located at the intersection with nontransform offsets ntos whereas only basaltic rocks crop out on the nodal basin floors we suggest that the combination of low magmatic budget and extension taking place at the ntos during a segment retreat favors the uplift and exposure of ultramafic massifs

coastal evolution on volcanic oceanic islands a complex interplay between volcanism erosion sedimentation sea level change and biogenic production abstract the growth and decay of oceanic hotspot volcanoes are intrinsically related to a competition between volcanic construction and erosive destruction and coastlines are at the forefront of such confrontation in this paper we review the several mechanisms that interact and contribute to the development of coastlines on oceanic island volcanoes and how these processes evolve throughout the islands lifetime volcanic constructional processes dominate during the emergent island and subaerial shield building stages during the emergent island stage surtseyan activity prevails and hydroclastic and pyroclastic structures form these structures are generally ephemeral because they can be rapidly obliterated by marine erosion with the onset of the subaerial shield building stage coastal evolution is essentially characterized by rapid but intermittent lateral growth through the formation of lava deltas largely expanding the coastlines until they typically reach their maximum extension with the post shield quiescence in volcanic activity destructive processes gradually take over and coastlines retreat adopting a more prominent profile mass wasting and marine and fluvial erosion reshape the landscape and if conditions are favorable biogenic processes assume a prominent role post erosional volcanic activity may temporarily reverse the balance by renewing coastline expansion but islands inexorably enter in a long battle for survival above sea level reef growth and or uplift may also prolong the island s lifetime above the waves the ultimate fate of most islands however is to be drowned through subsidence and or truncation by marine erosion

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

geology of the northern cleft segment juan de fuca ridge recent lava flows sea floor spreading and the formation of megaplumes geologic mapping and lava sampling were carried out after the discovery of large bursts of hydrothermal fluids megaplumes over the southern juan de fuca ridge in 1986 and 1987 our investigations of the northernmost section of the cleft segment have discovered 1 semicontinuous low temperature venting and one major high temperature vent site along 17 km of the neovolcanic zone and 2 very glassy lightly sedimented sheet flows and pillow mounds superimposed on older terrain over about 24 km along the northern most part the pillow mounds are documented to have erupted between 1981 and 1987 the occurrence of the megaplumes during this same time period strengthens the hypothesis that megaplumes are caused by sea floor extension events although the basalts from the entire length of the neovolcanic zone of the cleft segment appear to have been derived from the same mantle source a systematic northward increase in mg number along the segment within the neovolcanic zone indicates less shallow level differentiation to the north possibly related to the development of new magma chambers during the recent phase of sea floor spreading that has occurred there

paleointensity applications to timing and extent of eruptive activity 9 10 n east pacific rise placing accurate age constraints on near axis lava flows has become increasingly important given the structural and volcanic complexity of the neovolcanic zone at fast spreading ridges geomagnetic paleointensity of submarine basaltic glass sbg holds promise for placing quantitative age constraints on near axis flows in one of the first extensive tests of paleointensity as a dating tool or temporal marker we present the results of over 550 successful sbg paleointensity estimates from 189 near axis 4 km sites at the east pacific rise 9 10 n paleointensities range from 6 to 53 t and spatially correspond to the pattern expected from known temporal variations in the geomagnetic field samples within and adjacent to the axial summit trough ast have values approximately equal to or slightly higher than the present day samples out to 1 3 km from the ast have values higher than the present day and samples farther off axis have values lower than the present day the on axis samples 500 m from the ast provide a test case for using models of paleofield variation for the past few hundred years as an absolute dating technique results from samples collected near a well documented eruption in 1991 1992 suggest there may be a small negative bias in the paleointensity estimates limiting resolution of the dating technique possible explanations for such a bias include local field anomalies produced by preexisting magnetic terrain anomalously high magnetic unblocking temperatures leading to a small cooling rate bias and or the possibility of a chemical remanence produced by in situ alteration of samples likely to have complicated thermal histories paleointensity remains useful in approximating age differences in young flows and a clear along axis paleointensity contrast near 9 50 n is suggestive of a 150 200 year age difference paleointensity values of off axis samples are generally consistent with rough age interpretations based on side scan data furthermore spatial patterns in the paleointensity suggest extensive off axis flow emplacement may occur infrequently with recurrence intervals of 10 20 kyr results of a stochastic model of lava emplacement show that this can be achieved with a single distribution of flows with flow size linked to time between eruptions

cooling rates of mid ocean ridge lava deduced from clinopyroxene spherulites abstract we present a compositional analysis of spherulites and their surrounding groundmass in basaltic andesite lava samples collected from the pacific antarctic ridge the spherulites consist of radiating dendritic branches of clinopyroxene and contain abundant vesicles that are stretched parallel to the branches stretched vesicles require that the spherulites grew when the groundmass was liquid and thus while it was hotter than its glass transition although chemical components incompatible in clinopyroxene should have been enriched in the melt by spherulite growth no compositional variations occur at a scale larger than the 10 m wide slit aperture used for laser ablation icp ms the absence of large scale gradients implies that the spherulites grew faster than the elements could diffuse 10 m because diffusion is temperature controlled cooling must have been rapid enough to prevent movement if the spherulites nucleated when the melt was at between 1380 and 1223 k i e undercooled by 0 to 157 k then the constant concentrations of li na and k the fastest diffusing elements analyzed require temperature to have cooled faster than 10 6 7 k min 1 if instead the spherulites nucleated at undercoolings of 357 to 465 k or as cold as 915 k equal to the glass transition temperature then the cooling rate could have been as slow as those inferred for glassy rinds on submarine lavas by relaxation geospeedometry at all possible cooling rates however the spherulites must have grown as fast as 10 3 5 m s 1 to reach their final sizes of 1 4 to 3 2 mm we speculate that the rapid growth resulted from low kinetic barriers to clinopyroxene growth in the basaltic andesite melt

subaqueous basaltic lava dome and carapace breccia on king george island south shetland islands antarctica on king george island during latest oligocene earliest miocene time submarine eruptions resulted in the emplacement of a small ca 500 m estimated original diameter basalt lava dome at low head the dome contains a central mass of columnar rock enveloped by fractured basalt and basalt breccia the breccia is crystalline and is a joint block deposit lithic orthobreccia interpreted as an unusually thick dome carapace breccia cogenetic with the columnar rock it was formed in situ by a combination of intense dilation fracturing and shattering caused by natural hydrofracturing during initial dome effusion and subsequent endogenous emplacement of further basalt melt now preserved as the columnar rock muddy matrix with dispersed hyaloclastite and microfossils fills fractures and diffuse patches in part of the fractured basalt and breccia lithofacies the sparse glass rich clasts formed by cooling contraction granulation during interaction between chilled basalt crust and surrounding water together with muddy sediment they were injected into the dome by hydrofracturing local steam fluidisation and likely explosive bulk interaction the basalt lava was highly crystallised and degassed prior to extrusion together with a low effusion temperature and rapid convective heat loss in a submarine setting these properties significantly affected the magma rheology increased the viscosity and shear strength and influenced the final dome like form of the extrusion conversely high heat retention was favoured by the degassed state of the magma minimal undercooling a thick breccia carapace and viscous shear heating which helped to sustain magmatic eruption temperatures and enhanced the mobility of the flow