Outrunner Blocks Research Articles

Quantitative analysis of facies variation using ground-based lidar and hyperspectral imaging in Mississippian limestone outcrop near Jane, Missouri

Ground-based hyperspectral imaging is useful for geologic mapping because of its high spectral and spatial resolutions at a millimeter to centimeter scale. We have used hyperspectral and terrestrial laser scanner (TLS) data collected in close range to a roadcut near Jane, Missouri, that contains a subvertical outcrop of Lower Mississippian limestone. The outcrop consists of the Compton, Northview, and Pierson Formations, which we evaluated for facies heterogeneity. The sequence near Jane, Missouri, was deposited in shelf margin with high-frequency sea-level fluctuations. These fluctuations introduced lithologic and geometric heterogeneity to the facies, and debris flows brought in carbonate mounds referred to as outrunner blocks. These are important to interpret accurately because of their equivocal depositional origin, which is highly debated by previous workers. We combined hyperspectral data with TLS for an integrated spatial analysis of geometric and compositional variations in facies by accurate, point cloud-registered mineralogical mapping. We mapped several carbonate facies based on spectral signatures of calcite, silt, and clay particles and distinguished pure limestone outrunner blocks from surrounding mud-prone limestone facies with various proportions of silt and clay (a total of approximately 60%). By tracing the classified facies from combined hyperspectral and TLS imagery, we produced a lithostratigraphic framework, which indicates rapid changes in lithology and the presence of shale baffles that vary the character of the Compton through Pierson interval and contribute to heterogeneity in this outcrop. The data suggest a lower energy depositional environment and support the hypothesis of transported outrunner blocks in a distally steepened ramp system. The information that we have evaluated in our study could help to explain reservoir heterogeneity in equivalent carbonate fields.

Pipeline–soil–water interaction modelling for submarine landslide impact on suspended offshore pipelines

The submarine landslide is one of the major geohazards in deep-water oil and gas developments. The impacts of glide blocks or out-runner blocks, which carry the geotechnical properties of the parent soil mass before the landslide, on pipelines normal to the direction of slide, are investigated in this study. A computationally efficient numerical modelling technique is developed using a computational fluid dynamics approach, incorporating a strain-rate and strain-softening dependent model for the undrained shear strength of clay sediment, to simulate the lateral penetration of a pipe in a clay block. The role of water in the cavity and channel formed behind the pipe during the lateral penetration on drag force is successfully simulated. Numerical simulations for varying depths of the pipe explain the change in soil failure mechanisms in which the channel behind the pipe and berm play a significant role, especially at shallow depths. As the cavity behind the pipe may not be completely filled with soil, the limitations of smooth/rough and bonded/unbonded interface conditions, as used typically in pipe–soil interaction analysis, are discussed. Based on a comprehensive parametric study, calibrated against centrifuge test results, a set of empirical equations is proposed to calculate drag force for practical applications. The effects of inertia on drag force are examined.

Friction and dynamics of rock avalanches travelling on glaciers

Rock avalanches travelling on glaciers often exhibit effective friction coefficient lower than those on a rocky terrain. After briefly considering some data of rock avalanches on glaciers, the physics of sliding of solid objects on icy surfaces is reviewed, and a model is put forward for the mechanics of rock avalanche sliding on ice accounting for the formation of a natural lubricating layer. It is suggested that at the beginning of the flow of a rock avalanche, friction results from rocky blocks ploughing on ice. As the erosion continues, a gouge of ice particles results, which clogs the interstices between blocks and may partially melt as a consequence of the production of frictional heat. This conceptual model is numerically investigated for a slab travelling on ice. The results show an increase in mobility as a function of slab thickness, travelled length, and the gravity field, in agreement with case studies. The results are useful to interpret the peculiar features of rock avalanches travelling on icy surfaces such as digitations, out-runner blocks, and longitudinal furrows. The lubrication theory for landslides on ice proposed here may provide a framework for understanding landslides on Earth and for future modelling; in addition, it may help elucidate the presence of similar landslide deposits on the surface of Mars.

Mass transport deposits and gas hydrate occurrences in the Ulleung Basin, East Sea – Part 1: Mapping sedimentation patterns using seismic coherency

Seismic coherency measures, such as similarity and dip of maximum similarity, were used to characterize mass transport deposits (MTDs) in the Ulleung Basin, East Sea, offshore Korea. Using 2-D and 3-D seismic data several slope failure masses have been identified near drill site UBGH1-4. The MTDs have a distinct seismic character and exhibit physical properties similar to gas hydrate bearing sediment: elevated electrical resistivity and P-wave velocity. Sediments recovered from within the MTDs show a reworked nature with chaotic assemblage of mud-clasts. Additionally, the reflection at the base of MTDs is polarity reversed relative to the seafloor, similarly to the bottom-simulating reflector commonly used to infer the presence of gas hydrates. The MTDs further show regional seismic blanking (absence of internal reflectivity), which is yet another signature often attributed to gas hydrate bearing sediments. At the drill site UBGH1-4, no gas hydrate was recovered in sediment-cores from inside a prominent MTD unit. Instead, pore-filling gas hydrate was recovered only within thin turbidite sand layers near the base of the gas hydrate stability zone. With the analysis of seismic attributes, the seismic character of the prominent MTD (Unit 3) was investigated. The base of the MTD unit exhibits deep grooves interpreted as gliding tracks from either outrunner blocks or large clasts that were dragged along the paleo-seafloor. Similar seismic features were identified on the seafloor although the length of the gliding tracks on the seafloor is much shorter (a few hundred meters to ∼1 km), compared to over 10 km long tracks at the base of the MTD. The seismic coherency attributes allowed to estimate the volume of the failed sediment as well as the direction of the flow of sediment. Tracking the MTD and extrapolating its spatial extent from the 3-D seismic volume to adjacent 2-D seismic profiles, a possible source region of this mass failure was defined ∼50 km upslope of Site UBGH1-4.

Sliding of outrunner blocks from submarine landslides

Outrunner blocks are nearly intact pieces of debris that detach from a slowing‐down submarine landslide and flow ahead of the front. Data gathered from different sliding areas highlight some properties of outrunner blocks and in particular their inordinate mobility reflected in runouts of up to 25 kilometres, even on very gentle slopes. Blocks may produce an erosion glide track on the sea floor few centimetres to several metres deep, which in some cases exhibits regularly spaced grooves along the flow direction. Understanding the dynamics of outrunner blocks may shed light on the flow and lubrication of submarine landslides. We develop a simple hydrodynamic model of a rigid block interacting with ambient water and subject to lubrication with the sea floor, and calculate numerically the equation of motion for the block. We find that as a consequence of lift forces and water lubrication, the block may reach long runouts, in agreement with data. When the block is moving at high speed, we find an oscillating solution to the equations of motion which could explain the creation of dashed grooves.

Slope failure dynamics and impacts from seafloor and shallow sub-seafloor geophysical data: case studies from the COSTA project

Holocene and slightly pre-Holocene submarine landslide are found both in high-latitude glacial-dominated margins and in lower latitude, river-dominated margins. This paper constitutes a major assessment on some of the best-studied submarine instabilities in the world. We review and update from original data and literature reports the current state of knowledge of Storegga, Traenadjupet and Finneidfjord slides from the mid-Norwegian margin, Afen Slide from the Faeroe-Shetland Channel, BIG'95 Slide and Central Adriatic Deformation Belt (CADEB) from continental slope and inner continental shelf settings off the Ebro and Po rivers in the Mediterranean Sea, Canary Slide west of the westernmost, youngest Canary Islands and Gebra Slide off the northern tip of the Antarctic Peninsula in the southern hemisphere, i.e. those studied in the Continental Slope Stability (COSTA) project. The investigated slides range in size from the gigantic 90,000 km 2 and almost 3000 km 3 Storegga Slide to the tiny 1 km 2 and 0.001 km 3 Finneidfjord Slide. Not only do individual submarine landslides rarely involve processes precisely fitting with pre-established categories, mostly based on subaerial research, but also they display complex mechanical behaviors within the elastic and plastic fields. Individual events can involve simultaneous or successive vertical to translational movements including block detachment, block gliding, debris flow, mud flow and turbidity currents. The need for an in-depth revision of the classification criteria, and eventually for a new classification system, based on the new imaging capabilities provided by modern techniques, is more than obvious. We suggest a new system, which, for the moment, is restricted to debris flows and debris avalanches. Volume calculation methods are critically reviewed and the relations between some key geomorphic parameters are established for the selected slides. The assumed volume missing from scar areas does not necessarily match the actual volume of sediment remobilised by an individual event since in situ sediment can be remoulded and eventually incorporated during the slide downslope journey. CADEB, a shore-parallel prodelta detached from its source, is the exception to the good correlation found between across slope width and alongslope length with slide area. Height drop measured from the headwall upper rim to its foot correlates with the debris deposit maximum thickness unless the slide moves into restricted areas, which prevent farther forward expansion of the deposit, such as Gebra and BIG'95. In such cases, “over-thickened” deposits are found. A particularly loose and fluid behavior can be deduced for slides showing an “over-thinned” character, such as the Canary Slide that traveled 600 km. Scar areas and slip planes have been investigated with particular emphasis. Although slide headwalls might present locally steep gradients (up to 23° for Storegga Slide), the slope gradients of both the failed segment margins and the main slip planes are very low (max. 2° and usually around 1° and less). An exception is the Finneidfjord Slide (20°–<5°) that occurred in 1996 because of a combination of climatic and anthropogenic factors leading to excess pore pressure and failure. Mechanically distinct, low permeable clayey “weak layers” often correspond to slip planes beyond the slide headwall. Since not only formation of these “weak layers” but also sedimentation rates are climatically controlled, we can state that slide pre-conditioning is climatically driven too. Run-out distances reflect the degree of disintegration of the failed mass of sediment, the total volume of initially failed material and transport mechanisms, including hydroplanning. Commonly, specific run-outs could be attributed to distinct elements, such as cohesive blocks and looser matrix, as nicely illustrated by the BIG'95 Slide. Total run-outs usually correspond to matrix run-outs since the coarser elements tend to rest at shorter distances. Outrunner blocks are, finally, a very common feature proving the ability of those elements to glide over long distances with independence of the rest of the failed mass. In addition to pre-conditioning factors related to geological setting and sedimentation conditions, a final trigger is required for submarine landslides to take place, which is most often assumed to be an earthquake. In high latitude margins, earthquake magnitude intensification because of post-glacial isostatic rebound has likely played a major role in triggering landslides. Although it cannot be totally ruled out, there is little proof, at least amongst the COSTA slides, that gas hydrate destabilisation or other processes linked to the presence of shallow gas have acted as final triggers.

On the frontal dynamics and morphology of submarine debris flows

Several submarine debris flows show an apparently chaotic frontal part with blocks of variable size (from roughly tens to some hundreds of metres) located some distance beyond the front of the main deposits. This outrunner phenomenon was studied both in the field and in laboratory experiments. Depositional patterns in a field case (Finneidfjord, northern Norway) are classified from the outer distal part of the debris flow to the outermost outrunner block. Similar patterns were found in experimental debris flows, and we suggest that flow processes in the laboratory are applicable to the field example. Theoretical investigations are applied to assess frontal dynamics and especially the formation and motion of outrunner blocks. As the front of the debris flow pushes through ambient water, a combination of front pressure and lift force allows for intrusion of a water layer underneath the front (hydroplaning). This water layer reduces basal friction and induces tensile stresses farther behind the front, leading to a possible detachment and decoupling with respect to the main slide body. These outrunner blocks show an increased mobility compared to the main slide body and deposition of such blocks may occur far away from the main slide body.

Debris flow outrunner blocks, glide tracks, and pressure ridges identified on the Nigerian continental slope using 3-D seismic coherency

The Nigerian continental slope, approximately 100 km offshore from the northwestern flank of the Niger Delta, is in the earliest phases of exploration; therefore, no well control is available to aid in the interpretation of the paleodepositional setting of this area. However, a 500-km2 portion of the area is covered by a 3-D seismic survey, and in the absence of well control, 3-D seismic coherency images have played an important role in the interpretation and confirmation of the paleoenvironment and depositional systems of the area.

3-D seismic attributes applied to carbonates

Coherency mapping has become a widely used tool within Amoco and is being applied in both frontier exploration and exploitation areas. Coherency and other 3-D seismic attributes have been successfully used to identify and delineate features in clastic depositional environments, including reworked deltaic sand bodies, deltaic channels with associated point bars, slump features, debris flow outrunner blocks, and various geologic drilling hazards including faults, salt diapirs, buried channels, and shallow gas pockets.

Debris Flow Outrunner Blocks, Glide Tracks, and Pressure Ridges Identified on the Continental Slope of West Africa Using 3-D Seismic Coherency :ABSTRACT

Debris Flow Outrunner Blocks, Glide Tracks, and Pressure Ridges Identified on the Continental Slope of West Africa Using 3-D Seismic Coherency :ABSTRACT