Numerical Simulation for the Evolution of Internal Solitary Waves Propagating over Slope Topography

In this study, the propagation and evolution characteristics of internal solitary waves on slope topography in stratified fluids were investigated. A numerical model of internal solitary wave propagation based on the nonlinear potential flow theory using the multi-domain boundary element method was developed and validated. The numerical model was used to calculate the propagation process of internal solitary waves on the topography with different slope parameters, including height and angle, and the influence of slope parameters, initial amplitude, and densities jump of two-layer fluid on the evolution of internal solitary waves is discussed. It was found that the wave amplitude first increased while climbing the slope and then decreased after passing over the slope shoulder based on the calculation results, and the wave amplitude reached a maximum at the shoulder of the slope. A larger height and angle of the slope can induce larger maximum wave amplitude and more obvious tail wave characteristics. The wave amplitude gradually decreased, and a periodic tail wave was generated when propagating on the plateau after passing the slope. Both frequency and height of the tail wave were affected by the geometric parameters of the slope bottom; however, the initial amplitude of the internal solitary wave only affects the tail wave height, but not the frequency of the tail wave.

Evaluation of Ground Motion Amplification Effects in Slope Topography Induced by the Arbitrary Directions of Seismic Waves

The incident directions of seismic waves can change the ground motions of slope topography. To elaborate on the influences of the directions of seismic waves, a dynamic analysis of the slope topography was performed. Seismic waves were input using an equivalent nodal force method combined with a viscous-spring artificial boundary. The amplification of ground motions in double-faced slope topographies was discussed by varying the angles of incidence. Meanwhile, the components of seismic waves (P waves and SV waves), slope materials and slope geometries were all investigated with various incident earthquake waves. The results indicated that the pattern of the amplification of SV waves was stronger than that of P waves in the slope topography, especially in the greater incident angels of the incident waves. Soft materials intensely aggravate the acceleration amplification, and more scattered waves are produced under oblique incident earthquake waves. The variations in the acceleration amplification ratios on the slope crest were much more complicated at oblique incident waves, and the ground motions were underestimated by considering only the vertical incident waves. Therefore, in the evaluation of ground motion amplification of the slope topography, it is extremely important to consider the direction of incident waves.

Paraglacial Rock Slope Stability Under Changing Environmental Conditions, Safuna Lakes, Cordillera Blanca Peru

Landslides or landslide-induced impact waves in high mountain lakes represent a high hazard for society, calling for realistic assessments of rock slope stability responsible for the process chain initiation. This task is often hampered by complex interplays of triggers, which effects on slope stability may be delayed by decades or even millennia, while historical records describing slope topography or landslide occurrences are usually shorter and incomplete. This article builds on rarely available detailed historical data describing the site of the 2002 rock avalanche in the Cordillera Blanca, Peru. It caused a dangerous impact wave in the Safuna Alta Lake resulting in a minor flood, but ongoing downstream development significantly increased the risk of a comparable event. Pre-2002 and post-2002 failure slope topography, 70 years long history of glaciation and landslide occurrences were combined with non-invasive field geological surveys and laboratory geotechnical analyses to characterize the distinct morphological parts of the failed slope with reliable engineering geological slope models. Slope stability was calculated for a series of environmental scenarios providing insights into the 2002 rock avalanche failure mechanism and dynamics as well as the role of glacier slope support for its stability. Results show that the rock slope stability is governed by discontinuous slip planes where rock bridges represent the most likely additional resisting forces. The effect of glacier support on the slope stability is limited under full-water saturation of the rocks and due to specific morpho-structural conditions. Importance of the long-term, progressive deterioration of the rock slope strength under paraglacial environment and repeated seismic shaking is illustrated by the fact that even the Little Ice Age maximum glacier extend only had minor positive effect on the pre-2002 rock avalanche slope stability. Despite of that, the slope remained without a major failure for decades or possibly even centuries. Its collapse in 2002 caused retrogressive movements of the adjacent slope, which remains highly unstable until now. Therefore the future safety of the lake would largely benefit from the implementation of a reliable slope movement monitoring system.

Distributed modeling of runoff and soil erosion in vegetated slopes with man-made mountain tracks

<p>Mountain tracks and slope cuts are important sources of runoff and sediment transport in a watershed. Some slope instabilities are also observed nearby mountain roads and tracks. Most of the current literature points out as relevant the modifications of the slope topography, and the concentration of runoff at the bends of the trackways. However, quantitative analysis of runoff generation and sediment delivery are still uncommon. Moreover, the role of vegetation removal or modification along/nearby tracks is not addressed. A physically-based distributed modelling of water runoff, soil erosion and deposition on a natural slope is performed considering the impacts of a mountain track, either in terms slope topography modifications or for the infiltration-runoff patterns. The erosion scenarios for a 30° steep slope are computed with different rainstorms and initial soil suction considered. The numerical analyses provide a comprehensive set of erosion scenarios. Particularly, the numerical results outline the bend of the mountain roads as a major confluence path for water runoff, consistently with the in-situ evidences. The highest loss of soil is found besides and downslope the bends. Very unfavorable combinations of vegetation removal and change in slope topography may finally lead to extensive rill erosions and/or shallow slope failures.</p>

A Deep Marine Origin for the Tajau Sandstone Member of the Kudat Formation, Kudat Peninsula, Sabah: Evidence from Facies Analysis and Ichnology

There have been many disagreements regarding the depositional environment of the Oligocene Tajau Sandstone Member of the Kudat Formation, Northern Sabah. We present here, the first detailed sedimentary facies analysis for the Tajau Sandstone Member, exposed on the Kudat Peninsula. The identified facies are interpreted as the deposits of subaqueous sediment density flows, which are common processes in deep marine depositional settings. These include debrites, hyperconcentrated density flow deposits, and turbidites. Several of the turbidite facies display evidence for hydraulic jumps, which are also common processes in deepwater settings and probably indicate changes in slope topography or loss of flow confinement. Trace fossils characteristic of the Nereites ichnofacies are also diagnostic of a deep marine depositional environment. Facies previously identified by previous workers as hummocky cross-stratification in the Tajau Sandstone Member, which was used to support a shallow marine interpretation, is better interpreted as supercritical antidunes developed in high density turbidites, based on the coarse-grained texture, spaced layering and association with other subaqeuoues density flow deposits.

Progress of Studies on Circulation Dynamics in the East China Sea: The Kuroshio Exchanges With the Shelf Currents

This paper reviews recent advances in the circulation dynamics of the Kuroshio and its interaction with shelf currents in the East China Sea (ECS). The annually averaged Kuroshio volume transport varies between 19 and 24 Sv, based on different observations, but there is no consensus on which season its volume transport peaks. The Kuroshio is intensified over the central slope of the ECS from that off the northeast of Taiwan. The total Kuroshio intrusion into the ECS shelf is estimated to be 1.3–1.4 Sv, deduced from the observed volume transport of exchange flow in the Taiwan and Tsushima Straits, based on the assumption of volume conversation over the shelf. However, the uncertainty regarding this estimation remains due to the absence of sufficient observations and understanding of the Kuroshio dynamics. The Kuroshio intrusions over the shelf off the northeast of Taiwan and southwest of Kyushu are stimulated by planetary or topographic β -effect associated with the alongshore variations in the ECS slope topography and altered by variations in the Kuroshio intensity, shear stress, and baroclinicity. Multilayered exchanges between the Kuroshio and shelf currents were found between 100- and 200-m isobaths along the central ECS slope. The spatial variations in these exchanges are governed by cross-isobath transport by geostrophy, whereas bottom Ekman transport may play a predominant role in altering the integrated exchange flow along the slope. Although the intrusion is greatly modulated along the path of the Kuroshio in the ECS by variable slope topography, there are few observations on the spatial variations of these exchange flows. The characteristics and variations in the circulation and hydrographic properties of waters between 100- and 200-m isobaths significantly determine the general ECS circulation, about which consensus has still not been attained.

Depositional patterns constrained by slope topography changes on seamounts

Slope topography is known to control the spatial distribution of deposits on intraplate seamounts; however, relatively little is known about how slope topography changes constrain those depositional patterns. In this study, we analyse data on four lithotypes found on seamount slopes, including colloidal chemical deposits comprising mainly cobalt-rich crusts, and examine the relationships between the spatial distribution of these lithotypes and current slope topography. We use these relationships to discuss depositional patterns constrained by slope topography changes. Some depositional units in drill core samples are interpreted to have resulted from past topographic changes that created the current slope topography. Two or more types of deposits that accumulated at the same location implies that the slope topography changed over time and that the depositional patterns on seamount slopes are constrained by changes in slope topography.