water magma interaction some theory and experiments on peperite formation experiments using molten thermite as a magma analog produce peperite when the melt interacts with wet sand these experiments also show explosive behavior developing strombolian and surtseyan like bursts the results demonstrate that the application of fuel coolant interaction fci theory is appropriate for interpretation of peperites the theory described includes discussion of the importance of mass interaction ratios of wet sediment and magma rs which determine thermal equilibrium temperature limits and contact interface dynamics the dynamics of the interface between magma and wet sediments involves heat transfer over a wide range of rates from passive quenching to explosive fragmentation a vapor film layer develops at the interface and acts both as an insulating barrier promoting passive quenching as well as a potential energy reservoir that can cause magma fragmentation mingling of the magma with wet sediments and explosive quenching when the vapor film becomes unstable an important parameter in determining the behavior of the vapor film is the value of rs which controls whether heat can be convectively removed from the layer as more is being added from its contact with magma if rs 1 for fully saturated sediments there is enough water in the sediments to make convective heat flow effective in quenching the magma but below that value there is the potential that the vapor film will be unstable producing highly dynamic phenomena including explosive fragmentation at values of rs 0 1 there is insufficient water to allow the escalation of explosive fragmentation

paleogene evolution of the kodiak islands alaska consequences of ridge trench interaction in a more southerly latitude the kodiak islands of alaska are principally composed of a late cretaceous and paleogene complex of accreted deep sea rocks an early paleocene magmatic event invaded the accretionary complex with mid ocean ridge basalt morb andesite and granodiorite geochemical evidence suggests both the andesite and granodiorite are mixtures of morb and sediment the volcanic rocks are interlayered with coarse clastic sediments and deformed with the latter the granodioritic intrusions with k ar ages as old as 62 ma postdate emplacement of the early paleocene sedimentary and volcanic rocks interaction of the subduction complex with the kula farallon ridge most simply explains this early paleocene magmatic episode paleomagnetic studies of the volcanic rocks indicate this interaction occurred at 40 3 6 north latitude which is 25 3 9 south of the expected position of the kodiak islands relative to north america the magmatic arc presently northwest of the kodiak accretionary complex was active during the late cretaceous and early paleocene diminished after the ridge trench interaction and resurged from late eocene into miocene time the magmatic resurgence is coeval with the obductive offscraping of eocene to oligocene submarine fan deposits in the kodiak islands the petrology of these fan deposits indicates they are the most likely proximal equivalent for the zodiac fan thereby limiting its relative motion with respect to the kodiak islands possible models accounting for the northward motion of the kodiak accretionary complex include 1 coupling the accretionary complex and possibly related arc to the northward moving kula plate and closing an ocean basin north of the arc in paleogene time 2 emplacing the kodiak accretionary complex at the northward limit of the paleomagnetic data with subsequent northward motion accomplished by closure of a small back arc basin and or intracontinental shortening and 3 transcurrent faulting and northward motion of the kodiak accretionary complex without the presently adjacent arc

accretion of southern alaska abstract paleomagnetic data from southern alaska indicate that the wrangellia and peninsular terranes collided with central alaska probably by 65 ma ago and certainly no later than 55 ma ago the accretion of these terranes to the mainland was followed by the arrival of the ghost rocks volcanic assemblage at the southern margin of kodiak island poleward movement of these terranes can be explained by rapid motion of the kula oceanic plate mainly from 85 to 43 ma ago according to recent reconstructions derived from the hot spot reference frame after accretion much of southwestern alaska underwent a counterclockwise rotation of about 50 as indicated by paleomagnetic poles from volcanic rocks of late cretaceous and early tertiary age compression between north america and asia during opening of the north atlantic 68 44 ma ago may account for the rotation

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

model for the origin of the yakutat block an accreting terrane in the northern gulf of alaska a composite oceanic and continental terrane the yakutat block is currently colliding with and accreting to north america in the northern gulf of alaska marine geophysical data indicate that the block has moved with the pacific plate during pliocene and quaternary time but are indeterminant about its previous movement history a model that explains some observed geologic and structural features of the block is that it originated as a result of subduction of the kula farallon spreading center beneath north america in this model the spreading center that formed the basaltic basement of the yakutat block was offset from a spreading center to the south by a left lateral transform fault 400 500 km long subduction of the northern spreading center about 45 m y ago sliced off part of the north america continental margin attached it to the kula plate and initiated northward movement of the composite terrane as the yakutat block during eocene and oligocene time migration of the southern spreading center toward north america truncated the yakutat block on the south and left a fossil fracture zone that is now seen as the transition fault the southern spreading center subducted about 25 m y ago and the yakutat block has since traveled with the pacific plate to southern alaska

a transition phase teleconnection of the pacific quasi decadal oscillation the atmospheric circulation patterns associated with the pacific quasi decadal oscillation qdo are investigated using available observational data from 1948 to 2007 previous studies indicate that the pacific qdo is characterized by a distinct lifecycle in the form of sea surface temperature sst patterns in the warm and cool phases of the pacific qdo the sst patterns resemble those associated with the el nino southern oscillation enso during the warm cool and cool warm transitions of the pacific qdo recurrent sst patterns are also clearly visible the rotated empirical orthogonal function analysis on the 10 15 year filtered data shows that the evolutions of sst and atmospheric circulation are well coupled while the warm cool phase pacific qdo generates an enso like circulation pattern the transition phases form a distinct short wave train emanating from southeast asia towards north america this short wave train is particularly robust in the streamfunction of water vapor flux diagnostic analyses of the heat budget the stationary wave flux and a barotropic model indicate that this short wave train is thermodynamically maintained and is likely forced by diabatic heating near southeast asia additional modulations of forcing sources in the western and eastern tropical pacific on this short wave teleconnection are also discussed

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

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

characteristics and origin of peperite involving coarse grained host sediment peperite involving basalt and polymictic volcanic conglomerate occurs in the pliocene ba volcanic group at yaqara in northern viti levu fiji because the host sediment is coarse grained and dominated by basalt clasts the peperite could be easily overlooked and mistaken for another coarse volcaniclastic facies however the presence of groups of basalt clasts that show jigsaw fit texture fluidally shaped basalt clasts with complete glassy margins gradational contacts with adjacent sedimentary facies and the absence of stratification indicate that molten basalt mingled with unconsolidated gravel using these criteria we show that other superficially similar coarse polymictic facies with fluidal basalt clasts are not peperite both blocky and fluidal basalt clasts occur together in the peperite the amoeboid basalt clasts in the fluidal peperite result from dismembering of ductile low viscosity relatively hot magma at this stage propagating magma lobes were probably insulated from direct contact with the wet sediment by a vapour film the angular polyhedral basalt clasts in the blocky peperite indicate brittle disintegration of somewhat cooler higher viscosity magma the presence of jigsaw fit texture and polyhedral clasts with glassy margins suggest that quench fragmentation of the basalt was important in the formation of the blocky peperite although there is no positive evidence for steam explosivity the presence of steam could be recorded by small quartz filled cavities that occur within the host sediment the co existence of fluidal and blocky basalt clasts is interpreted to reflect successive ductile then brittle fragmentation of intruding magma the change from fluidal to blocky peperite might have resulted from progressive cooling of the magma during intrusion and also from the breakdown of fluidisation when the limited supply of fine sediment in the host gravel was exhausted

quantitative experiments on phreatomagmatic explosions abstract an experimental set up for controlled generation of thermal explosions fuel coolant interactions has been built by an interdisciplinary research group of volcanologists physicists and engineering scientists the tee haus thermal explosion experiment during the last 3 years more than 500 experimental runs were performed aim of the project was not to build a mini volcano but to produce igniteable mixtures of water and hot melt on a small scale in order to investigate basic physical aspects such small scale mixtures however most probably also occur during phreatomagmatic events in nature mixtures of water and magma on a large scale may be modelled by combination of small elements earlier experimental studies of thermal explosions were carried out with the use of metal melts nearly exclusively therefore a carbonate melt approx 0 3 kg of 1 1 mass ratio na2co3 k2co3 was used for initial experimental series because of easy handling and more magma similarity by injection of water into this melt explosive mixtures were produced and ignited self triggering explosive interactions occurred in a wide melt temperature range 720 to 1040 c at melt temperatures exceeding 1000 c co2 increasingly degassed presence of non condensible gas bubbles in the melt strongly reduced the explosivity the intensity of explosions only slightly increased with higher melt temperatures but strongly increased with higher water injection velocities because of more intensive mixing a minimum injection velocity was found to be approx 0 7 m s 1 experiments with silicate melts derived from diverse remelted volcanic rocks were carried out with a slightly modified set up explosions were ignited by an additional trigger a shock wave of approx 8 j in volcanic systems shock waves of this magnitude are abundant volcanic tremor etc strong explosions with silicate melts were produced at melt temperatures between 1350 and 1750 c the produced explosions exerted repulsion forces of up to 24 000 n with a typical pulse duration of 1 ms carbonate melt resp 1 5 ms silicate melts the ejection velocity was found to be in a range between 200 and 400 m s 1 explosion energy values up to 500 j were calculated the maximum explosion pressure was calculated to be in the range between 10 and 100 mpa only part of the melt so called interactive melt reacts explosively with injected water most of the melt is passively ejected by and after the thermal explosion different fragmentation processes result in specific grain size and grain shape populations that can be distinguished from each other particles resulting from the fine fragmentation process that precedes and causes the thermal explosion are characterized by angular to subrounded shapes and grain sizes ranging from 20 m to 180 m the amount of interactive melt is proportional to the intensity of the explosion the maximum amount of water vapourized at the explosive interaction so called interactive water was estimated thus the water melt mass ratio for explosive interactions could be calculated the values range between 1 25 and 1 35 carbonate melt resp between 1 6 and 1 25 silicate melts

paleoclimatic evidence for cenozoic migration of alaskan terranes chronostratigraphic and paleoclimatic comparisons of microfossils from deep sea cores from samples of an exploratory drill hole and from dredged rock of the gulf of alaska with coeval microfossil assemblages on the north american continent provide constraints on the northward migration of the yakutat block the prince william terrane and the pacific plate during tertiary time the comparative paleolatitudes of microfauna and flora provide three main constraints 1 the prince william terrane was in its present position with respect to north america at high latitudes 50 5 n by middle eocene time 40 42 ma consistent with models derived from paleomagnetic data 2 the adjacent yakutat block was 30 5 south of its present position in early eocene 50 ma 20 5 south in middle eocene 40 44 ma and 15 5 south in late eocene time 37 40 ma thus requiring a northward motion of about 30 since 50 ma moreover the yakutat block was at least 10 south of the prince william terrane during eocene time these data are consistent with migration of the yakutat block with the pacific and kula plates for at least the last 50 ma 3 site 192 on the pacific plate was at about 15 5 n latitude in the late cretaceous 68 ma at 30 5 n in early eocene 50 ma at 40 5 n in middle eocene 40 44 ma at 45 5 n in late eocene 37 40 ma and north of 50 5 n in latest eocene to early oligocene time 34 37 ma these paleolatitudes based on planktonic foraminiferal assemblages indicate northward drift consistent with the north america pacific plate reconstructions from about 68 ma to 40 ma engebretson 1982 however from cretaceous to early eocene time faunal data indicate significantly lower latitudinal positions and from oligocwne to early miocene time significantly higher latitudinal positions these discrepancies can be explained by the northward expansion of tropical faunas during the globally warm early tertiary and southward expansion of cold subarctic faunas as a result of global cooling during oligocene time

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

subkilometer martian volcanoes properties and possible terrestrial analogs kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of mars based on examination of more than 12 000 high resolution viking orbiter images most of these very small cones are located in parts of eastern acidalia and utopia isidis elysium planitia measurements of base and pit diameter for some 2000 well resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater cone diameter ratios this suggests that the small cones had a similar origin with only minor variations in local conditions the acidalia cones are generally larger more widely distributed and occur on a greater variety of terrains than those in utopia isidis elysium based on morphology distribution and the crater cone ratio histograms the smallest martian cones may be similar to icelandic pseudocraters somewhat larger steeper cones with smaller crater cone ratios which also occur in eastern acidalia may be analogs of terrestrial cinder cones

biochronology and paleoclimatic implications of middle eocene to oligocene planktic foraminiferal faunas abstract planktic foraminiferal assemblages have been analyzed quantitatively in six dsdp sites in the atlantic site 363 pacific sites 292 77b 277 and indian ocean sites 219 253 in order to determine the nature of the faunal turnover during middle eocene to oligocene time biostratigraphic ranges of taxa and abundance distributions of dominant species are presented and illustrate striking similarities in faunal assemblages of low latitude regions in the atlantic pacific and indian oceans a high resolution biochronology based on dominant faunal characteristics and 55 datum events permits correlation between all three oceans with a high degree of precision population studies provide a view of the global impact of the paleoclimatic and paleoceanographic changes occurring during middle eocene to oligocene time planktic foraminiferal assemblage changes indicate a general cooling trend between middle eocene to oligocene time consistent with previously published oxygen isotope data major faunal changes indicating cooling episodes occur however at discrete intervals in the middle eocene 44 43 ma p13 the middle late eocene boundary 41 40 ma p14 p15 the late eocene 39 38 ma p15 p16 the eocene oligocene boundary 37 36 ma p18 and the late oligocene 31 29 ma p20 p21 with the exception of the e 0 boundary faunal changes occur abruptly during short stratigraphic intervals and are characterized by major species extinctions and first appearances the eocene oligocene boundary cooling is marked primarily by increasing abundances of cool water species this suggests that the e 0 boundary cooling which marks a major event in the oxygen isotope record affected planktic faunas less than during other cooling episodes planktic foraminiferal faunas indicate that the e 0 boundary event is part of a continued cooling trend which began during the middle eocene two hiatus intervals are recognized in low and high latitude sections at the middle late eocene boundary and in the late eocene p15 p16 these hiatuses suggest that vigorous bottom water circulation began developing in the middle eocene consistent with the onset of the faunal cooling trend and well before the development of the psychrosphere at the e 0 boundary

hydrovolcanic explosions the systematics of water pyroclast equilibration the initial contact of external water with erupting magma and the mass ratio of water to magma govern the development of hydrovolcanic phenomena the phase relations of water within the runout system and the separation of vapor or liquid from the pyroclasts explain gradational transitions between some pyroclastic flows base surges mud hurricanes mudflows and sheetfloods

a field investigation of the basaltic ring structures of the channeled scabland and the relevance to mars abstract the basaltic ring structure brs is a class of peculiar features only reported in the channeled scabland of eastern washington state they have been suggested to be good analogs however for some circular features on mars brss are found where pleistocene floods scoured the columbia river basin stripping off the uppermost part of the miocene columbia river basalt group and exposing structures that were previously embedded in the lava the odessa craters near odessa wa are 50 500 m wide brss that are comprised of discontinuous concentric outcrops of subvertically jointed basalt and autointrusive dikes detailed field investigation of the odessa craters in planform and a cross sectional exposure of a similar structure above banks lake wa lead us to propose that brss formed by concurrent phreatovolcanism and lava flow inflation in this model phreatovolcanic a k a rootless cones formed on a relatively thin active lava flow the lava flow inflated around the cones locally inverting topography tensile stresses caused concentric fracturing of the lava crust lava from within the molten interior of the flow exploited the fractures and buried the phreatovolcanic cones and subsequent erosive floods excavated the structures another population of brss near tokio station wa consists of single ringed raised rimmed structures that are smaller and more randomly distributed than the odessa craters we find evidence for a phreatovolcanic component to the origin as well and hypothesize that they are either flood eroded phreatovolcanic cones or odessa crater like brss this work indicates that brss are not good analogs to the features on mars because the martian features are found on the uneroded surfaces despite this the now superseded concepts for brs formation are useful for understanding the formation of the martian features

relative influences of the interdecadal pacific oscillation and enso on the south pacific convergence zone 1 the south pacific convergence zone spcz one of the most extensive features of the global atmospheric circulation is shown to vary its location according to both the polarity of the el nino southern oscillation enso and of the interdecadal pacific oscillation ipo we first demonstrate that the ipo can be regarded as the quasi symmetric pacific wide manifestation of the pacific decadal oscillation that has been described for the north pacific shifts in the position of the spcz related to enso on interannual time scales and to the ipo on decadal time scales appear to be of similar magnitude and are largely linearly independent a station pressure based index of variations in spcz latitude is shown to be significantly related to the polarity of the ipo when enso influences are accounted for movements of this sensitive section of the spcz have occurred in phase with those of the ipo since the 1890s

seismic reflection images of the crust of the northern part of the chugach terrane alaska results of a survey for the trans alaska crustal transect tact deep crustal seismic reflection data show strong reflections from the middle and lower crust of the convergent continental margin near the eastern end of the aleutian trench these data were collected across the border ranges fault system a major suture zone that separates the peninsular and chugach tectonostratigraphic terranes the chugach terrane consists of metamorphosed strongly deformed flysch subduction melange as well as blueschist and greenschist facies rocks even so highly reflective rocks lie at great depth within or beneath this terrane the shallow part of the seismic section 0 5 s reveals only a few reflections which undulate and interweave indicating that some of them originate outside of the plane of the seismic section other undulating events could reveal early cenozoic granitic plutons or antiformal stacks of rock imbricated along thrust faults in contrast to this shallow reflection pattern three reflection bands contain most of the events on the middle part of the seismic section 5 12 s or 12 34 km we interpret divergent reflections within the uppermost band 5 5 5 s as gently north dipping thrust faults and subparallel reflections truncated at the boundaries of the upper and middle bands may image a metamorphic foliation or thrust faults if the truncated reflections represent thrust faults then the reflection geometry suggests that subparallel roof and floor thrust faults bound imbricated rocks forming duplex structures the upper and middle bands are separated by an area on the seismic section that reveals few reflections this area correlates approximately in depth with a high velocity 7 5 km s layer evident in refraction models the poorly reflective high velocity unit might be volcanic rocks like those exposed in the structurally lowest part of the chugach terrane if so then the bottom of the poorly reflective rocks indicates the base of the chugach terrane rocks that cause the upper and middle reflection bands and the intervening poorly reflective volcanic rocks may form a midcrustal shear zone that is about 10 km thick the deepest band of subparallel reflections 30 35 km correlates closely in depth with the top of the wadati benioff zone associated with the underthrusting pacific plate the reflections probably stem from the decollement that separates lithospheric plates within the subduction zone this reflection band increases abruptly in thickness possibly indicating local underplating of subducted sediment no events from the oceanic moho have been recognized neither the border ranges fault system the suture between the chugach and peninsular terranes nor deep crustal layers of the peninsular terrane are evident in these seismic reflection data

accretion in the wake of terrane collision the neogene accretionary wedge off kenai peninsula alaska subduction accretion and repeated terrane collision shaped the alaskan convergent margin the yakutat terrane is currently colliding with the continental margin below the central gulf of alaska during the neogene the terrane s western part was subducted after which a sediment wedge accreted along the northeast aleutian trench this wedge incorporates sediment eroded from the continental margin and marine sediments carried into the subduction zone on the pacific plate prestack depth migration was performed on six seismic reflection lines to resolve the structure within this accretionary wedge and its backstop the lateral extent of the structures is constrained by high resolution swath bathymetry and seismic lines collected along strike accretionary structure consists of variably sized thrust slices that were deformed against a backstop during frontal accretion and underplating toward the northeast the lower slope steepens the wedge narrows and the accreted volume decreases notwithstanding a doubling of sediment thickness in the trench in the northeasternmost transect near the area where the terrane s trailing edge subducts no frontal accretion is observed and the slope is eroded the structures imaged along the seismic lines discussed here most likely result from progressive evolution from erosion to accretion as the trailing edge of the yakutat terrane is subducting

eocene underplating along the kodiak shelf alaska implications and regional correlations structural geology and geophysical data from the kodiak shelf suggest that the mesozoic rocks exposed on the shelf are structurally underlain at about 12 km depth by several kms of eocene age strata kinematic data from the late cretaceous to paleocene ghost rocks formation indicate that this formation and probably all of the kodiak islands were uplifted vertically to nearly their present elevations landward tilting and imbrication are not indicated the age of uplift is indicated by a regional angular unconformity of early eocene to early oligocene age that separates deep sea rocks from shallow water to non marine rocks the uplift of the accretionary prism is believed to have been caused by underplating of an eocene sedimentary sequence because 1 a band of seismic reflections that occur 12 to 20 km beneath the shelf is interpreted as the top of the underplated material and 2 an obductively offscraped sequence of eocene deep sea rocks crops out on the seaward side of the kodiak shelf suggesting that a thick trench fill sequence may have been present prior to uplift of the prism the underplated material is interpreted to be part of either a previously unrecognized turbidite fan of early eocene age or a proximal equivalent of the zodiac fan of late eocene to early oligocene age other possible on land remnants of the underplated material may be present in prince william sound the montague belt the gulf of alaska lower sections of the yakutat block and in the coast ranges of oregon and washington the large volume of underplated material beneath the kodiak shelf suggests that underplating may be the dominant process in the growth of convergent margins

ice volcano interaction of the 1996 gjalp subglacial eruption vatnajokull iceland volcanic eruptions under glaciers can cause dangerous floods and lahars1 2 3 and create hyaloclastite fragmented glassy rock mountains4 5 6 7 8 but processes such as the rate of heat transfer between ice and magma edifice formation and the response of the surrounding glacier are poorly understood because of the lack of data here we present observations from the fissure eruption at vatnajokull ice cap iceland in october 1996 in the 13 days of the eruption 3 km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6 7 km long and 200 300 m high under 500 750 m of ice meltwater of temperatures of 15 20 c flowed along a narrow channel at the glacier bed into the grimsvotn subglacial lake for five weeks before draining in a sudden flood or jokulhlaup subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path whereas elsewhere the glacier surface remained intact suggesting that subglacial eruptions do not trigger widespread basal sliding in warm based glaciers

late cenozoic offsets on the offshore connection between the fairweather and queen charlotte faults off southeast alaska abstract closely spaced seismic reflection profiles permit us to extend the onshore fairweather fault across the continental margin off southeast alaska to the queen charlotte fault evidence for quaternary movement along this major plate boundary includes 20 40 m high sea floor scarps offset subsurface seismic reflectors sea floor bathymetry that indicates as much as 70 km of right lateral offset in the last 1 m y 5 6 cm yr of movement on the onshore fairweather fault and recorded seismicity along the fault the fairweather queen charlotte fault system similar in dimension to the san andreas fault system is a dextral transform fault that truncates the continental margin of north america much of the late cenozoic motion between the pacific and north american plates has been taken up along the fault system the fairweather queen charlotte fault evolved to its present form after passage of the yakutat block the youngest of the allochthonous terranes that form southern alaska

physical controls and resulting morphological forms of quaternary ice contact volcanoes in western canada abstract volcanism in association with large quantities of ice manifests itself in a variety of morphological forms developed under differing physical conditions these physical conditions include the location amount thickness and type of confining ice the location and quantity of trapped water and the surrounding topography ice in the form of thick continental ice sheets thinner alpine glaciers or even perennial accumulations of snow can influence the resulting morphological form of the volcano the chemical composition of the erupting magma effusion rate and total erupted volume will also affect the shape of the resulting edifice quaternary volcanoes influenced by many of these factors are found in western canada the morphological forms range from tuyas to subglacial mounds to stratovolcanoes this paper provides a review of ice contact volcanism and volcanic products formed in these environments using canadian examples for illustration

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

late paleocene early eocene paleosols and a new measure of the transport distance of alaska s yakutat terrane abstractan intensely weathered paleosol representing a nearly isochronous landscape exists at many places in continental late paleocene early eocene strata in north america most commonly a single siderite spherule bearing horizon is found from which 18o values were obtained to construct a paleolatitudinal gradient for late paleocene early eocene north america comparison of the paleosol siderite spherule 18o composition from the displaced yakutat terrane of alaska to the north american paleolatitudinal gradient indicates that during the late paleocene early eocene the terrane existed at 44 paleonorth thus supporting hypotheses for a far traveled terrane history

mars a review and synthesis of general environments and geological settings of magma h2o interactions the advent of a global cryosphere likely occurred very early in the history of mars and much of the available water and related volatiles co 2 clathrates etc were sequestered within and below the cryosphere this means that magmatism plutonism and volcanism as a geological process throughout the history of mars cannot be fully understood without accounting for the interaction of magma and water and related species in both solid and liquid form we review and outline the probable configuration of water and ice deposits in the history of mars describe environments and modes of magma h 2o interaction and provide specific examples from the geological record of mars magma and water ice interactions have been interpreted to have formed 1 massive pyroclastic deposits 2 large scale ground collapse and chaotic terrain 3 major outflow channels 4 mega lahars dwarfing terrestrial examples 5 sub ice sheet eruptions and edifices 6 pseudocraters 7 landslides on volcanic edifice flanks and 8 hydrothermal sites the global nature of the cryosphere its longevity and the diversity of environments means that mars is an excellent laboratory for the study of magma h 2o interactions and the role of related volatile species

palaeomagnetism of volcanic rocks of the kodiak islands indicates northward latitudinal displacement in the past decade it has become widely accepted that southern alaska is composed of allochthonous terranes1 4 but the times of amalgamation and their accretion to north america remain controversial palaeomagnetists and geologists generally agree that the talkeetna superterrane consisting of the wrangellia and peninsular terranes fig 1 was far to the south of its present position with respect to north america in triassic and jurassic time1 4 this consensus is lost when it comes to the question of the relative position of these terranes in the tertiary previously limited palaeomagnetic evidence suggested that the peninsular terrane may have lain substantially south of its present position4 but the timing of deformational and thermal events and the apparent absence of a tertiary suture zone argue for a cretaceous docking of wrangellia and the peninsular terrane5 6 here we present new palaeomagnetic results demonstrating that the kodiak islands were indeed at a more southerly latitude 62 myr ago around 43 n and discuss the implications of this conclusion

updated streamflow reconstructions for the upper colorado river basin 1 updated proxy reconstructions of water year october september streamflow for four key gauges in the upper colorado river basin were generated using an expanded tree ring network and longer calibration records than in previous efforts reconstructed gauges include the green river at green river utah colorado near cisco utah san juan near bluff utah and colorado at lees ferry arizona the reconstructions explain 72 81 of the variance in the gauge records and results are robust across several reconstruction approaches time series plots as well as results of cross spectral analysis indicate strong spatial coherence in runoff variations across the subbasins the lees ferry reconstruction suggests a higher long term mean than previous reconstructions but strongly supports earlier findings that colorado river allocations were based on one of the wettest periods in the past 5 centuries and that droughts more severe than any 20th to 21st century event occurred in the past

continuous uplift near the seaward edge of the prince william sound megathrust middleton island alaska middleton island located at the seaward edge of the continental shelf 50 km from the base of the inner wall of the aleutian trench affords an opportunity to make land based measurements of uplift near the toe of the prince william sound megathrust site of the 1964 m 9 2 alaska earthquake leveling surveys 1973 1993 on middleton island indicate roughly uniform tilting 1 rad a down to the northwest of the island and gps surveys 1993 2012 show an uplift rate of 14 mm a of the island relative to fixed north america the data are consistent with a combined coseismic and postseismic uplift in meters due to the 1964 earthquake as a function of time years after the earthquake u 3 5 1 21 log10 1 1 67 h where 3 5 is the coseismic uplift and h is 0 for 0 and 1 otherwise the current uplift on middleton island is attributed to continuous slip on a fault splaying off from the megathrust and the long term uplift is the superposition of the effects of past earthquakes each earthquake being similar to the 1964 event then the predicted uplift at time t due to a sequence of earthquakes at times ti would be iut ti from studies of strandlines associated with the uplifted terraces on middleton island plafker et al 1992 estimated the occurrence times of the last six earthquakes and measured the present day elevations of those strandlines the predicted uplift is in rough agreement with those measurements about half of the predicted uplift is due to postseismic relaxation from previous earthquakes

clustering within rootless cone groups on iceland and mars effect of nonrandom processes 1 this study aims at quantifying the spatial distribution of cones within rootless cone groups rcgs our data set consists of 1 seven icelandic rcgs identified through field investigations 2 seven candidate rcgs on mars identified through mars orbiter camera moc and thermal emission imaging system themis images and 3 four groups of impact craters on mars also identified through moc and themis images to determine if they can be remotely distinguished from the rcgs purely on the basis of their spatial distribution several independent statistical techniques are used including nearest neighbor analysis analysis of variance anova and linear alignment detection analysis our results indicate that the spatial distribution of each rcg is not random within a cone group cones preferentially form near existing cones the presence of at least one significant linear cone alignment in each rcg and strong linear alignments in some groups suggests that rootless cones form as the surface signature of preferred lava pathways an anova on mean nearest neighbor distances reveals the martian cone groups to be statistically indistinguishable from the icelandic rcgs supporting existing interpretations that they represent rootless cone groups a similar anova showed that the martian cone groups do not resemble the martian impact crater clusters studied the impact craters have significantly greater nearest neighbor distances and show no evidence of aggregation within a crater group

using the characteristics of rootless cone deposits to estimate the energetics of explosive lava water interactions during volcanic eruptions the interaction of magma and groundwater can produce thermohydraulic explosions capable of significantly increasing the eruption energy the most well known mechanism by which explosive magma water interactions occur molten fuel coolant interaction mfci is a complex series of macro and microscale processes which have been simulated using laboratory scale experiments as a natural analog for mfci experiments we utilize rootless cone beds formed by lava water explosions to estimate explosion energy the specific mechanical energy of the lava water explosions studied here occurs over a broader range 4 to 178 kj kg than mfci experiments and includes estimates for the highest energy lava water explosions studied to date explosion energy is partitioned similarly over the two systems with kinetic transport and fragmentation energy making up 25 40 and 42 80 of the mechanical energy respectively which overlap the ranges estimated for mfci experiments our study of lava water explosions therefore provides a field scale analog of mfci laboratory experiments for understanding the energetics and therefore hazards of mfci in natural systems

icelandic pseudocraters as analogs to some volcanic cones on mars pseudocraters are rootless vents formed by the interaction of lava flows with surface or near surface water this interaction can produce mild explosions and the accumulation of scoria and spatter into small constructs pseudocraters in several localities in iceland were examined in the field and compared to similar appearing features observed on mars the icelandic pseudocrater cones in this study range in size from 6 to 70 m in diameter have summit craters which range from 2 to 28 m in diameter many cones lack craters entirely and have flanks that are either concave up or convex up the size and spacing of icelandic pseudocraters might be a function of the availability of water in which larger closely spaced features result from efficient lava water interaction as suggested by the environments in which the features formed possible martian pseudocrater cones in amazonis planitia range in diameter from 30 to 180 m and have craters 12 to 80 m in diameter a numerical model for volcanic explosions was adapted to study the formation of pseudocraters under terrestrial and martian conditions the results suggest that explosions forming martian cones require significantly less water calculated masses are less by a factor of 4 to 16 than those forming icelandic pseudocraters despite their larger sizes this is attributed to the low gravity and atmospheric pressure in the mars environment and is consistent with the likely lower abundance of water which might be present as interstitial ice at shallow depths in the regolith locations of potential pseudocraters on mars at latitudes as low as 8 n imply the presence of crustal ice stores at the time of their formation

north south precipitation patterns in western north america on interannual to decadal timescales the overall amount of precipitation deposited along the west coast and western cordillera of north america from 258 to 558n varies from year to year and superimposed on this domain average variability are varying north south contrasts on timescales from at least interannual to interdecadal in order to better understand the north south precipitation contrasts their interannual and decadal variations are studied in terms of how much they affect overall precipitation amounts and how they are related to large scale climatic patterns spatial empirical orthogonal functions eofs and spatial moments domain average central latitude and latitudinal spread of zonally averaged precipitation anomalies along the westernmost parts of north america are analyzed and each is correlated with global sea level pressure slp and sea surface temperature series on interannual defined here as 3 7 yr and decadal 7 yr timescales the interannual band considered here corresponds to timescales that are particularly strong in tropical climate variations and thus is expected to contain much p

mapping the megathrust beneath the northern gulf of alaska using wide angle seismic data in the northern gulf of alaska and prince william sound we have used wide angle seismic reflection refraction profiles earthquake studies and laboratory measurements of physical properties to determine the geometry of the prince william and yakutat terranes the aleutian megathrust and the subducting pacific plate in this complex region the yakutat terrane is underthrust beneath the prince william terrane and both terranes are interpreted to be underlain by the pacific plate wide angle seismic reflection refraction profiles recorded along five seismic lines are used to unravel this terrane geometry modeled velocities in the upper crust of the prince william terrane to 18 km depth agree closely with laboratory velocity measurements of orca group phyllites and quartzofeldspathic graywackes the chief components of the prince william terrane to hydrostatic pressures as high as 600 mpa 6 kbar a landward dipping reflector at depths of 16 24 km is interpreted as the base of the prince william terrane this reflector corresponds to the top of the wadati benioff zone seismicity and is interpreted as the megathrust immediately beneath the megathrust is a 4 km thick 6 9 km s refractor which we infer to be the source of a prominent magnetic anomaly and which is interpreted by us and previous workers to be gabbro in eocene age oceanic crust of the underthrust yakutat terrane wide angle seismic data magnetic anomaly data and tectonic reconstructions indicate that the yakutat terrane has been underthrust beneath the prince william terrane for at least a few hundred kilometers wide angle seismic data are consistent with a 9 to 10 landward dip of the subducting pacific plate beneath the outer shelf and slope distinctly different from the inferred average 3 to 4 dip of the overlying 6 9 km s refractor and the wadati benioff seismic zone beneath the inner shelf our preferred interpretation of the geophysical data is that one composite plate composed of the pacific plate of a fairly uniform thickness and the yakutat plate of varying thickness is subducting beneath southern alaska

athabasca valles mars a lava draped channel system athabasca valles is a young outflow channel system on mars that may have been carved by catastrophic water floods however images acquired by the high resolution imaging science experiment camera onboard the mars reconnaissance orbiter spacecraft reveal that athabasca valles is now entirely draped by a thin layer of solidified lava the remnant of a once swollen river of molten rock the lava erupted from a fissure inundated the channels and drained downstream in geologically recent times purported ice features in athabasca valles and its distal basin cerberus palus are actually composed of this lava similar volcanic processes may have operated in other ostensibly fluvial channels which could explain in part why the landers sent to investigate sites of ancient flooding on mars have predominantly found lava at the surface instead

reflections from midcrustal rocks within the mesozoic subduction complex near the eastern aleutian trench seismic reflection data collected in 1973 by western geophysical company show that highly reflective rocks make up the midcrust of the convergent margin adjacent to the eastern aleutian trench these rocks form an arch that strikes obliquely across the strongly expressed northeast southwest structural grain of exposed mesozoic rocks in an earlier report we proposed that the deep events mark the location of either the presently subducting plate or the top of underplated rocks however the short radius of curvature of this arch precludes the possibility that the deep events indicate the igneous oceanic crust instead the deep reflections could be from underplated rocks that have been arched by the imbrication or underplating of strata below the reflective rocks high amplitude water layer and interbed multiples prevent precise connection of shallow and deep geology for example the border ranges fault a suture between major tectonostratigraphic terranes is not revealed on any of our seismic sections we speculate however that one band of reflections that rises toward but does not reach the surface is from the eagle river thrust fault which separates late cretaceous melange from deformed turbidite sequences of the same age

lava water interaction and hydrothermal activity within the 2014 2015 holuhraun lava flow field iceland abstract lava that erupted during the 2014 2015 holuhraun eruption in iceland flowed into a proglacial river system resulting in aqueous cooling of the lava and an ephemeral hydrothermal system we carried out a monitoring study of this system from 2015 to 2018 to document the cooling of the lava over this time using thermocouple measurements and data logging sensors the heat loss rate from advection through this hydrothermal system in august 2015 was 5 5 108 w since eruption aqueous cooling likely accounted for 1 of the total heat loss from the lava this estimate excludes steam losses from fumaroles as well as any groundwater that was not released to the surface and thus is a lower bound near the terminus of the flow advection of heat by flowing water may have locally accounted for tens of percent of the total cooling of that part of the flow our data quantify the importance of water cooling for this lava flow and can be compared with models to better understand lava water interactions more generally we also provide detailed methods for simple low cost monitoring of similar instances in the future

tree ring based reconstruction of precipitation in the bighorn basin wyoming since 1260 a d abstract cores and cross sections from 79 douglas fir pseudotsuga menziesii and limber pine pinus flexilis trees at four sites in the bighorn basin of north central wyoming and south central montana were used to develop a proxy for annual june june precipitation spanning 1260 1998 a d the reconstruction exhibits considerable nonstationarity and the instrumental era post 1900 in particular fails to capture the full range of precipitation variability experienced in the past 750 years both single year and decadal scale dry events were more severe before 1900 dry spells in the late thirteenth and sixteenth centuries surpass both magnitude and duration of any droughts in the bighorn basin after 1900 precipitation variability appears to shift to a higher frequency mode after 1750 with 15 20 yr droughts becoming rare comparisons between instrumental and reconstructed values of precipitation and indices of pacific basin variability reveal that precipitation in the bighorn basin generally responds

topographic and stochastic influences on pahoehoe lava lobe emplacement a detailed understanding of p hoehoe emplacement is necessary for developing accurate models of flow field development assessing hazards and interpreting the significance of lava morphology on earth and other planetary surfaces active p hoehoe lobes on k lauea volcano hawai i were examined on 21 26 february 2006 using oblique time series stereo photogrammetry and differential global positioning system measurements during this time the local discharge rate for peripheral lava lobes was generally constant at 0 0061 0 0019 m3 s but the areal coverage rate of the lobes exhibited a periodic increase every 4 13 0 64 min this periodicity is attributed to the time required for the pressure within the liquid lava core to exceed the cooling induced strength of its margins the p hoehoe flow advanced through a series of down slope and cross slope breakouts which began as 0 2 m thick units i e toes that coalesced and inflated to become approximately meter thick lobes the lobes were thickest above the lowest points of the initial topography and above shallow to reverse facing slopes defined relative to the local flow direction the flow path was typically controlled by high standing topography with the zone directly adjacent to the final lobe margin having an average relief that was a few centimeters higher than the lava inundated region this suggests that toe scale topography can at least temporarily exert strong controls on p hoehoe flow paths by impeding the lateral spreading of the lobe observed cycles of enhanced areal spreading and inflated lobe morphology are also explored using a model that considers the statistical likelihood of sequential breakouts from active flow margins and the effects of topographic barriers

patterns of coherent decadal and interdecadal climate signals in the pacific basin during the 20th century two distinct low frequency fluctuations are suggested from a joint frequency domain analysis of the pacific ocean 30 s 60 n sea surface temperature sst and sea level pressure slp the lowest frequency signal reveals a spatially coherent interdecadal evolution in phase sst and slp anomalies are found along the subarctic frontal zone safz it is symmetric about the equator with tropical sst anomalies peaking near 15 latitudes in the eastern pacific the other low frequency signal reveals a spatially coherent decadal evolution it is primarily a low latitude phenomenon tropical sst anomalies peak in the central equatorial ocean with evidence of atmospheric teleconnections these interdecadal and decadal signals join the enso and quasi biennial signals in determining dominant patterns of pacific ocean natural climate variability relative phasing and location of the sst and slp anomalies for the decadal enso and the quasi biennial signals are similar to one another but significantly different from that of the interdecadal signal

tree ring reconstruction of the level of great salt lake usa utah s great salt lake gsl is a closed basin remnant of the larger pleistocene age lake bonneville the modern instrumental record of the gsl level i e elevation change is strongly modulated by pacific ocean coupled ocean atmospheric oscillations at low frequency and therefore reflects the decadalscale wet dry cycles that characterize the region a within basin network of seven tree ring chronologies was developed to reconstruct the gsl water year september august level based upon the instrumental record of gsl level from 1876 to 2005 the result was a 576 year reconstruction of the gsl level that extends from 1429 to 2005 all calibration verification tests commonly used in dendroclimatology were passed the reconstruction explains 48 of the variance in the instrumental gsl level and exhibits significant periodicity at sub decadal scales over the past six centuries meanwhile predominance of multi decadal periodicity in the early half of the record shifted to quasi decadal dominance in the latter half and this is consistent with that of proxy reconstructions of the pacific decadal oscillation the gsl level reconstruction is a crucial component to improving our insight into the possible controls of coupled ocean atmosphere interactions on precipitation delivery

paleomagnetism of the paleocene ghost rocks formation prince william terrane alaska the mean paleomagnetic inclination of paleocene volcanics from two regions on kodiak island in the ghost rocks formation suggests that the prince william terrane originated at mid latitudes about 25 south of its expected alaskan latitude in paleocene time the remanent magnetization of these rocks passes both the fold and reversal tests and is well constrained in age the mean declinations of the two regions however differ by approximately 120 suggesting they have rotated with respect to each other perhaps during emplacement we suggest that despite the lack of evidence for a major tertiary suture zone between the prince william terrane and central alaska the prince william and perhaps adjacent terranes may have lain substantially south of their present position in the early tertiary

fragmentation mechanisms associated with explosive lava water interactions in a lacustrine environment rootless cones form when partially outgassed lava interacts explosively with external water the explosions represent an end member system that can elucidate mechanisms of explosive magma water interactions in the absence of magmatic fragmentation induced by outgassing the proportion of finely fragmented ejecta i e ash generated in rootless explosions may contribute significantly to the energy of the explosion even if the ash volume is small relative to coarser ejecta laboratory experiments indicate that the degree of melt water mixing and energy release are proportional to the abundance of blocky grains fragmented by brittle disintegration which effectively contribute thermal energy to the system to constrain the mechanisms and dynamics of rootless explosive activity we assess the nature and modes of fragmentation and ejecta characteristics through morphological textural and density analysis of rootless tephra associated with a p hoehoe lava flow in a lacustrine lake basin environment we observe strong correlations between the mean grain size and the mass percentage of both blocky negative power law trend and fluidal positive logarithmic tephra clasts of all sizes we interpret these trends as scale dependent fragmentation behavior due to the decreasing efficacy of hydrodynamic fragmentation as it occurs over finer scales especially over the ash size range additionally all analyzed beds contain fine ash sized blocky and mossy clasts which are thought to be diagnostic of a high transfer rate of thermal to mechanical energy characteristic of molten fuel coolant interactions these results agree with a recent model of rootless cone formation prior fragmentation theory and scaled laboratory experiments and therefore provide a field based analog for future experimental and modeling efforts

morphology of rubbly pahoehoe simple flows from the deccan volcanic province implications for style of emplacement abstract lava flows with preserved bases and brecciated upper crusts constitute a morphological type that differs in character from typical pahoehoe and a a such flows have been reported from many provinces around the world previous studies had referred to these flows informally as pahoehoe flows with rubbly tops broken top pahoehoe and rubbly pahoehoe recent studies have formally applied the latter term to describe parts of the well studied laki flow in iceland as well as flows from the columbia river basalt province rubbly pahoehoe flows are abundant in the upper stratigraphic formations of the deccan volcanic province dvp and are more commonly known as simple flows this study presents detailed observations of such flows from various parts of the dvp and discusses their implications for understanding flow emplacement these flows which appear to be single units at the outcrop scale are generally much thicker and significantly more extensive than individual pahoehoe lobes that dominate the lower formations of the deccan stratigraphy they are characterised by preserved gently undulating tachylitic bases but variably disrupted crustal zones that grade into flow top breccias the breccias are constituted of highly vesicular and oxidised fragments of varying sizes that appear to have been derived from previously formed pahoehoe crusts previous work has indicated that the morphology of these flows might be related to initial inflation accompanied by rapid volatile exsolution and an increase in effusion rate and or viscosity with time this agrees reasonably well with the qualitative and quantitative models of emplacement developed for the laki flow the abundance of such flows in the upper formations of the deccan stratigraphy clearly hints at a significant shift in the nature of the deccan eruptions this could be indicative of higher eruption rates during this period this in turn raises the possibility of hazardous impact on the climate during the eruption of these flows which is also discussed in the paper

coherence between the great salt lake level and the pacific quasi decadal oscillation the lake level elevation of the great salt lake gsl a large closed basin lake in the arid western united states is characterized by a pronounced quasi decadal oscillation qdo the variation of the gsl elevation is very coherent with the qdo of sea surface temperature anomalies in the tropical central pacific also known as the pacific qdo however such coherence denies any direct association between the precipitation in the gsl watershed and the pacific qdo because in a given frequency the precipitation variation always leads the gsl elevation variation therefore the precipitation variation is phase shifted from the pacific qdo this study investigates the physical mechanism forming the coherence between the gsl elevation and the pacific qdo pronounced and coherent quasi decadal signals in precipitation streamflow water vapor flux and drought conditions are found throughout the great basin recurrent atmospheric circulation patterns develop over the gulf of alaska during the warm to cool and cool to warm transition phases of the pacific qdo these circulation patterns modulate the water vapor flux associated with synoptic transient activities over the western united states and in turn lead to the qdo in the hydrological cycle of the great basin as the gsl integrates the hydrological responses in the great basin the hydrological qdo is then transferred to the gsl elevation because the gsl elevation consistently lags the precipitation by a quarter phase about 3 yr in the quasidecadal time scale these processes take an average of 6 yr for the gsl elevation to eventually respond to the pacific qdo this creates a half phase delay of the gsl elevation from the pacific qdo thereby forming the inverse yet coherent relationship between them tree ring reconstructed precipitation records confirm that the quasi decadal signal in precipitation is a prominent feature in this region

paleolatitudes versus time for southern alaska paleomagnetic determinations of the inclination of the ancient geomagnetic field for localities in the alaska peninsula wrangellia chugach and kuskokwim tectonostratigraphic terranes of alaska show systematic northward motion from late cretaceous time until the present prior to this the ambiguity of polarity of the ancient geomagnetic field allow several interpretations however the preferred interpretation involves southerly motion of the terranes from triassic to early jurrassic time and steady northward motion from then up to the present the latitudinal rate is about 6 cm yr

a subaqueous rootless cone field at niuluut disko paleocene of west greenland abstract during the formation of the lavas of the malig t formation 60 ma on disko in west greenland lava flows erupted from subaerial vents were emplaced into an extensive and deep lake resulting in the formation of hyaloclastite breccias subaqueous lava flows and invasive flows in the central part of the lake unusual mounds of volcaniclastic material mingled with sediment were formed on the lake floor two well exposed mounds are about 25 m high and 100 200 m wide and each is composed of three normally graded units the lowest units are coarse deposits with pillows pillow fragments and large shale fragments fining upwards through lapilli tuff into tuffaceous layers rich in small shale clasts the upper units in the mounds are tuffaceous with sediment matrix and grade into dark shale horizons each mound has a central sediment filled chimney the mounds are overlain by 2 8 m shale followed by a c 50 m thick subaqueous lava flow that disturbed the soft sediments and filled local depressions between the mounds the mounds are interpreted as subaqueous rootless cones that formed by hydroclastic explosions where a subaqueous lava flow was locally brecciated throughout thereby providing outlets for the pressurized and heated water in the underlying mud the three normally graded units in the mounds may correspond to successive flow pulses in the central liquid part of the flow the distribution of breccia deposits and lava pillars suggests the presence of a rootless cone field around 1 5 km in diameter the structure of the mounds contrasts to the structure of subaerial rootless cones which have inversely graded units and upwards decreasing amounts of sediment this is explained by higher water magma mass ratios in the subaqueous than in the subaerial environment which were situated on either side of an explosive energy maximum in both environments the water magma mass ratio decreased during formation of the cones but the explosivity of the subaqueous cones moved towards the maximum whereas the explosivity of the subaerial cones moved away from the maximum

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

rootless cones on mars indicating the presence of shallow equatorial ground ice in recent times high resolution mars orbiter camera moc images have revealed the existence of clusters of small cones in the cerberus plains marte valles and amazonis planitia mars these cones are similar in both morphology and planar dimensions to the larger of icelandic rootless cones which form due to explosive interactions between surficial lavas and near surface groundwater impact crater size frequency relationships indicate that surfaces upon which the cones sit are no older than 10 ma if martian cones form in the same manner as terrestrial rootless cones then equatorial ground ice or ground water must have been present near the surface in geologically recent times

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

structures textures and cooling histories of columbia river basalt flows flood basalt flows of the columbia river basalt group commonly exhibit well developed colonnade and entablature structures formed during cooling of individual flows the colonnade refers to the well defined columnar structure of many flows which appears in the lowermost 10 to 30 and in places the uppermost 10 to 20 entablature refers to those parts of a flow that have smaller column diameters and more irregular pattern fractures than those of colonnade entablature commonly occupies the central 60 to 70 of a flow in some cases however the entablature is interrupted by colonnade in such cases the entablature and colonnade may be repeated once or twice within a single flow in other cases flows may lack an entablature entirely petrographic examination reveals a pronounced correlation between structural and textural features thin sections of colonnade basalt have relatively coarse cruciform or octahedral fe ti oxide crystals and 20 glassy mesostasis the central entablature basalt in contrast has much more mesostasis as much as 60 and has textural features such as feathery fe ti oxide crystals indicative of more rapid cooling these features are the reverse of what might be expected for normal conductive cooling because cooling rates at the flow margins should be greater than those in the flow interior we reconciled the observed basalt textures with thermal models by taking into account rainfall and deranged drainage during crystallization of the flow downward migration of water through cracks would cause convective cooling of underlying unsolidified lava this effect and its consequences have been modeled numerically in order to clarify the physical constraints on the mechanism by which the central part of the lava can be quenched we have found that a water infiltration front can explain the presence of a thick quenched flow interior provided that the infiltration front moves downward just behind the lava solidification front despite heavy rainfall on hawaii for example 250 cm yr at kilauea iki exposed prehistoric lava flows on that island exhibit only colonnades we deduce from this that heavy rainfall alone is inadequate to quench flow interiors extensive flooding by deranged drainage or perhaps extremely heavy rainfall 250 cm yr is apparently required to produce entablatures the model also can be used to explain the occurrence of repeated entablature and colonnade by considering the effects of intermittent inundation the imposition of boundary conditions that mimic the removal and reoccurrence of flooding yields cooling histories that are consistent with the development of multiple colonnades and entablatures

characteristics of rootless cone tephra emplaced by high energy lava water explosions the effects of external water during hydrovolcanic eruptions are difficult to quantify however research investigating the explosive interactions between surface lava flows and water has provided new insights into explosion dynamics previous work has focused on relatively low energy lava water explosions from a 100 m diameter cone in the rau holar cone group in iceland for comparison we study ejecta derived from higher energy explosions at the 400 m diameter pu u k holo rootless cone in hawai i one of the largest rootless cones on earth this comparative approach elucidates the effect of lava water mixing conditions and range of explosivity on ejecta characteristics utilizing grain size analysis we found that pu u k holo beds typically have median grain sizes at the cone rim that are smaller than 3 8 mm and are on average finer grained than those of the rau holar cone ash sized grains the most energetically significant ejecta size fraction typically make up 20 of bed ejecta with a maximum of 90 both greater proportions than found in beds of the rau holar cone utilizing grain morphology crystal texture and surface feature analysis we found that the abundance of ash sized grains associated with high heat transfer rates i e active particles increases at pu u k holo as explosivity increases which is an important consideration for energy modeling this dataset also includes ejecta from the finest grained beds and therefore highest energy lava water explosions studied to date

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

middle oligocene cooling from equatorial pacific dsdp site 77b an apparently complete 150 m oligocene sequence of pelagic sediment at equatorial pacific deep sea drilling project site 77b has been analyzed for stable isotope and quantitative planktonic foraminiferal studies lower abundance of inferred warm water species and enrichment of 18 o and 12 c in foraminiferal tests during the interval 29 to 32 m y ago suggest cooler climate lowered sea level and significant volume of continental ice compared to earlier and later times in the oligocene

explosive lava water interactions in elysium planitia mars geologic and thermodynamic constraints on the formation of the tartarus colles cone groups 1 volcanic rootless constructs vrcs are the products of explosive lava water interactions vrcs are significant because they imply the presence of active lava and an underlying aqueous phase e g groundwater or ice at the time of their formation combined mapping of vrc locations age dating of their host lava surfaces and thermodynamic modeling of lava substrate interactions can therefore constrain where and when water has been present in volcanic regions this information is valuable for identifying fossil hydrothermal systems and determining relationships between climate near surface water abundance and the potential development of habitable niches on mars we examined the western tartarus colles region 25 27 n 170 171 e in northeastern elysium planitia mars and identified 167 vrc groups with a total area of 2000 km2 these vrcs preferentially occur where lava is 60 m thick crater size frequency relationships suggest the vrcs formed during the late to middle amazonian modeling results suggest that at the time of vrc formation near surface substrate was partially desiccated but that the depth to the midlatitude ice table was 42 m this ground ice stability zone is consistent with climate models that predict intermediate obliquity 35 between 75 and 250 ma with obliquity excursions descending to 25 32 for lava thicknesses ranging from 30 to 60 m and ground ice fractions ranging from 0 1 to 0 3 an ice volume of 4 23 km3 could have been melted and or vaporized by the time the lava solidified and the associated hydrothermal systems could have retained temperatures 273 k for up to 1300 years

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

explosive lava water interactions ii self organization processes among volcanic rootless eruption sites in the 1783 1784 laki lava flow iceland we have applied quantitative geospatial analyses to rootless eruption sites in the hnuta and hrossatungur groups of the 1783 1784 laki lava flow to establish how patterns of spatial distribution can be used to obtain information about rootless cone emplacement processes and paleo environments this study utilizes sample size dependent nearest neighbor nn statistics and voronoi tessellations to quantify the spatial distribution of rootless eruption sites and validate the use of statistical nn analysis as a remote sensing tool our results show that rootless eruption sites cluster in environments with abundant lava and water resources but competition for limited groundwater in these clusters can cause rootless eruption sites to develop repelled distributions this pattern of self organization can be interpreted within the context of resource availability and depletion topography tends to concentrate lava fuel and water coolant within topographic lows thereby promoting explosive lava water interactions in these regions given an excess supply of lava within broad sheet lobes rootless eruption sites withdraw groundwater from their surroundings until there is insufficient water to maintain analogs to explosive molten fuel coolant interactions rootless eruption sites may be modeled as a network of water extraction wells that draw down the water table in their vicinity rootless eruptions at locations with insufficient groundwater may either fail to initiate or terminate before explosive activity has ceased at nearby locations with a greater supply of water thus imparting a repelled distribution to observed rootless eruption sites

syn and posteruptive hazards of maar diatreme volcanoes abstract maar diatreme volcanoes represent the second most common volcano type on continents and islands this study presents a first review of syn and posteruptive volcanic and related hazards and intends to stimulate future research in this field maar diatreme volcanoes are phreatomagmatic monogenetic volcanoes they may erupt explosively for days to 15 years above the preeruptive surface a relatively flat tephra ring forms below the preeruptive surface the maar crater is incised because of formation and downward penetration of a cone shaped diatreme and its root zone during activity both the maar crater and the diatreme grow in depth and diameter inside the diatreme which may penetrate downwards for up to 2 5 km fragmented country rocks and juvenile pyroclasts accumulate in primary pyroclastic deposits but to a large extent also as reworked deposits ejection of large volumes of country rocks results in a mass deficiency in the root zone of the diatreme and causes the diatreme fill to subside thus the diatreme represents a kind of growing sinkhole due to the subsidence of the diatreme underneath the maar crater is a subsidence crater and also grows in depth and diameter with ongoing activity as long as phreatomagmatic eruptions continue the tephra ring grows in thickness and outer slope angle syneruptive hazards of maar diatreme volcanoes are earthquakes eruption clouds tephra fall base surges ballistic blocks and bombs lahars volcanic gases cutting of the growing maar crater into the preeruptive ground formation of a tephra ring fragmentation of country rocks thus destruction of area and ground changes in groundwater table and potential renewal of eruptions the main hazards mostly affect an area 3 to possibly 5 km in radius distal effects are comparable to those of small eruption clouds from polygenetic volcanoes syneruptive effects on infrastructure people animals vegetation agricultural land and drainage are pointed out posteruptive hazards concern erosion and formation of lahars inside the crater a lake usually forms and diverse types of sediments accumulate in the crater volcanic gases may be released in the crater compaction and other diagenetic processes within the diatreme fill result in its subsidence this posteruptive subsidence of the diatreme fill and thus crater floor is relatively large initially but will decrease with time it may last millions of years various studies and monitoring are suggested for syn and posteruptive activities of maar diatreme volcanoes erupting in the future the recently formed maar diatreme volcanoes should be investigated repeatedly to understand more about their syneruptive behaviour and hazards and also their posteruptive topographic limnic and biologic evolution and potential posteruptive hazards for future maar diatreme eruptions a hazard map with four principal hazard zones is suggested with the two innermost ones having a joint radius of up to 5 km areas that are potentially endangered by maar diatreme eruptions in the future are pointed out

generation of pyroclastic flows by explosive interaction of lava flows with ice water saturated substrate abstract we describe a new type of secondary rootless phreatomagmatic explosions observed at active lava flows at volcanoes klyuchevskoy russia and etna italy the explosions occurred at considerable up to 5 km distances from primary volcanic vents generally at steep 15 35 slopes and in places where incandescent basaltic or basaltic andesitic lava propagated over ice water saturated substrate the explosions produced high up to 7 km vertical ash steam laden clouds as well as pyroclastic flows that traveled up to 2 km downslope individual lobes of the pyroclastic flow deposits were up to 2 m thick had steep lateral margins and were composed of angular to subrounded bomb size clasts in a poorly sorted ash lapilli matrix character of the juvenile rock clasts in the pyroclastic flows poorly vesiculated with chilled and fractured cauliflower outer surfaces indicated their origin by explosive fragmentation of lava due to contact with external water non juvenile rocks derived from the substrate of the lava flows comprised up to 75 in some of the pyroclastic flow deposits we suggest a model where gradual heating of a water saturated substrate under the advancing lava flow elevates pore pressure and thus reduces basal friction in the case of frozen substrate water is initially formed by thawing of the substrate along the contact with lava on steep slope this leads to gravitational instability and sliding of a part of the active lava flow and water saturated substrate the sliding lava and substrate disintegrate and intermix triggering explosive fuel coolant type interaction that produces large volume of fine grained clastic material relatively cold steam laden cloud of the phreatomagmatic explosion has limited capacity to transport upward the produced clastic material thus part of it descends downslope in the form of pyroclastic flow similar explosive events were described for active lava flows of llaima chile pavlof alaska and hekla iceland indicating that this type of explosions and related hazard is common at snow ice clad volcanoes and sometimes happens also on fluid saturated hydrothermally altered slopes

discrete blasts in granular material yield two stage process of cavitation and granular fountaining a discrete blast within granular material such as a single subterranean explosion within a debris filled diatreme structure is typically considered to produce a single uprush of material our experiments demonstrate that apparent debris jet deposits can be formed by a two stage process of cavitation and subsequent granular fountaining bench scale experiments reported here demonstrate that for a range of overpressures and depths individual discrete buried gas blasts open space and expel particles from the blast site in two largely decoupled stages expanding gas initially pierces material nearest the blast source to open a cavity above it then a fountain of grains rises from the source into the cavity this staged motion dynamically segregates source grains from host material grains and the rates of cavity opening versus fountain rise show a power law decay relationship with initial pressure our experimental analysis has implications for maar diatreme systems field scale detonation experiments and underground nuclear testing

a possible transoceanic tsunami directed toward the u s west coast from the semidi segment alaska convergent margin the semidi segment of the alaska convergent margin appears capable of generating a giant tsunami like the one produced along the nearby unimak segment in 1946 reprocessed legacy seismic reflection data and a compilation of multibeam bathymetric surveys reveal structures that could generate such a tsunami a 200 km long ridge or escarpment with crests 1 km high is the surface expression of an active out of sequence fault zone recently referred to as a splay fault such faults are potentially tsunamigenic this type of fault zone separates the relatively rigid rock of the margin framework from the anelastic accreted sediment prism seafloor relief of the ridge exceeds that of similar age accretionary prism ridges indicating preferential slip along the splay fault zone the greater slip may derive from quaternary subduction of the patton murray hot spot ridge that extends 200 km toward the east across the north pacific estimates of tsunami repeat times from paleotsunami studies indicate that the semidi segment could be near the end of its current inter seismic cycle gps records from chirikof island at the shelf edge indicate 90 locking of plate interface faults an earthquake in the shallow semidi subduction zone could generate a tsunami that will inundate the us west coast more than the 1946 and 1964 earthquakes because the semidi continental slope azimuth directs a tsunami southeastward this article is protected by copyright all rights reserved

lava and ice interaction at stratovolcanoes use of characteristic features to determine past glacial extents and future volcanic hazards structures resulting from lava and ice interaction are common at glaciated stratovolcanoes during summit eruptions at stratovolcanoes meltwater is produced and travels freely down steep slopes and thin permeable valley glaciers eroding the ice and enlarging preexisting glacial drainages as a result eruptions in this environment have produced few catastrophic floods lava flowing into the open channels and voids in the glaciers becomes confined and grows thicker filling the available space and producing steep sided bodies with smooth bulbous contact surfaces quenching of lava against ice or by water forms small scale features such as tensional fractures and glass as the amount of meltwater in contact with the lava increases the type and abundance of smaller scale features become similar to those produced during subglacial eruptions into meltwater lakes identification of large and small scale lava ice contact features in the field can be used to reconstruct paleoglacial extent and combined with geochronology of lavas to determine past paleoclimate an understanding of lava ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volcanoes

some geometrical aspects of uncertainties in combined plate reconstructions the uncertainties in both the position of a pole of rotation and the rotation angle describing a plate reconstruction depend not only on the number and quality of data used but also on two geometrical factors the length of plate boundary represented by the data and the distance from the best fit pole to the center of the data region we describe a simple geometrical method that can be used to calculate minimum uncertainties in reconstructions based on positions of magnetic anomalies and fracture zones with finite uncertainties uncertainties in pole positions and angles corresponding to 10 km uncertainty in individual data points can when combined yield uncertainties in reconstructed positions greatly in excess of 10 km per rotation for example an uncertainty of 10 km in anomaly 6 reconstructions in the south pacific southeast indian northwest indian and north atlantic oceans would result in uncertainty of up to 190 km in the reconstructed position of the pacific plate with respect to north america at 19 8 m y b p existing data show that the realistic uncertainties for this case are twice as large as the calculated minimum uncertainties

rootless cones on mars a consequence of lava ground ice interaction fields of small cratered cones on mars are interpreted to have formed by rootless eruptions due to explosive interaction of lava with ground ice contained within the regolith beneath the flow melting and vaporization of the ice and subsequent explosive expansion of the vapour act to excavate the lava and construct a rootless cone around the explosion site similar features are found in iceland where flowing lava encountered water saturated substrates the martian cones have basal diameters of c 30 1000 m and are located predominantly in the northern volcanic plains high resolution mars orbiter camera images offer significant improvements over viking data for interpretation of cone origins a new model of the dynamics of cone formation indicates that very modest amounts of water ice are required to initiate and sustain the explosive interactions that produced the observed features this is consistent with the likely low availability of water ice in the martian regolith the scarcity of impact craters on many of the host lava flows indicates very young ages suggesting that ground ice was present as recently as less than 10 l00 ma and may persist today rootless cones therefore act as a spatial and temporal probe of the distribution of ground ice on mars which is of key significance in understanding the evolution of the martian climate the location of water in liquid or solid form is of great importance to future robotic and human exploration strategies and to the search for extraterrestrial life

rootless cone eruption processes informed by dissected tephra deposits and conduits rootless cones result from the explosive interaction between lava flows and underlying water saturated sediment or volcaniclastic deposits rootless explosions can represent a significant far field hazard during basaltic eruptions but there are few detailed studies of their deposits a rootless cone field in the 8 5 ma ice harbor flow field of the columbia river basalt province nw usa is revealed by sections through rootless conduit and cone structures the ice harbor lava flow hosting the rootless cones was emplaced across a floodplain or lacustrine environment that had recently been mantled by a layer of silicic volcanic ash from a major explosive eruption our observations indicate a two stage growth model for the rootless cones 1 initial explosions generated sediment rich tephra emplaced by fallout and pyroclastic density currents and 2 later weaker explosions that generated spatter rich fountains variable explosive activity resulted in a wide range of pyroclast morphologies and vesicularities cross sections through funnel shaped conduits also show how the conduits were constructed and stabilised the growth model is consistent with decreasing water availability with time as inferred for rootless cones described in iceland the ice harbor rootless cones provide further lithological data to help distinguish between rootless cone derived tephra and tephra generated above an erupting dyke

the morphology and formation of flow lobe tumuli on icelandic shield volcanoes three types of tumuli are recognized on monogenetic shield volcanoes in iceland namely 1 lava coated tumuli 2 upper slope tumuli and 3 flow lobe tumuli flow lobe tumuli grade into lava rises which are larger inflation structures but both structures have a similar mode of emplacement the areal distribution of flow lobe tumuli in the flow field differs from that of lava coated tumuli and upper slope tumuli flow lobe tumuli are frequent in the medial and distal parts of pahoehoe flow fields whereas the other two tumulus types are more frequent in the proximal parts of the flow fields the flow lobe tumuli also differ from the two other tumulus types as regards their morphology they are significantly larger have shallower flanks and do not have extensive outflows from the cracks the vesicle distribution within the flow lobe tumuli is similar to that of p type flow lobes a fairly dense zone is situated between the upper and lower vesicular zones each flow lobe tumulus is an individual lobe that inflates and forms tension cracks in the lava crust major lava tubes are mostly absent from the areas where flow lobe tumuli form and therefore the emplacement of flow lobe tumuli must be related to secondary short lived pathways of lava the flow lobe tumuli inside the flow fields of icelandic shield volcanoes are morphologically identical to those flow lobe tumuli that are found in the margins of flow fields of other icelandic volcanoes these observations allow us to model the flow lobe tumuli as morphological variants of p type flow lobes forming along terminating secondary lava paths flow lobe tumuli form at low lava supply rates of the order of 10 2 10 5 m3 s and are generated by inflation of the lava crust as a result of magmatic overpressure in the associated lava core we model the tumulus as a circular elastic plate that becomes uplifted inflated and fractured by a uniform magmatic overpressure at its bottom we conclude that 1 the effective thickness of the lava crust that is subject to bending is 0 2 0 4 m and remains essentially constant during the formation of the tumulus and 2 for flow lobe tumuli that are supplied with magma from tubes that originate in overflow from the lava lake of a shield volcano the elevation difference between the tumuli and the surface of the source lava lake is commonly around 100 m this elevation difference can give rise to a static magmatic overpressure of 2 5 mpa in the tumulus whereas the overpressure needed to form a typical flow lobe tumulus is only 0 2 1 mpa

lapse rates and other variables applied to estimating paleoaltitudes from fossil floras abstract a previous method for determining paleoaltitude from fossil floras has used the difference between sea level and upland paleotemperatures which is then multiplied by the reciprocal of a normal lapse rate the present study examines other variables that can significantly influence such results terrestrial lapse rates have been calculated for 39 areas of the world based upon mean annual temperature mat mean warm month temperature mat and mean cold month ttemperature cmt these show regional and seasonal variability that is explained by factors including continentality elevation of large massifs or high base levels cold air drainage fog mountain barrier effects and the location of the subtropical high pressure zone lapse rates and projected sea level temperatures based on data from the western united states show distinct regional patterns these indicate that within this region the highest lapse rate and temperature values are correlated with 1 continental climates in the subtropical high pressure zone and 2 areas having relief where the lowest elevation land surfaces base levels occur at high altitude the data are applied to evaluate and revise the methodology for estimating paleoaltitudes variables of climatic change sea level fluctuation and paleogeography are also considered limitations in application of the method are emphasized the method is exemplified by application to the latest eocene florissant flora of colorado u s a although the results are conjectural they strongly suggest that the late eocene erosion surface in the southern rocky mountains occurred at a much higher paleoaltitude than previously thought this high elevation may have resulted from earlier laramide crustal thickening

explosive lava water interactions i architecture and emplacement chronology of volcanic rootless cone groups in the 1783 1784 laki lava flow iceland to determine the relationships between rootless cone emplacement mechanisms morphology and spatial distribution we mapped the hnuta and hrossatungur groups of the 1783 1784 laki lava flow in iceland we based our facies maps on differential global positioning system dgps measurements photogeological interpretations and supporting field observations the study area covers 2 77 km2 and includes 2216 explosion sites to establish the timing of rootless cone formation we incorporated tephrochronological constraints from eighty eight stratigraphic sections and determined that the hnuta and hrossatungur groups are composite structures formed by the emplacement of six geographically and chronologically discrete domains rootless eruptions initiated in domain 1 on the first day of the laki eruption june 8 1783 and lasted 1 2 days the second episode of rootless activity began in domain 2 on june 11 and lasted 1 3 days the four domains of the hrossatungur group dominantly formed after june 14 and exhibit a complex emplacement sequence that reflects interactions between the laki lava contemporaneously emplaced rootless cones and an existing topographic ridge in the study area we identify three distinct rootless cone archetypes i e recurring morphological forms that are related to tube channel and broad sheet lobe fed eruptions we assert that emplacement of lava above compressible substrates e g unconsolidated sediments may trigger rootless eruptions by causing subsidence induced flexure and failure of the basal crust thereby allowing molten lava fuel to come into direct contact with groundwater coolant and initiating analogs to explosive molten fuel coolant interactions mfcis

tree ring based streamfiow reconstruction for ashley creek northeastern utah implications for palaeohydrology of the southern uinta mountains two ring width chronologies from douglas fir pseudotsuga menzeisii and one from pinyon pine pinus edulis were used to reconstruct mean annual discharge of ashley creek in the uinta mountains utah for the years ad 1637 1970 a backward elimination multiple linear regression model identified six statistically significant variables including annual lags ranging from 1t o 2 years the final model explains 71 of variability r 2 adjusted for degrees of freedom lost when regressed against the annual discharges recorded for 1915 72 statistical analysis of the model reconstruction using the reduction of error statistic the durbin watson statistic and the hypergeometric distri bution all indicate fidelity of the model for reconstructing discharge the lilliefors test indicates that years of extreme discharge greater than the 90th percentile or less than the 10th percentile are non randomly distributed between 1637 and 1970 persistent years of above median discharge as well as non random clustering of years above the 90th percentile occurred from 1692 1704 and 1898 1945 analysis of the modern gauge data set shows that mean annual discharge on ashley creek explains between 81 and 91 of the variations of mean annual discharge on the other main stream in the southern uinta mountains indicating that reconstructed mean annual discharge on ashley creek is representative of palaeohydrologic conditions across the south flank of the range these data suggest that the southern uinta mountains experienced persistent below median discharge for 1741 1897 through the peak of the little ice age as identified in numerous surrounding mountain ranges in the central rockies this interpretation agrees with lichenometric evidence for extremely limited little ice age glacial activity in the uintas indicating that the range experienced unusually warm dry conditions at this time

paleoclimatic analyses of middle eocene through oligocene planktic foraminiferal faunas quantitative faunal analyses and oxygen isotope ranking of individual planktic foraminiferal species from deep sea sequences of three oceans are used to make paleoceanographic and paleoclimatic inferences species grouped into surface intermediate and deep water categories based on 18o values provide evidence of major changes in water mass stratification and individual species abundances indicate low frequency cool warm oscillations these data suggest that relatively stable climatic phases with minor cool warm oscillations of 0 5 m y frequency are separated by rapid cooling events during middle eocene to early oligocene time five major climatic phases are evident in the water mass stratification between middle eocene through oligocene time phase changes occur at p14 p15 p15 p16 p20 p21 and p21 p22 zone boundaries and are marked by major faunal turnovers rapid cooling in the isotope record hiatuses and changes in the eustatic sea level a general cooling trend between middle eocene to early late oligocene is indicated by the successive replacement of warm middle eocene surface water species by cooler late eocene intermediate water species and still cooler oligocene intermediate and deep water species increased water mass stratification in the latest eocene p17 indicated by the coexistence of surface intermediate and deep dwelling species groups suggest that increased thermal gradients developed between the equator and poles nearly coincident with the development of the psychrosphere this pattern may be related to significant ice accumulation between late eocene and early late oligocene time