effects of bottom water warming and sea level rise on holocene hydrate dissociation and mass wasting along the norwegian barents continental margin 1 gas hydrate gh stability modeling results explain why some major holocene submarine landslides along the norwegian barents margin could have been triggered by gh dissociation during the early to middle holocene not during the lowest sea levels of the last glacial maximum lgm our model results show that subbottom depths of 170 260 m below the pre slide continental slope ca 350 475 m present water depth must have passed out of gas hydrate stability zone ghsz by 8 15 ka as the effect of warm bottom water inflow at 11 ka penetrated into the subbottom overcoming the effects of pressure increase due to sea level rise slr the component of local slr due to the isostatic response to fennoscandian deglaciation is shown to be relatively insignificant particularly for the part of the upper continental slope where the slide probably began the stability relations show that gh could have formed under the ice sheet before deglaciation and below deeper shelf areas after sea levels began to rise but before significant warming near the ghsz base to the extent water deeper than 800 m has remained cold 1 to 0 c since lgm times the ghsz continued to thicken in deep water and gh dissociation could not have triggered holocene failure in that regime the present distribution of gh stability is limited to water depths greater than about 400 m in the storegga slide area and the thickness of the ghsz increases with water depth

a new model for the emplacement of columbia river basalts as large inflated pahoehoe lava flow fields extensive flows of the columbia river basalt crb group in washington oregon and idaho are dominantly inflated compound pahoehoe sheet lavas early studies recognized that crb lavas are compound pahoehoe flows with textures suggesting low flow velocities but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks however small volume 1 km compound pahoehoe flows on kilauea hawai i demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger 10 20 km3 pahoehoe flows in iceland the vertical distribution of vesicles and other morphologic features within crb lava flows indicate that they grew similarly by inflation small pahoehoe lobes at the base and top of many crb pahoehoe lava flows indicate emplacement in a gradual piecemeal manner rather than as a single flood we propose that each thick crb sheet flow was active for months to years and that each group of flows produced by a single eruption a flow field was emplaced slowly over many years

evolution of structural and physical parameters of clays during experimental compaction abstract to provide a better understanding of sedimentary basin geological history it is important to describe correctly the evolution of the various physical mechanical and hydraulic properties of clayey rocks as a function of burial depth as a contribution to this field a programme of experimental studies on reworked clay samples compacted under various load pressures in oedometric conditions has been set up the evolution of samples under compaction was followed with microscopic and macroscopic measurements in a specially designed oedometric cell samples are compacted under different total stresses from 0 1 to 50 mpa in this cell cylindrical cores are submitted to progressive loading from both ends under controlled pore pressure conditions the symmetrical loading allows more even deformation about the midplane of the sample this device allows the evolution of hydraulic pressure radial stress displacement and expelled pore fluid to be followed as a function of time in a first step kaolinite was chosen because it retains a high permeability compared with other clays such as illite or smectite which allows compaction tests to be performed within a few days a complete set of measurements was performed after the tests these measurements are 1 micro structures investigated by means of transmission electron microscopy tem mercury porosimetry water removal under low water vapour pressure granulometry and specific area measured by ethylene glycol adsorption and 2 various physical parameters measured including hydraulic conductivity and thermal conductivity tem gives an understanding of the arrangement of particles it was found that each particle is composed of several crystal units each unit formed by 25 individual kaolinite layers during compaction these particles remain undeformed but are rotated the angular distribution of grain orientation is a function of the applied effective stress this reorientation is in agreement with the observed decrease in porosity and pore size it also explains the occurrence of a strong anisotropy in the thermal conductivity and hydraulic permeability the combination of these experimental results allows a qualitative and quantitative understanding of the behaviour of kaolinite with respect to parameters such as permeability porosity mechanical and thermal properties the knowledge of which are necessary for basin modelling

the lobes of lava flows on earth and olympus mons mars the lobate distal margins of lava flows provide a useful source of morphological information on the rheology of the lava if the lobes are assumed to represent the arrest of free flowing isothermal bingham fluids on a slope the widths of lobes are a more useful practical index than lobe thicknesses because they are about an order of magnitude larger and can be more accurately measured from aerial photographs and other remote images lobes do not suffer from the changes in morphology that channels undergo during the course of eruptions a terrestrial data set of flow lobe and ancillary measurements from lavas throughout the range alkali olivine basalt to rhyolite shows some features that are predicted by the isothermal bingham fluid model these are correlation of width and thickness over more than two orders of magnitude and essentially no correlation of aspect ratio with slope there is a positive correlation of lobe width with silica content of the lava from a data set of measurements on lava flow lobes from the martian volcano olympus mons the mean value of aspect ratio 0 07 was found to be significantly less than that for the terrestrial data set 0 19 higher general levels of effusion rate on olympus mons are probably the factor responsible after normalisation lobe widths on olympus mons are found to be largely equivalent to those expected for terrestrial flows with andesitic basaltic silica contents

flow field stratigraphy surrounding sekmet mons volcano kawelu planitia venus i detailed mapping has revealed several stratigraphic components among lobate plains in the vicinity of sekmet mons volcano 44 5 n lat 240 5 long located on the northern lowland plains of kawelu planitia on venus volcanic effusion events produced discrete lobate plains throughout the area superposition of flow margins between adjacent lobate plains components indicate that the effusive activity generally progressed from southwest to northeast across the sekmet mons area leading to a cumulative total of 1 5 million km 2 covered by adjacent lobate plains components source areas for the effusion responsible for the lobate plains components occur primarily along fracture zones or from concentrations of low volcanic domes shield fields instead of from single constructs magellan radar backscatter values from a mixture of both radar bright and radar dark flow components within the flow fields are well below values typical of clinkery a a lava flows on earth but they are consistent with values from terrestrial pahoehoe flows detailed mapping of strenia fluctus centered on 41 5 n lat 251 0 long one of the latest lobate plains units in the area does not show a systematic trend among effusive centers that contributed to the generation of this flow field instead the strenia fluctus flow field is a complex mixture of flows that emanated from a shield field along mist chasma and that flowed down a very gentle 0 1 regional slope to the east a 4 km diameter cone north of strenia fluctus was the source of a flow complex traceable for more than 200 km over a slope of only 0 03 individual flows within strenia fluctus are composed of intermixed lobes similar to relationships observed on the distal portion of the 75 km long carrizozo basalt flow in new mexico which also displays abundant inflation features and a predominant pahoehoe surface texture if the venusian lobate plains consist of pahoehoe flows comparable to the carrizozo flow they were most likely emplaced at modest effusion rates 50 to 500 m 3 s and even with inflation the flows are likely 15 m in thickness under these conditions all of the lobate plains surrounding sekmet mons could have been emplaced in 14 000 to 1400 earth years assuming continuous effusion with only one source vent active at a time at similar rates all of the lowland plains in the northern hemisphere of venus could have been resurfaced by 15 m thick flows through continuous single vent effusion in 1 4 million to 140 thousand earth years

towards improved ground models for slope instability evaluations through better characterization of sediment hosted gas hydrates recently developed effective stress controlled geophysical property models are used in passive margin slope instability analyses including simulated earthquake motion the pressure temperature p t history of sediment hosted gas hydrate may significantly alter the geophysical property profile of the sediment column e g metastable cement or increased pore pressures this can result in significant amplification of earthquake ground motion and thus seabed instability where hydrates are present published studies suggest destabilization of these high pressure low temperature sediment hosted hydrates could trigger catastrophic slope failures with consequent liberation of greenhouse gases and significant effects on global climate to provide improved ground models for slope instability analyses we are investigating the influence of p t history on hydrate distribution in sediments through the development of laboratory techniques to enable geophysical quantification of hydrate morphology and fabric on hydrate stability

methane hydrate bearing sediments pore habit and implications abstract hydrate bearing sediments are relevant to the organic carbon cycle seafloor instability and as a potential energy resource sediment characteristics affect hydrate formation gas migration and recovery strategies we combine the physics of granular materials with robust compaction models to estimate effective stress and capillary pressure in order to anticipate the pore habit of methane hydrates as a function of the sediment characteristics and depth then we compare these results to an extensive database of worldwide hydrate accumulations compiled from published studies results highlight the critical role of fines on sediments mechanical and flow properties hydrate pore habit and potential production strategies the vast majority of hydrate accumulations 92 of the sites are found in fines controlled sediments at a vertical effective stress between z 400 kpa and 4 mpa where grain displacive hydrate pore habit prevails in the form of segregated lenses and nodules while permeation based gas recovery by depressurization is favored in clean coarse sediments gas recovery from fines controlled sediments could benefit from enhanced transmissivity along gas driven fractures created by thermal stimulation

origin of gas in gas hydrates as interpreted from geochemistry data obtained during the national gas hydrate program expedition 02 krishna godavari basin offshore india abstract this report presents the result of geochemical studies carried out on cores recovered from krishna godavari basin k g basin during the national gas hydrate program expedition 02 nghp 02 nghp 02 targeted gas hydrate accumulations in sand facies in the k g basin off the east coast of the indian peninsula three areas area b area c and area e in the k g basin were investigated during this expedition 10 research sites in k g basin were cored and samples for geochemistry analysis were collected high toc tn ratios indicate an input from terrestrial organic matter analysis of gas samples from pressure cores also acquired during nghp 02 were composed of mostly methane carbon isotopic studies show that methane gas sampled from recovered gas hydrate samples were derived from biogenic microbial sources this list of factors appears to indicate that the gas associated with the recovered hydrate bearing core samples were derived from a microbial source however the biogeochemical processes responsible for generating the microbial gases found with the recovered gas hydrates may not have been limited to current limits off the gas hydrate stability zone it is important to note here that microbial process likely extend to more than 1 km deep into the basin so gas coming from below the gh stability zone can still be from a microbial source in addition the microbial gas within the stability zone was likely in part recycled from hydrate accumulations that has passed through the base of the gas hydrate stability zone as a product of sedimentation with the dissociated microbial gas migration again vertically in the section entering the gas hydrate stability zone and reforming gas hydrates although the organic carbon required for in situ methanogenesis and gas hydrate formation is abundant in the shallow sedimentary section of the kg basin the faulted fractured and deformed stratigraphy observed in the kg basin coupled with high pore filling gas hydrate saturations at many sites suggests that advective processes may be contributing to the supply of methane to the gas hydrates in the kg basin the possible migration of gas from greater depths is also supported by seismic evidence of through going migration pathways that can connect the gas hydrate system with deeper petroleum systems it is important to note here that the deep conventional gas accumulations in the basin also contain microbially sourced gas

simulations of the 2004 lava flow at etna volcano using the magflow cellular automata model since the mechanical properties of lava change over time lava flows represent a challenge for physically based modeling this change is ruled by a temperature field which needs to be modeled magflow cellular automata ca model was developed for physically based simulations of lava flows in near real time we introduced an algorithm based on the monte carlo approach to solve the anisotropic problem as transition rule of ca a steady state solution of navier stokes equations was adopted in the case of isothermal laminar pressure driven bingham fluid for the cooling mechanism we consider only the radiative heat loss from the surface of the flow and the change of the temperature due to mixture of lavas between cells with different temperatures the model was applied to reproduce a real lava flow that occurred during the 2004 2005 etna eruption the simulations were computed using three different empirical relationships between viscosity and temperature

ancient wet aeolian environments on earth clues to presence of fossil live microorganisms on mars abstract ancient wet aeolian wet sabkha environments on earth represented in the entrada and navajo sandstones of utah contain pipe structures considered to be the product of gas water release under pressure the sediments originally had considerable porosity allowing the ingress of living plant structures microorganisms clay minerals and fine grained primary minerals of silt and sand size from the surface downward in the sedimentary column host rock material is of a similar size and porosity and presumably the downward migration of fine grained material would have been possible prior to lithogenesis and final cementation recent field emission scanning electron microscopy fesem and eds energy dispersive spectrometry examination of sands from fluidized pipes in the early jurassic navajo sandstone reveal the presence of fossil forms resembling fungal filaments some bearing hyphopodium like structures similar to those produced by modern tropical leaf parasites the tropical origin of the fungi is consistent with the paleogeography of the sandstone which was deposited in a tropical arid environment these fossil fungi are silicized with minor amounts of caco 3 and fe and in some cases a si al ratio similar to smectite they exist as pseudomorphs totally depleted in nitrogen adhering to the surfaces of fine grained sands principally quartz and orthoclase similar wet aeolian paleoenvironments are suspected for mars especially following catastrophic sediment charged floods of enormous magnitudes that are believed to have contributed to rapid formation of large water bodies in the northern plains ranging from lakes to oceans these events are suspected to have contributed to a high frequency of constructional landforms also known as pseudocraters related to trapped volatiles and water enriched sediment underneath a thick blanket of materials that were subsequently released to the martian surface forming piping structures at the near surface and constructional landforms at the surface this constructional process on mars may help unravel the complex history of some of the piping structures observed on earth on earth evidence for the constructional landforms has been all but erased and the near surface piping structures exposed through millions of years of differential erosion and topographic inversion now occur as high standing promontories if the features on both earth and mars formed by similar processes especially involving water and other volatiles and since the piping structures of earth provided suitable environments for life to thrive in the martian features in the northern plains should be considered as prime targets for physico mineral chemical microbiological analyses once the astrobiological exploration of the red planet begins in earnest

methane rich plumes on the carolina continental rise associations with gas hydrates seafloor venting of microbial gases occurs at 2167 m water depth over the blake ridge diapir gas rich plumes were identified acoustically in the water column up to 320 m above a pockmarked sea floor associated with active chemosynthetic biological communities plumes and venting fluids emanate from near a small fault that extends downward toward a dome in the bottom simulating reflector indicating that fluid and or gas migration is associated with gas hydrate bearing sediment below these plumes might be caused by gas bubbles or buoyant dumps of gas hydrate that float upward from the seafloor 18 refs 3 figs

relationship of gas hydrate concentration to porosity and reflection amplitude in a research well mackenzie delta canada abstract well logs acquired at the mallik 2l 38 gas hydrate research well mackenzie delta canada reveal a distinct trend showing that the resistivity of gas hydrate bearing sediments increases with increases in density porosities this trend opposite to the general trend of decrease in resistivity with porosity implies that gas hydrates are more concentrated in the higher porosity using the mallik 2l 38 well data a proportional gas hydrate concentration pghc model which states that the gas hydrate concentration in the sediment s pore space is linearly proportional to porosity is proposed for the general habitat of gas hydrate in sediments anomalous data less than 6 of the total data outside the dominant observed trend can be explained by local geological characteristics the anomalous data analysis indicates that highly concentrated gas hydrate bearing layers would be expected where sediments have high proportions of gravel and coarse sand using the parameters in the pghc model determined from resistivity porosity logs it is possible to qualitatively predict the degree of reflection amplitude variations in seismic profiles moderate to strong reflections are expected for the mallik 2l 38 well

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

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

detection of gas hydrates in faults using azimuthal seismic velocity analysis vestnesa ridge w svalbard margin accepted for publication in journal of geophysical research solid earth copyright 2020 american geophysical union further reproduction or electronic distribution is not permitted

nature and characteristics of the flows that carved the simud and tiu outflow channels mars 1 geomorphic and topographic relations of higher and lower levels of dissection within the simud and tiu valles outflow channels on mars reveal new insights into their formational histories we find that the water floods that carved the higher channel floors were primarily sourced from hydaspis chaos the floods apparently branched into distributaries downstream that promoted rapid freezing and sublimation of water and limited discharge into the lowlands in contrast we suggest that the lower outflow channels were carved by debris flows from hydraotes chaos surges within individual debris flows possessed variable volatile contents and led to the deposition of smooth deposits marked by low relief longitudinal ridges lower outflow channel discharges resulted in widespread deposition within the simud tiu valles as well as within the northern plains of mars

numerical modeling of lava flow cooling applied to the 1997 okmok eruption approach and analysis 1 throughout february and march of 1997 okmok volcano in the eastern aleutian islands of alaska erupted a 6 km long lava flow of basaltic a a within its caldera a numerical model for lava flow cooling was developed and applied to the flow to better understand the nature of its cooling radiation and convection from the surface as well as conduction to the ground were used to transport the flow s heat to its surroundings in the model internally a conduction only approach moved heat from the interior outward vesiculation latent heat generation and thermal conductivity changes with temperature are among the other factors that were dynamically accounted for results indicate that ambient temperature fluctuations on the scale of days to weeks must be taken into account to create an accurate short term prediction of lava surface temperature daily data of rainfall and ambient temperature as opposed to yearly averages greatly increased the accuracy of the model furthermore convective cooling of the lava surface was observed to be a dominant heat loss process during the first 200 days indicating the convective heat transfer coefficient is a prime determinant of the accuracy of the model for predicting surface temperatures over a longer cooling period 2 years thermal conductivity and porosity proved to be among the dominating factors for heat loss because of the limiting role of conductive heat flow in the interior the model s flexibility allows application to flows other than the 1997 okmok eruption

cooling rate of an active hawaiian lava flow from nighttime spectroradiometer measurements a narrow band spectroradiometer has been used to make nighttime measurements of the phase 50 eruption of pu u o o on the east rift zone of kilauea volcano hawaii on february 19 1992 a ger spectroradiometer was used to determine the cooling rate of an active lava flow this instrument collects 12 bit data between 0 35 to 3 0 m at a spectral resolution of 1 5 nm thirteen spectra of a single area on a pahoehoe flow field were collected over a 59 minute period 21 27 22 26 hst from which the cooling of the lava surface has been investigated a two component thermal mixing model flynn 1992 applied to data for the flow immediately on emplacement gave a best fit crustal temperature of 768 c a hot component at 1150 c and a hot radiating area of 3 6 of the total area over a 52 minute period within the time interval between flow resurfacings the lava flow crust cooled by 358 c to 410 c at a rate that was as high as 15 c min 1 our observations have significance both for satellite observations of active volcanoes and for numerical models of the cooling of lava flows during their emplacement

mylitta fluctus venus rift related centralized volcanism and the emplacement of large volume flow units mylitta fluctus is a volcanic flow field that covers approximately 300 000 km2 in southern lavinia planitia the flows are typically radar bright with uniform surface textures central channels are common maximum flow lengths range from 400 to 1000 km flow widths range 30 100 km in the medial and distal portions of the flow field the total volume of the flow field based on estimates of flow thickness is of the order of 2 104 km3 the flow field is composed of six smaller flow fields that are interpreted to represent major eruption events in the evolution of mylitta an asymmetric shield volcano 200 km in radius with a central caldera has been identified as the single major source it is located along a possible rift zone at the northern edge of lada terra no evidence for fissure fed eruptions is observed although eruptions may have occurred along fissures within the rift before the main vent centralized mylitta is similar in scale to many terrestrial flood basalt provinces although it is lower in total estimated volume and is distinguished by the presence of a central source edifice the origin of mylitta is proposed to be linked to regional extension and possible hotspot activity in a manner similar to that suggested for the origin of terrestrial flood basalts the lower apparent volume of mylitta relative to terrestrial flood basalts suggests that the amount of material upwelling from the mantle may have been lower in this case or that the formation of the flow field has not yet finished detailed studies of the morphology and distribution of flow fields similar to mylitta should yield insight into the variation and evolution of hotspot related volcanism and the formation of possible flood basalts on venus

a method for estimating eruption rates of planetary lava flows abstract a model that accounts for radiative losses from a partially crusted hotter core can be used to constrain eruption rates of single lobed planetary lava flows by assuming thermal characteristics are similar to terrestrial flows eruption rate can be expressed as a function of the area fraction of core exposed initial core temperature core temperature when the flow stops advancing crust thickness flow thickness and the density and heat capacity of the lava

multi frequency seismic study of gas hydrate bearing sediments in lake baikal siberia abstract in this paper we present and discuss the frequency dependent behaviour of the acoustic characteristics of methane hydrate bearing sediments in lake baikal siberia five different types of seismic sources airgun array two types of single airguns watergun and sparker are used encompassing a frequency bandwidth from 10 up to 1000 hz on low frequency airgun array data the base of the hydrate stability zone hsz is observed as a high amplitude bottom simulating reflection bsr with reversed polarity the amplitude and continuity of the bsr decrease or even disappear on medium to high frequency data a feature explained in terms of vertical and horizontal resolution the increasing reflection amplitude of the bsr with increasing offset the calculated reflection coefficient of the bsr and the occurrence of enhanced reflections below the bsr suggest the presence of free gas below the hsz the observation of some enhanced reflections extending above the bsr may be interpreted as an indication for free gas co existing with hydrates within the hsz amplitude blanking above the bsr is highly variable while the bsr itself appears to act as a low pass frequency filter for medium to high frequency data new single channel airgun profiles provide the first seismic information across the baikal drilling project bdp 97 deep drilling site at which hydrate bearing sediments were retrieved at about 200 m above the base of the local hsz at the drilling site there are no seismic characteristics indicative of the presence of hydrates combination of the drilling and seismic information has allowed us to make a rough estimation of the volume of hydrates and carbon stored in the sediments of lake baikal which lead us to conclude that the lake baikal gas hydrate reservoirs do not form a prospective energy resource

risk evaluation detection and simulation during effusive eruption disasters lava ingress into a vulnerable population will be difficult to control so that evacuation will be necessary for communities in the path of the active lava followed by post event population infrastructural societal and community replacement and or relocation there is a pressing need to set up a response chain that bridges scientists and responders during an effusive crisis to allow near real time delivery of globally standard products for a timely and adequate humanitarian response in this chain the scientific research groups investigating lava remote sensing and modelling need to provide products that are both useful to and trusted by the crisis response community requirements for these products include a formats that can be immediately integrated into a crisis management procedure and b in an agreed and stable standard a review of current capability reveals that we are at a point where the community can provide such a response as is the aim of the red seed risk evaluation detection and simulation during effusive eruption disasters working group this book is the first production of this group and is intended not only as a directory of current capabilities and operational service providers but also as a statement of intent and need while providing a simulation designed to demonstrate how a truly pan disciplinary response to an effusive crisis could work

vtfs project development of the lava flow simulation code lavasim with a model for three dimensional convection spreading and solidification 1 the lava flow simulation code lavasim has been developed to give accurate predictions of volcanic disasters and to support evacuation plans the code uses three dimensional analysis with free surface evaluation including boundary transport between the melt and the crust it is therefore applicable to various types of lava flows and flow behaviors such as flood basalts subaqueous lava flows and levee formation heat transfer between the lava and the ground air and water and between the melt and crust of the flow is calculated by using appropriate relations the code has been verified by applying it to actual lava flows and the simulation results have been compared with observations of the izu osima flows of 1986 the lava flow rate temperature and properties were assigned values based on data from existing literature the comparisons demonstrated the code s capability for prediction of inundated areas and maximum flow lengths the present code is expected to be useful for real time prediction during eruptions in addition to assessing volcanic hazards and designing protection structures for existing installations against possible future lava flows

methane migration within the submarine gas hydrate stability zone under deep water conditions abstract possible pathways of methane migration and associated gas hydrate accumulation are considered gas hydrates precipitate in water filtration routes when the methane concentration in water exceeds its solubility which significantly decreases within the hydrate stability zone towards the sea floor in the vicinity of the ascending free gas flows gas hydrates are formed within a diffusion aureole resulting from the difference between chemical potentials of gaseous and water dissolved methane the role of diffusion is also essential in the vicinity of gas saturated water flows as well as within and above the sections where biochemical methane is intensively generated a chemical potential gradient of dissolved methane which is a necessary condition for gas hydrate accumulation is created due to inhomogeneity of the geological medium manifested as temperature and water salinity gradients or changes of permeability the thermobaric gas hydrate stability zone is a geochemical barrier for hydrocarbon gas emigrating from sediments into the water column however methane is not completely preserved in a hydrate state it is unknown yet which fraction of migrating methane is detained on this barrier

potential impact on climate of the exploitation of methane hydrate deposits offshore abstract considerable attention has focussed on methane hydrates as a potential energy resource but much less on the potential environmental problems of exploiting these deposits in fact methane hydrate deposits represent a dynamic system formed as a result of the continuous migration of methane gas along fracture systems any exploitation of methane hydrates offshore will perforce take place in these unstable systems and could lead to the large scale release of ch 4 under unfavourable circumstances however most of this ch 4 would be oxidized to co 2 within the water column under steady state conditions only under exceptional circumstances would large scale release of ch 4 into the atmosphere take place the impact of exploiting these deposits offshore on global climate may therefore be limited provided serious efforts are made to minimize environmental impacts at present prospects for the commercial exploitation of methane hydrates are in their infancy considerable ingenuity will be required to satisfy the requirements of safe operating conditions mitigation of environmental hazards and commercial viability the need to exercise caution before attempting to exploit these deposits is emphasized

thickness of the gas hydrate stability zone gulf of mexico continental slope the maximum thickness of the gas hydrate stability zone ghsz at key gas hydrate study sites was estimated and a generalized ghsz profile across part of the central gulf of mexico slope was constructed maximum thickness of the ghsz increases with water depth at the shallowest site 540 m water depth from about 450 m to about 1150 m at the deepest site 1930 m water depth the occurrence of gas hydrate in the subsurface is largely controlled by structural focussing of hydrocarbons with gas hydrate most abundant at the rims of salt withdrawal basins and less abundant within intrasalt basins the postulated geometry of large subsurface gas hydrate accumulations shows strong structural control bottom simulating reflectors bsrs are absent or infrequently observed in the gulf of mexico because of structural focusing of the free hydrocarbon gases that form gas hydrate new insight to the geometry of the ghsz in the gulf of mexico continental slope will contribute to improved application of geophysics to map the distribution of gas hydrates improved understanding of three dimensional geometry of gas hydrate accumulations will contribute to better assessment of gas hydrate volumes as a future energy resource as a geohazard and will constrain theories relating the role of gas hydrate in past climate change

analysis of regional slope characteristics on venus and earth regional slope values for earth and venus are calculated for each 3 o x 3 o region of topography and the global characteristics of these magnitudes are examined and compared the effects on terrestrial regional slope due to ocean loading are treated by approximating the component of seafloor depth due to the weight of the overlying water column and removing this component from the ocean topography although regional slopes on venus and earth span the same range 0 00 2 4 o 0 07o the slope frequency distributions for the two planets differ significantly the most abundant regional slope values for the terrestrial cases earth and unloaded earth are 0 0 o and reflect the presence of vast plains associated with the continental interiors and ocean abyssal plain in contrast venus exhibits a peak in slope frequency at approximately 0 09 o perhaps indicating less effective planation processes in the absence of a hydrosphere surfaces with regional slope values of 0 07o 0 24 o are substantially more common on venus than on earth slopes in this range are associated with discrete features in the lowland and upland rolling plains provinces of venus and may be indicative of a geologic process that is not commonly observed on earth only 14 1 of all venus surfaces have regional slopes above 0 24 o compared to 26 1 for earth when mean regional slope is calculated as a function of elevation a distinctive positive correlation is expressed on venus in contrast the terrestrial cases exhibit a complex relationship marked by four modes related to the presence on earth of an active hydrosphere driven weathering regime a distinctive crustal dichotomy and plate tectonics the distinctions in the regional slope characteristics between venus and earth point to a simpler less diversified geology on venus

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

breaking wave induced cross shore tracer dispersion in the surf zone model results and scalings 1 the dispersion of surf zone tracers including pollutants and bacteria is determined by many processes acting over a range of timescales and space scales breaking waves bores are clearly important to cross shore tracer dispersion in the surf zone but little is known about the dispersal effects of bores here a simple model for bore induced cross shore dispersion are developed based upon the diffusion equation with an eddy diffusivity that propagates with the bores depth uniform tracer and bore induced mixing along with alongshore uniformity are assumed the bores are assumed well developed and the dispersion results are for a self similar constant wave height to water depth ratio surf zone four nondimensional parameters are identified and solution space is explored the tracer center of mass is approximately constant and tracer width grows with the square root of time tracer distribution becomes initially skewed after the passage of the first bore but becomes symmetric after multiple bores have passed the nondimensional tracer patch growth and dilution rates depend strongly upon the nondimensional phase speed and wave period the simple model results are consistent with the a boussinesq wave model where the breaking wave eddy viscosity is used for the bore eddy diffusivity the scaling of the dimensional parameters regarding the bore eddy diffusivity and the ranges of the nondimensional parameters are examined covariation of the nondimensional phase speed and wave period suggest that nondimensional tracer dispersion is largely cross shore independent

volcflow capabilities and potential development for the simulation of lava flows volcflow is a finite difference eulerian code based on the depth averaged approach and developed for the simulation of isothermal geophysical flows its capability for reproducing lava flows is tested here for the first time the field example chosen is the 2010 lava flow of tungurahua volcano ecuador the emplacement of which is tracked by projecting thermal images onto a georeferenced digital topography results show that at least for this case study the isothermal approach of volcflow is able to simulate the velocity of the lava through time as well as the extent of the solidified lava however the good fit between the modelled and the natural flow may be explained by the short emplacement time c 20 h of a thick lava c 5 m which could limit the influence of cooling on the flow dynamics thus favouring the use of an isothermal rheology

the end of the ice age methane gas hydrates may have contributed to the rapid rise in atmospheric ch4 co2 and global temperatures at the end of the last major glaciation about 13 500 years ago given suitable orbital conditions and insolation at high latitude a small triggering event such as the release of one or more arctic gas pools may have initiated massive release of methane from hydrate under ice and in permafrost the consequent greenhouse warming would have provided strong positive feedback amplifying emission this warming driven by ch4 may have induced the release of co2 from the oceans to the biosphere stabilizing the interglacial carbon cycle

eruption and emplacement of flood basalt an example from the large volume teepee butte member columbia river basalt group flows of the teepee butte member grande ronde basalt issued from a vent system in southeastern washington northeastern oregon and western idaho three distinct basalt flows were erupted the limekiln rapids flow the joseph creek flow and the pruitt draw flow together these mappable flows cover more than 52 000 km sup 2 and have a volume exceeding 5 000 km sup 3 a portion of the vent system for the joseph creek flow is exposed in cross section in joseph canyon washington it is one of the best preserved columbia river basalt group vent complexes known the vent complex is about 1 km in cross section 30 m high and composed of deposits characteristic of hawaiian type volcanism the vent is asymmetrical the eastern rampart consists of intercalated pyroclastic deposits and thin pahoehoe flows the western rampart is composed wholly of pahoehoe flows flows of the teepee butte member are compositionally homogeneous and were emplaced as sheet flows each having several local flow units our study supports the importance of linear vent systems and the westward palouse slope along with the large volume lava flows in controlling the distribution of columbia river basalt group flows other factors including the number of active fissure segments andmore topography modified the shape of the flows and the number of flow units 45 refs 19 figs 2 tabs less

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

gas hydrates free gas distribution and fault pattern on the west svalbard continental margin summary a 3 d tomographic analysis of seismic velocity and attenuation fields is presented with the purpose to analyse the intimate relation of gas hydrates and free gas distribution with the fault pattern the 3 d four component seismic data have been acquired offshore western svalbard the analysis of the subbottom topography of the base of the stability field of gas hydrates indicated by the bottom simulating reflector and the thickness of the underlying free gas bearing zone suggest a fault induced compartmentalization of the gas reservoir the proposed fluid and gas circulation scheme assumes deep sourced warm fluids moving upwards mainly along high permeability faults and fractures below the gas hydrate stability zone faults change from being a pathway of fluid flow to being barriers to fluid flow in the hydrate stability zone consequently below the hydrate stability zone free gas is transferred from the permeable faults to non faulted but fault bounded sediments where it accumulates below the base of the hydrate stability zone producing a significantly thicker free gas layer the tomographic approach is therefore proposed as an effective procedure to provide detailed information on 3 d p and s wave velocity and attenuation distribution in marine sediments and specifically to examine the details of the distribution of the gas hydrates and of the free gas for which the dependence on the vp vs and qp is now fairly well known

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

regional correlation of grande ronde basalt flows columbia river basalt group washington oregon and idaho the tholeiitic flood basalts of the columbia river basalt group of middle and late miocene age cover more than 200 000 km2 in washington oregon and idaho the most voluminous formation of the group the grande ronde basalt erupted for 2 m y from north northwest trending fissure systems concentrated in southeast washington and adjacent oregon and idaho four magnetostratigraphic units designated r1 n1 r2 and n2 from oldest to youngest are recognized on the basis of polarity in the grande ronde and provide the broad stratigraphic framework for the formation in this study major element chemistry and relative stratigraphic position within the polarity intervals are used to identify and correlate individual flows and sequences of flows within the grande ronde basalt on a regional scale systematic examination of more than 350 analyses from 47 stratigraphic sections show that most flows fall into one of five major chemical groupings which are distinguished primarily by small but significant variations in mgo tio2 and p2o5 content in addition four minor chemical types local to the eastern part of the province have been identified feeder dikes of each chemical type have also been located flows or packets of flows of each chemical type can be correlated between field sections to define specific chemical stratigraphic subunits these subunits consist of several flows collectively 30 150 m thick subunits of most chemical types are repeated at irregular intervals throughout the formation no progressive chemical trend occurs within the grande ronde many of the chemical stratigraphic subunits extend to the margins of the province although most are confined to the source region in eastern washington although the total number of subunits is less in the west away from the fissure systems the total thicknesses of the n2 and r2 magnetostratigraphic units are each as thick or thicker than the corresponding units in eastern washington the greatest thicknesses occur in the central part of the province within the pasco basin the distribution of basalt relative to the location of vents as well as the relative east west thicknesses suggests that basalt flowed hundreds of kilometres westward during the most voluminous grande ronde eruptions ponding against the irregular margin of the cascade range and being diverted through the ancestral columbia gorge toward the washington oregon coast between these huge sheetflood events smaller eruptions blanketed areas within the source region and ongoing regional subsidence created a shallow westward draining basin in the center of the province

a model for the shape of lava flow fronts 1 the shape of the front of a lava flow is controlled by the forces acting on the lava and in turn controls the flow dynamics we present an analysis of the shape of the front of an advancing lava flow considering both a newtonian fluid and a bingham fluid which is the most commonly used non newtonian rheological model for lava we assume than the flow front is moving at constant velocity on a sloping plane the flow is considered as having an infinite extent perpendicularly to the flow direction so that the problem is two dimensional the forces producing the flow advance are the gravity force and the pressure gradient due to the curvature of the flow surface the differential equation for the shape of the front is solved analytically both in the case of a newtonian fluid and in the case of the bingham fluid since the fluid is considered as homogeneous and isothermal the calculated shape applies to the fluid core of the flow front the presence of a solid crust at the top of the flow producing variable amounts of solid debris at the flow snout alters the observable shape of the front and is taken into account in order to compare the model front shapes to those observed in the field

gas hydrate physical properties imaging by multi attribute analysis blake ridge bsr case history abstract we analysed the bottom simulating reflector bsr of the blake ridge by using the multi attribute analysis this technique allows prediction of petrophysical geological parameters along seismic lines velocity porosity density resistivity etc starting from log data seismic attributes can be thought of as all parameters derived from seismics by assuming that a seismic trace is the real component of a complex one the first attributes that can be calculated are the instantaneous amplitude the instantaneous phase and the instantaneous frequency all the other attributes that will be considered are derived from the previous ones the algorithm that allows the correlation between logs and seismics is the generalised multiple linear regression this equation is solved by a least squares approach called training phase which effectively consists of training the seismics to predict the reservoir parameter of interest at the tie locations the resulting function is then applied to the seismic profile generating a target log predicted section we obtained five sections vsp and p wave velocity density porosity and resistivity each of them representing the distribution of the corresponding property along the profile they permitted better characterisation of the nature of the bsr present in the blake ridge area the obtained velocity section was finally translated in terms of gas hydrate and free gas distribution by using theoretical approach

lava flows as kinematic waves a recently proposed model for the emplacement of lava flows is reinterpreted as a kinematic wave theory for the depth of the flow with this interpretation the longitudinal profile of an advancing flow is considered to be a propagating waveform with its length limited continuously by the amount of lava extruded the application of kinematic wave formalism provides new insights into the effects of time dependent source behavior on the shape and extent of the wave eruption behavior with a period of increasing flow depth at the source is shown to produce so called breaking points in the depth profile where the kinematic wave model itself could be invalid two models of such eruption behavior are investigated and this is shown not to be the case specifically when the conservation of lava volume is imposed the breaking points always reside beyond the front of the wave in general it is found that source behavior propagates downstream faster than the flow advances thus only a fraction of the source time dependence is reflected in the shape of the kinematic wave the remainder of the time dependent source effects must be deposited in the flow front lateral margins or solidifying crust or be dissipated irretrievably by processes not included in the model the fraction of eruption history contained in the advancing waveform depends crucially on the nature of the flow rate flow depth relation for the lava distal surface waves budding at the nose of the flow distal levee collapse and other volcanological observations may be manifestations of time dependent source behavior that advanced beyond the kinematic wave front

rheology and topography control the path of a lava flow insight from numerical simulations over a preexisting topography 1 determination of flow path is strongly controlled by both the preexisting topography and rheology of the lava flow using the okmok 1997 eruption as an example lava flow we perform numerical simulations of bingham fluids flowing over preexisting topography and find that flow rheology determines whether or not new lobe formation or bifurcation occurs from the main flow at a topographic divide or remains confined by local topography therefore lobe or branch length may increase for higher viscosity flows when considering the effect of topographic control also even one order of magnitude difference in the rheological properties allows lava flows to move in completely different paths which may suggest that flow bifurcation due to topographic control provides insight to the local rheological properties of a lava flow the effect reported here should be taken into account in risk assessments of future volcanic hazards

a mechanism for the formation of methane hydrate and seafloor bottom simulating reflectors by vertical fluid expulsion bottom simulating reflectors bsr are observed commonly at a depth of several hundred meters below the seafloor in continental margin sedimentary sections that have undergone recent tectonic consolidation or rapid accumulation they are believed to correspond to the deepest level at which methane hydrate clathrate is stable we present a model in which bsr hydrate layers are formed through the removal of methane from upward moving pore fluids as they pass into the hydrate stability field in this model most of the methane is generated below the level of hydrate stability but not at depths sufficient for significant thermogenic production the methane is primarily biogenic in origin the model requires either a mechanism to remove dissolved methane from the pore fluids or disseminated free gas carried upward with the pore fluid the model accounts for the evidence that the hydrate is concentrated in a layer at the base of the stability field for the source of the large amount of methane contained in the hydrate and for bsrs being common only in special environments strong upward fluid expulsion into the hydrate stability field does not occur in normal sediment depositional regimes so bsrs are uncommon upward fluid expulsion does occur as a result of tectonic thickening and loading in subduction zone accretionary wedges and in areas where rapid deposition results in initial undercconsolidation in these areas hydrate bsrs are common the most poorly quantified aspect of the model is the efficiency with which methane is removed and hydrate is formed as pore fluids pass into the hydrate stability field the critical boundary in the phase diagram between the fluid plus hydrate and fluid only fields is not well constrained however the amount of methane required to form the hydrate and limited data on methane concentrations in pore fluids from deep sea boreholes suggest very efficient removal of methane from rising fluid that may contain less than the amount required for free gas production in most fluid expulsion regimes the quantity of fluid moved upward to the seafloor is great enough to continually remove the excess chloride and the residue of isotope fractionation resulting from hydrate formation thus as observed in borehole data there are no large chloride or isotope anomalies remaining in the local pore fluids the differences in the concentration of methane and probably of co2 in the pore fluid above and below the base of the stability field may have a significant influence on early sediment diagenetic reactions

transient phenomena in vesicular lava flows based on laboratory experiments with analogue materials realistic lava flow models require a comprehensive understanding of the rheological properties of lava under a range of stress conditions previous measurements have shown that at typical eruption temperatures lavas are non newtonian this is commonly attributed to the formation and destruction of crystal networks in the present study the effects of bubbles on the time dependent non newtonian properties of vesicular melts are investigated experimentally using analogue materials the shear thinning behaviour of bubbly liquids is shown to be dependent on the previous shearing history this thixotropic behaviour which was investigated using a rotational vane viscometer is caused by delayed bubble deformation and recovery when subjected to changes in shear stress the viscoelastic transition and the transient flow behaviour of analogue fluids were studied using both a rotational vane viscometer and oscillatory shear apparatus these experiments have shown that vesicular suspensions are viscoelastic fluids with a yield strength power law rheology and a non zero shear modulus these properties are also found in polymer fluids commonly used as analogue materials for lava such as gum rosin we show that when materials with this rheology are accelerated in channels they may be fragmented and when they flow through a narrowing conduit pulsating flow can develop as a consequence of a transition from slip to non slip conditions at the conduit wall this has important implications both for effusive and explosive volcanic eruptions

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

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

variations in temperature gradients identify active faults in the oregon accretionary prism abstract a multi channel seismic survey mcs yields high resolution images of geologic structures within the oregon accretionary prism in addition to revealing the internal geometry of the prism a prominent bottom simulating reflector bsr provides indirect estimates of temperature gradients the bsr marks the phase transition within the pore space of the sediments of small amounts of solid gas hydrate above the reflector to free gas below although the absolute value of temperature gradients depends on assumptions of gas hydrate stability conditions velocity functions and seafloor temperature relative differences reflecting regional trends and local anomalies are unaffected by the assumptions involved in calculation of temperature gradient from the position of the bsr broad scale landward decreases in temperature gradient reflect the increasing depth to the oceanic crust across the accretionary prism correlation of anomalously high temperature gradients with two out of sequence thrusts indicates that these structures are currently acting as conduits for warm fluids

putative ice flows on europa geometric patterns and relation to topography collectively constrain material properties and effusion rates europa s surface exhibits numerous small dome like and lobate features some of which have been attributed to fluid emplacement of ice or slush on the surface we perform numerical simulations of non newtonian flows to assess the physical conditions required for these features to result from viscous flows our simulations indicate that the morphology of an ice flow on europa will be at least partially influenced by pre existing topography unless the thickness of the flow exceeds that of the underlying topography by at least an order of magnitude three classes of features can be identified on europa first some possibly most putative flow like features exhibit no influence from the pre existing topography such as ridges although their thicknesses are generally on the same order as those of ridges therefore flow processes probably cannot explain the formation of these features second some observed features show modest influence from the underlying topography these might be explained by ice flows with wide ranges of parameters ice temperatures 230 k effusion rates 10 7 m 3 year 1 and a wide range of grain sizes although surface uplift e g by diapirism and in situ disaggregation provide an equally compelling explanation third several observed features are completely confined by pre existing topographic structures on at least one side these are the best known candidates for flow features on europa if these features resulted from solid ice flows then temperatures 260 k and grain sizes 2 m are required such small grain sizes seem unlikely low viscosity flows such as ice slurries or brines provide a better explanation for these features our results provide theoretical support for the view that many of europa s lobate features have not resulted from solid ice flows

mapping hydrate stability zones offshore scotland one practical method to reduce environmentally damaging greenhouse gas emissions is through the geological storage of carbon dioxide deep warm storage of carbon dioxide is currently taking place at sleipner north sea and weyburn canada it is however also possible to store carbon dioxide as a liquid and hydrate in cool sub seabed sediments offshore north and west of scotland seafloor pressures and temperatures are suitable for hydrate formation in addition to the possibility of natural methane hydrate being present in this region conditions may also be favourable for carbon dioxide storage as a liquid and hydrate a computer program has been developed to calculate the depth to the base of the carbon dioxide and methane hydrate stability zones in two offshore regions the faeroe shetland channel and the northern rockall trough results predict that methane hydrate remains stable to a maximum depth of 650 m below the seabed in the faeroe shetland channel and 600 m below the seabed in the northern rockall trough the carbon dioxide hydrate stability zone extends below the seabed to a depth of 345 and 280 m respectively no physical evidence for the existence of natural hydrate in these regions has been confirmed suitable conditions for carbon dioxide storage as a liquid and hydrate exist and should this storage method be developed further a more refined program and greater offshore investigations to improve data sets would be necessary to scope the full potential