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

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

drivers of explosivity and elevated hazard in basaltic fissure eruptions the 1913 eruption of ambrym volcano vanuatu sw pacific abstract fissure eruptions along linear structures can extend for several tens of kilometres with distinct separate manifestations of volcanism along their length they typically involve low viscosity mafic magmas forming long lava flows and cinder cones eruptions in 1894 and 1913 on ambrym volcano vanuatu showed how these mildly explosive eruptions can rapidly transform into violent explosive events producing significant hazard and widespread volcanic ash clouds during the 1913 episode a fissure began in the central caldera and basaltic magmas broke out in a series of locations down the island s western flank in all sites over 100 m in elevation fissure outbreaks produced vigorous lava fountains and highly fluid lava flows that travelled rapidly to the shoreline when the outbreaks propagated along the island s axis into coastal plain areas a climactic series of explosive eruptions occurred producing a 1 2 km long by 600 m wide maar and tephra ring a further small tuff ring was formed later creating a temporary island 400 m offshore the onshore tephra ring destroyed a hospital and associated buildings its last evacuating occupants were close witnesses to the eruption processes deposits exposed in the lower portion of the tephra ring show that this part of the eruption began with a mild phreatomagmatic explosive eruption from a narrow vent followed by a magmatic scoria producing phase subsequently a complex sequence of highly explosive phreatomagmatic eruptions occurred producing pyroclastic surges along with repeated distinctive breccia horizons rich in coral and lava country rock these features tally with eye witness accounts to indicate that the main eruption phase was produced by a periodically shifting locus of phreatomagmatic fragmentation and eruption along a single e w fissure the glassy and vesicle poor pyroclasts produced during this eruption phase were dominantly fragmented in a brittle manner by magma water interaction low volatile content of the magma upon fragmentation is confirmed by ftir analysis showing

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

petrology and chemistry of mil 03346 and its significance in understanding the petrogenesis of nakhlites on mars antarctic meteorite miller range mil 03346 is a nakhlite composed of 79 clinopyroxene 1 olivine and 20 vitrophyric intercumulus material we have performed a petrological and geochemical study of mil 03346 demonstrating a petrogenetic history similar to previously discovered nakhlites quantitative textural study of mil 03346 indicates long 1 x 101 yr residence times for the cumulus augite whereas the skeletal fe ti oxide fayalite and sulfide in the vitrophyric intercumulus matrix suggest rapid cooling probably as a lava flow from the relatively high forsterite contents of olivine up to fo43 compared with other nakhlites and compositions of augite cores wo38 42en35 40fs22 28 and their hedenbergite rims we suggest that mil 03346 is part of the same or a similar martian cumulate rich lava flow as other nakhlites however mil 03346 has experienced less equilibration and faster cooling than other nakhlites discovered to date calculated trace element concentrations based upon modal abundances of mil 03346 and its constituent minerals are identical to whole rock trace element abundances parental melts for augite have ree patterns that are approximately parallel with whole rock and intercumulus melt using experimentally defined partition coefficients this parallelism reflects closed system crystallization for mil 03346 where the only significant petrogenetic process between formation of augite and eruption and emplacement of the nakhlite flow has been fractional crystallization a model for the petrogenesis of mil 03346 and the nakhlites nakhla governador valadares lafayette yamato 000593 northwest africa nwa 817 nwa 998 would include 1 partial melting and ascent of melt generated from a long term lree depleted mantle source 2 crystallization of cumulus augite olivine magnetite in a shallow level martian magma chamber 3 eruption of the crystal laden nakhlite magma onto the surface of mars 4 cooling crystal settling overgrowth and partial equilibration to different extents within the flow 5 secondary alteration through hydrothermal processes possibly immediately succeeding or during emplacement of the flow this model might apply to single or multiple flow models for the nakhlites ultimately mil 03346 and the other nakhlites preserve a record of magmatic processes in volcanic rocks on mars with analogous petrogenetic histories to pyroxene rich terrestrial lava flows and to komatiites

ridge like lava tube systems in southeast tharsis mars abstract lava tubes are widely distributed in volcanic fields on a planetary surface and they are important means of lava transportation we have identified 38 sinuous ridges with a lava tube origin in southeast tharsis the lengths vary between 14 and 740 km and most of them occur in areas with slopes

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

identification of volcanic rootless cones ice mounds and impact craters on earth and mars using spatial distribution as a remote sensing tool 1 this study aims to quantify the spatial distribution of terrestrial volcanic rootless cones and ice mounds for the purpose of identifying analogous martian features using a nearest neighbor nn methodology we use the statistics r ratio of the mean nn distance to that expected from a random distribution and c a measure of departure from randomness we interpret r as a measure of clustering and as a diagnostic for discriminating feature types all terrestrial groups of rootless cones and ice mounds are clustered r 0 51 0 94 relative to a random distribution applying this same methodology to martian feature fields of unknown origin similarly yields r of 0 57 0 93 indicating that their spatial distributions are consistent with both ice mound or rootless cone origins but not impact craters each martian impact crater group has r 1 00 i e the craters are spaced at least as far apart as expected at random similar degrees of clustering preclude discrimination between rootless cones and ice mounds based solely on r values however the distribution of pairwise nn distances in each feature field shows marked differences between these two feature types in skewness and kurtosis terrestrial ice mounds skewness 1 17 1 99 kurtosis 0 80 4 91 tend to have more skewed and leptokurtic distributions than those of rootless cones skewness 0 54 1 35 kurtosis 0 53 1 13 thus nn analysis can be a powerful tool for distinguishing geological features such as rootless cones ice mounds and impact craters particularly when degradation or modification precludes identification based on morphology alone

extensive young silicic volcanism produces large deep submarine lava flows in the ne lau basin new field observations reveal that extensive up to 402 km2 aphyric glassy dacite lavas were erupted at multiple sites in the recent past in the ne lau basin located about 200 km southwest of samoa this discovery of volumetrically significant and widespread submarine dacite lava flows extends the domain for siliceous effusive volcanism into the deep seafloor although several lava flow fields were discovered on the flank of a large silicic seamount niuatahi two of the largest lava fields and several smaller ones northern lava flow fields were found well north of the seamount the most distal portion of the northernmost of these fields is 60 km north of the center of niuatahi caldera we estimate that lava flow lengths from probable eruptive vents to the distal ends of flows range from a few km to more than 10 km camera tows on the shallower near vent areas show complex lava morphology that includes anastomosing tube like pillow flows and ropey surfaces endogenous domes and or ridges some with crease like extrusion ridges and inflated lobes with extrusion structures a 2 1 5 km 30 m deep depression could be an eruption center for one of the lava flow fields the lau lava flow fields appear to have erupted at presumptive high effusion rates and possibly reduced viscosity induced by presumptive high magmatic water content and or a high eruption temperature consistent with both erupted composition 66 sio2 and glassy low crystallinity groundmass textures the large areal extent 236 km2 and relatively small range of compositional variation 0 60 for wt si02 within the northern lava flow fields imply the existence of large eruptible batches of differentiated melt in the upper mantle or lower crust of the ne lau basin at this site the volcanism could be controlled by deep crustal fractures caused by the long term extension in this rear arc region submarine dacite flows exhibiting similar morphology have been described in ancient sequences from the archaean through the miocene and in small batches on present day seafloor spreading centers this study shows that extensive siliceous lavas can erupt on the modern seafloor under the right conditions

reconciling channel formation processes with the nature of elevated outflow systems at ophir and aurorae plana mars 1 many hesperian outflow channels head at elevations compatible with aquifer recharge beneath the martian south polar cap and such channels are widely interpreted as the products of this recharge some outflow channels head at greater elevations that are inconsistent with southern recharge including three systems located in aurorae planum and eastern ophir planum these three systems have previously been interpreted as having formed through aqueous outbursts from local aquifers recharged by the meltwaters of ancient upland glaciers to the west however the viability of this interpretation is weakened by the lack of a geomorphic record supportive of past meltwater flow from western uplands inconsistencies between hypothesized processes and the nature of regional topography and mineralogy and the absence of satisfactory analog processes for catastrophic aqueous flow from the subsurface in contrast a volcanic origin for the ophir and aurorae systems appears to be in accord with the basic characteristics of constituent channels and associated landforms the volcanotectonic nature of the valles marineris system and adjacent upland plains and the nature of available analog landforms and processes though numerous uncertainties remain a volcanic interpretation of these outflow systems can more simply account for the existence of component channels the attributes of other elevated outflow systems on mars similarly appear to be most consistent with volcanic origins if the ophir and aurorae systems formed volcanically thermal considerations imply minimum erupted lava volumes of 6 4 103 km3 for allegheny vallis and 6 2 104 km3 for elaver vallis

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

ring moat dome structures rmdss in the lunar maria statistical compositional and morphological characterization and assessment of theories of origin ring moat dome structures rmdss are positive morphologic features found clustered across many mare regions on the moon of which only a few isolated examples have been previously reported our continuing survey has expanded the known locations of the rmdss from 2 600 to over 8 000 indicating that rmdss are more common geological features than previously thought this work presents a detailed geomorphological analysis of 532 rmdss identified in several mare basins the combination of detailed elemental mapping morphological and morphometric analyses spatial distribution relationships with other geologic structures and comparison with terrestrial analogs lead us to conclude that 1 rmdss represent low circular mounds with diameters of a few hundred meters average about 200 m and a mean height of 3 5 m the mounds are surrounded by moats ranging from tens to over 100 m in width and up to several meters in depth 2 there is a wide variation of titanium abundances although rmdss are more commonly found in mare regions of moderate to high titanium content 3 wt tio2 3 rmdss are found to occur on or around fractures graben and volcanic edifices small shields and cones 4 a spatial association between rmdss and irregular mare patches see braden et al 2014 https doi org 10 1038 ngeo2252 is observed suggesting that both may form from related lava flows 5 comparisons between rmdss and lava inflationary structures on earth support an inflation related extrusive nature and a genetic relationship with host lava flow processes and 6 rmds embayment relationships with craters of different degradation ages superposed on the host mare and regolith development models produces conflicting age relationships and divide theories of rmds origin into two categories 1 synchronous with the emplacement and cooling of the host lava flows 3 4 ga and 2 emplaced substantially after the host mare lava unit in the period 0 3 ga we outline the evidence supporting this age conundrum and implications for the different theories of origin and describe future research avenues to help resolve these outstanding questions 2020 american geophysical union all rights reserved

ice rich terrain in gusev crater mars abstract the morphology of materials on the floor of gusev crater 14 s 175 w mars imply a history of volcanism and subsequent removal of an ice rich deposit fluid lava flows observed in the western portion of gusev crater paradoxically terminate in a steep thick 60 m flow front adjacent to hummocky terrain the hummocky terrain is morphologically similar to deglaciated terrain on earth generated when glacial debris are left behind after the glacier has retreated we propose the following scenario for the floor of gusev crater first ice rich material was deposited adjacent to thira crater second fluid lavas were emplaced and ponded against the ice rich deposits at some later time the ice within the deposit sublimated leaving hummocky terrain current age estimates for the gusev flows are hesperian suggesting that the ice removal occurred in the upper hesperian or more recently if this hypothesis is correct quench features glassy rinds columnar jointing should be observed at the lava flow margin the hummocky deposit should be poorly sorted angular debris

features and evolution of slip structures in badlands areas se spain abstract slips are little known mud coated structures several centimeters thick produced by gravity driven flows on free vertical surfaces we have differentiated a sequence formed by three main morphologies mud drips slips and pseudo stalactites this study located in the badlands of the guadix and baza basins se spain suggests that formation of muddy morphologies on subvertical walls is determined by the physico chemical characteristics of colloidal suspensions slurries related to rainy periods and does not indicate any substrate decay multiple braided microchannels internally structured like irregular book pages are commonly found each formed by mudflows during rainy episodes these morphologies constitute a temporary sink of fine erosive materials they consist of scarcely sorted mixtures of heterogeneous matter of a detrital cohesive nature with low clay contents which inherit the features of the parent materials the current semiarid environmental conditions appear to favor conservation rather than development the differences observed in the slips of the guadix and baza basins can be determined by the different geomorphological evolution of the two basins and to a lesser extent by the properties of the slurries that fed the slips

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

late holocene lava flow morphotypes of northern harrat rahat kingdom of saudi arabia implications for the description of continental lava fields a lava morphotype refers to the recognizable and distinctive characteristics of the surface morphology of a lava flow after solidification used in a similar way to a sedimentary facies this classification method is explored on an example volcanic field in the kingdom of saudi arabia where copious lava outpourings may represent an important transition between monogenetic and flood basalt fields here young and well preserved mafic lava fields display a wide range of surface morphologies we focussed on four post 4500 yrs bp lava flow fields in northern harrat rahat 10 ma and propose a framework for describing systematic changes in morphotypes down flow the morphotypes give insight into intrinsic and extrinsic parameters of emplacement rheology and dominant flow behavior as well as the occurrence and character of other lava structures the harrat rahat lava flow fields studied extend up to 23 km from the source and vary between 1 2 m and 12 m in thickness areas of the lava flow fields are between 32 and 61 km2 with individual flow field volumes estimated between 0 085 and 0 29 km3 they exhibit shelly slabby and rubbly pahoehoe platy cauliflower and rubbly a a and blocky morphotypes morphotypes reflect the intrinsic parameters of composition temperature crystallinity and volatile content vesicularity along with external influences such as emission mechanism effusion rate topography and slope control of flow velocity one morphotype can transition to another in individual flow units or lobes and they may dominate zones not all morphotypes were found in a single lava flow field pahoehoe morphotypes are related to the simple mechanical disaggregation of the crust whereas a a morphotypes are related to the transitional emergence and subsequent transitional disappearance of clinker blocky morphotypes result from fracturing and auto brecciation a a morphotypes i e platy cauliflower rubbly a a dominate the lava flow field surfaces in northern harrat rahat which suggests that core dominated flows were predominant during flow movement lava structures are well developed and well preserved and some may be related to some morphotypes down flow changes exhibit key illustrative and easy recognizable features in the lava flow fields and might provide insights into real time monitoring of future flows in this region

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

lava flows at arsia mons mars insights from a graben imaged by hirise abstract hirise has imaged a graben wall on the western flank of arsia mons volcano mars this graben is 3 16 km in plan view size and is oriented almost perpendicular to the general volcano slope we have identified 1318 individual sub horizontal layers which we interpret to be lava flows in the 885 m high nearly vertical eastern wall of this graben the average and median outcrop widths of each layer are 149 and 85 m respectively no layers extend 1 72 km across the width of the section arguing against these being either areally extensive ash or paleo glacial deposits which has implications for the reoccurrence interval of glacial events and or the long term magma production rate of the volcano measurements n 118 made at a 100 m spacing across the width of the section reveal that there are on average 17 3 layers at each location this implies an average layer thickness of 51 m locally however as many as 7 layers can be counted within a 70 m high part of the section implying if these layers are indeed lava flows that arsia mons occasionally erupted flows that were only 10 m thick

tectonic and volcanic controls on early jurassic rift valley lake deposition during emplacement of karoo flood basalts southern namibia abstract the karoo igneous province of southern africa is one of the classic mesozoic flood basalt provinces of the world in the case of the early jurassic kalkrand formation of namibia the succession comprises three major flood basalt units that are separated by two stratigraphically important fluvio lacustrine interlayers these horizons preserve a record of the complex interplay between sedimentation effusion of karoo flood basalts and extensional tectonics that predated and accompanied the break up of gondwanaland both sediment layers start with the dominantly local derivation of weathered and eroded lava debris followed by the emplacement of subaqueous mass flows and subsequent deposition of chemical sediments the latter are characterised by interbedded stromatolitic carbonates grass like structured gypsum and plane bedded sandstones and mudstones containing euhedral displacive gypsum crystals that grew in the subsurface as well as rosettes which nucleated on the sediment surface the central parts of the lacustrine units are overlain by thin deltaic sandstones showing bottomset foreset and topset layering and finally braided fluvial trough cross bedded sandstones evidence of subsidence synchronous with the formation of lake bodies can be explained by two principal mechanisms the first acted in localised areas only and is reflected by the development of small centrally subsiding basins from the repeated occurrence of onlapping geometries within such a pool a multiphase history of sagging is deduced being most likely related to periodic magma withdrawal and reduction in magmatic pressures in subsurface lava feeders beneath the basin floor abundant syn subsident fracture features at lava sediment contacts such as sediment hydrothermal calcite and sometimes basic lava filled fissure systems indicate the pronounced interaction between the underlying volcanics and these small areas of pronounced subsidence fluids passing through the volcanic pile exhaled into the lake giving it the characteristics of alkaline lake systems described from more recent flood basalt areas associated with the modern african rift system on the regional scale however northerly trending extensional fault systems controlled half graben basin geometries and both facies and thickness variations across faults indicate that tectonism operated contemporaneously with volcanism and lacustrine sedimentation the analysis of faults and associated structures such as regularly aligned sediment filled fissures sets of micro faults folds and basaltic dykes constrains the extensional opening direction for the karoo graben structures in this area that heralded the opening of the south atlantic and thus provides a basis to discuss the extensional history of the namibian coastal margin within the regional tectonic framework

effect of slope on development of pahoehoe flow fields evidence from mount etna abstract we describe and compare two types of pahoehoe on mount etna one similar to an hawaiian inflated flow field consisting of tumuli lava rises and lava rise pits and the other a coalescing complex of rootless centres of ephemeral boccas fed from lava tubes and superimposed on an initial a a flow field the former we define as a primary pahoehoe field that results from relatively slow advance rate of lava over an almost horizontal surface the latter is a result of an eruption of long enough duration to allow tube formation over a substantial portion of the flow field over steeper slopes at breaks in slope in the underlying topography centres of ephemeral boccas develop giving rise to low effusion rate pahoehoe lavas covering the original channelled a a surface these we refer to as secondary pahoehoe flow fields

aeromagnetic study of the island of hawaii an aeromagnetic study of the island of hawaii provides new insight on magnetic properties of subsurface rock and geologic structure on a regional scale spectral depth analysis delineates two shallow magnetic zones each roughly 1 5 km thick lying at a depth of 1 km one zone of unknown origin lies in the center of the island and correlates with a regional magnetic high the other zone coincides with pronounced magnetic lows paralleling kilauea s active east rift zone these magnetic lows probably depict rocks chemically altered by hydrothermal fluids in which titanomagnetite has been destroyed analysis of magnetic terrain effects indicates that magnetization also decreases with depth within mauna kea and mauna loa we estimate that magnetization is reduced by about half at a depth of 1 km the magnetic method is particularly useful in delineating the lateral extent of local shield structures such as rifts summit calderas pit craters and vent fissures rifts possess characteristic magnetic patterns primarily long wavelength linear magnetic low zones we propose alteration processes reduce magnetizations along the flanks of rifts on the other hand along young rifts e g kilauea s east rift zone short wavelength magnetic anomalies probably reflect slowly cooled unaltered intrusions altered rock may also produce magnetic lows that help define buried summit calderas

volcanic features of the north rockall trough application of visualisation techniques on 3d seismic reflection data understanding the volcanic processes operating during continental break up is hampered by the subsequent burial of the majority of the volcanic pile beneath thick sedimentary sequences currently located in bathymetrically deep offshore regions although portions of these volcanic systems are currently exposed on land a full understanding of the volcanic structure the eruptive styles and their evolution is not possible as these localities have been partially eroded furthermore as the onshore exposure represents a volumetrically minor part of the entire system the documented eruptive styles may not be representative the increasing availability of 3d seismic reflection data has the potential to significantly enhance our understanding of break up related volcanism as it allows direct access to detailed information from the buried volcanic succession however conventional seismic interpretation methodologies cannot determine lava flow morphologies and as a result eruptive styles and their evolution are still largely based on extrapolation from the accessible onshore outcrop data new 3d seismic volume visualisation techniques allow the buried basalt morphologies to be examined for the first time in a manner similar to outcrop aerial photographic or satellite based observations applying this new approach for 3d seismic data to the north rockall trough u k atlantic margin demonstrates that a range of volcanic features indicative of eruptive style can be determined the data reveal a complex terrain containing lava flows originating from discrete volcanic centres contemporaneous normal faults linear fissures a few kilometres long radial fissures and inflation ridges lava flow morphologies that are indicative of tube fed inflated sheetflows intracanyon flows and elongate subaerial flows that enter water downslope to produce a large hyaloclastite delta are observed

hawaiian xenolith populations magma supply rates and development of magma chambers hawaiian volcanoes pass through a sequence of four eruptive stages characterized by distinct lava types magma supply rates and xenolith populations magma supply rates are low in the earliest and two latest alkalic stages and high in the tholeiitic second stage magma storage reservoirs develop at shallow and intermediate depths as the magma supply rate increases during the earliest stage magma in these reservoirs solidifies as the supply rate declines during the alkalic third stage these magma storage reservoirs function as hydraulic filters and remove dense xenoliths that the ascending magma has entrained during the earliest and latest stages no magma storage zone exists and mantle xenoliths of lherzolite are carried to the surface in primitive alkalic lava during the tholeiitic second stage magma storage reservoirs develop and persist both at the base of the ocean crust and 3 7 km below the caldera only xenoliths of shallow origin are carried to the surface by differentiated lava during the alkalic third stage magma in the shallow subcaldera reservoir solidifies and crustal xenoliths including oceanic crustal rocks are carried to the surface in lava that fractionates in an intermediate depth reservoir worldwide xenolith populations in tholeiitic and alkalic lava may reflect the presence or absence of subvolcanic magma storage reservoirs

emplacement of subaerial pahoehoe lava sheet flows into water 1990 kūpaianaha flow of kilauea volcano at kaimū bay hawai i episode 48 of the ongoing eruption of kilauea hawai i began in july 1986 and continuously extruded lava for the next 5 5 years from a low shield k paianaha the flows in march 1990 headed for kalapana and inundated the entire town under 15 25 m of lava by the end of august as the flows advanced eastward they entered into kaim bay replacing it with a plain of lava that extends 300 m beyond the original shoreline the focus of our study is the period from august 1 to october 31 1990 when the lava buried almost 406 820 m2 of the 5 m deep bay when lava encountered the sea it flowed along the shoreline as a narrow primary lobe up to 400 m long and 100 m wide which in turn inflated to a thickness of 5 6 m the flow direction of the primary lobes was controlled by the submerged delta below the lavas and by damming up lavas fed at low extrusion rates breakout flows through circumferential and axial inflation cracks on the inflating primary lobes formed smaller secondary lobes burying the lows between the primary lobes and hiding their original outlines inflated flow lobes eventually ruptured at proximal and or distal ends as well as mid points between the two ends feeding new primary lobes which were emplaced along and on the shore side of the previously inflated lobes the flow lobes mapped with the aid of aerial photographs were correlated with daily observations of the growing flow field and 30 primary flow lobes were dated excluding the two repose periods that intervened while the bay was filled enlargement of the flow field took place at a rate of 2 440 22 640 square meters per day in the bay lobe thickness was estimated to be up to 11 m on the basis of cross sections of selected lobes measured using optical measurement tools measuring tape and hand level the total flow lobe volume added in the bay during august 1 october 31 was approximately 3 95 million m3 giving an average supply rate of 0 86 m3 s

emplacement history and inflation evidence of a long basaltic lava flow located in southern payenia volcanic province argentina abstract the el corcovo lava flow from the huanul shield volcano in the southern mendoza province central western argentina traveled a distance of 70 km and covered a minimum area of 415 km 2 the flow emplacement was controlled both by extrinsic e g topography and intrinsic e g lava supply rate lava physicochemical characteristics factors the distal portion of the lava flow reached the colorado river valley in la pampa province where it spread and then was confined by earlier river channels cross sections through the flow surveyed at several localities show two vesicular layers surrounding a dense central section where vesicles are absent or clustered in sheet shaped and cylindrical shaped structures lavas of the el corcovo flow are alkaline basalts with low values of viscosity the morphological and structural characteristics of the flow and the presence of landforms associated with lava accumulation are the evidence of inflation this process involved the formation of a tabular sheet flow up to 4 m of thick with a large areal extent in the proximal sectors while at terminal sectors frontal lobes reached inflation values up to 10 m the numerous swelling structures present at these portions of the flow suggest the movement of lava in lava tubes we propose that this aspect and the low viscosity of the lava allowed the flow travel to a great distance on a gentle slope relief

disruption of tephra fall deposits caused by lava flows during basaltic eruptions observations in the usa iceland and tenerife canary islands reveal how processes occurring during basaltic eruptions can result in complex physical and stratigraphic relationships between lava and proximal tephra fall deposits around vents observations illustrate how basaltic lavas can disrupt dissect spatially and temporally and alter sheet form fall deposits complexity arises through synchronous and alternating effusive and explosive activity that results in intercalated lavas and tephra deposits tephra deposits can become disrupted into mounds and ridges by lateral and vertical displacement caused by movement including inflation of underlying p hoehoe lavas and clastogenic lavas mounds of tephra can be rafted away over distances of 100 s to 1 000 s m from proximal pyroclastic constructs on top of lava flows draping of irregular topography by fall deposits and subsequent partial burial of topographic depressions by later lavas can result in apparent complexity of tephra layers these processes deduced from field relationships have resulted in considerable stratigraphic complexity in the studied proximal regions where fallout was synchronous or alternated with inflation of subjacent lava sheets these mechanisms may lead to diachronous contact relationships between fall deposits and lava flows such complexities may remain cryptic due to textural and geochemical quasi homogeneity within sequences of interbedded basaltic fall deposits and lavas the net effect of these processes may be to reduce the usefulness of data collected from proximal fall deposits for reconstructing basaltic eruption dynamics

poleward displaced electron precipitation from lightning generated oblique whistlers new simulation results show that obliquely propagating lightning generated whistlers which fill vast volumes of the magnetosphere readily induce significant energetic electron precipitation over large regions of the ionosphere depositing appreciable energy flux to the upper atmosphere at locations substantially poleward of the lightning source these results provide a new interpretation for the observed spatial relationships between lightning discharges and subsequently disturbed ionospheric regions inferred from subionospheric signal perturbations i e trimpi events reported in several lightning induced electron precipitation lep studies

rootless shield and perched lava pond collapses at kīlauea volcano hawai i effusion rate is a primary measurement used to judge the expected advance rate length and hazard potential of lava flows at basaltic volcanoes the rapid draining of lava stored in rootless shields and perched ponds can produce lava flows with much higher local effusion rates and advance velocities than would be expected based on the effusion rate at the vent for several months in 2007 2008 lava stored in a series of perched ponds and rootless shields on k lauea volcano hawai i was released episodically to produce fast moving a lava flows several of these lava flows approached royal gardens subdivision and threatened the safety of remaining residents using time lapse image measurements we show that the initial time averaged discharge rate for one collapse triggered lava flow was approximately eight times greater than the effusion rate at the vent though short lived the collapse triggered a lava flows had average advance rates approximately 45 times greater than that of the p hoehoe flow field from which they were sourced the high advance rates of the collapse triggered lava flows demonstrates that recognition of lava accumulating in ponds and shields which may be stored in a cryptic manner is vital for accurately assessing short term hazards at basaltic volcanoes

rootless tephra stratigraphy and emplacement processes volcanic rootless cones are the products of thermohydraulic explosions involving rapid heat transfer from active lava fuel to external sources of water coolant rootless eruptions are attributed to molten fuel coolant interactions mfcis but previous studies have not performed systematic investigations of rootless tephrostratigraphy and grain size distributions to establish a baseline for evaluating relationships between environmental factors mfci efficiency fragmentation and patterns of tephra dispersal this study examines a 13 55 m thick vertical section through an archetypal rootless tephra sequence which includes a rhythmic succession of 28 bed pairs each bed pair is interpreted to be the result of a discrete explosion cycle with fine grained basal material emplaced dominantly as tephra fall during an energetic opening phase followed by the deposition of coarser grained material mainly as ballistic ejecta during a weaker coda phase nine additional layers are interleaved throughout the stratigraphy and are interpreted to be dilute pyroclastic density current pdc deposits overall the stratigraphy divides into four units unit 1 contains the largest number of sediment rich pdc deposits units 2 and 3 are dominated by a rhythmic succession of bed pairs and unit 4 includes welded layers this pattern is consistent with a general decrease in mfci efficiency due to the depletion of locally available coolant i e groundwater or wet sediments changing conduit vent geometries mixing conditions coolant and melt temperatures and or coolant impurities may also have affected mfci efficiency but the rhythmic nature of the bed pairs implies a periodic explosion process which can be explained by temporary increases in the water to lava mass ratio during cycles of groundwater recharge

geology of the gusev cratered plains from the spirit rover transverse 1 the cratered plains of gusev traversed by spirit are generally low relief rocky plains dominated by impact and eolian processes ubiquitous shallow soil filled circular depressions called hollows are modified impact craters rocks are dark fine grained basalts and the upper 10 m of the cratered plains appears to be an impact generated regolith developed over intact basalt flows systematic field observations across the cratered plains identified vesicular clasts and rare scoria similar to original lava flow tops consistent with an upper inflated surface of lava flows with adjacent collapse depressions crater and hollow morphometry are consistent with most being secondaries the size frequency distribution of rocks 0 1 m diameter generally follows exponential functions similar to other landing sites for total rock abundances of 5 35 systematic clast counts show that areas with higher rock abundance and more large rocks have higher thermal inertia plains with lower thermal inertia have fewer rocks and substantially more pebbles that are well sorted and evenly spaced similar to a desert pavement or lag eolian bed forms ripples and wind tails have coarse surface lags and many are dust covered and thus likely inactive deflation of the surface 5 25 cm likely exposed two toned rocks and elevated ventifacts and transported fines into craters creating the hollows this observed redistribution yields extremely slow average erosion rates of 0 03 nm yr and argues for very little long term net change of the surface and a dry and desiccating environment similar to today s since the hesperian or 3 ga

magnetic fabric and flow direction in basaltic pahoehoe lava of xitle volcano mexico abstract we sampled five basaltic lava flow units from xitle volcano mexico city to study the variation of anisotropy of magnetic susceptibility within their cooling boundaries we find that the mean maximum susceptibility parallels the geologically inferred flow direction in the units that were emplaced on a steeper slope whereas for those on a negligible slope the mean intermediate susceptibility points in the flow direction we propose however that the maximum susceptibility always points in the direction of local movement and that a change in slope produces a deviation of the local motion from that of the unit as a whole the axis of susceptibility closest to the geologically inferred flow direction usually plunges upflow in the basal part of the flow unit comprising an imbrication which clearly marks the flow azimuth of the lava thus the scenario of emplacement may influence the results in a predictable way we suggest that the degree of anisotropy could bear a direct relationship to either the viscosity of the lava the morphology of the flows or both based on a comparison with lavas from azufre argentina and ko olau o ahu volcanoes also we suggest that the shape of the susceptibility ellipsoid may be related to the degree of internal deformation of the lava flows we also compare the two methods currently available to calculate regions of confidence around the mean principal susceptibilities

lava tubes terraces and megatumuli on the 1614 24 pahoehoe lava flow field mount etna sicily the 1614 1624 lava flow of mt etna was formed during a long duration flank eruption involving predominantly pahoehoe flows which produced unusual surface features including mega tumuli here defined and terraces detailed mapping of the flow units surface features and associated tubes reveals a complex sequence of emplacement for the field the stair stepped terraces appear to have been formed as a consequence of self damming of tube fed flows which developed perched ponds of lava surges of lava through tubes elevated sections of crusted lava at the distal ends of the flow to generate tumuli some as high as 130 m as a consequence of pressure via hydrostatic head conditions within the tube although pahoehoe lavas and the related features described here are atypical of mt etna they may reflect styles of eruption and lava emplacement found on volcanoes elsewhere

toothpaste lava from the barren island volcano andaman sea abstract toothpaste lava is a basaltic lava flow type transitional between pahoehoe and aa and has been described from paricutin kilauea and etna volcanoes here we describe a spectacular example of toothpaste lava forming part of a recent possibly 1994 95 aa flow on the active volcano of barren island andaman sea this flow of subalkalic basalt shows abundant squeeze ups of viscous toothpasate lava near its entry into the sea the squeeze ups are sheets and slabs up to several meters across and tens of centimeters thick extruded from boccas they are often prominently curved have striated upper surfaces with close spaced en echelon linear ridges and grooves broad wave like undulations perpendicular to the striations and sometimes clefts textural geochemical and sr nd isotopic data on the squeeze ups and the exposed aa flow core indicate very crystal rich viscous and isotopically very homogeneous lava we envisage that a greatly reduced speed of this viscous flow at the coastline possibly aided by a shallowing of the basal slope led to lateral spreading of the flow which caused tension in its upper parts this with continued albeit dwindling lava supply at the back led to widespread tearing of the flow surface and extrusion of the squeeze ups the larger slabs while extruding in a plastic condition curved under their own weight whereas their surfaces experienced brittle deformation forming the en echelon grooves the extruded detached and rotated sheets and slabs were carried forward for some distance atop the very slowly advancing aa core before the flow solidified

newly discovered ring moat dome structures in the lunar maria possible origins and implications we report on a newly discovered morphological feature on the lunar surface here named ring moat dome structure rmds these low domes a few meters to 20 m height with slopes 5 are typically surrounded by narrow annular depressions or moats we mapped about 2 600 rmdss in the lunar maria with diameters ranging from tens to hundreds of meters four candidate hypotheses for their origin involving volcanism are considered we currently favor a mechanism for the formation of the rmds related to modification of the initial lava flows through inflated flow squeeze ups and or extrusion of magmatic foams below a cooling lava flow surface these newly discovered features provide new insights into the nature of emplacement of lunar lava flows suggesting that in the waning stages of a dike emplacement event magmatic foams can be produced extrude to the surface as the dike closes and break through the upper lava flow thermal boundary layer crust to form foam mounds and surrounding moats

constructing the upper crust of the mid atlantic ridge a reinterpretation based on the puna ridge kilauea volcano the volcanic morphology of a number of segments of the slow spreading mid atlantic ridge mar have been reinterpreted based on our understanding of dike emplacement dike propagation and eruption at the east rift zone of kilauea volcano hawaii and its submarine extension the puna ridge the styles of volcanic eruption at the submarine puna ridge are remarkably similar to those of the axial volcanic ridges avrs constructed on the median valley floor of the mar we use this observation to relate volcanic processes occurring at kilauea volcano to the mar we now consider that volcanic features e g seamounts and lava terraces built on the flanks of the avrs are secondary features that are fed from lava tubes or channels not primary features fed directly from an underlying dike we examine simple models of pipe flow and conclude that lava tubes can transport lava down the flanks of submarine rifts to build all of the volcanic features observed there in addition deep water lava tubes are strong enough to withstand the pressures of a few megapascals that the building of a volcanic structure 150 m high at the end of the tube would generate the volumes of individual volcanic terraces and seamounts on the puna ridge and at the mar are large 0 1 1 km3 and similar to the volumes of lava flows that are broadly distributed at the subaerial east rift zone of kilauea this striking difference in the volcanic morphology on a scale of 1 2 km producing terraces and seamounts underwater and low relief flows on land must be related to the enhanced cooling and to the greater mechanical stability of tubes in the submarine environment we suggest that at the mar a crustal magma reservoir most likely located beneath shallow flat sections of the segment provides magma to the rift axis through dikes that propagate laterally tens of kilometers the zone of dike intrusion at least in the neighborhood of the magma body is likely narrower than the width resurfaced by flows yielding a crustal structure that has a rapid vertical transition from lavas to sheeted dikes at segment ends the zone of dike intrusion is likely to be wider giving a resulting structure with a more gradual transition from lavas to dikes

emplacement and inflation of the al halaq al kabir lava flow field central part of the al haruj volcanic province central libya abstract numerous of lava rise plateaus and tumuli developed in the medial and distal portions of the al halaq al kabir lava flow field during the last holocene eruption in the central part of the al haruj volcanic province ahvp these inflation structures provide important data on the lava emplacement mechanism in this part of the al haruj region where the widespread occurrence of tumuli and lava rise plateaus are good indicators of the mode of emplacement we report the results of detailed measurements of the maximum and minimum diameters in plan view of 551 lava rise plateaus and 289 tumuli from the distal part of the al halaq al kabir lava field using arcgis and field observations tumuli and lava rise plateaus may be divided into subpopulations according to abrupt changes in the scaling exponents on log log plots of their frequency versus diameter using the estimated stiffness young s modulus of the basaltic rocks in the study area of 10 34 gpa numerical and analytical results show that theoretical maximum tensile stresses in the inflated upper solidified crustal layers of the developing tumuli and lava rises at tens of mega pascals mpa this theoretical stress is orders of magnitude higher than typical in situ tensile strengths of rocks 0 5 9 mpa and thus high enough to rupture the crustal layers of the lava rises and tumuli the high tensile stresses are generated during crustal doming driven by a magmatic overpressure of only about 1 mpa our results partly explain the abundance of tension fractures at the surface of the al halaq al kabir lava flow field tumuli observed in the area are remarkably similar in morphology and aspect height width ratios to the flow lobe tumuli in holocene lava flow fields in iceland suggesting an analogous mechanics of formation there appears to be a coincidence between the age of an initial volcanism in the ahvp 7 9 5 3 ma and a local fauna and flora disappearance in the as sahabi area ne sirt basin during messinian zanclean time 7 5 to 5 ma we speculate that the volcanism may have had a local negative environmental impact and contributed to the reported decline in the fauna and flora in the area

morphology internal architecture and emplacement mechanisms of lava flows from the central atlantic magmatic province camp of argana basin morocco abstract the morphology internal architecture and emplacement mechanisms of the central atlantic magmatic province camp lava flows of argana basin in morocco are presented the volcanic pile was produced by two volcanic pulses the first represented by the tasguint formation corresponds to a succession of 3 13 individual flows created by 1 8 eruptions the second alemzi formation is composed of 2 7 individual flows formed by 1 4 eruptions these formations geochemically distinct are separated by thin silty or sandy horizons or by palaeosols they include compound pahoehoe flows and simple flows the first type is almost exclusive of the lower formation while the second type dominates the upper formation the lava flows show clear evidence of endogenous growth or inflation the characteristics of the volcanic pile suggest slow emplacement during sustained eruptive episodes and are compatible with a continental basaltic succession facies model

structural control of young basaltic fissure eruptions in the plateau basalt area of the arabian plate northeastern jordan abstract in the el hamadieh region part of the large intracontinental basalt plateau extending nw se from syria to jordan and saudi arabia in the northern part of the arabian plate young volcanic edifices formed by fissure eruptions have been investigated all geometrical dimensions and parameters of the ridges have been measured the field relationships documented the data evaluated and the structural patterns analysed using the attitude of the fissures as palaeostress indicators a stress strain model is introduced showing the superimposition of stress fields magma was extruded at the intersection of two regional structures the ne sw striking amman hallabat fold belt and the nw se trending azraq sirhan graben a first effusion with a relatively fluid magma took place in reactivated fold related conjugated hk 0 shear fractures with a compressional 1 stress trending nw se a second phase of fissure effusions produced a more viscous lava these fissures represent a hk 0 planes with an acute angle about the fold axis and b planes of normal faults along the southwestern shoulder of the azraq sirhan graben in the position of fold related reactivated conjugated 0 hl shear planes the geometrical relationships between the amman hallabat folds the azraq sirham faults and the volcanic fissures indicate a rotation of the local stress field with the originally nw se trending compressional 1 and the ne sw trending 3 stress changing into a ne sw acting tensional 1 stress

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

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

fracture and surface crust development in a holocene pahoehoe lava flow on the island of tenerife canaries abstract an almost horizontal pahoehoe surface in a holocene plagioclase basanite lava on tenerife displays three scales of fracture within the surface crust an early formed set of large scale fractures divides up the surface into an orthogonal set of rectangular slabs with dimensions of several metres and depths of 10 12 cm the shortest slab dimension is parallel to the flow emplacement direction inferred from a strong surface lineation the slabs are domed with the centre an average of 9 6 cm with range 4 19 6 cm above the edges of the slabs profiles of the slabs normal and perpendicular to the margins and through the crest indicate that they can be described by a power law in which the deflection of the slab h is related to the distance from the crest x with an exponent between 2 and 3 analysis of joints within the slabs indicates two smaller scale networks an intermediate scale joint network bounds blocks with rectilinear to polygonal shapes in plan view and has a characteristic mean spacing of 24 2 cm range 10 5 48 cm the major fractures in this set are normal and parallel to the slab margins a smaller scale joint network bounds polygonal equant blocks in plan view and has characteristic spacing of 6 4 cm range 3 7 10 5 cm a model of cooling from the pahoehoe surface is used to constrain the growth of the crust and timing of fracture development the large scale slabs are attributed to localised accumulation of gas beneath the growing crust causing buoyant forces the tensile stresses caused by uplift are sufficient to form the large scale fractures after 2 or 3 h of cooling the intermediate scale fracture network is attributed to the flexure of the slab crust the smaller scale polygonal joint network is related to the build up of isotropic tensile stresses in the cooling slab crust due to thermal contraction with fracture development being promoted by the flexure of the slabs an analysis of the slab deformation indicates that lava crust is weak the weakness is explained by division of the crust into three zones an outer zone with small scale joints that cause negligible strength a middle zone of elastic behaviour in which stress can build up and a lower zone of plastic deformation the crustal slabs display profiles similar to that expected in a bending elastic plate the deformation of the 10 cm thick crust can be explained if the elastic zone was about 2 cm thick this result agrees with an independent calculation of elastic zone thickness based on the position of the brittle ductile transition being located at the 600 c isotherm at a depth of about 2 cm when the crustal slabs were rifted apart

tumulus development on lava flows insights from observations of active tumuli and analysis of formation models here we use observations of active flows along with detailed morphometric field measurements of more than 70 tumuli on flows at mount etna italy kilauea and hualalai us volcanoes to constrain a previously published model that estimates the pressure needed to form tumuli in an attempt to discover the nature and magnitude of pressure variations within active lava flow interiors we then consider how tumuli differ from idealized circular plates we incorporate observations of active tumuli and find that they may grow asymmetrically yet produce a symmetrical tumulus and can form where the flow path significantly changes direction bending models of clamped edges provide the most reasonable head estimates for the tumuli in our study tumulus formation requires the proper combination of cooling and effusion rate if cooling is too extensive and effusion rate too low the crust will provide too much resistance to bending if cooling is too limited and effusion rates too high crusts will not develop or have insufficient strength to resist fracture and subsequent breakouts we do not find it surprising that tumuli are rarely found over well established lava tubes that typically have rigid walls overlying crusts that exceed 2 m in thickness and provide too much resistance to bending silicic flows lack tumuli because the viscosity gradients within the flow are insufficient to concentrate stress in a localized area

radiation belt electron precipitation fluxes associated with lightning in this study we consider the dependence of precipitation fluxes arising from whistler induced radiation belt losses on the strength of the associated lightning s return stroke current as a result of this work it will be possible to use lightning activity data sets to estimate globally induced precipitation flux rates and thus determine the lightning induced effect on the radiation belts more accurately four study days were selected during which a high proportion of the lightning activity occurring near the east coast of north america produced observable trimpi effects on vlf transmitter signals propagating in the region of the antarctic peninsula similar tol 2 2 5 the lack of lightning in antarctica gives this location a unique advantage for this study the functional dependence of the relative scattered field amplitude with the return stroke peak current of the lightning discharge suggests that during these events diffusion conditions are occurring near the precipitating radiation belt particles loss cone due to strong whistler wave fields probably caused by ducted signals the range of observed trimpi scatter amplitude of 10 to 35 db was produced by precipitation bursts with energy fluxes estimated to range over 6 5 0 4 x 10 3 ergs cm 2 s 1 the largest fluxes were found to be driven by lightning currents of about 250 ka while the smallest detectable fluxes relate to lightning currents of 70 ka although 3 of the 4 study days showed a high degree of consistency between the levels of lightning return stroke peak current required to produce any given perturbation scatter amplitude value conditions were significantly different on 23 april 1994 on this day observed trimpi signatures were 6 7 db greater for any given lightning intensity than on the other study days these events are consistent with a significantly harder radiation belt precipitation spectra probably caused by geomagnetic storm time acceleration processes of radiation belt electrons

discussion of pulsed inflation of pahoehoe lava flows implications for flood basalt emplacement by s w anderson e r stofan e r smrekar j e guest and b wood earth planet sci lett 168 1999 7 18

emplacement of lobate sheet flows with hyaloclastites onto soft sediment the erquy neoproterozoic lava pile armorican massif france abstract the neoproterozoic volcano sedimentary succession of the heussaye headland erquy belongs to the cadomian block located in the north east of the armorican massif france the volcanism dated at approximately 608 7 ma zircon u pb data occurred in a back arc basin this site exhibits a noteworthy verticalized pile of moderately metamorphosed greenschist facies basaltic andesite flows of arc back arc tholeiite affinity alternating with metasedimentary layers sandstones and siltstones a large range of volcanic facies characteristic of an underwater soft substrate environment can be continuously studied for over than 200 m parallel to the flow edges they include pillow lavas lava lobes fluidal peperites and sediment matrix hyaloclastites the presence of parallel lava lobes in a sector where one lava flow is capped by a variably thick hyaloclastite carapace together with the occurrence of asymmetric turbiditic folds in interbedded metasedimentary layers suggests the existence of an easterly facing gentle paleoslope the sudden thinning of this hyaloclastite carapace in two spots located approximately 60 m from each other is attributed to the synvolcanic activity of two conjugate normal paleofaults this hypothesis is supported by the observation of a hyaloclastite accumulation in one of the two spots close to a strike slip fault which may have been extensional at the time of the volcanism water entered the lava flow along the faults resulting in an interstitial network of hyaloclastites by quench fragmentation in the upper part of the hanging wall block all these observations are consistent with a model of lava emplacement along a subaqueous slope resulting from synmagmatic extensional faulting in a marginal basin context

spongy pahoehoe in hawaii a study of vesicle distribution patterns in basalt and their significance a well defined pahoehoe lava type that is very common medially and distally in hawaii is characterized by a high concentration and fairly uniform distribution of spherical or near spherical vesicles measurements of vesicle sizes and concentrations have been made on ten of these spongy pahoehoe lava flow units the vesicles increase in size toward the middle accompanied by a moderate increase in lava porosity the close approach to bilateral symmetry on either side of the horizontal median plane and the common occurrence of a median gas blister shows that no significant upward movement of vesicles occurred suggesting that the lava possessed a yield strength and was more or less static olivine phenocrysts when present are however concentrated in the lower half of the same flow units showing that the lava previously lacked a significant yield strength the vesicles are regarded as early inherited from the vent but the size characteristics of the vesicle population are a late formed feature vesicles grew in static lava mostly by coalescence and it is postulated that coalescence was promoted by the presence of abundant diktytaxitic voids which punctured the walls of contiguous vesicles zones in which the vesicle concentration is lower and the vesicles are larger and strongly deformed interrupt the symmetry of some spongy pahoehoe units and gas blisters higher than the median plane occur in many examples these zones are interpreted to result from late stage shearing and point to a mechanism by which vesicles may be eliminated from a lava

growth destruction and facies architecture of effusive and explosive volcanics in the miocene shama basin southwest of saudi arabia subaqueous subaerial volcanism in a lacustrine setting abstract this paper presents for the first time detailed stratigraphical and petrographical analyses of the harrat shama volcanic basin hsvb of miocene age in sw saudi arabia this basin is filled by abundant volcanics intercalated with fluvio lacustrine sedimentary successions these successions are characterized by a syneruptive intereruptive cycle which results from the intercalation periods of volcanics and volcaniclastic sedimentation along with periods of fluvial incision two depositional sequences showing an overall fining upward trend are preserved within the hsvb the first comprises hyaloclastites zeolite bearing bedded tuffs and bedded accretionary lapilli tuffs interpreted as deep lake whereas the second is made up of extensive pumiceous pyroclastic flows peperitic breccias and basaltic lava flows which are in turn capped by siliciclastic deposits of lacustrine deposits the passage between two sequences is defined by lateral variations of the lithofacies and textural features reflecting a change in paleogeography the fining upward volcaniclastic deposits of the hsvb sequence are interpreted to represent the sedimentation pattern induced by tectonic subsidence with the influence of volcaniclastic sediment input indicating well established proximal distal relationship hsvb was evolved through three stages including pre syn and post caldera stages the first two stages correspond to proximal aggradational syn eruptive event whereas the latter stage refers to distal degradational inter eruptive event these stages overlap in time as shown by the alternation of explosive effusive and their resedimented deposits reflecting diverse eruptive sequences formed by different fragmentation processes the difference in the latter coupled with the variability in the magma water interaction and the nature of substrate are responsible for such diversity resulting in progressive environmental changes from subaqueous to subaerial regime from bottom to top the development of such contrast in the depositional sequences reflects variation in the sediment flux and subsidence rate during the evolution of the hsvb

morphologic and thermophysical characteristics of lava flows southwest of arsia mons mars abstract the morphologic and thermophysical characteristics of part of the extensive lava flow fields southwest of arsia mons 22 5 27 5 s 120 130 w have been examined using a combination of orbital vnir and tir datasets themis images provide context for the regional geology and record diurnal temperature variability that is diverse and unusual for flow surfaces in such close proximity ctx images were used to distinguish dominant flow types and assess local age relationships between individual lava flows ctx and hirise images provide detailed information on flow surface textures and document aeolian effects as they reveal fine grained deposits in many low lying areas of the flow surfaces as well as small patches of transverse aeolian ridges although this region is generally dust covered and has a lower overall thermal inertia the themis data indicate subtle spectral variations within the population of lava flows studied these variations could be due to compositional differences among the flows or related to mixing of flow and aeolian materials specific results regarding flow morphology include a two main lava flow types bright rugged and dark smooth as observed in ctx images dominate the southwest arsia mons ne daedalia planum region b the bright rugged flows have knobby ridged and or platy surface textures commonly have medial channel levee systems and may have broad distal lobes c the dark smooth flows extend from distributary systems that consist of combinations of lava channels lava tubes and or sinuous ridges and plateaus and d steep sided terraced margins digitate breakout lobes and smooth surfaced plateaus along lava channel tube systems are interpreted as signatures of flow inflation within the dark smooth flow type these flows exhibit smoother upper surfaces are thinner and have more numerous smaller lobes which along with their the channel tube fed nature indicate a lower viscosity lava than for the bright rugged flows flow patterns and local interfingering and overlapping relationships are delineated in ctx images and allow reconstruction of the complex flow field surfaces darker channel tube fed flows are generally younger than adjacent thicker bright rugged flows however the diversity and complexity of temporal relationships observed along with the thermophysical variability suggests that lava sources with different eruptive styles and magnitudes and or lavas that experienced different local emplacement conditions were active contemporaneously

relationships between pahoehoe surface units topography and lava tubes at mauna ulu kilauea volcano hawaii lava flow field development at mauna ulu was analyzed by characterizing pahoehoe surface units and their distribution relative to pre mauna ulu topography and the main lava tube system four pahoehoe surface units were identified in the field and described on the basis of color surface texture and morphology broad flat sheets unit i networks of interconnected glassy surfaced toes unit ii late stage breakout lobes of viscous toes unit iii and irregular surfaces exhibiting meter scale roughness which typically occur as channels unit iv the distribution of these units was mapped on high resolution aerial photographs using an automated supervised classification technique geographical information systems gis analyses utilized digitized 6 m 20 foot contour interval topography of the pre mauna ulu surface and the mapped lava tube network to assess the influence of topography and lava tubes on the emplacement of surface flows the four pahoehoe units represent variations in emplacement conditions on the basis of the various flow regimes sheet toe and channel and surface textures smooth glassy and rough displayed these surface units show a limited correlation to pre mauna ulu topography based on their mean underlying slopes the higher flow rates indicated by the channelized surfaces of unit iv are spatially correlated with higher 22 2 mean underlying slopes relative to those of the sheets of unit i 14 2 and the toe networks representing units ii 15 2 and iii 15 9 the distribution of the four units does not appear to be directly related to their proximity to the largest scale of lava tubes suggesting two possible scenarios the main lava tubes do not significantly affect surface unit emplacement within the study area and or these tubes do not preferentially emplace any of the four units identified in this study

the formation of circular littoral cones from tube fed pāhoehoe mauna loa hawai i pyroclastic cones along the southwest coast of mauna loa volcano hawai i have a common structure a an early formed circular outer rim 200 400 m in diameter composed mostly of scoria and lapilli and b one or more later formed inner rims composed almost exclusively of dense spatter the spatter activity locally fed short lava flows that ponded within the outer rims based on various lines of evidence these cones are littoral in origin relationships between the cones and associated flows the degassed nature of the pyroclasts and although not unequivocal the position of the cones relative to known eruptive vent locations on mauna loa additional support for the littoral interpretation comes from their similarity to smaller littoral cones that have been observed forming during the ongoing kilauea eruption the structure of these mauna loa cones however contrasts with that of standard hawaiian littoral cones in that there is or once was a complete circle of pyroclastic deposits furthermore they are large even though associated with tubefed p hoehoe flows instead of a the following origin is proposed an initial flow of tube fed p hoehoe into the ocean built a lava delta with a base of hyaloclastite collapse of an inland portion of the active tube into the underlying wet hyaloclastites or a water filled void allowed sufficient mixing of water and liquid lava to generate strong explosions these explosions broke through the top of the flow and built up the outer scoria lapilli rims on the solid carapace of the lava delta eventually the supply of water diminished the explosions declined in intensity to spattering and the initial rim was filled with spatter and lava

control of early formed vesicle cylinders on upper crustal prismatic jointing in compound pāhoehoe lavas of elephanta island western deccan traps india upper crustal prismatic joints and vesicle cylinders common in p hoehoe lava flows form early and late respectively and are therefore independent features however small scale compound p hoehoe lava lobes on elephanta island western deccan traps india which resemble s type spongy p hoehoe in some aspects contain vesicle cylinders which apparently controlled the locations of upper crustal prismatic joints the lobes are decimeters thick did not experience inflation after emplacement and solidified rapidly they have meter scale areas that are exceptionally rich in vesicle cylinders up to 68 cylinders in 1 m2 with a mean spacing of 12 1 cm separated by cylinder free areas and pervasive upper crustal prismatic jointing with t curved t and quadruple joint intersections a majority 76 5 of the cylinders are located exactly on joints or at joint intersections and were not simply captured by downward growing joints as the cylinders show no deflection in vertical section we suggest that large numbers of cylinders originated in a layer of bubble rich residual liquid at the top of a basal diktytaxitic crystal mush zone which was formed very early probably within the first few minutes of the emplacement history the locations where the rising cylinders breached the crust provided weak points or mechanical flaws towards which any existing joints formed by thermal contraction propagated new joints may also have propagated outwards from the cylinders and linked up laterally some cylinders breached the crust between the joints and thus formed a little later than most others the elephanta island example reveals that whereas thermal contraction is undoubtedly valid as a standard mechanism for forming upper crustal prismatic joints abundant mechanical flaws such as large concentrations of early formed crust breaching vesicle cylinders can also control the joint formation process

high resolution imaging science experiment hirise images of volcanic terrains from the first 6 months of the mars reconnaissance orbiter primary science phase 1 in the first 6 months of the mars reconnaissance orbiter s primary science phase the high resolution imaging science experiment hirise camera has returned images sampling the diversity of volcanic terrains on mars while many of these features were noted in earlier imaging they are now seen with unprecedented clarity we find that some volcanic vents produced predominantly effusive products while others generated mostly pyroclastics flood lavas were emplaced in both turbulent and gentle eruptions producing roofed channels and inflation features however many areas on mars are too heavily mantled to allow meter scale volcanic features to be discerned in particular the major volcanic edifices are extensively mantled though it is possible that some of the mantle is pyroclastic material rather than atmospheric dust support imaging by the context imager ctx and topographic information derived from stereo imaging are both invaluable in interpreting the hirise data

numerical simulations of flood basalt lava flows roles of parameters on lava flow morphologies using a three dimensional numerical simulation model of lava flow we studied the effects of parameters on the morphologies of simple flood basalt lava flows the model can provide a more realistic description of morphologies of lava flows than two dimensional models because it can evaluate the complex relationship between erupted volume and length of lava by considering lateral spreading of flows moreover our model can calculate lava morphologies on a very moderate slope or even on a flat plane without mesh direction dependency it can simulate not only small scale flows on individual volcanoes but also large scale 100 km flows without numerical instability although the length of a lava flow is controlled by many parameters including rheological properties and eruption rate the length is not a simple function of these parameters we confirm that small changes in parameters such as slope angle and viscosity can affect the length of the flow increasing the eruption rate up to 107 m3 s makes basaltic lava flows longer however at eruption rates higher than 107 m3 s on 0 3 slopes flow length does not increase beyond that of the 107 m3 s eruption rate due to volume conservation of erupted lava thus eruption conditions cannot be estimated from the length of a lava flow alone therefore the estimated eruption rate obtained by previous two dimensional models which essentially estimate eruption rate from the length of the flow will not always reveal useful values on the other hand the width of a simple lava flow is a good measure of its eruption rate because the width is mainly controlled by the eruption rate and yield strength a simple lava whose width is greater than 100 km was almost certainly emplaced at eruption rates higher than 107 m3 s if the yield strength of the flow is in a basaltic range

late pliocene volcanic island growth and flood basalt like lava emplacement in the hyblean mountains se sicily 1 since 200 ma the hyblean mountains southeastern sicily have been the site of recurrent mainly submarine mafic volcanism in the upper pliocene large volumes of tholeiitic products were erupted in a shallow marine environment leading to the growth of volcanic islands the deposits of this tholeiitic episode can be grouped into two main facies associations 1 pillow lavas and hyaloclastite tuffs erupted and deposited entirely under water and 2 submarine pillow breccias fed from subaerial lava flows entering the ocean and subaerial lavas which are distinguished into a coastal lava platform facies and an inland facies lava flows into the ocean led to the growth of lava deltas consisting of a basal flow foot breccia and an overlying sequence of p hoehoe flow units the latter rarely exceeding 0 5 m in thickness in outcrop this facies association shows evidence for significant instability of the lava deltas during growth indicating very similar processes to those observed during the current eruption of k lauea volcano hawaii away from the coast of the growing island the inland facies is characterized by thicker up to several meters p hoehoe flow units showing evidence for sheet flow inflation and limited outcrops of scoria and or bomb deposits evidence for lava transport through tubes exists in the form of tumuli and multiple vesicle layers drained tubes are absent all tholeiitic products were emitted in a single instantaneous voluminous event 120 km3 consistent with very high effusion rates similar to those of flood basalts or the 1783 skaftar fires iceland eruption

anisotropy of magnetic susceptibility of silicic rocks from quarries in the vicinity of sao marcos rio grande do sul south brazil implications for emplacement mechanisms abstract the parana etendeka large igneous province includes acid volcanic rocks that can be found throughout its extension several aspects concerning those rocks remain controversial including their mechanism of emplacement and location of their eruptive sources opening of several quarries of dimension stone near the city of sao marcos rio grande do sul brazil offers a unique opportunity to study in detail the acid products here we present the results of a study of the anisotropy of magnetic susceptibility ams completed in some rocks that had been interpreted as the roots of volcanic conduits our results and reexamination of the textural features of the rocks lead to a reinterpretation that suggests that these rocks were emplaced subaerially and involved assimilation and remelting of clastic components of previous products due to the inferred conditions of emplacement it is unlikely that the eruptive vents are located far from the area of study therefore ruling out the long travelled nature of these products

subionospheric vlf signatures of oblique nonducted whistler induced precipitation subionospheric very low frequency vlf signal perturbations observed at multiple sites in association with individual lightning discharges exhibit onset delays which steadily increase with increasing l value the timing of the onsets and the inferred spatial extent 1000 km of the ionospheric disturbance are consistent with those expected for electron precipitation induced by obliquely propagating i e nonducted whistlers

lava rise ridges of the toomba basalt flow north queensland australia unusually long lava rises occur in the distal portion of the toomba basalt flow up to 120 km from the source in the lolworth creek region three parallel lava rise ridges occur over a 6 km section two of these ridges are continuous for the entire 6 km the ridges average 7 m in height and range from 35 m to 300 m in width lava inflation clefts are numerous and lava rise pits also occur down flow a single lava rise ridge averaging 18 m high and up to 500 m wide extends for a further 10 km this ridge has a generally level surface with abrupt edges sloping between 45 and 90 accurate surveys across the ridges show that in some cases there has been some stretching of the surface presumably prior to the formation of the prominent clefts the ridges were formed from an initially thin flow that was inflated by a continuous layer of lava that underlay almost the entire width of each ridge rather than by a system of lava tubes of more limited dimensions inflated material represents over 90 of the volume of the distal parts of the flow estimates of the time required to inflate the lava rise ridges range from 60 days to a year

investigating the volcanic versus aqueous origin of the surficial deposits in eastern elysium planitia mars abstract the elysium volcanic province consists of numerous overlapping flow units and may include the youngest lava flows on mars however it is possible that these volcanic units have been modified or overprinted by aqueous processes understanding the timing of the igneous and aqueous events in this region is therefore essential for constraining the geological and environmental history of mars during the amazonian period we investigate the geologic evolution of eastern elysium planitia to determine the relationship between major units with the support of a geological map and chronological constraints from crater size frequency distributions we also evaluate the hypothesized origin of these units via volcanic fluvial and or fluvioglacial processes using a detailed facies mapping approach the study area includes the eastern cerberus fossae rahway valles and marte vallis the surficial deposits in rahway valles were formerly interpreted to be modified by fluvial and fluvioglacial processes however our facies map reveals that the surface of eastern elysium planitia includes nineteen morphologically distinct regions i e facies which are interpreted to be the products of flood lava volcanism including a p hoehoe and transitional lava flow types in contrast to previous studies which determined that rahway valles and marte vallis consist of two distinct geologic units with middle to late amazonian ages the results of this work show that the region was resurfaced by at least two volcanic flows with much younger ages of 20 0 ma and 8 8 ma furthermore by coupling results of our geologic and facies mapping with chronological constraints as well as subsurface information provided by shallow radar reflectors we show that there is an erosional unconformity located between the two youngest lava flow units in marte vallis we interpret that this unconformity was generated by a catastrophic aqueous flooding event that occurred only 8 8 20 0 ma ago this implies alternating episodes of volcanism and aqueous flooding that have continued into the geologically recent past on mars and may again occur within elysium planitia

the caldera of volcan fernandina a remote sensing study of its structure and recent activity air photographs taken in 1946 1960 and 1982 together with spot hvr 1 images obtained in april and october of 1988 are used to characterize recent activity in and around the caldera of fernandina volcano west galapagos islands the eruptive and collapse events during this time span appear to be distributed in a nw se band across the summit and caldera on the flanks of the volcano subtle topographic ridges indicate that this is a long term preferred orientation of extra caldera activity as well although radial and arcuate fissures are found on all sectors the caldera is formed from the coalescence of multiple collapse features that are also distributed along a nw se direction and these give the caldera its elongate and scalloped outline the nw and se benches consist of lavas that ponded in once separated depressions that have been incorporated into the caldera by more recent collapse the volume of individual eruptions within the caldera over the observed 42 years appears to be small 4x106 m3 in comparison to the volumes of individual flows exposed in the caldera walls 120 150x106 m3 field observations in 1989 of lavas exposed in the caldera walls and their cross cutting relationships show that there have been at least three generations of calderas and that at times each was completely filled an interplay between a varying supply rate to the volcano and a regional stress regime is suggested to be the cause of long term spatial and volumetric variations in activity when supply is high the caldera is filled in relative to collapse and dikes tend to propagate in all directions through the edifice at other times such as the present supply is relatively low eruptions are small the caldera is far from being filled in and dike propagation is influenced by an extra volcano stress regime

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

multiple generation folding and non coaxial strain of lava crusts viscoelastic strain in lava flows is commonly expressed as gravity driven buckling of the lava crust this surface folding process creates the well known ropy p hoehoe texture of basaltic lavas and the ogives and surface ridges of more compositionally evolved lava flows previous work has shown that surface fold wavelengths are proportional to the viscosity contrast between the lava crust and core and to the thickness of the crust thus fold analysis can be an important tool for understanding lava flow rheology we analyze fold wavelength patterns of solidified natural lava flows from the myvatn lava fields iceland piton de la fournaise la reunion and experimental lava flows from the syracuse university lava project in each case lava flows exhibited two dominant wavelengths consistent with multiple generations of coaxial folding the ratio of the two dominant wavelengths for basalt iceland la reunion is 5 1 whereas the wavelength ratio for basaltic andesite syracuse is 3 1 suggesting a compositional control on deformation as proposed by previous studies video analysis of incrementally folded syracuse lava crusts reveals significant non coaxial strain which violates the assumptions of plane strain used in crustal buckling models these results show that interpreting lava rheology from finite strain requires careful consideration of complex three dimensional strain fields despite these complexities the correlation between fold wavelength ratios and lava flow composition persists and may provide important insight into flow characterization

supervolcanoes within an ancient volcanic province in arabia terra mars several irregularly shaped craters located within arabia terra mars represent a new type of highland volcanic construct and together constitute a previously unrecognized martian igneous province similar to terrestrial supervolcanoes these low relief paterae possess a range of geomorphic features related to structural collapse effusive volcanism and explosive eruptions extruded lavas contributed to the formation of enigmatic highland ridged plains in arabia terra outgassed sulphur and erupted fine grained pyroclastics from these calderas probably fed the formation of altered layered sedimentary rocks and fretted terrain found throughout the equatorial region the discovery of a new type of volcanic construct in the arabia volcanic province fundamentally changes the picture of ancient volcanism and climate evolution on mars other eroded topographic basins in the ancient martian highlands that have been dismissed as degraded impact craters should be reconsidered as possible volcanic constructs formed in an early phase of widespread disseminated magmatism on mars several irregularly shaped craters located within arabia terra mars are interpreted as a new type of highland volcanic construct similar to supervolcanoes on earth fundamentally changing the picture of ancient volcanism and climate evolution on mars the geological evolution of mars is largely a story of volcanic activity about 70 of the planet s crust was resurfaced by basaltic volcanism but a significant fraction of that volcanic material is from unknown sources in this issue joseph michalski and jacob bleacher report new results suggesting that supervolcanoes existed in the arabia terra region of mars an area with many deposits of layered rocks of unknown origins that has not previously been considered a volcanic terrain they propose that ancient martian calderas might have been misinterpreted as impact craters that were degraded by erosion if supervolcanoes were common on ancient mars it would have major implications for estimates of volcanic outgassing climate evolution and formation of the planet s layered fragmented upper crust

plateaus and sinuous ridges as the fingerprints of lava flow inflation in the eastern tharsis plains of mars abstract the tharsis montes rift aprons are composed of outpourings of lava from chaotic terrains to the northeast and southwest flank of each volcano sinuous and branching channel networks that are present on the rift aprons suggest the possibility of fluvial processes in their development or erosion by rapidly emplaced lavas but the style of lava flow emplacement throughout rift apron development is not clearly understood to better characterize the style of lava emplacement and role of fluvial processes in rift apron development we conducted morphological mapping of the pavonis mons southwest rift apron and the eastern tharsis plains using images from the high resolution imaging science experiment hirise mars orbiter camera moc context camera ctx thermal emission imaging system themis and high resolution stereo camera hrsc along with the mars orbiter laser altimeter mola precision experiment data records pedrs and gridded data our approach was to 1 search for depositional fans at the slope break between the rift apron and adjacent low slope plains 2 determine if there is evidence that previously formed deposits might have been buried by plains units 3 characterize the tharsis plains morphologies east of pavonis mons and 4 assess their relationship to the rift apron units we have not identified topographically significant depositional fans nor did we observe evidence to suggest that plains units have buried older rift apron units flow features associated with the rift apron are observed to continue across the slope break onto the plains in this area the plains are composed of a variety of small fissures and low shield vents around which broad channel fed and tube fed flows have been identified we also find broad flat topped plateaus and sinuous ridges mixed among the channels tubes and vents flat topped plateaus and sinuous ridges are morphologies that are analogous to those observed on the coastal plain of hawai i where lava flows have advanced from the volcano s several degree flank onto the nearly zero degree coastal plain when local volumetric flow rates are low flow fronts tend to spread laterally and often thicken via endogenous growth or inflation of the sheet like flow units if flow advance is restricted by existing topography into narrow pathways inflation can be focused into sinuous elongate ridges the presence of plateaus and ridges emplaced from the rift zones across the plains to the east of pavonis mons and a lack of fan like features or evidence for their burial are consistent with rift apron lavas crossing a slope break with low local volumetric flow rates that led to inflation of sheet like and tube fed lava flows

analysis of active lava flows on kilauea volcano hawaii using sir c radar correlation measurements precise eruption rates of active pahoehoe lava flows on kilauea volcano hawaii have been determined using spaceborne radar data acquired by the space shuttle imaging radar c sir c a coastal site downslope from the pu9u o9o vent was imaged once per day on each of the four days of october 7 10 1994 day to day decorrelation due to resurfacing was determined by interferometric combination of the data at 15 m resolution over a wide area on successive days new lava resurfaced 335700 m 2 368775 m 2 and 356625 m 2 assuming an average pahoehoe flow thickness of 50 cm a mean effusion rate for this period is approximately 2 m 3 s the radar observations show persistent surface activity at each site rather than downslope migration of coherent lava flows

using satellite imagery to identify and analyze tumuli on earth and mars abstract tumuli are small dome like features that form when magmatic pressures build within a subsurface lava pathway causing the overlying crust to bulge upwards as the appearance of these features has been linked to lava flow structure e g underlying lava flow tubes and conditions there is interest in identifying such features in satellite images so they can be used to expand our understanding of lava flows within regions difficult to access such as on other planets here we define a methodology for identifying and measuring tumuli within satellite imagery and validate it by comparing our results with fieldwork results of terrestrial tumuli reported in the literature and with independent measurements we made within amboy field ca in addition we present aggregated results from the application of our methodology to satellite images of six terrestrial fields and seven martian fields with 2100 tumuli identified per planet comparisons of tumuli morphometrics on earth and mars yield similarities in size and overall shape which were surprising given the many differences in the environmental and planetary conditions within which these features have formed given our measurements we identify constraints for tumulus formation models and drivers that would yield similar shapes and sizes on two different planets furthermore we test a published hypothesis regarding the number of tumuli that form per a square kilometer and find it unlikely that a diagnostic tumuli density value exists

thermal mapping of a pāhoehoe lava flow kīlauea volcano abstract p hoehoe lava flows are a major component of hawaiian eruptive activity and an important part of basaltic volcanism worldwide in recent years p hoehoe lava has destroyed homes and threatened parts of hawai i with inundation and disruption in this study we use oblique helicopter borne thermal images to create high spatial resolution 1 m georeferenced thermal maps of the active p hoehoe flow on k lauea volcano s east rift zone thermal maps were created on 27 days during 2014 2016 in the course of operational monitoring encompassing a phase of activity that threatened the town of p hoa our results illustrate and reinforce how p hoehoe flows are multicomponent systems consisting of the vent master tube distributary tubes and surface breakouts the thermal maps accurately depict the distribution and character of p hoehoe breakouts through time and also delineate the subsurface lava tube surface breakouts were distributed widely across the p hoehoe flow with significant portions concurrently active well upslope of the flow front often concentrated in clusters of activity that evolved through time gradual changes to surface breakout distribution and migration relate to intrinsic processes in the flow including the slow evolution of the distributary tube system abrupt disruptions to this system and the creation of new breakouts and associated hazards were triggered by extrinsic forcing namely fluctuations in lava supply rate at the vent which disrupted the master lava tube although the total area of a p hoehoe flow has been suggested to relate to effusion rate our results show that changes in the proportion of expansion vs overplating can complicate this relationship by modifying existing techniques we estimate time averaged discharge rates for the flow during 2014 2016 generally in the range of 1 2 m 3 s 1 mean 1 3 0 4 m 3 s 1 less than half of k lauea s typical eruption rate on the east rift zone and suggestive of a weak eruptive regime during 2014 2016 we caution however that this discharge rate approach requires further independent corroboration the thermal maps provide the first synoptic characterization of p hoehoe flow activity at high spatial resolution essential both for operational hazard assessment and fundamental understanding of p hoehoe behavior

statistical distribution of tumuli on pahoehoe flow surfaces analysis of examples in hawaii and iceland and potential applications to lava flows on mars 1 spatial distributions of tumuli on lava flow surfaces can be quantitatively linked to subsurface inflation processes three distinct styles of flow emplacement are studied 1 lava flows undergo inflation that changes as a function of space and time resulting in random spatial distributions of tumuli 2 lava flows with preferred pathways result in systematic clustering of inflation features and 3 established tubes or narrow pahoehoe flows produce chains of tumuli statistical analyses are required to distinguish between styles one and two comparison of the spatial distribution of tumuli on a portion of a lava flow at mauna ulu with the poisson distribution indicates that tumuli are randomly distributed on the flow surface typical of style one emplacement where small scale topographic variability and low slope influence development of preferred pathways that evolve over time at thrainsskjoldur direct statistical comparisons to the poisson spatial distribution are inconclusive but nearest neighbor analysis indicates significant clustering an initially random spatial distribution is inferred that developed preferred pathways and systematic clustering of inflation features as with style two at elysium planitia on mars the flow margin is significantly deficient in inflation features while away from the margin the flow exhibits a random spatial distribution of tumuli typical of style one emplacement the flow is interpreted as multiple units or a single flow that migrated in space during emplacement at the 1843 flow on mauna loa tumuli occur on a linear trend consistent with style three emplacement

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

three long lava flows in north queensland the kinrara toomba and undara basaltic lava flows are from 55 to 160 km long and range in age from 13 to 190 ka the lavas were emplaced down low gradients 0 2 to 0 4 with volumes ranging up to 30 km3 they were not unusually hot at eruption 1130 1160 nor unusually fluid gentle topography controlled the flows and shallow drainage lines captured them lava tubes operated in places and some drained to form caves injection under surface crust was widespread producing inflation features ranging from tumuli and low plateaus to extensive ridges sustained eruption was essential for the development of the long flows but each is composite with pauses between successive pulses that partially covered the earlier longer flows the lava structures are mainly pahoehoe but some a a lavas are present of the three volcanoes involved undara is a simple low angle lava cone with a 200 m wide crater toomba is a low angled cone with several eruption centers and kinrara has a deep crater with evidence of strong fountaining effusion rates are not known but may have been relatively low similar to those observed in hawaiian volcanoes lava tubes most of which remained undrained are believed to have been of major importance in flow emplacement given the evidence of successive flows and the time needed to develop widespread inflation it is suggested that the two long flows over 100 km involved many decades of eruption

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

emplacement of inflated pāhoehoe flows in the naude s nek pass lesotho remnant karoo continental flood basalt province use of flow lobe tumuli in understanding flood basalt emplacement physical volcanological features are presented for a 710 m thick section of the naude s nek pass within the lower part of the lesotho remnant of the karoo large igneous province the section consists of inflated p hoehoe lava with thin impersistent sedimentary interbeds towards the base there are seven discreet packages of compound and hummocky p hoehoe lobes containing flow lobe tumuli making up approximately 50 of the section approximately 45 of the sequence consists of 14 sheet lobes between 10 and 52 m thick the majority of the sheet lobes are in two packages indicating prolonged periods of lava supply capable of producing thick sheet lobes the other sheet lobes are as individual lobes or pairs within compound flows suggesting brief increases in lava supply rate we suggest contrary to current belief that there is no evidence that compound flows are proximal to source and sheet lobes simple flows are distal to source and we propose that the presence of flow lobe tumuli in compound flows could be an indicator that a flow is distal to source we use detailed previously published studies of the thakurvadi formation deccan traps as an example we show that the length of a lobe and therefore the sections that are medial or distal to source are specific to each individual lobe and are dependent on the lava supply of each eruptive event and as such flow lobe tumuli can be used as an indicator of relative distance from source

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

characterization and evolution of fractures in low volume pahoehoe lava flows eastern snake river plain idaho we characterize fracture evolution in pahoehoe lava flows of the eastern snake river plain idaho and highlight significant differences to flood basalt sheet flows and implications for hydrologic models there are four distinct fracture types in east ern snake river plain flows 1 column bounding 2 column normal 3 entablature and 4 inflation fractures types 1 3 are driven by thermal stress whereas type 4 is induced by lava pressure from within the flow thermal stress distribution in a flow is dictated by its aspect ratio width height which controls the shape of isotherms isotherms control column bounding fracture orientations resulting in increasingly radial fracture patterns as the aspect ratio approaches unity column normal fractures form in response to thermal stress and fracture induced stress within basalt columns overlap in the timing of column bounding and column normal fracture growth has resulted in complex fracture relationships column normal fracture growth is strongly influenced by vesicular layers which act as mechanical heterogeneities creating preferential pathways for fracture growth as well as causing jogs or terminations along column bounding fractures eastern snake river plain entablatures which preserve the shape of the central lava core during the final stages of cooling have distinctly different origins and fracture styles compared to sheet flows entablatures formed by penetration of the edges of pressurized lava cores by inflation fractures causing rapid convective cooling in addition inflation fractures significantly perturb isotherm shapes in lava flows affecting flow scale fracture patterns and densities the overall effect of all these processes is a complex pattern of fracturing that attests to a strong impact by each fracture type on the growth behavior of all other fracture types

widespread inflation and drainage of a pāhoehoe flow field the nesjahraun þingvellir iceland this study describes the emplacement of the nesjahraun a basaltic lava flow that entered the lake ingvallavatn sw iceland high resolution remotely sensed data were combined with fieldwork to map the flow field onshore the nesjahraun exhibits a variety of textures related to the widespread inflation and collapse of a p hoehoe flow field its emplacement is interpreted as follows initially the eruption produced sheet p hoehoe in the central part of the flow field the lava has a platy ridged surface which is similar to some other lava flows in iceland and on mars here the texture is interpreted to have formed by unsteady inflation of the brittle crust of stationary sheet p hoehoe causing it to break into separate plates the ridges of broken p hoehoe slabs formed as the plates of crust moved vertically past each other in a process similar to the formation of shatter rings upstream fresh lava overflowed repeatedly from channels and tubes covering the surface with shelly p hoehoe formation of a 250 m wide open channel through the flow field allowed the inflated central part of the flow to drain rapidly this phase produced a lava which eroded the channel walls carrying broken p hoehoe slabs lava balls and detaching large 200 m long rafts of compound shelly p hoehoe lava much of this channelized lava flowed into the lake leaving a network of drained channels and tubes in the upstream part of the flow as in other locations the platy ridged texture is associated with a low underlying slope and high eruption rate here its formation was possibly enhanced by lateral confinement hindered entry into the lake and an elevated vent location we suggest that formation of this type of platy ridged lava where the plates are smooth and the ridges are slabs of broken p hoehoe can occur without significant horizontal transport as the surface crust is broken into plates in situ this reconstruction of the emplacement of the nesjahraun also demonstrates that high resolution aerial survey data are extremely useful in the mapping and measurement of lithofacies distributions in large flow fields but that fieldwork is still necessary to obtain the detailed textural information necessary to interpret them

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

terrestrial analogues for lunar impact melt flows abstract lunar impact melt deposits have unique physical properties they have among the highest observed radar returns at s band 12 6 cm wavelength implying that they are rough at the decimeter scale however they are also observed in high resolution optical imagery to be quite smooth at the meter scale these characteristics distinguish them from well studied terrestrial analogues such as hawaiian p hoehoe and a lava flows the morphology of impact melt deposits can be related to their emplacement conditions so understanding the origin of these unique surface properties will help to inform us as to the circumstances under which they were formed in this work we seek to find a terrestrial analogue for well preserved lunar impact melt flows by examining fresh lava flows on earth we compare the radar return and high resolution topographic variations of impact melt flows to terrestrial lava flows with a range of surface textures the lava flows examined in this work range from smooth hawaiian p hoehoe to transitional basaltic flows at craters of the moon cotm national monument and preserve in idaho to rubbly and spiny p hoehoe like flows at the recent eruption at holuhraun in iceland the physical properties of lunar impact melt flows appear to differ from those of all the terrestrial lava flows studied in this work this may be due to a differences in post emplacement modification processes or b fundamental differences in the surface texture of the melt flows due to the melts unique emplacement and or cooling environment information about the surface properties of lunar impact melt deposits will be critical for future landed missions that wish to sample these materials

tumuli and associated features from the western deccan volcanic province india whale back shaped uplifts called tumuli are common in the pahoehoe flows of the western deccan volcanic province dvp although they usually occur in hummocky flows they are also associated with thicker sheet lobes they have been subjected to a detailed morphometric and petrographic study for the first time the tumuli are characterised by positive relief and lava inflation clefts occupied by squeeze ups they display elongate as well as equant forms some are constituted of a single flow lobe whereas others display multiple flow lobes some tumuli appear to have developed along anastomosing tube systems the detailed study of one of the tumuli reveals considerable petrographic and textural variations among the constituent flow units some of these such as the enrichment of phenocrysts in squeeze ups and breakouts could be related to the emplacement dynamics of the tumulus all the observed tumuli display much evidence of inflation or endogenous growth field observations and measurements reveal that the tumuli and associated pahoehoe features display a close similarity with their hawaiian counterparts this is a very significant observation since it points out to a similarity in nature and style of eruptions in hawaii and at least in the western part of the dvp this has an important bearing on determining the short medium and long term effusion rates in the deccan however any concrete inference will have to await systematic volcanological studies of the lava features in the dvp