Overpressure Build-up Research Articles

A 3D model for chimney formation in sedimentary basins

This paper introduces a 3D model for chimney formations in tight rocks in sedimentary basins. This is an adaption of a model for hydraulic fracturing in an anisotropic stress field by fluid injection (fracking). The model assumes that a chimney formation is triggered and sourced by overpressure build-up in permeable units, such as reservoirs or aquifers. Cells in the numerical models fracture when the fluid pressure exceeds the least compressive stress and a random rock strength. Chimney growth is represented by chains of cells (branches) that emanate from the base of the cap rock. The branches have an enhanced permeability during ascension, because the fluid pressure in the fracture network is greater than the least compressive stress. When the branches reach the hydrostatic surface, the fluid pressure drops below the fracture pressure and the fracture network closes. The reservoir is drained by the branches in the closed fracture network that reaches the seafloor. The model produces pipe-like structures and chimneys as accumulations of branches that reach the surface. The degree of random rock strength controls how pipe-like the chimneys become. Chimney formation stops when the rate of fluid leakage through the chimneys surpasses the production of excess fluid by the overpressure-building process. A “low” permeability of the chimney branches produces wide chimneys with many branches, and a “high” permeability gives narrow chimneys made of just a few branches. The model is demonstrated in a setup that could be relevant for the chimneys observed in the cap rock over the Utsira aquifer in the North Sea. By using the proposed model, the permeability of such chimneys is estimated to be of the order of 10 μD.

On the propagation dynamics of lean H2/CO/air premixed flame

Syngas is a promising alternative fuel. The combustion of lean H2/CO meets the demand of high efficiency with low emission. In this paper, the propagation dynamics of lean H2/CO/air premixed flame in a closed duct were experimentally investigated at an atmospheric condition. Propagation of the premixed flame is recorded by using high-speed cinematograph, and results show that the tulip flame is attained in all cases while the occurrence of tulip distortion is determined by both equivalence ratios and hydrogen volume fractions. The flame tip location and speed are attained through using image processing technique. Results show that the analytical theory, which is firstly proposed to model the flame acceleration in tulip flame propagation phase, can be used to predict the early phase flame tip motion in some limited cases. In fuel-lean combustion, with the effect of the diffusive-thermal instability, the analytical theory underestimates the flame tip motion, but overestimates the time instant of the flame initial touching the lateral walls. The overpressure build-up is specially scrutinized in conjunction with the scaled flame tip speed. The disorderly scaled flame tip speed of distorted tulip flame indicates that the distorted tulip flame is a phenomenon which relates to pressure waves. The pressure wave is of importance for tulip distortion, but it cannot change the overpressure build-up directly. Finally, both the flame-wall interaction and the combustion instability have a crucial effect on flame propagation dynamics, and these factors should be accounted for the build of flame propagation models.

The behavior of methane/hydrogen/air premixed flame in a closed channel with inhibition

Hydrogen enriched natural gas (HNG) is a promising alternative fuel. But the blended fuel will inevitably have different ignition and combustion characteristics as compared to natural gas. The extent of the resulting difference depends on the percentage of hydrogen addition. It may affect the compatibility of combustion systems and have safety implications. The present study was aimed at enhancing the safety of HNG through inhibition by inert gases. Laboratory tests were conducted for methane/hydrogen/air premixed flame propagating in a closed channel with either nitrogen (N2) or carbon dioxide (CO2) as the inhibitor. Mixtures with different hydrogen volumetric fractions in fuel, including 0%, 20%, 50% or 80% were investigated. The flame shape evolution and the overpressure in the channel were recorded by high-speed Schlieren photography and pressure sensor, respectively. The flame shape was found to change in various ways depending on the inhibitor and hydrogen content. The pressure wave had remarkable impacts on flame and pressure dynamics. The effect of buoyancy on the flame deformation was observed and discussed. Both N2 and CO2 were found to have considerable inhibiting effect on the flame speed and overpressure build-up in the channel while the inhibiting effect of CO2 was stronger. The inhibition mechanisms of either N2 or CO2 were revealed from thermal and kinetic aspects.

AN OVERVIEW OF CLASTIC DIKES: SIGNIFICANCE FOR EARTHQUAKE STUDY

Clastic dikes are often the only evidence of past disasters in poorly exposed areas and therefore their findings are extremely important for earthquake study. However, the variety of their origins greatly complicates the use of clastic dikes to assess the seismic hazards within the manifold environments. This paper systematizes main triggers, formation mechanisms and some matching indicative features of tabular and cylindrical bodies with an emphasis on the importance of revealing the injection dikes formed by fluidized injection of clastic material into the host sedimentary layers (from the bottom upwards) and associated with overpressure buildup and hydraulic fracturing. Based on the revision of known seismic liquefaction features and specific descriptions of the injection dikes, this overview defines 12 general and 12 individual geological and structural criteria (for study in sectional view), which make it possible to establish confidently the earthquake origin of the dikes caused by fluidization from seismic liquefaction. In addition, ground penetrating radar data correlating with trenching suggest indicative searching criteria of the injection dikes on radargrams, namely: a pipe‐shaped anomaly or a composite anomaly combining a tubular form in the lower part with an isometric – in the upper [i]; relatively high values of unipolar positive echoes on the trace of GPR signal [ii]; an occurrence of the same anomaly on adjacent parallel profiles located the first tens of meters apart [iii]; and stratigraphic disruptions of the radar events on the background of their continuous horizontal position [iv]. Finally, the paper illustrates that the clastic dikes can be successfully applied to determine the age and the recurrence interval, the epicenter location and a lower‐bound magnitude/intensity of paleoearthquakes, thus providing geological data for seismic hazard assessments in the regions, in which unconsolidated deposits capable to liquefaction are common.

Linking CO2 degassing in active fault zones to long-term changes in water balance and surface water circulation, an example from SW Turkey

Calcite veins are commonly found at shallow depth (a few metres below the surface) in damage zones of active normal fault systems in southwest Turkey. Although earlier studies demonstrated the link between the vein formation and seismicity, the association of near-surface carbonate precipitation with climate-driven hydrological conditions (water table, amount of precipitation and evaporation, and water discharge) is poorly understood. In this study, using the U/Th dating method we investigate the timing of vein formation and the interrelationship between tectonic and climatic-related hydrological processes. Carbonate precipitation is interpreted to occur as a result of sudden pressure drops and CO2 release after earthquake-induced fracturing. Vein formation mostly occurred during glacial periods, which coincide with slow growth rates and higher oxygen isotope values of speleothems from the Eastern Mediterranean region. We relate these episodes to reduced winter rainfall due to the decrease in westerly flow in SW Turkey. These somewhat drier conditions influenced the chemical composition of circulating water, creating conditions conducive to carbonate precipitation and sealing of damage zones. These conditions also facilitated CO2 accumulation and overpressure build-up in the rupture zones. Failure of the faults resulted in the release of large volumes of CO2-rich fluids and the generation of shallow carbonate veins. It is proposed that during phases of increased winter rainfall CO2 is advected to the surface and discharged as passive degassing when meteoric water circulation is enhanced. While regional tectonics is the ultimate driver of fault activity and fracture formation, climate-driven near-surface hydrological changes may have played an important role in modulating CO2-rich fluid circulation and surface discharge.

Overpressure development in sedimentary basins induced by chemo-mechanical compaction of sandstones

Abstract Mechanisms of overpressure build-up resulting from chemically-induced compaction are investigated by considering that intergranular pressure-solution, controlled by temperature and effective stresses, is the dominant process of chemical deformation in sandstones. The numerical simulations are performed using a thermo-poro-mechanical tool based on the finite element method specifically devised to deal with sedimentary basin modeling. At the material level, purely mechanical and chemo-mechanical deformations are respectively addressed by means of plastic and viscoplastic constitutive components. Porosity data of the Middle Jurassic Garn Formation from the Haltenbanken area of the Mid-Norwegian Continental Shelf are taken as reference for calibration of the sandstone model to be used on synthetic cases of a siliciclastic basin in oedometric conditions. Two situations are proposed involving different depositional sequences of sandy and shaly sediments with the aim to assess the permeability effect in the numerical model. The results have shown that early overpressure development in low permeability formations preserves sandstone porosities by reducing effective stresses and thus retarding pressure-solution compaction, whereas higher effective stresses associated with permeable depositional environments may lead to important chemo-mechanical deformation, resulting in low porosity sandstones and significant overpressure generation at later stages of basin history. An additional case is finally analyzed to investigate the consequences of pressure-solution inhibition due to diagenetic grain coating in a sandstone reservoir. The simulation resulted in porosity preservation and lower overpressure values, showing that a sedimentary basin submitted to an important level of chemo-mechanical compaction can present substantially higher overpressure distribution than basins where this phenomenon did not take place. The paper highlights the importance of integrating stresses, fluid pressure and temperature to represent the porous material evolution in order to describe the geological state of sedimentary basins.

Estimation of Vent Radii From Video Recordings and Infrasound Data Analysis: Implications for Vulcanian Eruptions From Sakurajima Volcano, Japan

AbstractWe estimated the vent radius within Showa Crater of Sakurajima volcano from ejection velocity and flow rate of gas‐particle mixtures. The ejection velocity was calculated from video recordings, and the flow rate and volume from infrasound data. Based on the assumption that the vent shape does not change during an explosion, the vent radius was estimated from 201 impulsive Vulcanian eruptions at Showa Crater, yielding values of 6.4–42.3 m (median 23.8 m), which is comparable with the width of fresh lava capping the vent, as photographed from a helicopter. Long‐term changes in vent radius (i.e., over several months) show a relationship with magma accumulation within a reservoir 2–5 km beneath the crater. If the top of the conduit is assumed to be cylindrical, then the vertical extent of the gas‐rich zone is estimated to be 120 m, which may reflect the depth of gas accumulation and buildup of significant overpressure.

NE Atlantic continental slope stability from a numerical modeling perspective

Trough mouth fans are environments characterized by high sediment supply during glacial stages and the occurrence of large-scale instabilities. The geological record indicates that several of these environments have failed repeatedly resulting in large submarine landslides. The roles of sedimentation rate, weak layers, glacial loading and unloading as well as seismic activity on triggering megaslides in trough-mouth-fan systems is still unclear. A better understanding of the preconditioning factors, triggers and consequences of these landslides is crucial due to the hazard they pose to coastal communities and offshore industries.In this paper, we focus on the North Sea Trough Mouth Fan, which is the result of massive glacial sediment input delivered to the shelf edge through the Norwegian Channel, southeast Nordic Seas margin. The Tampen Slide, one of several large paleo-landslides that have happened within the North Sea Trough Mouth Fan, took place at c. 130 ka (end of MIS 6), and removed an estimated 1800 km3 of sediment.Here, we use boundary conditions from the Tampen Slide and 2D Finite Element Modeling (Abaqus software from Simulia) to evaluate the effects of variations in sedimentation rates as well as sediment properties on the generation of excess pore pressure, fluid flow, and slope stability along the axis of the trough-mouth-fan system. The model domain, 40 km in length and 2 km in height, is dominated by glacigenic debris flows and glacimarine sediment deposits. We use geotechnical data measured on samples of glacigenic and glacimarine sediment deposits from the nearby Ormen Lange gas field area to constrain the model. We evaluate the stability of the slope under various scenarios, including constant sediment loading, episodic changes in sedimentation rates and abrupt pulses in sediment delivery for a 61 kyr period (MIS 6). The models show that increased sedimentation rates during glacial stages do not generate sufficient excess pore pressure to set off a landslide. Furthermore, the simulated overpressures for the different sedimentation scenarios do not significantly differ at the end of the model runs. The results also highlight the importance of a basal glacimarine sediment layer underneath the rapidly-deposited sediments for the build-up of overpressure. Consequently, this glacimarine sediment layer has the inherited potential to act as a weak layer facilitating instability. However, as overpressure due to sediment deposition alone does not result in slope failure, we couple the preconditioned slope with earthquake ground shaking. Based on attenuation models, an earthquake of approximately M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the landslide. Therefore, we suggest glacial sedimentation and a glacimarine sediment layer to represent preconditioning factors, and seismic shaking as the final trigger mechanism for the Tampen Slide, i.e. similar to the situation that lead to the development of the Storegga Slide in the same area.

Oscillatory nature of the Okmok volcano's deformation

The time-dependent deformation of volcanic edifices can help one understand the dynamics of pre-eruptive overpressure build-up in magma chambers. Thus, geodetic time series recorded at the Okmok volcano, in Alaska, show a pattern of fast and short inflations — referred to as “pulses” — followed by either slower and longer deflations, or time intervals with no deformation. This pattern is superimposed onto a longer-period inflation. A rapid inflation occurred just before the 2008 eruption, which suggests that the underlying process may lead to eruptions. It is crucial to understand whether such a behavior is driven by external forcing, such as melt supply variations, or whether it can develop spontaneously within the volcano's plumbing system. Here we model the observed oscillations (2004–2008) as resulting from the hydraulic interaction between two shallow magma chambers fed by a deeper source region, a geometry that is consistent with geochemical, petrological, and geophysical data. The model shows that episodes of periodic fast inflations occur (i) when a viscosity gradient is present in the vertical pipe, for instance as the result of a temperature gradient; and (ii) when the flux supplying the shallower chamber lies between two bounds that we derive analytically. The deformation pulses observed at Okmok can, therewith, be fully explained by the internal variability of the magmatic system and do not require time-variable external forcing. The proposed model can also be seen as an improvement upon the classic hydraulic models regularly used to explain a commonly observed pattern of volcanic deformations, i.e. exponential inflation.

The interplay of magmatism and tectonics: An example based on the satellite scoria cones at Llaima volcano, Chile

We present a geochemical and mineralogical study of the satellite scoria cones at Llaima volcano, Chile, providing insights on magmatic processes and how these are affected by the local and regional tectonics. At Llaima, we identify two different and distinctive groups of satellite scoria cones with a common magmatic source but different petrological evolutions. Cones from group 1 (the “glomeroporphyritic group”), predominantly occur in the NE flank of the volcano, are characterized by basaltic to basaltic andesitic compositions (51–55 wt% SiO2) and have glomeroporphyritic textures. We have interpreted these cones as the product of magma replenishment, followed by an unimpeded propagation of their feeder dikes controlled mainly by the regional stress. As a result, dikes are emplaced parallel to the regional σ1, and perpendicular to the axis of local crustal extension. Cones from the group 2 (the “pilotaxitic group”), appear at the NE, NW and SW flanks of the volcano, they have more evolved compositions (55–60 wt% SiO2) and textures lacking glomerocrysts. Their location and morphometric parameters suggest that their feeder dike emplacement is mainly controlled by the stress exerted by the load of the volcanic edifice, where the compressional stress hinders magma ascent, allowing fractionation and volatile overpressure buildup. The characteristic texture of these cones is interpreted as fractionation, followed by a single crystallization event upon eruption. The lack of scoria cones at the SE flank is attributed to the local horizontal compressional stress caused by the local tectonic deformation associated to the Liquiñe-Ofqui Fault Zone.

Submarine slope failures due to pipe structure formation

There is a strong spatial correlation between submarine slope failures and the occurrence of gas hydrates. This has been attributed to the dynamic nature of gas hydrate systems and the potential reduction of slope stability due to bottom water warming or sea level drop. However, 30 years of research into this process found no solid supporting evidence. Here we present new reflection seismic data from the Arctic Ocean and numerical modelling results supporting a different link between hydrates and slope stability. Hydrates reduce sediment permeability and cause build-up of overpressure at the base of the gas hydrate stability zone. Resulting hydro-fracturing forms pipe structures as pathways for overpressured fluids to migrate upward. Where these pipe structures reach shallow permeable beds, this overpressure transfers laterally and destabilises the slope. This process reconciles the spatial correlation of submarine landslides and gas hydrate, and it is independent of environmental change and water depth.

Early overpressuring in organic-rich shales during burial: evidence from fibrous calcite veins in the Lower Jurassic Shales-with-Beef Member in the Wessex Basin, UK

Field, petrographic and geochemical analysis of fibrous calcite veins in the Lower Jurassic Shales-with-Beef Member in the Wessex Basin was conducted to investigate the formation mechanism of the veins. Bedding-parallel fibrous calcite veins, including beef veins and tabular cone-in-cone structures, are widespread in the black shales. The calcite veins consist of subvertical fibrous crystals and a dark median zone. The median zone contains scattered clays, pyrite microcrystals, skeletal fragments and amorphous organic matter. The veins exhibit moderate carbon isotope values, ranging from −1.515 to 2.732‰. The oxygen isotope composition ranges from −8.872 to −4.521‰, which is possibly too negative to reflect the primary porewater oxygen isotope signatures and indicates a porewater modification. It is interpreted that the veins mainly derive carbonates from seawater inorganic carbon and bioclasts. The veins formed as closed-system hydraulic fractures in overpressured cells during sediment degassing in the methanogenic zone. The shale beds with a high total organic carbon content could have generated abundant CO 2 , which may have resulted in either the cementing of the pores in the matrix or overpressure buildup. The skeletal fragments provide a control on the spatial distribution of veins as nuclei for calcite precipitation from supersaturated pore fluids.

Novel basin modelling concept for simulating deformation from mechanical compaction using level sets

As sedimentation progresses in the formation and evolution of a depositional geologic basin, the rock strata are subject to various stresses. With increasing lithostatic pressure, compressional forces act to compact the porous rock matrix, leading to overpressure buildup, changes in the fluid pore pressure and fluid flow. In the context of petroleum systems modelling, the present study concerns the geometry changes that a compacting basin experiences subject to deposition. The purpose is to track the positions of the rock layer interfaces as compaction occurs. To handle the challenge of potentially large geometry deformations, a new modelling concept is proposed that couples the pore pressure equation with a level set method to determine the movement of lithostratigraphic interfaces. The level set method propagates an interface according to a prescribed speed. The coupling term for the pore pressure and level-set equations consists of this speed function, which is dependent on the compaction law. The two primary features of this approach are the simplicity of the grid and the flexibility of the speed function. A first evaluation of the model concept is presented based on an implementation for one spatial dimension accounting for vertical effective stress. Isothermal conditions with a constant fluid density and viscosity were assumed. The accuracy of the implemented numerical solution for the case of a single stratigraphic unit with a linear compaction law was compared to the available analytical solution [38]. The multi-layer setup and the nonlinear case were tested for plausibility.

Uncertainty quantification of overpressure buildup through inverse modeling of compaction processes in sedimentary basins

This study illustrates a procedure conducive to a preliminary risk analysis of overpressure development in sedimentary basins characterized by alternating depositional events of sandstone and shale layers. The approach rests on two key elements: (1) forward modeling of fluid flow and compaction, and (2) application of a model-complexity reduction technique based on a generalized polynomial chaos expansion (gPCE). The forward model considers a one-dimensional vertical compaction processes. The gPCE model is then used in an inverse modeling context to obtain efficient model parameter estimation and uncertainty quantification. The methodology is applied to two field settings considered in previous literature works, i.e. the Venture Field (Scotian Shelf, Canada) and the Navarin Basin (Bering Sea, Alaska, USA), relying on available porosity and pressure information for model calibration. It is found that the best result is obtained when porosity and pressure data are considered jointly in the model calibration procedure. Uncertainty propagation from unknown input parameters to model outputs, such as pore pressure vertical distribution, is investigated and quantified. This modeling strategy enables one to quantify the relative importance of key phenomena governing the feedback between sediment compaction and fluid flow processes and driving the buildup of fluid overpressure in stratified sedimentary basins characterized by the presence of low-permeability layers. The results here illustrated (1) allow for diagnosis of the critical role played by the parameters of quantitative formulations linking porosity and permeability in compacted shales and (2) provide an explicit and detailed quantification of the effects of their uncertainty in field settings.

Application of the developed CFD analysis methodology to H2 explosion accidents in an open space

We developed a CFD (Computational Fluid Dynamics) analysis methodology for predicting an overpressure buildup due to a hydrogen explosion as well as the blast wave propagation from the near field to the far field of the hydrogen explosion site with an error range of about ±30% on the basis of test results with the small-scale obstacle at the stoichiometry condition in an open space in the previous research. In this paper, we confirmed the applicability of the developed CFD analysis method to the evaluation of the safety distance between a VHTR (Very High Temperature Reactor) and a hydrogen production facility through the CFD analysis conducted on the HTTR (High Temperature Test Reactor) and the hydrogen production facility in JAEA (Japan Atomic Energy Agency) under an assumption of a hypothetical hydrogen explosion. The application study showed physically reasonable results when compared to the test data performed by SRI (Stanford Research Institute) International, and the CFD analysis methodology is a more useful tool in the evaluation of the safety distance than the MEM (Multi-Energy Method) because the MEM has some drawbacks that it cannot predict an asymmetric explosion phenomenon due to a complicated geometry and an ambient temperature effect on an overpressure buildup. Finally, the developed CFD analysis methodology will be applied to evaluate the safety distance between a VHTR and a hydrogen production facility after KAERI (Korea Atomic Energy Reaches Institute) completes a design work of a VHTR and a production facility.

The dynamic influence of microbial mats on sediments: fluid escape and pseudofossil formation in the Ediacaran Longmyndian Supergroup, UK

Microbial mats are thought to have been widespread in marine settings before the advent of bioturbation, and the range of their influence on sediments is gradually becoming recognized. We propose that mat sealing can dynamically affect porewater conditions, and allow the build-up of overpressure that can drive dewatering and degassing to produce a suite of atypical fluid-escape features. Finely bedded silty and sandy laminae from the c . 560 Ma Burway Formation of the Longmyndian Supergroup, Shropshire, England, reveal evidence for sediment injection, including disrupted bedding, clastic injections, sill-like features and sediment volcanoes at sub-millimetre scale. These features are associated with crinkly laminae diagnostic of microbial matgrounds. Matground-associated sediment injection can explain the formation of several types of enigmatic discoidal impressions, common in rocks of this age, which have previously been attributed to the Ediacaran macrobiota. Serial grinding of Longmyndian forms previously described as Medusinites aff. asteroides and Beltanelliformis demonstrates that such discoidal features can be fully explained by fluid escape and associated load structures. Our observations emphasize the non-actualistic nature of shallow-marine Ediacaran sediments. Matground-associated sediment injection features provide a new insight into the interpretation of Proterozoic rocks and the biogenicity of their enigmatic discoidal markings. Supplementary materials: A document containing further images of fluid escape and loading features observed in the upper Burway Formation at Ashes Hollow, together with an annotated diagram of features appearing in one typical vertical cross-section, is available at www.geolsoc.org.uk/SUP18870 .

Budge–Fudge method of pore-pressure estimation from wireline logs with application to Cretaceous mudstones at Haltenbanken

Using wireline logs to estimate pore pressure in mudstones at the chemical compaction stage is not straightforward because clay diagenesis proceeds independently of effective stress, and neither density nor velocity is uniquely related to the maximum effective stress experienced by the mudstones. We propose the Budge–Fudge method, in which we assume there is a unique trend on the sonic–density cross-plot for mudstones at the chemical compaction stage that have not been unloaded. In addition to the sonic–density chemical compaction trend, an initial guestimate of maximum effective stress previously experienced by the mudstones is required. Additional overpressure from unloading processes is then estimated from the sonic log, referenced to the density response. The initial guestimate of maximum effective stress may be adjusted to fit any available measured pressures or pressures estimated from geological knowledge. We have applied the Budge–Fudge method to Cretaceous mudstones at Haltenbanken, and find that estimated pressures match measured pressures and expected pressure–depth profiles. Furthermore, the analysis suggests that the lateral variations in mudstone porosity, previously reported, result from lateral variations in overpressure build-up immediately following rapid burial by glaciogenic sediments; subsequently, overpressures have increased through clay diagenesis and equilibrated laterally across the area.

Gas-controlled seafloor doming

The upward migration of gas through marine sediments typically manifests itself as gas chimneys or pipes in seismic images and can lead to the formation of cold seeps. Gas seepage is often linked to morphological features like seabed domes, pockmarks, and carbonate build-ups. In this context, sediment doming is discussed to be a precursor of pockmark formation. Here, we present parametric echosounder, sidescan sonar, and two-dimensional seismic data from Opouawe Bank, offshore New Zealand, providing field evidence for sediment doming. Geomechanical quantification of the stresses required for doming show that the calculated gas column heights are geologically feasible and consistent with the observed geophysical data. The progression from channeled gas flow to gas trapping results in overpressure build-up in the shallow sediment. Our results suggest that by breaching of domed seafloor sediments a new seep site can develop, but contrary to ongoing discussion this does not necessarily lead to the formation of pockmarks.

Methodology of CFD analysis for evaluating H2 explosion accidents in an open space

One of the critical regulation issues for the development of a very high temperature reactor (VHTR) with a hydrogen production facility is the safety distance between a VHTR and a hydrogen production facility. The multi-energy method (MEM) was found as the effective correlation because it predicts an overpressure buildup rising from a detonation shock to a weak explosion. However, the MEM has several drawbacks that include the inability to predict an asymmetric explosion phenomenon. Therefore, we developed a CFD analysis methodology for predicting an overpressure buildup caused by a hydrogen explosion with an error range of approximately ±30% on the basis of test results. Furthermore, we observed the important physics of hydrogen explosion due to the small-scale obstacle through a comparison between the CFD results and the test results. The obstacle structure may delay the pressure wave propagation and give rise to a superposition of the pressure waves.

The Fram Slide off Svalbard: a submarine landslide on a low-sedimentation-rate glacial continental margin

Submarine slope failures are a widespread, hazardous phenomenon on continental margins. The prevailing opinion links large submarine landslides along the glaciated NW European continental margins to overpressure generated by the alternation of rapidly deposited glacigenic and hemipelagic material. Here, we report a newly discovered large landslide complex off NW Svalbard. It differs from all known large slides off NW Europe, as the available data rule out that this slope failure resulted from rapid glacigenic deposition. This suggests that processes such as contour currents, tectonic faulting, and overpressure build-up related to the gas hydrate system must be considered for hazard assessment. Supplementary material: Supplementary data are available at http://www.geolsoc.org.uk/SUP18803 .