Underwater Slope Research Articles

Numerical simulation of the undrained stability of slopes in anisotropic fine-grained soils

ABSTRACTThe undrained stability of slopes in anisotropic fine-grained soils is studied in this paper using the finite element method (FEM). A constitutive model is presented, able to account for the observed variation of undrained strength with loading direction. The model is able to encompass the different strength distributions observed in normally, slightly overconsolidated and heavily overconsolidated soils. A series of stability analyses have been performed to explore the effect of the type of undrained strength anisotropy on the stability and failure mechanisms of slopes of different inclinations. In addition, a real case study of the failure of an underwater slope is analysed with the numerical approach presented. It suggests that, by considering undrained strength anisotropy, the failure can be satisfactorily explained.

Seismic architecture of the tip of the Hel Peninsula, Poland

The article presents results of a pioneering research on the main geological features of the Hel Peninsula based on the analysis of seismic profiles and their comparison with geological cross-sections made on the basis of drillings. The following three parts of the tip structure have been identified: barrier basement (1), barrier core (2) and barrier upper part(3). Seismic facies distinguished therein were subsequently geologically interpreted as follows: Cretaceous marl and limestone (1.1), glacial till and diamicton (1.2), silt and clay of limnoglacial/limnic/marine origin (1.3), barrier sand of the core (2), and sand and peat of the barrier upper part(3). Geological cross-sections covering the geological structure of the tip of the Hel Peninsula underwater slope and the surrounding seabed. The slope base and the distal sand colluvium extent on the seafloor were determined. This paper is the first to present a crosswise section in this part of the Hel Peninsula.

Pollution of the sediments of the coastal zone of the Sambia Peninsula and the Curonian Spit (Southeastern Baltic Sea).

The detailed environmental survey of the coastal zone of the Kaliningrad Region northern coast was carried out. The pollutants distribution in the silty clay fraction and calculation of ecological indexes allowed the evaluation of distribution of potentially harmful elements (PHEs). The sources of pollution in the most intensively used areas were identified, and transit and accumulation zones were allocated. A large area of anomalous content of PHEs was revealed on the underwater coastal slope of the Curonian Spit National Park, which is situated far from the sources of pollution. The alongshore bed load transport provides the contamination of the underwater slope whereas the beaches are less exposed to pollution.

Combining in situ monitoring using seabed instruments and numerical modelling to assess the transient stability of underwater slopes

Abstract The stability of submarine slopes is often characterized using campaign-based geophysical and geotechnical measurements in combination with numerical modelling. However, such one-off measurements do not reflect transient changes in slope stability. In situ monitoring of physical parameters critical for slope stability over periods of months to years can provide crucial information on slope stability and can also be used in an early-warning system for submarine landslides and the possibly resulting tsunamis. We review existing techniques that are capable of monitoring seafloor deformation over long periods of time. Based on numerical models we can identify the magnitude of parameters related to landslide-induced seafloor deformation. Simulations of three different failure scenarios up to the point of failure show that the development of the stress state of a slope and hence stability over time can be captured by measurements of tilt, pressure and strain at the seafloor. We also find that different failure mechanisms induce different deformation signals at the seafloor, in particular tilt. Hence, with a site- and target-specific survey design (or a large pool of instruments), seafloor deformation measurements in combination with numerical modelling can be used to determine the temporal evolution of slope stability as well as to identify underlying failure mechanisms.

New Evidence on the Relief of the Southern Underwater Slope in the South Baikal Basin

A high-resolution bathymetric survey of the entire underwater slope in South Baikal was carried out for the first time by means of the multibeam echosounder. New elements were revealed in the underwater relief of the southern slope of the basin from the Kultuchnaya river to the Mysovka river, and a relevant regionalization was carried out into three areas according to the presence of ancient landforms and the intensity of the processes of their reworking, with the boundaries along the delta-front and the river fan of the Utulik and Pereemnaya. We reconstructed the formation process of the modern relief of this area of the underwater slope and determined a dominant role of the underwater-erosion processes in the formation of the modern relief, with the tectonic movements served as the “trigger” for them. The study revealed a direct correlation between the reworking of the ancient geomorphological surfaces and the occurrence of separate large underwater elevations or group ridges (remnants), canyons and linear depressions. It is determined that the pivotal role in the appearance of the modern relief of the underwater slope in the second area of extensive plano-convex (in section) and fan-shaped (in plan) delta-fronts of large rivers and debris fans enveloping the remnants. The existence of a steep underwater slope from the mouth of the Pereemnaya to the mouth of the Bol’shaya Tel’naya and of two large benches, and also the proximity of the maximum depths of the southern basin at the foot of this slope are explained by a more intense step-like lowering of this part of the lake when compared with the western part of the basin. This also accounts for the absence of large remnants in this part of the slope. The area of occurrence of lacustrine-fluvial and lacustrine-delta deposits of the Tankhoi paleobasin within the southern basin of Baikal is reconstructed. Four new hydrate-bearing structures associated with these deposits and morphologically pronounced in the vertex parts of the remnants were discovered. The morphological exploration indicators of the presence of new accumulations of gas hydrates on the underwater slopes of Baikal have been expanded.

New evidence on the relief of the southern underwater slope in the South Baikal basin.

New evidence on the relief of the southern underwater slope in the South Baikal basin.

Slope failures within and upstream of Lake Quinault, Washington, as uneven responses to Holocene earthquakes along the Cascadia subduction zone

AbstractInvestigation of Lake Quinault in western Washington, including a reflection seismic survey, analysis of piston cores, and preliminary mapping in the steep, landslide-prone Quinault River catchment upstream of the lake, reveals evidence for three episodes of earthquake disturbance in the past 3000 yr. These earthquakes triggered failures on the lake’s underwater slopes and delta front, as well as subaerial landsliding, partial channel blockage, and forced fluvial sediment aggradation. The ages of the three Lake Quinault disturbance events overlap with those of coseismically subsided, coastal marsh soils nearby in southwest Washington that are interpreted to record ruptures of the Cascadia megathrust. Absent from Lake Quinault, however, are signals of obvious disturbance from five additional subduction earthquakes inferred to have occurred during the period of record. The lack of evidence for these events may reflect the limitations of the data set derived from the detrital, river-dominated lake stratigraphy but may also have bearing on debates about segmentation and the distribution of slip along the Cascadia subduction zone during prior earthquakes.

INFLUENCE OF FLOW ON THAWING OF UNDERWATER SLOPES AND THE PACE COASTAL EROSION OF RIVERS, OCCURRING IN THE PERMAFROST ZONE

In the hydraulic laboratory of department of architecture & civil engineering RUDN University was performed studies of destruction of underwater and above-water coastal slopes in conditions simulating permafrost, depending on the soil type, the initial slope, and the slope angle. It was shown by authors, the speed of erosion of the underwater slope lags behind the speed of thawing of frozen ground. Water flow's influence is much higher than the impact of other factors (temperature, effect of wind, solar radiation), resulting in the formation of the washout niches. Thus, the main goal of the work was to identify the most important factors that affect on the changes of the river bed in permafrost zone.

Numerical Simulation of Gravity Waves Excited in the Ocean by Low-Frequency Surface Seismic Waves Based on GPS Recordings

A numerical experiment for reproducing the generation of free gravity waves in the ocean by low-frequency surface seismic waves passing across the bottom is described. The dynamics of the bottom movement is reconstructed based on the real GPS data recorded during the disastrous Tohoku earthquake of March 11, 2011. Results of the numerical simulation show that horizontal movements of underwater slopes play a key role in the generation of free gravity waves.

Biodiversity of Pigmented Fungi Isolated from Marine Environment in La Réunion Island, Indian Ocean: New Resources for Colored Metabolites.

Marine ecosystems cover about 70% of the planet surface and are still an underexploited source of useful metabolites. Among microbes, filamentous fungi are captivating organisms used for the production of many chemical classes of secondary metabolites bound to be used in various fields of industrial application. The present study was focused on the collection, isolation, screening and genotyping of pigmented filamentous fungi isolated from tropical marine environments around La Réunion Island, Indian Ocean. About 150 micromycetes were revived and isolated from 14 marine samples (sediments, living corals, coral rubble, sea water and hard substrates) collected in four different locations. Forty-two colored fungal isolates belonging to 16 families, 25 genera and 31 species were further studied depending on their ability to produce pigments and thus subjected to molecular identification. From gene sequence analysis, the most frequently identified colored fungi belong to the widespread Penicillium, Talaromyces and Aspergillus genera in the family Trichocomaceae (11 species), then followed by the family Hypocreaceae (three species). This study demonstrates that marine biotopes in La Réunion Island, Indian Ocean, from coral reefs to underwater slopes of this volcanic island, shelter numerous species of micromycetes, from common or uncommon genera. This unstudied biodiversity comes along with the ability for some fungal marine inhabitants, to produce a range of pigments and hues.

Formation mechanism of diapirs of relict lagoonal sediments on the underwater slope of the Curonian Spit

Geological-geophysical methods were applied to provide deeper insight into the nature of unique relict lagoonal sediments exposed on the underwater slope of the Curonian Spit. The study of textural features and morphology of the deformed lagoonal sediments indicates a similarity of their formation mechanism with clay diapirism. Analysis of seismoacoustic data and side scan sonar survey allowed us to establish the configuration of paleolagoon and to determine the direction of dune migration in the past.

ЛАБОРАТОРНОЕ ИССЛЕДОВАНИЕ ВЛИЯНИЯ ПОТОКА НА ПРОТАИВАНИЕ ПОДВОДНОГО СКЛОНА И ТЕМПЫ БЕРЕГОВОЙ ЭРОЗИИ В УСЛОВИЯХ КРИОЛИТОЗОНЫ

In the RUDN hydraulic laboratory researches of destruction of an underwater and surface coastal slope in the conditions imitating a kriolitozona depending on type of the soil composing a slope and a bias corner are executed. It is shown that the speed of an erosion of an underwater slope lags behind the speed of thawing of frozen soil. Work of a water stream considerably exceeds influence of other factors (temperature, wind influence, solar radiation), leading to formation of niches of washing away. Work is continuation of a research of dynamics of a coastal slope of water objects in the conditions of a kriolitozona [1-4].

Crossing Lake Washington

The world's longest floating bridge, SR 520 Evergreen Point Floating Bridge, was opened by the Washington State Department of Transportation in April 2016. The new crossing carries State Route 520 across Lake Washington, near Seattle, as did the structure it replaces. The bridge's transition spans are pinned to the fixed, land-based structures by a built-up steel weldment, and in order to accommodate the bridge's motions, spherical bearings with identical radii form a sphere that acts like a trailer hitch. Immense gravity anchors are used in places where soil conditions permit on the underwater slopes, and due to their size, required special logistical considerations.

THE ABRASION-BAY COAST MORPHODYNAMICS UNDER THE DIFFERING INTENSITY OF THE WAVE ACTION (IN TERMS OF THE NORTH KALININGRAD PENINSULA, THE SOUTH-EAST BALTIC)

The study is based on estimation of abrasion-embayed coast lithodynamics on the basis of bathymetric data and equilibrium profi le of the underwater coastal slope. Model of R. Dean and model of storm relief deformations were used. Based on the underwater coastal slope relief comparison with Dean’s equilibrium profi le the principles of large-scale regionalization of the coastal zone were put forward. The comparison with storm relief deformations was led to conclude that maximum of relief transformation is occur under extreme heaving and lead to irregular distribution of sandy sediments in the central part of the bay. In the following, these relief transformations are the cause of the intensifi cation of abrasion processes under the less powerful storms.

Paleoseismic potential of sublacustrine landslide records in a high-seismicity setting (south-central Alaska)

Sublacustrine landslide stratigraphy is considered useful for quantitative paleoseismology in low-seismicity settings. However, as the recharging of underwater slopes with sediments is one of the factors that governs the recurrence of slope failures, it is not clear if landslide deposits can provide continuous paleoseismic records in settings of frequent strong shaking. To test this, we selected three lakes in south-central Alaska that experienced a strong historical megathrust earthquake (the 1964 Mw9.2 Great Alaska Earthquake) and exhibit high sedimentation rates in their main basins (0.2cmyr−1–1.0cmyr−1). We present high-resolution reflection seismic data (3.5kHz) and radionuclide data from sediment cores in order to investigate factors that control the establishment of a reliable landslide record. Seismic stratigraphy analysis reveals the presence of several landslide deposits in the lacustrine sedimentary infill. Most of these landslide deposits can be attributed to specific landslide events, as multiple landslide deposits sourced from different lacustrine slopes occur on a single stratigraphic horizon. We identify numerous events in the lakes: Eklutna Lake proximal basin (14 events), Eklutna Lake distal basin (8 events), Skilak Lake (7 events) and Kenai Lake (7 events). The most recent event in each basin corresponds to the historic 1964 megathrust earthquake. All events are characterized by multiple landslide deposits, which hints at a regional trigger mechanism, such as an earthquake (the synchronicity criterion). This means that the landslide record in each basin represents a record of past seismic events. Based on extrapolation of sedimentation rates derived from radionuclide dating, we roughly estimate a mean recurrence interval in the Eklutna Lake proximal basin, Eklutna Lake distal basin, Skilak Lake and Kenai Lake, at ~250yrs., ~450yrs., ~900yrs. and ~450yrs., respectively. This distinct difference in recording can be explained by variations in preconditioning factors like slope angle, slope recharging (sedimentation rate) and the sediment source area: faster slope recharging and a predominance of delta and alluvial fan failures, increase the sensitivity and lower the intensity threshold for slope instability. Also, the seismotectonic setting of the lakes has to be taken into account. This study demonstrates that sublacustrine landslides in several Alaskan lakes can be used as reliable recorders of strong earthquake shaking, when a multi-lake approach is used, and can enhance the temporal and spatial resolution of the paleoseismic record of south-central Alaska.

Lipid composition in muscle and liver of sympatric coregonid fishes from Lake Baikal (Coregonus spp.) under common garden experiment

The content of total lipids, total phospholipids, and fatty acids of total lipids in muscles and liver of juvenile Lake Baikal sympatric coregonid fishes have been analyzed for the first time under a common garden experiment. Baikal omul, Coregonus migratorius Georgi, is an active migrant of the pelagic zones of the lake. Baikal (lacustrine) whitefish, C. baicalensis Dybowski, is a colonizer of the bottom habitats, which are relevant to the pelagic zones of the littoral and underwater slope. Structural lipids (phospholipids and cholesterol) dominated in total lipids of the tissues of all fish under study. Spare lipids significantly prevailed in omul muscles when compared to whitefish. The highest variability of fatty acid composition was reported in muscles of coregonid fishes. Statistically significant differences were revealed in the content of the ω3 polyunsaturated fatty acids in muscles of lacustrine whitefish and omul. Associations of lipid compositions revealed in tissues of the whitefishes under the study with their respective ecotypes have been discussed.

Reflection of the Baltic Sea Lithuanian nearshore bottom peculiarities in the historical maps

Using the bathymetry information available from historical maps, the underwater slope of the Baltic Sea in the Lithuanian area of the shore is analysed south and north of the Klaipėda harbour. For this purpose, the old depth measurements have been converted into the metric system and cross profiles of the nearshore drawn, as well as, on this basis, the diagrams for the 3, 5, 7 and 10 m depth points have been constructed. The depth data from the maps compiled in 1743, 1855, 1875 and 1913 have been analysed. These periods correspond to specific conditions of the shore zone morpho- and litho-dynamics. In 1743 there was no beach protecting the dune ridge on the Curonian Spit, and sand was driven by wind from the shore zone to the large dunes. There were no hydro-engineering structures in the Klaipėda harbour; therefore nothing impeded sand migration along the shore. In 1855 the shores of the Klaipėda channel were fixed, but there were no harbour piers yet. In 1875, the piers were freshly built and a beachprotecting dune ridge partly formed. In 1913, this dune ridge was already finished and the Klaipėda port was fully functioning with 5–6 m depths at the port gates. Conclusions are made about the former bottom relief during different stages of the nearshore evolution and about the conditions which caused its changes.

SANDY COASTS OF INTERIOR SEAS UNDER LEVEL RISE: ASSESSMENT OF FUTURE DEVELOPMENT

Modern coastal zone is an open morpholithodynamics system characterized by a set of constant and variable parameters. Estimations of these parameters allows to assess the future development of the whole system. Constant parameters are geological and geomorphologic composition of the coast and its wind-wave mode. Variables are long-period fluctuations of water level due to eustatic variations, tectonic and glacio-isostatic movements. Prediction of the evolution of the coastal zone includes the assessment of the trends of the variable parameters of the morpholithodynamics system. In this study, the above problem is analyzed on the examples of south-eastern coast of the Baltic Sea and the Russian sector of the Caspian sea. The possible rise of the Baltic Sea level by 1.0–1.5 m by the end of the XXI century will result in the further destruction of sea coasts, flooding, waterlogging and salinization of coastal areas, which will lead to negative consequences for industrial, municipal and agricultural infrastructures. In the case of the Caspian Sea, the majority of its coasts regardless of the underwater slope has transformed into lagoons due to the sea level rise in recent decades. Coastal erosion will start only when the sea level reaches the 1929 yr stage from which the sea level drop started in the mid XX century. At this stage, a noticeable change of surface slope occurs. At the majority of Caspian coasts activation of coastal erosion will occur when the sea level rise above – 26 m a.s.l.

THE HARMIN RESERVOIR (IRAQ) COASTAL DYNAMICS

The Hamrin reservoir, located on the Diyala River (left tributary of the Tiger River), differ for its unusual shape, large surface area and small depth, a significant level fl uctuations in the long-term dynamics and great depth of drawdown, and intense siltation. Intensive siltation of the reservoir caused by the arrival of material from solid river fl ow and from hollow (basin) slopes in which bottom reservoir is located. In rainy season the material moved through the temporary streams channels and deposited on alluvial fans at the foot of the slopes. In winter and spring seasons of reservoir’s full filling, at high water-level and under the process of wave increasing the various forms of underwater and above-water coastal forms of relief are developed. In dry summer season part of water area is dry out. Accumulative processes develop under low level of wave action; at that a big role belongs to soaking of sandy-clay material which composes the lower parts of the underwater coastal slopes. Drained part is involved in agricultural productivity. Annual renewal of the coastal relief induce the activity and abrasion-accumulation, anthropogenic double quick erosion and natural slope processes, so the rate of banks retreat is not reduced. Anthropogenicnatural reservoir system is still on the stage of activation, when stable relations between elements of new relief and environmental factors not yet formed, so the intensity of banks re-formation is not reduced, and siltation of the reservoir will be continued.

BEACH CUSPS ON THE ACCUMULATIVE COASTS IN THE SOUTH-EAST OF THE BALTIC SEA

The existing hypotheses of beach cusps development are considered. Their formation is the combined action of the beach abrasion and accumulation processes depending on the bottom slope, bottom sediments, and wave parameters. In recent decades, there are active debates about the origin of cusps. However, none of the hypotheses fully explains the mechanism of their formation. Thence the existing of some yet poorly explored hydrodynamic processes near the water edge having a significant impact on the cusps formation is supposed. A dynamic equilibrium of the beach at given seaway and the presence of rhythmic splash having sufficient force to move sediments of a given fineness are the main factors of the cusps formation. It apparently depends also on the type of wave breaking. Thus, the emergence of the cusps, their sizes and wave step are directly dependent on local morphodynamic parameters. Scalloped landforms are well represented along the shores of the Curonian and Vistula spits at the South-East Baltic Sea, and they are particularly unique in the lagoon shores. The combination of wind effected phenomena and wave action with of certain slopes of the coastal zone, leads to the development of a special type of acuteangled cusps with long “rumps” on the underwater slope. Long-term observations show that the cusps formation on the lagoon shores is quite possible and regularly re-starts under favorable conditions. At the spit shores different underwater slope parameters and seaway conditions lead to the development of the cusps significantly different from the lagoon’s ones. They are mainly the large forms with smooth contours and rounded tops.