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

high resolution bathymetry of the east pacific rise axial summit trough 9 49 51 n a compilation of alvin scanning sonar and altimetry data from 1991 1995 bathymetric data acquired during six cruises to the east pacific rise crest 9 49 51 n are compiled into a single bathymetric database and used to create high resolution bathymetry maps of two geologically and biologically active areas scanning sonar and alvin altimetry were collected during 23 alvin dives to the p vent bio9 and biomarker 141 areas during 1991 95 bathymetry data were filtered edited and processed as individual dives then combined into a single database for each cruise and statistically evaluated cruise data sets were numerically and visually compared and cross correlated to known bottom features and fixed seafloor reference markers then horizontally shifted to establish a consistent database with 3 m vertical and 5 m horizontal resolutions the compiled and corrected bathymetry was used to produce bathymetric maps of two areas within the axial summit collapse trough a 2 104 m area around p and bio9 vents and a 1 1 10 m area around biomarker 141 the resulting detailed bathymetry maps reveal topography dominated by low relief volcanic constructional features and post eruptive collapse of lobate and sheet lava surfaces

volcanic morphology of west mata volcano ne lau basin based on high resolution bathymetry and depth changes high resolution 1 5 m mapping from the autonomous underwater vehicle auv d allan b of west mata volcano in the northern lau basin is used to identify the processes that construct and modify the volcano the surface consists largely of volcaniclastic debris that forms smooth slopes to the nw and se with smaller lava flows forming gently sloping plateaus concentrated along the ene and wsw rift zones and more elongate flows radiating from the summit two active volcanic vents prometheus and hades are located 50 and 150 m wsw of the 1159 m summit respectively and are slightly nw of the ridgeline so the most abundant clastic deposits are emplaced on the nw flank this eruptive activity and the location of vents appears to have been persistent for more than a decade based on comparison of ship based bathymetric surveys in 1996 and 2008 2010 which show positive depth changes up to 96 m on the summit and north flank of the volcano the widespread distribution of clastic deposits downslope from the rift zones as well as from the current vents suggests that pyroclastic activity occurs at least as deep as 2200 m the similar morphology of additional nearby volcanoes suggests that they too have abundant pyroclastic deposits

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

geochemistry of silicic magmas in the macolod corridor sw luzon philippines evidence of distinct mantle derived crustal sources for silicic magmas silicic volcanic deposits 65 wt sio2 which occur as domes lavas and pyroclastic deposits are relatively abundant in the macolod corridor sw luzon philippines at makiling stratovolcano silicic domes occur along the margins of the volcano and are chemically similar to the silicic lavas that comprise part of the volcano pyroclastic flows are associated with the laguna de bay caldera and these are chemically distinct from the domes and lavas at makiling stratovolcano as a whole samples from the laguna de bay caldera contain lower concentrations of mgo and higher concentrations of fe2o3 t than the samples from domes and lavas the laguna de bay samples are more enriched in incompatible trace elements the silicic rocks from the domes makiling volcano and laguna de bay caldera all contain high alkalis and high k2o na2o ratios melting experiments of primitive basalts and andesites demonstrate that it is difficult to produce high k2o na2o silicic magmas by fractional crystallization or partial melting of a low k2o na2o source however recent melting experiments sisson et al contrib mineral petrol 148 635 661 2005 demonstrate that extreme fractional crystallization or partial melting of k rich basalts can produce these silicic magmas our model for the generation of the silicic magmas in the macolod corridor requires partial melting of mantle derived evolved moderate to k rich crystallized calc alkaline magmas that ponded and crystallized in the mid crust major and trace element variations along with oxygen isotopes and ages of the deposits are consistent with this model

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

recent volcanic events and the distribution of hydrothermal venting at the lucky strike hydrothermal field mid atlantic ridge 1 we present new high resolution bathymetry and backscatter data acquired in 2006 with the rov victor 6000 over the lucky strike hydrothermal field mid atlantic ridge as long term monitoring of the lucky strike area momar project is being implemented these new high resolution data offer an unprecedented view of the distribution of hydrothermal edifices eruptive facies and small scale tectonic features in the lucky strike vent field we show that vents located in the nw and ne correspond with wide expanses of lumpy seafloor which we interpret as primarily made of broken chimneys and sulfide edifices they are found above scarps with relief 50 m or on associated mass wasting deposits by contrast the se and sw vents correspond with small expanses of lumpy seafloor and are located near smaller scarps which we interpret as more recent faults hydrothermal edifices in the sw venting area appear very recent postdating the emplacement and faulting of the most recent lava we propose that this difference in the age of hydrothermal edifices does not mean that hydrothermal venting itself is more recent in the southern part of the lucky strike field because preexisting sulfide deposits there may have been buried by recent volcanic deposits instead the older edifices in the northern part of the hydrothermal field may have been allowed more time to grow because they are set above the level of recent lava flows the formation of a lava lake is the most recent eruptive event detected at lucky strike lava drainback is evidenced by benches and lava pillars suggesting a close connection with an underlying magma reservoir which probably corresponds to the melt body imaged by singh et al 2006 we have found no evidence that this lake was active for months to decades as lava lakes at terrestrial volcanoes it may instead have formed as a lava pond with successive lava flows covering the eruptive vents as proposed for similar features at the epr the horizontal surface of the lake is deformed only near its southwestern shore along a nne trending set of faults and fissures which appear to control the distribution of hydrothermal chimneys

magmatic subsidence of the east pacific rise epr at 18 14 s revealed through fault restoration of ridge crest bathymetry 1 the fault restoration technique of de chabalier and avouac 1994 is applied to an ultra high resolution bathymetry data set from the east pacific rise epr at 18 14 s fault offsets are calculated and subtracted from the original seafloor bathymetry to examine the morphology of the unfaulted seafloor surface within an area encompassing the ridge axis 400 1600 m in dimension the restored topography reveals a gently sloping seafloor 200 m wide which slopes 5 inward toward the spreading axis we attribute this inward sloping seafloor to subsidence within the axial trough due to subsurface magmatic deflation the vertical deformation field extracted from the bathymetry is used to characterize the ridge axis fault population present in the area median fault throws 9 m for inward facing and 8 m for outward facing faults are comparable to values measured for nearby mature abyssal hill fault populations suggesting a genetic link however median fault spacings 70 and 46 m are an order of magnitude smaller and estimated total extensional strain is 3 4 greater than values measured for ridge flank faults these differences indicate the axial fault population at 18 14 s cannot be rafted onto the ridge flanks to form abyssal hill faults without significant modification presumably via volcanic burial we attribute the dense faulting observed in this area to slip on axial fissures during subsidence of the crestal region the surface subsidence of a volcanic edifice can be modeled in terms of volume change in the magma source reservoir and volume of magma withdrawn from the reservoir using the relationship derived for a sill like magma body we estimate that the axial depression at 18 14 s could represent magma withdrawal associated with a small number 4 22 of the frequent dike injection and eruption events required to build the upper crust during the evolution of the trough the subsidence volumes represented by the axial topography at 18 14 s are a small percentage of the underlying upper crustal sections 3 4 suggesting that only a minor mismatch between magma recharge and withdrawal from the axial melt lens during ongoing plate separation could account for this pronounced axial depression

the formation of deep sea limu o pele deep sea sheet hyaloclastite consists mostly of sand sized blocky and splinter shaped shards but also contains subordinate mm to cm sized thin curved and wrinkled plates and sheets of sideromelane this latter type of shard termed limu o pele has been observed forming subaerially on kilauea by entrapment of water in flowing lava followed by expansion of steam to form large bubbles which burst into thin fragments deep marine limu has been inferred from comparative morphological studies and assessment of physical bubble forming conditions to form in a similar way but with the increased ambient pressure and the higher viscosity of water reducing bubble expansion differing mechanisms of heat transfer and rates of magma chilling also modify the limu forming process in the deep sea this paper evaluates a variety of deep sea limu forming processes and develops a new and quantitatively supported model based on observed limu forming processes and criteria derived from dive samples and observations at seamount six cocos plate it is inferred that water and or water saturated sediment was trapped in extremely thin fluid and rapidly advancing lava flows by various processes bubble formation might also occur during small scale magma fountaining driven by magmatic volatile exsolution and extreme vent constriction or during collapse of pillows and rapid drainage of the magma but we found no deposits clearly resulting from these processes

tectonothermal history of the hercynian continental crust of the serre southern calabria italy monitored by rb sr biotite resetting in the serre mountains of calabria italy an exposed section of the continental crust as left by the hercynian orogeny consists of intermediate lower to upper crustal units huge masses of granitoids separate the lower from the upper crustal units many mica ages have been obtained from metamorphic and plutonic rocks which have been interpreted as reflecting continuous cooling or discrete mesozoic events a reappraisal of previously determined isotopic data integrated with new rb sr biotite ages is presented and assessed at regional scale to better constrain the post hercynian geological evolution of the continental crust of the serre the ages cover a wide span of time and form clusters which fit a model involving magmatic hydrothermal and tectonic events preceding and accompanying the opening and closure of the tethyan ocean

a new model for submarine volcanic collapse formation 1 collapse pits and an associated suite of collapse related features that form in submarine lava flows are ubiquitous on the global mid ocean ridge crest collapse pits the lava tube systems they expose and lenses of talus created by the collapse process combine to produce a permeable region in the shallow ocean crust and are thought to contribute significantly to the 100 300 m thick low velocity zone observed at intermediate to fast spreading mid ocean ridges this horizon of low density high porosity material is likely to be an important aquifer for the transfer of hydrothermal fluids in the upper ocean crust in a recent survey of the east pacific rise at 9 37 n we used photographs video and observations from the submersible alvin and dsl 120a side scan data to determine that 13 of the 720 000 m2 of seafloor imaged had foundered to form collapse pits in 98 of the images collapse pits occurred in lobate flows and the rest in sheet flows on the basis of our observations and analyses of collapse features and incorporating data from previous models for collapse formation plus laboratory and theoretical models of basalt lava behavior in the deep ocean we develop a detailed multistage physical model for collapse formation in the deep ocean in our model lava extruded on the seafloor traps pockets of seawater beneath the flow that are instantly vaporized to a briny steam the seawater is transformed to vapor at temperatures above 480 c with a 20 times expansion in volume bubbles of vapor rise through the lava and concentrate below the chilled upper crust of the lava flow creating gas filled cavities at magmatic temperatures fluid lava from the cavity roofs drips into the vapor pockets to create delicate drip and septa structures a process that may be enhanced by water vapor diffusing into the magma and reducing its melting point as the vapor pocket cools the pressure within it drops causing a pressure gradient to develop across the upper crust the pressure gradient often causes the roof crust to collapse during cooling though vapor pocket geometry may be such that the roof remains intact during subsidence of the underlying lava alternatively drainaway of the molten lava may cause collapse in locations where inflated lava roof crusts are not supported from below by bounding walls or lava pillars post eruption seismicity lava movement or hydrovolcanic explosions may cause continued collapse of the lava carapace after the eruption

lava deposition history in odp hole 1256d insights from log based volcanostratigraphy a log based volcanic stratigraphy of ocean drilling program hole 1256d provides a vertical cross section view of in situ upper crust formed at the east pacific rise epr with unprecedented resolution this stratigraphy model comprises ten electrofacies principally identified from formation microscanner images in this study we build a lava flow stratigraphy model for the extrusive section in hole 1256d by correlating these electrofacies with observations of flow types from the modern epr such as sheet flows and breccias and pillow lavas and their distribution the resulting flow stratigraphy model for the hole 1256d extrusive section represents the first realization of detailed in situ epr upper oceanic crust construction processes that have been detected only indirectly from remote geophysical data we correlated the flow stratigraphy model with surface geology observed from the southern epr 14 s by shinkai 6500 dives in order to obtain the relationship between lava flow types and ridge axis ridge slope morphology this dive information was also used to give a spatial time reference frame for modeling lava deposition history in hole 1256d in reconstructing the lava deposition history we interpreted that the origins of the 100 m thick intervals with abundant pillow lavas in hole 1256d are within the axial slope where pillow lavas were observed during the shinkai 6500 dives and previous epr surveys this correlation could constrain the lava deposition history in hole 1256d crust using the lateral scale of ridge axis ridge slope topography from the shinkai 6500 observations and assuming the paleospreading rate was constant 50 of the extrusive rocks in hole 1256d crust were formed within 2000 m of the ridge axis whereas nearly all of the remaining extrusive section was formed within 3000 m of the ridge axis these results are consistent with the upper crustal construction model previously suggested by seismic studies

geochemical variation and magmatic cyclicity within an ordovician continental arc volcanic field the lower borrowdale volcanic group english lake district abstract the origin differentiation and temporal evolution of magmas have been examined from the ordovician lower borrowdale volcanic group bvg a calc alkaline plateau andesite pile of continental arc affinity the basalt dacite compositional range can be modelled by poam type crystal fractionation of primitive melts allied with minor crustal assimilation derived from enriched mantle modified by fluids from the subduction zone detailed sampling of sections through 2 3 km of stratigraphy reveals localised and successive highly systematic magmatic evolutionary trends or cycles cycles in which magma becomes less differentiated with time can be viewed as episodes of rapid eruption of a compositionally zoned chamber possibly due to magma recharge by contrast increasing differentiation with time implies reduced recharge and eruption rates whereby fractionation processes dominate the lack of evidence for compositional change over time represents a balance between recharge eruption and differentiation processes successive cycles within a local sequence can be related in many cases to discrete batches of magma that ascend into sub volcanic chambers and undergo fractionation the differences between contemporaneous sequences confirms the current view of the lower bvg as a multicentred volcanic field it was deposited in a subsiding extensional volcano tectonic rift zone consistent with episodes of rapid upward magma flux with the eruption locally of primitive high mg ni and cr basaltic lavas

a synthesis and review of historical eruptions at taal volcano southern luzon philippines abstract the philippines is an area of persistent volcanism being located in one of the most tectonically active regions in the world taal volcano in southern luzon is the second most frequently erupting volcano of the 24 active volcanoes in the philippines a comprehensive and critical review of published and unpublished references describing the 33 known historical eruptions of taal may provide answers to knowledge gaps on past eruptive behavior processes and products that could be utilized for hazard and risk assessment of future eruptions data on the prehistoric eruptions and evolution of taal caldera and subsequent deposits are limited only four caldera forming events were identified based on four mapped ignimbrite deposits from oldest to youngest these are the silicic alitagtag ali and caloocan cal pumice flow deposits the dacitic sambong ignimbrite sam and the basaltic andesitic taal scoria flow renamed scoria pyroclastic flow sfl except for sfl with 14c dating yielding 5380 70 to 6830 80 ky there are no age constraints or estimates of extent for the three older deposits a comprehensive review of the historical eruptions of taal volcano is the central element of this paper and includes all eruptions from ad1572 the first known historic event to ad1977 eruption styles and the interplay between processes and products for each eruption are reinterpreted based on the narrative descriptions from all available accounts a change of classification of eruption styles and eruptive products is undertaken for some events at least nine reported eruptions were deemed uncertain including the ad1605 ad1611 event more likely seismic swarms the ad1634 ad1635 and ad1645 may simply be solfataric or hydrothermal activity events and the ad1790 ad1825 ad1842 ad1873 and ad1903 events that were listed in recent published and unpublished documents but do not provide any details to describe and confirm the eruptions except for listing a default vei of 2 pyroclastic density currents brought devastating impacts to the communities around taal during the ad1749 ad1754 ad1911 and ad1965 eruptions and remain the biggest threat in the case of renewed volcanic activity significant implications for aviation are implied by the narrative of tephra fall dispersal towards manila the central gateway of international aviation operation in the philippines during the ad1754 eruptions the dispersal of tephra in the event of an explosive eruption at taal towards metro manila would have catastrophic effects to transport utilities and business activity potentially generating enormous economic losses hazards from earthquake events associated with future volcanic activity may also have localized impacts occurrences of liquefaction phenomena as a consequence of severe ground shaking are interpreted during the ad1749 ad1754 and ad1911 eruptions more work needs to be done to develop a comprehensive understanding of the hazards and risks associated with an explosive eruption at taal volcano especially related to the older quaternary caldera forming eruptions that produced large volume pyroclastic deposits that are extensively distributed and exposed we acknowledge that there may be additional prehistoric eruptions where the eruptive products have not been preserved recognized or reported events that cannot be verified or do not have sufficient details to confirm the eruption have been downgraded to uncertain eruptions that are confirmed with identified dispersal and emplacement of tephra fall and other eruptive deposits as interpreted from narrated records could provide crucial information that may be utilized in hazard assessment

determining an age for the inararo tuff eruption of mt pinatubo based on correlation with a distal ash layer in core md97 2142 south china sea abstract the largest known eruption of mt pinatubo in the late quaternary was the inararo tuff formation itf eruption roughly estimated as five times larger than the 1991 eruption the precise age of the itf eruption has been uncertain here a correlative of the itf eruption layer d is identified in marine sediments and an age obtained tephras were identified in core md97 2142 of leg ii of the images iii cruise in northern offshore of palawan southeastern south china sea 12 41 33 n 119 27 90 e on the basis of the geochemical and isotopic fingerprints layer d can be correlated with the itf eruption of the modern pinatubo eruption sequence by means of the md97 2142 specmap chronology layer d was dated at around 81 2 ka this estimated age of the itf eruption and tephra layer d coincides with an anomalously high so4 2 spike occurring within the 5 millennia from 79 to 84 ka in the gisp2 ice core record

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

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

dynamics of active magmatic and hydrothermal systems at taal volcano philippines from continuous gps measurements 1 a dense network of continuous single and dual frequency gps receivers at taal volcano philippines reveals four major stages of volcanogenic deformation deflation from installation in june 1998 to december 1998 inflation from january to march 1999 deflation from april 1999 to february 2000 and inflation from february to november 2000 the largest displacements occurred during the february november 2000 period of inflation which was characterized by 120 mm of uplift of the center of volcano island relative to the northern caldera rim at average rates up to 216 mm yr deformation sources were modeled using a constrained least squares inversion algorithm the source of 1999 deflation and inflation in 2000 were modeled as contractional and dilatational mogi point sources centered at 4 2 and 5 2 km depth respectively beneath volcano island the locations of the inflationary and deflationary sources are indistinguishable within the 95 confidence estimates modeling using a running 4 month time window from june 1999 to march 2001 reveals little evidence for source migration we suggest that the two periods of inflation observed at taal result from episodic intrusions of magma into a shallow reservoir centered beneath volcano island subsequent deflation may result from exsolution of magmatic fluids and or gases into an overlying unconfined hydrothermal system

non explosive lava water interaction in skaelingar iceland and the formation of subaerial lava pillars hollow cylinders of basalt 2 5 m tall and generally 1 m in diameter were generated by non explosive lava water interactions during the emplacement of the laki lava flow in iceland during 1783 1784 we know of only one location within the laki lava flow where these basalt formations occur a valley called skaelingar located at 64 0 n 18 5 w which contains a tributary stream to the skafta river skaelingar was temporarily filled with laki lava when the main body of the lava flow advancing down the skafta river valley became blocked forcing lava to flow upstream into tributary valleys along the north side of the river after the blockage within the skafta river valley was removed the laki lava mostly drained out of these tributary valleys we refer to the remaining vertical hollow basalt pipes as lava pillars because they morphologically resemble subaerial lava trees and submarine lava pillars that have been observed at mid ocean ridges we propose that the subaerial pillars formed as an inflating lava flow advanced slowly over water saturated ground or perhaps into temporarily ponded water causing heated columns of water to rise between adjacent advancing lava lobes the subaerial pillars continued to grow in height and diameter as the lava flow inflated when the lava drained back out of the valley the lava pillars were left standing thus the icelandic subaerial pillars represent a non explosive interaction between lava and water

multi stage dehydration decompression in the metagabbros from the lower crustal rocks of the serre southern calabria italy porphyroblastic garnet bearing metagabbros from the base of the lower crust section of the serre southern italy exhibit multi stage dehydration and decompression after the panafrican emplacement of their protoliths the first dehydration event produced am opx cpx pl grt as the peak assemblage two decompression stages are documented by 1 coronas of opx pl and opx am and symplectites of opx am pl around clinopyroxene within the porphyroblastic garnet as well as in the matrix and 2 symplectites of pl am opx grt having different textures around the porphyroblastic garnet during the second decompression stage a new local somewhat intense dehydration occurred and produced rims of opx pl around the porphyroblastic amphibole or lenses of pl opx am spl bt between layers of dominant amphibole a deformation stage separates older from younger reaction textures the porphyroblastic garnet its inclusions and the matrix are affected by fractures which have been overgrown by coronas and symplectites around the porphyroblastic garnet and the amphibole of the matrix preferred p t estimates are 900 c and 1 1 gpa at the metamorphic peak 850 c and 0 8 0 9 gpa during the formation of corona around clinopyroxene 750 650 c and 0 7 0 8 gpa during the formation of corona around garnet all these textures formed under granulite facies conditions the subsequent metamorphic evolution consists of rehydration under amphibolite facies conditions the p t t path agrees with the path shown by the uppermost migmatites of the serre section and the p t estimates at the top and the bottom of the section are consistent with the thickness 7 8 km of the lower crustal segment a contractional regime which caused a crustal thickening of about 35 km was followed by an extensional one producing significant crustal thinning the change of tectonic regime probably occurred about 300 ma ago when the emplacement of voluminous granitoids and the initial stages of exhumation of the lower crustal section had taken place

geochemical evidence of magma intrusion inferred from diffuse co 2 emissions and fumarole plume chemistry the 2010 2011 volcanic unrest at taal volcano philippines we report herein significant increases in the diffuse co2 emission through the lake and soils of the taal volcano main crater philippines during a volcano seismic unrest period in april 2010 june 2011 monitoring of co2 emissions from the taal main crater lake and soils in the fumarole areas started in 2008 with a collaborative project between iter and phivolcs in august 2010 the total diffuse co2 emission from the taal main crater lake increased almost three times from a previously measured baseline emission value 1 000 t day 1 to 2 716 54 t day 1 this increase occurred during anomalous seismic activity which started in april 2010 the highest co2 emission value in the crater lake was measured in march 2011 at 4 670 159 t day 1 when the volcano was still showing signs of unrest significant changes in the co2 so2 co2 h2o and so2 h2s ratios in the fumarole gases suggest the occurrence of a magmatic injection several weeks before the onset of the volcano seismic unrest period these observed changes in the co2 emission rate and the fumarole gas composition as the result of magmatic activity were likely caused by magma moving from a deep reservoir to a shallow reservoir

geochemical and isotopic evidence for seawater contamination of the hydrothermal system of taal volcano luzon the philippines the hydrologic structure of taal volcano has favored development of an extensive hydrothermal system whose prominent feature is the acidic main crater lake ph 3500 mg kg and low so4 cl ratios 0 3 the br cl ratio of most samples suggests incorporation of seawater into the hydrothermal system water and dissolved sulfate isotopic compositions reveal that the main crater lake and spring discharges are derived from a deep parent fluid t approximate to 300 degrees c which is a mixture of seawater volcanic water and lake taal water the volcanic end member is probably produced in the magmatic hydrothermal environment during absorption of high temperature gases into groundwater boiling and mixing of the parent water give rise to the range of chemical and isotopic characteristics observed in the thermal discharges incursion of seawater from the coastal region to the central part of the volcano is supported by the low water levels of the lakes and by the fact that lake taal was directly connected to the china sea until the sixteenth century the depth to the seawater meteoric water interface is calculated to be 80 and 160 m for the main crater lake and lake taal respectively additional data are required to infer the hydrologic structure of taal geochemical surveillance of the main crater lake using the so4 cl na k or mg cl ratio cannot be applied straightforwardly due to the presence of seawater in the hydrothermal system

age dependent porosity of young upper oceanic crust insights from seafloor gravity studies of recent volcanic eruptions 1 an october 1997 alvin program collected a series of seafloor gravity stations over the february 1996 volcanic eruption site on the northern gorda ridge 46 41 n 126 47 w these measurements yielded estimates of the density and porosity of mid ocean ridge crust in the first few decades following formation the estimated crustal density for this pillow eruption of 2270 260 kg m3 is very low but in good agreement with the estimated densities of other recent seafloor volcanic flows rock matrix densities measured from hand samples retrieved from the study area give a bulk porosity for this flow of 34 16 this data when included with similar estimates of upper crustal porosity argue for a rapid evolution of upper crustal porosities from very high values 30 for recent eruptions to much lower values 10 15 where the seafloor is older than 0 5 million years these variations of density and porosity are of a magnitude consistent with previously observed changes in seismic compressional wave velocity and permeability of ocean crust

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

submarine lineated sheet flows a unique lava morphology formed on subsiding lava ponds lineated sheet flows are flat lying glassy lava flows characterized by a regular surface pattern of parallel grooves or furrows aligned with the flow direction they are unique to the submarine environment we propose that the lineations are developed within the collapsed interiors of partially ponded lobate sheet flows that initially inflate and then drain out during emplacement during lava drainout the original lobate crust founders and a new crust begins to grow on the subsiding lava surface lineated flow texture is created where molten lava emerges laterally from beneath a growing crust the lineations are formed by raking of the emerging lava surface by irregularities on the bottom edge of the crust and are preserved owing to rapid chilling by seawater therefore lineated sheet flows are the product of a specific sequence of events over a short period of time during the course of a deep submarine eruption

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

subaqueous lava flow lobes observed on rov kaiko dives off hawaii remotely operated vehicle rov kaiko dives north of oahu island hawaii and on the lower south rift zone of loihi seamount revealed diverse flow morphologies of submarine lava that correlate with slope and rate of lava delivery steep to moderate 10 slopes are covered with elongate pillows and narrow pahoehoe streams bulbous pillows and smooth pahoehoe lobes occur on flat areas and gentle slopes some gentle slopes are covered by lobate sheet flows that supply pillow flows smooth pahoehoe lobes change upslope into lobate sheets indicating that the sheets form by coalescence and inflation of successively emplaced flow lobes many pahoehoe flows contain hollow tumuli like lobes that have inflated and collapsed thin crusts 4 20 cm and large volumes 0 7 1050 m 3 of such inflated lobes suggest lava supply rates of 0 01 8 m 3 min these calculated supply rates are more than one order of magnitude larger than those for subaerial tumuli in iceland thinner viscoelastic layers of subaqueous lobes at the time of inflation allowed higher excess pressures and expansion rates

submarine lava flow inflation a model for the formation of lava pillars lava pillars are commonly observed in volcanic terrains at mid ocean ridges and are unique to the submarine volcanic environment they are hollow pipes that extend from the base of a lava flow to remnants of its collapsed upper crust pillars can be as tall as 5 m and have outer diameters typically between 0 5 and 2 m previous models proposed that they form in thick fluid fast moving sheet flows we present a new model for pillar formation based on sea floor observations and on results from laboratory and numerical models in which lava pillars form within initially thin 0 3 m slow moving lobate lava flows as gaps between neighboring lobes water escaping from beneath the flow acts to locally cool and thicken the crust at the gaps pillars attain their full height during subsequent lava flow inflation as the flow thickens pillars that do not continue to channel water are melted and resorbed into the molten flow interior pillars are typically preserved at the margins of ponded lava flows where the flow interior is relatively stagnant and less efficient at remelting pillars and where seawater is more accessible for circulation through the flow

a large hydrothermal reservoir beneath taal volcano philippines revealed by magnetotelluric resistivity survey 2d resistivity modeling taal volcano located in the southwestern part of luzon island philippines has frequently experienced catastrophic eruptions from both the main crater on volcano island and flank eruptions these eruptions have been magmatic phreatomagmatic and hydrothermal with the latter implying the existence of a large scale hydrothermal system beneath the volcano we conducted an electrical resistivity survey using the magnetotelluric method in order to identify the location and geometry of the hydrothermal reservoir and sealing cap rock two dimensional inversion using the observed data indicates four similar resistivity sections the structure at shallow depths corresponds to volcanic deposits and an aquifer below 1 km the structure features a relatively resistive zone beneath the main crater surrounded by a conductive shell we interpreted these to be a large hydrothermal reservoir with an impermeable cap rock sealing it recent ground deformation detected by gps measurements suggests that the hydrothermal reservoir is active the interpreted cap rock thins just beneath the main crater and could easily be destroyed by an imbalance in the hydrothermal system we conclude that this hydrothermal reservoir plays a significant role in driving catastrophic eruptions that begin with a hydrothermal explosion at the main crater

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

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

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

correlation between volcanic and tectonic segmentation of fast spreading ridges evidence from volcanic structures and lava flow morphology on the east pacific rise at 9 10 n 1 combined analyses of volcanic features in dsl 120 sonar data and argo i images along the ridge crest of the east pacific rise 9 09 54 n reveal a consistent decrease in inferred lava effusion rate toward the ends of third order segments the correlation of tectonic segmentation and volcanic style suggests that third order segmentation corresponds to the volcanic segmentation of the ridge along axis changes in volcanic structures from collapse troughs to basaltic lava domes and lava morphology from sheet to pillow flows coincide with the boundaries of morphologically defined third order tectonic segments of the ridge crest visible in shipboard multibeam bathymetry pillow lava flows cover 25 of the surveyed area of the ridge crest and are closely associated with small lava domes that occur primarily at third order segment ends an additional 25 of the surveyed area of the ridge crest is covered by sheet lava flows found in close association with an axial collapse trough the remaining terrain consists of lobate lava flows we interpret the spatial correlations of morphologic structural seismic and petrologic data as evidence that individual volcanic plumbing systems are organized at 20 km spacing along the ridge axis third order segment scale in agreement with the hypothesis that volcanic and tectonic segmentations are correlated for fast spreading ridges we estimate that the longevity of volcanic segments is 104 105 years 1 3 orders of magnitude longer than fourth order segments 102 103 years this implies the present pattern of hydrothermal activity may reorganize tens or hundreds of times while volcanic segmentation remains fairly stable

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

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

geodetic observations and modeling of time varying deformation at taal volcano philippines abstract we investigate active crustal deformation patterns associated with magmatic activity at taal volcano an active tholeiitic volcano located in southwestern luzon philippines we present comparisons of elastic and combined elastic viscoelastic modeling results with deformation observed by continuous gps measurements on and near the volcano continuous dual frequency and single frequency l1 gps data between 1998 and 2005 provide evidence for smoothly transitioning periods of inflation and deflation centered under the volcano within deformation phases that typically last 3 9 months with rates exceeding 200 mm yr 1 prominent inflationary phases were observed in february november 2000 and june 2004 march 2005 the 2000 period of inflation was characterized by up to 145 mm yr 1 surface extension and 220 mm yr 1 of uplift of the center of volcano island relative to the northern caldera rim while the 2005 inflation was characterized by as much as 116 mm yr 1 horizontal extension of the volcanic edifice and 180 mm yr 1 uplift inversions of observed surface deformation to determine the source location points to a relatively stable spherical source situated under volcano island s central crater at depths of 5 km based on the preferred mogi model using this source geometry we develop axisymmetric finite element models with annuli of concentric shells around the magma reservoir embedded within a multi layered elastic lithosphere using simply varying pressure histories as input a variety of forward models are fit to the time history of continuously observed deformation for gps stations located on volcano island though the inferred source geometry volume and near source rheological properties are non unique they represent more physically appropriate material properties than those assumed in simple elastic half space models the sources inferred using viscoelastic shell models suggest simpler pressure histories and reduced overall pressure changes relative to equivalent elastic half space models

a record of eruption and intrusion at a fast spreading ridge axis axial summit trough of the east pacific rise at 9 10 n 1 high resolution side scan sonar near bottom multibeam bathymetry and deep sea photo and bathymetry traverses are used to map the axial summit trough ast at the east pacific rise between 9 and 10 n we define three ridge axis morphologic types no ast narrow ast and wide ast which characterize distinct ridge crest domains spanning tens of kilometers along strike near bottom observations modeling of deformation above intruding dikes and comparisons to the geologic and geophysical structure of the ridge crest are used to develop a revised model of ast genesis and evolution this model helps constrain the record of intrusive and extrusive magmatism and styles of lava deposition along the ridge crest at time scales from hundreds to tens of thousands of years the grabens in the narrow ast domain 9 43 53 n are consistent with deformation above the most recent 10 diking events beneath the ridge crest frequent high effusion rate extrusive volcanism in this domain several eruptions every 100 years overprints near axis deformation and maintains a consistent ast width the most recent eruption at the ridge crest occurred in this area and did not significantly modify the physical characteristics of the ast the grabens in the wide ast domain 9 23 43 n originated with similar dimensions to the narrow ast spreading driven primarily by the intrusion of shallow dikes within a narrow axial zone causes the initial graben bounding faults to migrate away from the axis infrequent extrusive volcanism several eruptions every 1000 years fills a portion of the subsidence that accumulates over time but does not significantly modify the width of the ast outside of these domains lower effusion rate constructional volcanism without efficient drain back fills and erases the signature of the ast the relative frequency of intrusive versus extrusive magmatic events controls the morphology of the ridge crest and appears to remain constant over millennial time scales within the domains we have identified however over longer time scales 10 25 ka domain specific intrusive to extrusive ratios do not appear to be fixed in space resulting in a fairly consistent volcanic accretion over the length scale of the second order ridge segment between 9 n and 10 n

timescales and mechanisms of batholith construction constraints from zircon oxygen isotopes and geochronology of the late variscan serre batholith calabria southern italy abstract the late variscan serre batholith in central calabria represents the middle portion c 13 km thick of a tilted crustal section continuously exposed from lower crustal granulites to upper crustal phyllites the batholith is zoned consisting of several granitoid types that were emplaced at depths ranging from c 23 to c 6 km deep strongly foliated quartz diorites and tonalites were emplaced into migmatitic metapelites the intermediate level granitoids are weakly foliated to unfoliated porphyritic granodiorites and monzogranites and the shallowest bodies are two mica granodiorites and granites grading upward to biotite amphibole granodiorites emplaced into paragneisses and phyllites five samples representative of the main granitoid types in terms of both composition and emplacement depth have been dated by shrimp zircon from a lower crustal quartz diorite gave an emplacement age of 297 3 3 1 ma two middle crustal strongly peraluminous k feldspar megacrystic granites were emplaced at 296 1 1 9 ma and 294 9 2 7 ma a middle to upper crustal two mica monzogranite was emplaced at 294 2 2 6 ma and finally an upper crustal weakly peraluminous granodiorite from the batholith roof was emplaced at 292 2 2 6 ma these results are consistent with the development of the batholith by incremental multipulse overaccretion each granitoid body being in a dominantly rigid state before intrusion of the next with little or no possibility of magma mixing the difference in age between the oldest and youngest granitoids from the batholith floor and roof respectively is 5 1 4 0 ma providing an upper limit of about 9 ma on the time taken for batholith construction the presence in the c 296 294 ma granitoids of c 305 302 ma anatectic zircon with varied th u and oxygen isotope compositions indicates a time interval of 8 9 ma between incipient partial melting in the lower crust and magma emplacement in the middle crust the emplacement of the first granitoid bodies into the top of the lower crust was controlled tectonically by the activation of a deep seated shear zone the shallowest granodiorites were emplaced during the waning stages of the shear zone activity producing late to post tectonic contact metamorphism in the upper crustal phyllites and mylonitic paragneisses

formation of submarine lava channel textures insights from laboratory simulations 1 laboratory simulations using polyethylene glycol peg extruded at a constant rate and temperature into a tank with a uniform basal slope and filled with a cold sucrose solution generate channels that are defined by stationary levees and mobile flow interiors these laboratory channels consistently display the following surface textures in the channel smooth folded lineated and chaotic in the simulations we can observe specific local conditions including flow rate position within the channel and time that combine to develop each texture the textures in peg flows form due to relative differences in shear forces between the peg crust and the underlying liquid wax minimal shear forces form smooth crust whereas folded crust forms when the shear is sufficiently high to cause ductile deformation brittle deformation of solid peg creates a chaotic texture and lineated crust results from shear forces along the channel levee margin we observe similar textures in submarine lava channels with sources at or near the axial summit trough of the east pacific rise between 9 and 10 n we mapped the surface textures of nine submarine lava channels using high resolution digital images collected during camera tows these textural maps along with observations of the formation of similar features in analog flows reveal important information about the mechanisms occurring across the channel during emplacement including relative flow velocity and shear stress

channelized lava flows at the east pacific rise crest 9 10 n the importance of off axis lava transport in developing the architecture of young oceanic crust 1 submarine lava flows are the building blocks of young oceanic crust lava erupted at the ridge axis is transported across the ridge crest in a manner dictated by the rheology of the lava the characteristics of the eruption and the topography it encounters the resulting lava flows can vary dramatically in form and consequently in their impact on the physical characteristics of the seafloor and the architecture of the upper 50 500 m of the oceanic crust we have mapped and measured numerous submarine channelized lava flows at the east pacific rise epr crest 9 10 n that reflect the high effusion rate and high flow velocity end member of lava eruption and transport at mid ocean ridges channel systems composed of identifiable segments 50 1000 m in length extend up to 3 km from the axial summit trough ast and have widths of 10 50 m and depths of 2 3 m samples collected within the channels are n morb with mg indicating eruption from the ast we produce detailed maps of lava surface morphology across the channel surface from mosaics of digital images that show lineated or flat sheets at the channel center bounded by brecciated lava at the channel margins modeled velocity profiles across the channel surface allow us to determine flux through the channels from 0 4 to 4 7 103 m3 s and modeled shear rates help explain the surface morphology variation we suggest that channelized lava flows are a primary mechanism by which lava accumulates in the off axis region 1 3 km and produces the layer 2a thickening that is observed at fast and superfast spreading ridges in addition the rapid high volume flux eruptions necessary to produce channelized flows may act as an indicator of the local magma budget along the epr we find that high concentrations of channelized lava flows correlate with local across axis ridge morphology indicative of an elevated magma budget additionally in locations where channelized flows are located dominantly to the east or west of the ast the ridge crest is asymmetric and layer 2a appears to thicken over a greater distance from the ast toward the side of the ridge crest where the channels are located

geologic history of the summit of axial seamount juan de fuca ridge 1 multibeam 1 m resolution and side scan data collected from an autonomous underwater vehicle and lava samples radiocarbon dated sediment cores and observations of flow contacts collected by remotely operated vehicle were combined to reconstruct the geologic history and flow emplacement processes on axial seamount s summit and upper rift zones the maps show 52 post 410 ce lava flows and 20 precaldera lava flows as old as 31 2 kyr the inferred age of the caldera clastic deposits 1 2 m thick accumulated on the rims postcaldera between 31 ka and 410 ce there are no known lava flows near the summit the oldest postcaldera lava 410 ce is a pillow cone se of the caldera two flows erupted on the w rim between 800 and 1000 ce from 1220 to 1300 ce generally small eruptions of plagioclase phyric depleted mafic lava occurred in the central caldera and on the east rim larger post 1400 ce eruptions produced inflated lobate flows of aphyric less depleted and less mafic lava on the upper rift zones and in the n and s caldera all caldera floor lava flows and most uppermost rift zone flows postdate 1220 ce activity shifted from the central caldera to the upper s rift outside the caldera to the n rift and caldera floor and then to the s caldera and uppermost s rift where two historical eruptions occurred in 1998 and 2011 the average recurrence interval deduced from the flows erupted over the last 800 years is statistically identical to the 13 year interval between historical eruptions

morphology and dynamics of inflated subaqueous basaltic lava flows during eruptions onto low slopes basaltic pahoehoe lava can form thin lobes that progressively coalesce and inflate to many times their original thickness due to a steady injection of magma beneath brittle and viscoelastic layers of cooled lava that develop sufficient strength to retain the flow inflated lava flows forming tumuli and pressure ridges have been reported in different kinds of environments such as at contemporary subaerial hawaiian type volcanoes in hawaii la reunion and iceland in continental environments states of oregon idaho washington and in the deep sea at juan de fuca ridge the galapagos spreading center and at the east pacific rise this study these lava have all undergone inflation processes yet they display highly contrasting morphologies that correlate with their depositional environment the most striking difference being the presence of water lava that have inflated in subaerial environments display inflation structures with morphologies that significantly differ from subaqueous lava emplaced in the deep sea lakes and rivers their height is 2 3 times smaller and their length being 10 15 times shorter based on heat diffusion equation we demonstrate that more efficient cooling of a lava flow in water leads to the rapid development of thicker by 25 cooled layer at the flow surface which has greater yield strength to counteract its internal hydrostatic pressure than in subaerial environments thus limiting lava breakouts to form new lobes hence promoting inflation buoyancy also increases the ability of a lava to inflate by 60 together these differences can account for the observed variations in the thickness and extent of subaerial and subaqueous inflated lava flows

the basaltic to trachydacitic upper diliman tuff in manila petrogenesis and comparison with deposits from taal and laguna calderas abstract the basaltic to trachydacitic 50 65 wt sio2 upper diliman tuff is the youngest deposit of a sequence of tuffaceous deposits in metro manila the deposit is located north of taal caldera and northwest of laguna caldera which are both within the southwest luzon volcanic field chemical variations in the pumice fragments within the upper diliman tuff include medium k basalt to basaltic andesite high k basaltic andesite to andesite and trachyandesite to trachydacite magma mixing mingling is ubiquitous and is shown by banding textures in some pumice fragments considerable range in groundmass glass composition 54 to 65 wt sio2 in a single pumice fragment and zoning in plagioclase phenocrysts simple binary mixing modeling and polytopic vector analysis were used to further evaluate magma mixing trace element variations are inconsistent with the medium k and high k magmas being related by crystal fractionation the medium k basalts represent hotter intrusions which induced small degrees of partial melting in older crystallized medium k basaltic material within the crust to produce the high k magmas all melts likely differentiated in the crust but the emplaced and new basaltic intrusions originated from the mantle wedge and were generated by subduction zone processes the volcanic source vent for the upper diliman tuff has not been identified in comparisons with the deposits from adjacent taal and laguna calderas it is chemically distinct with respect to both major and trace element concentrations

contamination of basaltic lava by seawater evidence found in a lava pillar from axial seamount juan de fuca ridge a lava pillar formed during the 1998 eruption at axial seamount exhibits compositional and textural evidence for contamination by seawater under magmatic conditions glass immediately adjacent to anastomosing microfractures within 1 cm of the inner pillar wall is oxidized and significantly enriched in na and cl and depleted in fe and k with respect to that in glassy selvages from the unaffected outer pillar wall the affected glass contains up to 1 wt cl and is enriched by 2 wt na2o relative to unaffected glass consistent with a nearly 1 1 molar incorporation of nacl glass bordering the cl enriched glass in the inner pillar wall is depleted in na but enriched in k the presence of tiny 10 m grains of cu fe sulfides and fe sulfides as well as elemental ni ag and au in the na depleted k enriched glass of the inner pillar wall implies significant reduction of this glass presumably by hydrogen generated during seawater contamination and oxidation of lava adjacent to microfractures we interpret the compositional anomalies we see in the glass of the interior pillar wall as caused by rapid incorporation of seawater into the still molten lava during pillar growth probably on the time scale of seconds to minutes only one of seven examined lava pillars shows this effect and we interpret that seawater has to be trapped in contact with molten lava inside the lava pillar in this case to produce the effects we see thus under the right conditions seawater contamination of lavas during submarine eruptions is one means by which the oceanic crust can sequester cl during its global flux cycle however since very few recent lava flows have been examined in similar detail the global significance of this process in effecting earth s cl budget remains uncertain

eruptive and tectonic history of the endeavour segment juan de fuca ridge based on auv mapping data and lava flow ages high resolution bathymetric surveys from autonomous underwater vehicles abe and d allan b were merged to create a coregistered map of 71 7 km2 of the endeavour segment of the juan de fuca ridge radiocarbon dating of foraminifera in cores from three dives of remotely operated vehicle doc ricketts provide minimum eruption ages for 40 lava flows that are combined with the bathymetric data to outline the eruptive and tectonic history the ages range from modern to 10 700 marine calibrated years before present yr bp during a robust magmatic phase from 10 700 yr bp to 4300 yr bp flows erupted from an axial high and many flowed 5 km down the flanks some partly buried adjacent valleys axial magma chambers amcs may have been wider than today to supply dike intrusions over a 2 km wide axial zone summit seamount formed by 4770 yr bp and was subsequently dismembered during a period of extension with little volcanism starting 4300 yr bp this tectonic phase with only rare volcanic eruptions lasted until 2300 yr bp and may have resulted in near solidification of the amcs the axial graben formed by crustal extension during this period of low magmatic activity infrequent eruptions occurred on the flanks between 2620 1760 yr bp and within the axial graben since 1750 yr bp this most recent phase of limited volcanic and intense hydrothermal activity that began 2300 yr bp defines a hydrothermal phase of ridge development that coincides with the present day 1 km wide amcs and overlying hydrothermal vent fields

porosity of very young oceanic crust from sea floor gravity measurements porosity and density are two of the most important but under determined parameters in studies of igneous oceanic crust lacking quantitative measurements of crustal densities but with plausible expectations of substantial variation with age previous investigators have used estimates that have varied widely to address this problem more rigorously a recent alvin program obtained 133 on bottom gravity stations to calculate crustal densities for three recent volcanic eruptions on the juan de fuca ridge in the summer of 1995 a bell aerospace bgm 3 gravity meter was mounted in alvin and made fixed station gravity measurements on 11 transect lines from three distinct volcanic environments including 1 the recent coaxial segment volcanic eruption that occurred in 1993 2 two nearby flows with less well determined ages but dated post 1981 and 3 several older adjacent areas on the juan de fuca axial ridge densities for the recent eruptive units ranged between 2280 and 2450 kg m while the upper 50 meters of the older unfractured surrounding flows were approximately 2800 kg m laboratory grain densities measured from rocks collected in the study area allow crustal porosities to be calculated which are anomalously high for the recent flows in comparison to the surrounding axial ridge porosities for the three youngest flows range between 29 36 while the adjacent unfractured regions of the surrounding axial region had porosities near 10 two localized regions of intense surficial crustal fracturing in older crust located just south of the 1993 eruption site also had high porosities of 26 28 this high variability indicates that the evolution of crustal porosities from young to older oceanic crust is not related only to the collapse and infilling of macroscopic voids but that tectonic activity can significantly modify the porosity of older crustal structures

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

a 2 ma record of explosive volcanism in southwestern luzon implications for the timing of subducted slab steepening 1 new chemical and isotopic analyses of the tephra layers plus deep sea tephrostratigraphic record from two cores from either side of luzon island philippines have allowed the identification of two periods of explosive volcanic activity originating from the macolod corridor in the southwestern part of the luzon the first period extended from prior to 1355 ka to 1977 ka and the second period extended from 478 ka to the present separated by a period of relative quiescence the time intervals between large explosive eruption events in each period were 31 15 ka and 156 52 ka respectively combined with published chronological and geochemical data from onshore volcanic deposits the tephrostratigraphic record shows that the locus of large explosive eruptions has migrated southwestward from the northeastern section to the middle and southwestern sections of the macolod corridor the period of relative quiescence is characterized by monogenetic volcanism in the central section of the corridor the migration of active volcanism across the southwestern part of luzon during the quaternary is used to infer the evolution of the subducting south china sea crust the period of relative quiescence represents a period of adjustment of the subducted slab by steepening which began around 1355 ka or shortly thereafter and finished at around 478 ka

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