segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

tremor rich shallow dyke formation followed by silent magma flow at barðarbunga in iceland magma movement is thought to trigger volcanic tremor however analysis of seismic data suggests that tremor prior to the bar arbunga eruption in iceland instead marked the crust cracking open whereas subsequent magma flow was seismically silent

formation of lava tubes and extensive flow field during the 1991 1993 eruption of mount etna detailed mapping during the 1991 1993 eruption of mount etna has shown that there is a relationship between tumuli ephemeral vents lava tubes and their parent lava flows during this eruption many tubes formed in stationary inflated a a lava flows ephemeral vents at the fronts of these stationary flows and above lava tubes fed secondary lava flows many of which subsequently developed new tubes the resulting complex network of tubes ephemeral vents and secondary flows was responsible for most of the widening thickening and lengthening of the 1991 1993 etna lava flow field the supply of relatively uncooled lava via tubes to distal parts of this flow field allowed lava to flow 3 km farther from the vent than the longest channel fed lava flow our observations suggest that lava tubes play a more important role in the formation of extensive a a flow fields on etna than has previously been recognized

modelling satellite derived magma discharge to explain caldera collapse many effusive eruptions are characterized by effusion rates that decay exponentially with time a trend which is generally ascribed to elastic relaxation of a deep magma chamber thermal emissions detected by satellite during the a d 2014 2015 bar arbunga holuhraun eruption iceland indicate that the volume of the erupted magma and effusion rates followed an overall exponential trend that fits the observed major subsidence of the bar arbunga caldera floor this trend continued until a critical flow rate was reached hence the subsidence slowed down and the eruption rapidly ceased reflecting the ultimate closure of the magma path we present a model of inelastic magma withdrawal that very closely reproduces all the observed phenomena and provides new insights into the caldera collapses and the driving pressure of other effusive eruptions

toothpaste lava characteristics and origin of a lava structural type transitional between pahoehoe and aa toothpaste lava an important basalt structural type which illustrates the transition from pahoehoe to aa is particularly well displayed on the 1960 kapoho lava of kilauea volcano its transitional features stem from a viscosity higher than that of pahoehoe and a rate of flow slower than that of aa viscosity can be quantified by the limited settling of olivine phenocrysts and rate of flow by field observations related to the low angle slope on which the lava flowed much can be learned about the viscosity rheologic condition and flow velocity of lavas long after solidification by analyses of their structural characteristics and it is possible to make at least a semiquantitative assessment of the numerical values of these parameters

intense seismicity during the 2014 2015 barðarbunga holuhraun rifting event iceland reveals the nature of dike induced earthquakes and caldera collapse mechanisms

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

the significance of slab crusted lava flows for understanding controls on flow emplacement at mount etna sicily slab crusted flows on mount etna sicily are defined here as those whose crust has ridden on the flow core without significant disruption or deformation and have a high length to width ratio they typically erupt from ephemeral boccas as late stage products on dominantly aa flow fields such as that of the 1983 eruption on mount etna slab crusted flows tend to inflate mainly as they approach and after they reach the maximum length of slab crust formation the flow interior acting as a preferential pathway for injecting lava under a stable crust coalescence of vesicles under successive crusts causes separation between core and crust giving a new cooling surface within the flow on which ropy surfaces and occasionally aa textures of limited areal extent may develop slab crusted flows tend to form at ephemeral boccas together with other surface textural types including toes ropy pahoehoe sheets and aa flows this suggests that on etna slab crusted flows form from lava of the same rheological properties as both aa and pahoehoe textured flows they do not represent a transition between aa and pahoehoe as argued for toothpaste flows in hawaii we conclude that slab crusted flows on etna owe their morphology to a relatively high critical ratio of effusion rate to advance rate related to vent cross sectional area and the slope over which the flow forms

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

the distal segment of etna s 2001 basaltic lava flow etna s 2001 basaltic lava flow provided a good example of the distal flow segment between the flow front and stable channel across which the flow evolves from channel contained to dispersed this zone was mapped with meter precision using lidar data collected during 2004 and 2005 these data supported by field mapping show that the flow front comprised eight lobes each 10 to 20 m high the flow front appears to have advanced not as a single unit but as a series of lobes moving forward one lobe at a time primary lobes were centered on the channel axis and marginal lobes were off axis the lobes advanced as breakouts of low yield strength lava from the flow core of the stalled flow front marginal lobes were abandoned and contributed to marginal levees flanking the transitional channel for etna s 2001 flow the transitional channel is 140 m wide 700 m long and fed a 240 m long zone of dispersed flow the change from stable to transitional channel occurred at a major reduction in slope above this the stable channel is 5 2 km long 55 to 105 m wide and bounded by 15 to 25 m high levees and the stable channel is located over a previous channel in a final stage of activity lava ponding at the break in slope that marks the terminus of the stable channel put pressure on the eastern levee causing it to fail liberated lava then fed a final break out to the east similar flow front features occur at other volcanoes indicating that similar processes are characteristic of dispersed flow zones

fracture movements and graben subsidence during the 2014 barðarbunga dike intrusion in iceland abstract a dike propagated 48 km from the bar arbunga central volcano into one of its fissure swarms in august and early september 2014 the dike intrusion was accompanied by caldera subsidence in the ice covered bar arbunga central volcano as well as a propagating earthquake swarm graben subsidence and fissure eruptions in the fissure swarm most of the dike was emplaced in the glacier covered part of the fissure swarm but a 10 km long section at the distal northern end of the dike is ice free new ground fractures were observed in the ice free part during the dike propagation and prior to the outbreak of a major lava producing eruption the fractures delineate two graben structures in direct continuation of each other here we show the extent and depth of the grabens and maps of fractures and eruptive fissures that were formed or reactivated north of the vatnajokull glacier during the dike intrusion the active graben subsidence was identified 3 days after seismicity reached the ice free area then fractures delineated a 700 1000 m wide and 5 km long graben visible from the northern edge of the vatnajokull glacier farther north a narrower 250 450 m wide graben was seen a short lived minor eruption occurred between these grabens on the 29th of august 2014 2 days after the grabens were identified the northern graben was extended southwards during or before the eruption and included the eruptive fissure on the 31st of august 2014 a much larger eruption began on the same eruptive fissure the fissure quickly obtained its maximum length of 2 km this eruption lasted 6 months a minor eruption lasting 2 days or less occurred on the southern graben on the 5th of september 2014 the first two eruptions took place on the same eruptive fissure that formed the pre existing holuhraun lava presumably in the 18th century measurements in january 2015 show that the southern graben was 3 5 5 5 m deep but the northern graben had been covered by lava from the depth and the opening of the graben we estimate that the dip of the boundary faults of the graben is 75 the narrow grabens observed before the eruptions indicated that magma was at shallow depth likely much less than 300 m 2 days before it opened to the surface such observations can serve as a tool to estimate likelihood of eruptions during dike intrusions

morphology and mechanism of eruption of postglacial shield volcanoes in iceland postglacial icelandic shield volcanoes were formed in monogenetic eruptions mainly in the early holocene epoch shield volcanoes vary in their cone morphology and in the areal extent of the associated lava flows this paper presents the results of a study of 24 olivine tholeiite and 7 picrite basaltic shield volcanoes for the olivine tholeiitic shields the median slope is 2 7 the median height 60 m the median diameter 3 6 km the median aspect ratio height against diameter 0 019 and the median cone volume 0 2 km3 the picritic shield volcanoes are considerably steeper and smaller a shield volcano cone forms from successive lava lake overflows which are of shelly type pahoehoe a widespread apron surrounding the cone forms from tube fed p type pahoehoe the slopes of the cones have a a planar or slightly convex form b a concave form or c a convex concave form a successive stage of a shield volcano is determined on the basis of cone morphology and lava assemblages a shield producing eruption has alternating episodes of lava lake overflows and tube fed delivery to the distal parts of the flow field in the late stages of eruption the cone volume increases in response to the increased amount of rootless outpouring on the cone flanks normally only a small percentage of the total erupted volume of a shield volcano sometimes as little as 1 3 is in the shield volcano cone itself the main volume being in the apron of the shield

characterization of subaerial volcanic facies using acoustic image logs lithofacies and log facies of a lava flow deposit in the brazilian pre salt deepwater of santos basin abstract volcanic rock facies characterization in subsurface log data have always being challenging even though considerable types of well logs are acquired the results achieved on facies characterization with the conventional log suits are very limited conversely high resolution borehole image logs calibrated with side wall core samples can provide the necessary structural and textural information for facies definitions in this case study an integration of good quality acoustic image log data side wall core petrography and geochemical analyses provided a good understanding of volcanic facies and stratigraphic relationships additionally outcrop data from the analogous serra geral formation and other large igneous provinces were used for comparison in the studied well from santos basin brazil it was possible to identify several kinds of subaerial basaltic lava flow units such as compound pahoehoe sheet pahoehoe and rubbly pahoehoe lava flows vesicles amygdales vesicle cylinders sub horizontal vesicle sheets autobreccias and entablature are some of the structures described in this study as a result 2 image catalogues of subaerial volcanic rocks were produced characterizing facies and flow units along with a stratigraphic model of the history of this volcanism this is the first time that pahoehoe lava flow units could be characterized at an offshore brazilian basin the results achieved are important for the understanding of the cretaceous volcanism events in the pre salt layer and also provide support for the evaluation and geological modelling of the volcanic rocks in santos basin oil fields

tandem x time series analysis reveals lava flow volume and effusion rates of the 2012 2013 tolbachik kamchatka fissure eruption assessing eruption volumes is one of the major challenges in volcano research but provides valuable insights into the dynamics of an eruption and the associated hazard one way to estimate this important parameter is the generation and differencing of digital elevation models dems acquired before during and after an eruption the satellite mission tandem x enables generation of time series of dems using synthetic aperture radar satellite imagery we use these data to study the 2012 2013 eruption of tolbachik in kamchatka we developed a processing scheme for generation of 18 dems from tandem x imagery that relies on the generation of a preeruption dem which is used to process the syneruption and posteruption data pairs differencing each dem with the preeruption dem enables mapping the lava flows and measuring lava flow volume over time and to estimate lava extrusion rates we find a final lava flow volume of 0 53 km3 covering an area of 36 km2 by the end of the eruption an uncertainty analysis is performed while analyzing the dem differences in areas where no topographic change is expected leading to an error of 0 01 km3 for the final lava flow volume the lava effusion was with 247 92 m3 s very high in the first days of the eruption and rapidly decayed toward its end while many basaltic eruptions follow an exponentially decaying flow model the extrusion rates at tolbachik are more compatible with a 1 t model this special characteristic might be useful to gain further insight into the eruption process at tolbachik

pāhoehoe a ā and block lava an illustrated history of the nomenclature lava flows occur worldwide and throughout history various cultures and geologists have described flows based on their surface textures as a result surface morphology based nomenclature schemes have been proposed in most languages to aid in the classification and distinction of lava surface types one of the first to be published was likely the nine class italian language description based classification proposed by mario gemmellaro in 1858 by far the most commonly used terms to describe lava surfaces today are not descriptive but instead are merely words specifically the hawaiian words a rough brecciated basalt lava and p hoehoe smooth glassy basalt lava plus block lava thick brecciated lavas that are typically more silicic than basalt a and p hoehoe were introduced into the western geological vocabulary by american geologists working in hawai i during the 1800s they and other nineteenth century geologists proposed formal lava type classification schemes for scientific use and most of them used the hawaiian words in 1933 ruy finch added the third lava type block lava to the classification scheme with the tripartite system being formalized in 1953 by gordon macdonald more recently particularly since the 1980s and based largely on studies of lava flow interiors a number of sub types and transitional forms of all three major lava types have been defined this paper reviews the early history of the development of the p hoehoe a and block lava naming system and presents a new descriptive classification so as to break out the three parental lava types into their many morphological sub types

icecap and subglacial crustal deformation inferred from sar pixel tracking the 2014 dike intrusion episode in the barðarbunga volcanic system iceland

channel overflows of the pōhue bay flow mauna loa hawai i examples of the contrast between surface and interior lava a number of overflows from a large lava channel and tube system on the southwest rift zone of mauna loa were studied initial overflows were very low viscosity gas rich p hoehoe evidenced by flow unit aspect ratios and vesicle sizes and contents calculated volumetric flow rates in the channel range between 80 and 890 m3 s and those of the overflows between 35 and 110 m3 s after traveling tens to hundreds of meters the tops of these sheet like overflows were disrupted into a surface composed of clinker and p hoehoe fragments after these a overflows came to rest lava from the interiors was able to break out on to the surface as p hoehoe the surface structure of a lava flow records the interaction between the differential shear rate usually correlated with the volumetric flow rate and viscosity induced resistance to flow however the interior of a flow being better insulated may react differently or record a later set of emplacement conditions clefts of toothpaste lava occurring within fields of clinker on proximal type a flows also record different shear rates during different times of flow emplacement the interplay between viscosity and shear rate determines the final morphological lava type and although no specific portion of lava ever makes a transition from a back to p hoehoe parts of a flow can appear to do so

cooling and crystallization of lava in open channels and the transition of pāhoehoe lava to a ā samples collected from a lava channel active at kilauea volcano during may 1997 are used to con strain rates of lava cooling and crystallization during early stages of flow lava erupted at near liquidus tem peratures f1150 7c cooled and crystallized rapidly in upper parts of the channel glass geothermometry indi cates cooling by 12 14 7c over the first 2 km of trans port at flow velocities of 1 2 m s this translates to cooling rates of 22 50 7c h cooling rates this high can be explained by radiative cooling of a well stirred flow consistent with observations of non steady flow in proximal regions of the channel crystallization of plag ioclase and pyroxene microlites occurred in response to cooling with crystallization rates of 20 50 per hour crystallization proceeded primarily by nucleation of new crystals and nucleation rates of f10 4 cm 3 s are similar to those measured in the 1984 open channel flow from mauna loa volcano there is no evidence for the large nucleation delays commonly assumed for plagioclase crystallization in basaltic melts possibly a reflection of enhanced nucleation due to stirring of the flow the transition of the flow surface morphology from pahoehoe to a aoccurred at a distance of 1 9 km from the vent at this point the flow was thermally stratified with an interior temperature of f1137 7c and crystallinity of f15 and a flow surface tempera ture of f1100 7c and crystallinity of f45 a afor mation initiated along channel margins where crust was continuously disrupted and involved tearing and clotting of the flow surface both observations suggest that the transition involved crossing of a rheological threshold we suggest this threshold to be the develop ment of a lava yield strength sufficient to prevent vis cous flow of lava at the channel margin we use this concept to propose that a aformation in open chan nels requires both sufficiently high strain rates for con tinued disruption of surface crusts and sufficient groundmass crystallinity to generate a yield strength equivalent to the imposed stress in hawai i where lava is typically microlite poor on eruption these combined requirements help to explain two common observations on a aformation a a aflow fields are generated when effusion rates are high thus promoting crustal disruption and b under most eruption conditions lava issues from the vent as pahoehoe and changes to a aonly after flowing some distance thus permitting sufficient crystallization

an aeolian grainflow model for martian recurring slope lineae abstract recurring slope lineae rsl on mars have been enigmatic since their discovery their behavior resembles a seeping liquid but sources of water remain puzzling this work demonstrates that the properties of rsl are consistent with observed behaviors of martian and terrestrial aeolian processes specifically rsl are well explained as flows of sand that remove a thin coating of dust observed rsl properties are supportive of or consistent with this model which requires no liquid water or other exotic processes but rather indicates seasonal aeolian behavior these settings and behaviors resemble features observed by rovers and also explain the occurrence of many slope lineae on mars that do not meet the strict definition of rsl this indicates that rsl can be explained simply as aeolian features other processes may add complexities just as they could modify the behavior of any sand dune

the importance of pahoehoe abstract pahoehoe lava flows are common in every basaltic province and their submarine variants pillow lavas and sheet flows cover the bulk of the earth pahoehoe flows are emplaced by inflation the injection of molten lava underneath a solidified crust only in the past few years has an understanding of the inflation process and the ability to recognize ancient inflated lava flows been achieved all large terrestrial basaltic flow fields studied to date including flood basalts were emplaced as thermally efficient inflated compound pahoehoe sheet flows this leads us to propose that this is the standard way of emplacing large lavas the swell hypothesis the atmospheric impact of such flood basalt eruptions could have been protracted and severe providing a plausible link between flood basalt eruptions and mass extinctions

the millennium eruption of hekla in february 2000 the 18th historic eruption of hekla started on 26 february 2000 it was a short lived but intense event emitting basaltic andesitic 55 5 wt sio2 pyroclastic fragments and lava during the course of the eruption monitoring was done by both instruments and direct observations together providing unique insight into the current activity of hekla during the 12 day eruption a total of 0 189 km3 dre of magma was emitted the eruptive fissure split into five segments the segments at the highest altitude were active during the first hours while the segments at lower altitude continued throughout the eruption the eruption started in a highly explosive manner giving rise to a subplinian eruptive column and consequent basaltic pyroclastic flows fed by column collapses after the explosive phase reached its maximum the eruption went through three more phases namely fire fountaining strombolian bursts and lava effusion in this paper we describe the course of events of the eruption of hekla and the origin of its magma and then show that the discharge rate can be linked to different style of eruptive activity which are controlled by fissure geometry we also show that the eruption phases observed at hekla can be linked with inferred magma chamber overpressure prior to the eruption

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

formation of segregation structures in hafnarhraun pāhoehoe lobe sw iceland a window into crystal melt separation in basaltic magma to gain insights into crystal melt separation processes during basalt differentiation we have studied an 8 m thick p hoehoe lava lobe from the hafnarhraun lava flow field in sw iceland the lobe has abundant melt segregations porous cylindrical and sheet like structures generally interpreted as separated residual melts of a lava lobe we divide these melt segregations into three types based on morphology and composition vesicle cylinders vc type 1 horizontal vesicle sheets hvs1 and type 2 horizontal vesicle sheets hvs2 remarkably the studied vc are not simple residual melts generated by fractional crystallization but their composition points to removal of plagioclase from the parental lava hvs1 resemble vc but have fractionated more olivine ol plagioclase plg augite and have lost most if not all of their olivine phenocrysts hvs2 are fe rich and evolved corresponding to residual melts after 50 60 fractional crystallization of the lobe we suggest that the hafnarhraun vc formed in a two stage process firstly vc forming residual melt and vapor detached as rising diapirs from ol plg melt vapor mush near the lava base and later these vc diapirs accumulated ol phenocrysts and minor plg microphenocrysts in the lava core hvs1 represent accumulations of vc to the viscous base of the solidifying upper crust of the lobe and hvs2 formed as evolved vapor saturated residual melts seeped into voids within the upper crust such vapor aided differentiation here documented for the hafnarhraun lava may also apply to shallow crustal magma storage zones contributing to the formation of evolved basalts

proximal lava drainage controls on basaltic fissure eruption dynamics hawaiian basaltic eruptions commonly initiate as a fissure producing fountains spattering and clastogenic lava flows most fissures rapidly localize to form a small number of eruptive vents the location of which may influence the subsequent distribution of lava flows and associated hazards we present results from a detailed field investigation of the proximal deposits of episode 1 of the 1969 fissure eruption of mauna ulu k lauea hawai i exceptional preservation of the deposits allows us to reconstruct vent proximal lava drainage patterns and to assess the role that drainage played in constraining vent localization through detailed field mapping including measurements of the height and internal depth of lava tree moulds we reconstruct high resolution topographic maps of the pre eruption ground surface the lava high stand surface and the post eruption ground surface we calculate the difference in elevation between pairs of maps to estimate the lava inundation depth and lava drainage depth over the field area and along different segments of fissure aerial photographs collected during episode 1 of the eruption allow us to locate those parts of the fissure that are no longer exposed at the surface by comparing with the inundation and drainage maps we find that fissure segments that were inundated with lava to greater depths typically 1 6 m during the eruption later became foci of lava drainage back into the fissure internal drain back we infer that in these areas lava ponding over the fissure suppressed discharge of magma thereby favouring drain back and stagnation by contrast segments with relatively shallow inundation typically less than 1 m such as where the fissure intersects pre eruptive topographic highs or where flow away from the vent outflow was efficient are often associated with sub circular vent geometries in the post eruption ground surface we infer that these parts of the fissure became localization points for ongoing magma ascent and discharge we conclude that lava inundation and drainage processes in basaltic fissure eruptions can play an important role in controlling their localization and longevity

lava field evolution and emplacement dynamics of the 2014 2015 basaltic fissure eruption at holuhraun iceland abstract the 6 month long eruption at holuhraun august 2014 february 2015 in the bar arbunga vei ivotn volcanic system was the largest effusive eruption in iceland since the 1783 1784 ce laki eruption the lava flow field covered 84 km2 and has an estimated bulk i e including vesicles volume of 1 44 km3 the eruption had an average discharge rate of 90 m3 s making it the longest effusive eruption in modern times to sustain such high average flux the first phase of the eruption august 31 2014 to mid october 2014 had a discharge rate of 350 to 100 m3 s and was typified by lava transport via open channels and the formation of four lava flows no 1 4 which were emplaced side by side the eruption began on a 1 8 km long fissure feeding partly incandescent sheets of slabby p hoehoe up to 500 m wide by the following day the lava transport got confined to open channels and the dominant lava morphology changed to rubbly p hoehoe and a the latter became the dominating morphology of lava flows no 1 8 the second phase of the eruption mid october to end november had a discharge of 100 50 m3 s during this time the lava transport system changed via the formation of a 19 km2 of the flow field the primary lava morphology from this phase was spiny p hoehoe which superimposed on the a lava flows no 1 3 and extended the entire length of the flow field i e 17 km this made the 2014 2015 holuhraun a paired flow field where both lava morphologies had similar length we suggest that the similar length is a consequence of the p hoehoe is fed from the tube system utilizing the existing a lava channels and thereby are controlled by the initial length of the a flows

structure and origin by injection of lava under surface crust of tumuli lava rises lava rise pits and lava inflation clefts in hawaii tumuli are positive topographic features that are common on hawaiian pahoehoe lava flow fields particularly on shallow slopes and 75 measured examples are presented here to document the size range tumuli form by up tilting of crustal plates without any crustal shortening and are thus distinguished from pressure ridges which are up buckled by laterally directed pressure the axial or star like systems of deep clefts that characterize tumuli are defined here as lava inflation clefts their tips advanced into red hot lava and they widened as uplift proceeded and while the lava crust was thickening flat surfaced uplifts formed like tumuli by injection of lava under a surface crust were previously called pressure plateaus but lava rise is proposed instead the pits that abound among lava rises previously attributed to collapse or subsidence are generally formed because the lava around them rose and the name lava rise pit is proposed unique examples of tumuli and lava rises from which lava drained out under a surface crust 1 5 to 2 5 m thick are described from kilauea caldera these examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava and is able to do so because of its higher vesicle content the fluid lava loses many of its gas bubbles during residence beneath the crust the bulk densities of samples from tumuli show a general downward increase the form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust suggesting that the lava was stably density stratified it is inferred that stable stratification was regulated by out flows of the more vesicular lava fractions loss of bubbles through the lava inflation clefts and entry of injected lava at its level of neutral buoyancy below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava

strike slip faulting during the 2014 barðarbunga holuhraun dike intrusion central iceland over a 13 day period magma propagated laterally from the subglacial bar arbunga volcano in the northern rift zone iceland it created 30 000 earthquakes at 5 7 km depth along a 48 km path before erupting on 29 august 2014 the seismicity which tracked the dike propagation advanced in short bursts at 0 3 4 7 km h separated by pauses of up to 81 h during each surge forward seismicity behind the dike tip dropped moment tensor solutions from the leading edge show exclusively left lateral strike slip faulting subparallel to the advancing dike tip releasing accumulated strain deficit in the brittle layer of the rift zone behind the leading edge both left and right lateral strike slip earthquakes are observed the lack of non double couple earthquakes implies that the dike opening was aseismic

lava rise plateaus and inflation pits in the mccartys lava flow field new mexico an analog for pāhoehoe like lava flows on planetary surfaces

operational response and hazards assessment during the 2014 2015 volcanic crisis at barðarbunga volcano and associated eruption at holuhraun iceland abstract on august 16 2014 an intense seismic swarm started below the eastern part of bar arbunga caldera in the north western part of vatnajokull ice cap iceland marking the onset of a major rifting event the intense seismicity corroborated by a complicated deformation pattern migrated away from the bar arbunga caldera for 45 km until a small effusive eruption started in holuhraun outside of the ice cap on august 29 which lasted a few hours on august 31 a second more intense eruption started it lasted 180 days and is the largest effusive eruption in iceland since the laki event in 1783 1784 a lava field covered about 84 km2 in the middle of the highlands with a bulk volume of 1 44 km3 although the potential danger of ice melting and subsequent flooding coupled with tephra fallout was the main concern at the beginning of the crisis the main associated hazard turned out to be an abundant and constant release of volcanic gases that polluted the country threatening human health and the environment for several months very little or almost no ash was produced the impact of the holuhraun eruption outside of iceland was minor if compared with what happened in 2010 when eyjafjallajokull erupted however on three occasions the dense gas cloud released by the fissure eruption reached some european countries where unusually high so2 concentrations were measured at ground level managing and living with such a prolonged effusive event was a major effort for the icelandic scientific community and civil protection authorities and it significantly affected the local population in the northern and eastern parts of the country this paper retraces the main events that accompanied the volcanic crisis at bar arbunga and focuses on the scientific and operative response provided throughout its duration particular attention is given to the direct links between the observed phenomena monitoring effort hazard assessment and concrete actions taken by the authorities in charge of risk and mitigation assessment the different roles of the involved institutions are clarified and the wide and collaborative response on a national basis is explained a major finding of this post event analysis is that a strong internal collaboration between the scientific community and operative institutions is the basic element for proper crisis management iceland has established protocols that while imperfect ensured a well coordinated response to the holuhraun eruption and the preceding unrest and will continue to provide a prompt and effective response for future events important realizations including the need for a proper ground based alert level system have been raised and they will be a matter for further development

hyporheic flow and dissolved oxygen distribution in fish nests the effects of open channel velocity permeability patterns and groundwater upwelling many fish lay their eggs in nests or redds which they construct in sediment the viability of eggs depends on many factors particularly their oxygenation because dissolved oxygen is typically saturated within the stream channel the dissolved oxygen distribution within the redd depends on whether or not hyporheic flow and transport occur within the sediment we conducted a series of flume and numerical flow and age transport modeling experiments with the aim of understanding the effects of salmonid redds on the hyporheic transport of young oxygenated water hyporheic flow was visualized directly through dye injections dissolved oxygen throughout the fish nest was measured using a planar optode experiments were conducted at various open channel flow velocities in order to understand their effect on dissolved oxygen and computational simulations considered various sediment textures and ambient groundwater upwelling rates to add process level insight we found that as also shown by previous studies the redd topography induces multiscale hyporheic flow that effectively flushes the egg pocket location with younger presumably oxygenated water older water upwells and forms anoxic zones this pattern persists even at the lowest channel flow rates and at small upwelling velocities of older ambient groundwater which splits the multiscale hyporheic flow cells into isolated pockets large groundwater upwelling rates can shut down all the hyporheic flushing the relatively coarse texture of the redd further promotes hyporheic flushing of the redd sediment with oxygenated water thus redd morphology and sediment texture optimally combine to induce hyporheic exchange flow that delivers young oxygenated water to the egg pocket

the madinah eruption saudi arabia magma mixing and simultaneous extrusion of three basaltic chemical types during a 52 day eruption in 1256 a d 0 5 km3 of alkali olivine basalt was extruded from a 2 25 km long fissure at the north end of the harrat rahat lava field saudi arabia the eruption produced 6 scoria cones and a lava flow 23 km long that approached the ancient and holy city of madinah to within 8 km three chemical types of basalt are defined by data point clusters on variation diagrams i e the low k high k and hybrid types all three erupted simultaneously their distribution is delineated in both scoria cones and lava flow units from detailed mapping and a petrochemical study of 135 samples six flow units defined by distinct flow fronts represent extrusive pulses the high k type erupted during all six pulses the low k type during the first three and the hybrid type during the first two

holocene volcanic activity at grimsvotn bardarbunga and kverkfjoll subglacial centres beneath vatnajokull iceland assessment of potential future eruptive behaviour of volcanoes relies strongly on detailed knowledge of their activity in the past such as eruption frequency magnitude and repose time the eruption history of three partly subglacial volcanic systems grimsvotn bardarbunga and kverkfjoll was studied by analysing tephra from soil profiles around the vatnajokull ice cap which extend back to 7 6 ka well known regional holocene marker tephra e g h3 h4 h5 were utilized to correlate profiles stratigraphic positions and geochemical compositions were used for fine scale correlation of basaltic tephra around vatnajokull ice cap 345 tephra layers were identified of which 70 originated from grimsvotn bardarbunga or kverkfjoll the eruption frequency of each volcanic system was estimated grimsvotn has been the most active with an average of 7 eruptions 100 years range 4 14 during prehistoric time before 870 ad bardarbunga has been the second most active with 5 eruptions 100 years range 1 8 and kverkfjoll has remained essentially calm with 0 3 eruptions 100 years but showing periodic activity with repose times of 1000 years all three volcanic systems experienced lulls in activity from 5 ka to 2 ka referred to as the mid holocene low this reduced eruption frequency appears to have resulted from a decrease in magma generation and delivery from the mantle plume rather than from changes in ice load glacier thickness in prehistoric time there was a time lag of 1000 3000 years between a peak of activity at volcanoes directly above the mantle plume versus at volcanoes located in the non rifting part of the eastern volcanic zone closer to the periphery of the island this time space relationship suggests that a significant future increase in volcanism can be expected there following increased levels of volcanism above the plume

pahoehoe and aa lavas a discussion and continuation of the model of peterson and tilling abstract the graphical method of peterson and tilling for representing the behaviour of a lava flow is considered in terms of simple rheological theory assuming that a lava may be approximately described as a bingham fluid this approach helps resolve an apparent anomaly in the original treatment of peterson and tilling with respect to the representation of the pahoehoe to aa transition it also suggests further methods for quantitatively defining the limits of the pahoehoe and aa fields and the transition threshold zone

a shear heating origin for ridges on triton 1 triton and europa each display a variety of distinctive curvilinear ridges and associated troughs here we propose that ridges on triton may have formed by diurnal tidal stresses in a manner similar to that proposed for ridge formation on europa the greater width of ridges on triton is likely a consequence of the lower surface temperature and greater brittle ductile transition depth on this body compared to europa the magnitudes of the stresses and heat fluxes required to generate ridges of the correct scale are comparable to likely values generated during the latter part of triton s orbital evolution from an initial highly eccentric state

volcanism and hydrothermalism on a hotspot influenced ridge comparing reykjanes peninsula and reykjanes ridge iceland abstract current estimates indicate that the number of high temperature vents one of the primary pathways for the heat extraction from the earth s mantle at least 1 per 100 km of axial length scales with spreading rate and should scale with crustal thickness but up to present shallow ridge axes underlain by thick crust show anomalously low incidences of high temperature activity here we compare the reykjanes ridge an abnormally shallow ridge with thick crust and only one high temperature vent known over 900 km axial length to the adjacent subaerial reykjanes peninsula rp which is characterized by high temperature geothermal sites confined to four volcanic systems transected by fissure swarms with young holocene volcanic activity multiple faults cracks and fissures and continuous seismic activity new high resolution bathymetry gridded at 60 m of the reykjanes ridge between 62 30 n and 63 30 n shows seven axial volcanic ridges avr that based on their morphology geometry and tectonic regime are analogues for the volcanic systems and fissure swarms on land we investigate in detail the volcano tectonic features of all mapped avrs and show that they do not fit with the previously suggested 4 stage evolution model for avr construction instead we suggest that avr morphology reflects the robust or weak melt supply to the system and two or more eruption mechanisms may co exist on one avr in contrast to 4 stage evolution model our interpretations indicate that unlike on the reykjanes peninsula faults on and around avrs do not cluster in orientation domains but all are subparallel to the overall strike of avrs orthogonal to spreading direction high abundance of seamounts shows that the region centered at 62 47 n and 25 04 w between avr 5 and 6 is volcanically robust while the highest fault density implies that avr 1 and southern part of avr 6 rather undergo period of melt starvation based on our observations and interpretations we expect all of the avrs on reykjanes ridge to be hydrothermally active but morphological and hydrographic settings of this ridge may cause hydrothermal plumes to be quickly dispersed and diluted due to exposure to strong bottom currents therefore combined ctd and autonomous vehicles surveys are probably the most efficient methods for hydrothermal exploration along the reykjanes ridge