Entire Slope Research Articles

Spatial scale dependence of sediment dynamics in a gullied rolling loess region on the Loess Plateau in China

Sediment dynamics is still imperfectly understood, especially at spatial scale in the highly erodible region of the Loess Plateau, and few studies have been heretofore conducted. Using 5-year continuous water and sediment records, three plots and three basins in the gullied rolling loess region were selected and sediment dynamics at spatial scale was studied. Results showed that the floods, where the peak discharge (Qp) did not come earlier than the sediment peak, were predominant in slope zones, occupying >90 and >70% of the total for the Mao slope and for the Entire slope, respectively. However, in basins, most of the sediment peaks (Cp) lagged behind Qp, implying that slope zone was the main origin of sediment. More than 50% of the events presented clockwise hysteresis loops in the Mao slope area, while almost all the events had anticlockwise hysteresis loops in basins. This can be attributed to less occurring frequency of hyperconcentrated flow, as well as its instability in slope zones, compared to those in the basins. Within these contexts, gravitational erosion made the highest sediment concentration (C) in Tuanshangou basin and median developing status of C-discharge (C–Q) relationships in the Entire slope area. This study provides insights into the protection of slope surface and disruption of the development of hyperconcentrated flow to reduce soil loss.

Rockfall-induced impact force causing a debris flow on a volcanoclastic soil slope: a case study in southern Italy

Abstract. On 10 January 2003, a rockfall of approximately 10 m3 affected a cliff some 25 m high located along the northern slopes of Mt. St. Angelo (Nocera Inferiore, province of Salerno) in the southern Italian region of Campania. The impact of boulders on the lower sector of the slope, along which detrital-pyroclastic soils outcrop, triggered a small channelled debris flow of about 500 m3. Fortunately, no damage nor victims resulted from the landslide. Several marks of the impacts were observed at the cliff toe and outside the collapsed area, and the volumes of some fallen boulders were subsequently measured. By means of in-situ surveys, it was possible to reconstruct the cliff's geo-structural layout in detail. A rockfall back-analysis was subsequently performed along seven critical profiles of the entire slope (surface area of about 4000 m2). The results of this numerical modelling using the lumped-mass method were then used to map the kinetic iso-energy curves. In the triggering area of the debris flow, for a falling boulder of 1 m3, the mean kinetic energy was estimated at 120 kJ, this value being equivalent to an impact force, on an inclined surface, of some 800 kN. After landing, due to the locally high slope gradient (about 45°), and low angle of trajectory at impact (about 23°), some boulders slid down the slope as far as the endpoints. The maximum depth of penetration into the ground by a sliding block was estimated at about 16 cm. Very likely, owing to the high impact force of boulders on the saturated soil slope outcropping at the cliff base, the debris flow was triggered under undrained loading conditions. Initial failure was characterized by a translational slide involving a limited, almost elliptical area where the pyroclastic cover shows greater thickness in comparison with the surrounding areas.

Deep-seated gravitational slope deformations along the active Boconó Fault in the central portion of the Mérida Andes, western Venezuela

Two very large deep-seated gravitational slope deformations in the highlands of the Mérida Andes, Venezuela, are herein described: the Mucubají Pass and Cerro La Camacha. These slope movements have slid in post-Last Glacial Maximum times. In addition, both landslides are in very close association with the active Boconó Fault trace. The Cerro La Camacha (Camacha Range) landslide is fault bounded along its northwest flank, whereas the Mucubají pass mass movement is even cut by the active fault trace. The almost 10 km long Mucubají slide mobilizes LGM moraine deposits along the unconformable basement contact. La Camacha slope movement is a sackung-type landslide, involving two huge masses that affect the entire northwestern slope of the La Camacha Range. This sackung is at least 20 km long, paralleling the active Boconó Fault trace. Combination of high relief energy (gravitational forces) and seismic shaking related to an on-site active fault could be responsible for the destabilization of the slopes or massif in both cases. Although the seismically-induced (re-)activation of the La Camacha landslide is very likely, there is no proof for that yet. Conversely, the Mucubají slide shows geomorphic, geodetic and sedimentary evidence of episodic activity in recent times, which could be ascribed to seismic triggering. In the particular case of the La Camacha sackung, the combination of dextral slip along the Boconó Fault and a SE-dipping fault plane could additionally favor the destabilization of the NW slope of the La Camacha Range.

Estimation of potential failure risks in a mine slope using indicator kriging

AbstractIndicator kriging has been applied to the study of failure mechanisms in a mine slope in Minas Gerais, Brazil, to estimate potential failure risks in limited areas along this slope. Timbopeba Mine, Vale Company, is an open pit iron mine situated in the Quadrilátero Ferrífero, a very important mining district in Minas Gerais. A slope excavated in quartzite with a maximum height of 200 m at the time of this study, has presented many failure problems involving the sliding of blocks formed by discontinuities. These blocks are of limited size in comparison to the dimensions of the overall slope. They appear along the entire slope, wherever discontinuity orientations have led to the kinematic feasibility of these blocks. Geostatistics permits the estimation of local failure probability distributions associated to these local failures, which would not be possible with traditional statistical models. The geostatistical method employed in this study, indicator kriging, is quite suitable because it is unnecessary to assume a particular global distribution of the phenomena being modeled. The model was used for locating areas with a great tendency for sliding failure, as it considers the local spatial variability of discontinuity orientations. Copyright © 2010 John Wiley & Sons, Ltd.

Toppling mechanisms of rock slopes considering stabilization from the underlying rock mass

Soft-hard interbedded structures are commonly found in anti-dip rock slopes and endow the slopes with special properties. In this work, a simple two-beam model was first used to discuss the possible failure modes of rock layers with different lithology. The exact failure sequence of rock layers depends on their tensile strengths, elastic moduli, and thicknesses. Then, based on the deformation compatibility of rock layers, a novel theoretical method called the DCM for assessing the stability of soft-hard interbedded anti-dip rock slopes was proposed. A centrifuge test and a numerical model were used to verify the feasibility of the DCM. The calculated critical g-level of 47 g for the centrifuge model and a safety factor of 0.96 for the numerical model agree well with the results of the centrifuge test (45 g) and numerical simulation (0.98). Moreover, the traditional limit equilibrium method (LEM) was also adopted to explore these two models. The calculated results of 68 g and 1.79 using the traditional LEM were found to be much larger than the validated values, with deviations of more than 50%. This finding implies that the traditional LEM is not suitable for assessing the stability of soft-hard interbedded anti-dip rock slopes. In addition, the failure evolution of toppling failure in soft-hard interbedded anti-dip rock slopes was investigated using numerical modelling. The results show that the soft and hard rock layers do not fail at the same time; the rock layers of one type of lithology are destabilized first, then the other rock layers begin to fail until the entire slope undergoes flexural toppling.

Submarine landslides at subduction margins: Insights from physical models

Submarine landslides, which commonly develop along subduction margins at the front of accretionary prisms, have recently been recognized as one of the most serious geohazards. To investigate the mechanical processes involved in the development of these landslides, a series of sandbox experiments were performed, and the results were analyzed using the digital image correlation (DIC) technique. Numerous slope failures, which may be analogous to natural submarine landslides, were produced on the model surface. The slope failures can be classified as follows: Type I failures, which are relatively small but are frequently developed on the lower parts of the slope; and Type II failures, which are relatively large and cover the entire slope, but occur less frequently. Detailed observations reveal that the failure process can be divided into four stages: 1) pre-failure, 2) steepening of the lower slope, 3) Type I failure, and 4) Type II failure. The minor Type I slides act as precursors of major Type II failures. Each slope failure produces a topographic undulation, triggering events in adjacent areas and a lateral migration of discrete slope failures. Although such experiments provide useful insight into slope failure processes, a detailed 3D analysis of the failed sediment is vital if we are to understand the precise history of thrust activity at subduction margins. Recent and Miocene accretionary prisms along the Nankai Trough, Japan, display the geometric and lithologic characteristics of Type I and Type II failures in their slide deposits.

Along‐slope variability of barotropic transport in the Nordic Seas: Simplified dynamics tested against observations

The present study combines simple geostrophic considerations and observational data to examine the along‐slope evolution of the barotropic transport following the continental slope in the Nordic Seas and Arctic Ocean. Following geostrophic theory, the transport evolution is calculated from bottom densities in five different transects within the Nordic Seas. This theoretically predicted transport evolution is compared with transports estimated directly from velocity measurements. Between the Faroe‐Shetland Channel and the Svinøy section off southern Norway, across the Fram Strait (below 800 m), and between the Fram Strait and the Greenland Sea the agreement is generally good between geostrophic theory and observations. This indicates that many aspects of the barotropic flow in these regions are captured by geostrophic dynamics. Between the eastern and western Fram Strait above 800 m and between Svinøy and the eastern Fram Strait the observed flow fields differ to a large extent from the flow field predicted by geostrophic dynamics, indicating that ageostrophic dynamics play a more important role in these regions. The barotropic transport differences between the eastern and western Fram Strait contain information about the barotropic transport evolution along the entire Arctic continental slope. The good agreement between observations and theory across the strait (below 800 m) therefore indicates that the flow along the deeper part of the Arctic continental slope is well described by geostrophic dynamics. According to our results, the noticeably more baroclinic nature of the flow in the western Fram Strait, compared with the eastern strait, can then be ascribed to water mass modifications along the Arctic continental slope.

Altitudinal variability of climate–tree growth relationships along a consistent slope of Anyemaqen Mountains, northeastern Tibetan Plateau

In order to investigate climate–tree growth relationships at different elevations, tree-ring width chronologies of Qilian Juniper ( Sabina przewalskii) were developed from four sampling sites at different elevations of a south-facing slope in the central Anyemaqen Mountains, northeastern Tibetan Plateau. Statistical characteristics of the chronologies indicated most tree-ring parameters decreased with the increase of elevations. Response analysis on the first principal component of all four chronologies indicated 76% of tree growth could be explained by climatic variations. Correlation analysis between chronologies and climate variables indicated there were significant differences in climate–tree growth relationships along the altitudinal gradients. The lower forest border chronology was negatively correlated with monthly mean temperature, except for previous October and current January–March, while the upper forest border chronology had positive correlations with monthly mean temperature, excluding previous September and current April–May. There was a decreasing trend from significantly negative to weakly negative correlations of tree growth with May–June temperature from low to high elevations, and an increasing trend from weakly negative to significantly positive correlations with July temperature. Meanwhile, there were significant positive correlations of prior August–October and current July precipitation with the two low-elevation chronologies. The correlations between tree growth and January–April precipitation varied from negative to positive with the increase of elevations, although there were no significant correlations between precipitation and high-elevation chronologies. Response analysis on all chronologies indicated tree growth was more limited by temperature along the entire slope, while precipitation tends to influence tree growth at some drier or lower-elevation sites.

Subsidence and associated ground movements on the Pennines, northern England

The Pennines form a range of hills in northern England. The elevated parts are known locally as ‘the moors’, and these run from the Scottish border in the north, southwards to the Midlands. The area is dominated by elevated moorland plateaux, which have been incised by glacial and alluvial valleys. The plateaux are capped by strong, massive, cross-bedded Kinderscout Grit of Late Carboniferous (Namurian) age (known also as the Millstone Grit). Interbedded weak shales, mudstones and siltstones crop out on the valley floor, lower slopes and middle slopes, which have been eroded by landslides. The moorland is covered by a veneer of head and peat deposits that may be up to 4 m thick. Two types of subsidence, with associated ground movements, have been observed: (1) the large-scale regional tilting, landsliding and apparent lateral spreading of periglacial moorland plateaux with associated fault scarps and fissures; (2) ‘sinkholes’ in peat, which occur as distinct subsidence depressions up to 2 m in diameter. As these ‘sinkholes’ are not generated by mining subsidence or by the dissolution of (for example, karst or gypsiferous) bedrock, the term pseudo-sinkhole has been introduced, for the purpose of this paper. Pseudo-sinkholes may be occasionally associated with peat slides, bog bursts, subsidence depressions and concentric ring fissures on peat scars. The extent and magnitude of the subsidence and ground movements vary considerably. These may affect small, localized peat-covered slopes, no more than a few metres wide, or influence the morphology of entire moorland slopes. Because of the relative remoteness of ‘the moors’ these types of ground movements do not influence structures, or affect people, and therefore tend to have not been previously investigated, documented or reported. Similar features have been reported in the South Wales Coalfield, where there is a long, complex mining legacy. Since the Kinderscout (Millstone) Grit and associated interbedded sedimentary rocks do not contain any minerals of economic significance, the observed ground movements cannot be attributed to mining subsidence. The Pennine moors therefore provide a unique opportunity to investigate subsidence (tilt), scarps and fissures in the absence of mining (or other human) influences. Subsidence in peat is likely to have been generated by the subsurface fluvial erosion of layered fibrous and amorphous peat deposits. This leads to the generation ofsubsurface voids (pipes), which subsequently undergo collapse, followed by the migration of the collapsed zone towards the ground surface. This results in the generation of crescent-shaped, concentric fissures, subsidence depressions, graben and pseudo-sinkholes. The mechanism for the large-scale regional tilting and subsidence of moorland plateaux is more difficult to determine and still not fully understood. These ground movements are complex and are associated with deep-seated landslides, complex fissure networks and, in the study area, a reactivated fault-scarp that is up to 4 m high and over 700 m long. This paper suggests that these movements were possibly generated under conditions of periglacial erosion and weathering, during glacier retreat, deglaciation and gravitational stress relief of valley sides. This is most likely to have occurred during the closing stages of the Pleistocene ice age. This may have initiated the lateral spreading of moorland plateaux, subsequently resulting in fissuring, fault reactivation, tilting and subsidence. The aim of this paper is to document and draw attention to the different types of subsidence and associated ground movements on Pennine moorland, and to suggest causal mechanisms.

Interpretation of a Progressive Slope Movement Using Balanced Cross Sections and Numerical Integration

Gaussian quadrature, a numerical integration technique through fixed points, is applied to improve accuracy and efficiency in the cross-section balance modeling of a slope subjected to progressive displacements. This integration is employed to compute geometrical areas of individual stratigraphic units that have participated in the deformation. Given the initial and final states of a natural slope in which progressive failure has been carefully monitored for 7 years, the internal geometry of four stratigraphic layers that were displaced in a manner that characterizes the displacement kinematics of the entire slope has been analyzed. The area differences between the initial and final sections for three of the layers are zero. A fourth, basal, layer shows a unit area reduction of 13 percent, which can be accounted for by toe erosion. This implies that the total internal geometric area is found to be preserved during the course of the progressive deformation, a fact that is evident in repeated ground surveys conducted during the 7-year history of displacement. Also, factors of safety computed for the basal surface of slip at the initial and final stages of displacement monitoring demonstrate that the slope became less stable over a period of 7 years as a result of the progressive failure. Such a reduction in stability would be difficult to quantify without the application of numerical integration that allows the accurate construction of area-balanced geometrical models in a digital format amenable to validation and stability analysis.

Mediterranean shelf-edge muddy contourites: examples from the Gela and South Adriatic basins

We present new evidence of shallow-water muddy contourite drifts at two distinct locations in the central Mediterranean characterized by a relatively deep shelf edge (between 170 and 300 m below sea level): the south-eastern Adriatic margin and the north-western Sicily Channel. The growth of these shelf-edge contourite drifts is ascribed to the long-term impact of the Mediterranean themohaline circulation. The Levantine Intermediate Water flows continuously, with annual or inter-annual variations, and affects the shelf edge and the upper slope in both study areas. In addition, the SW Adriatic margin is impinged by the seasonally modulated off-shelf cascading of North Adriatic Dense Water. This water mass has formed ever since the large Adriatic continental shelf was drowned by the post-glacial sea-level rise. It energetically sweeps the entire slope from the shelf edge to the deep basin. These bottom currents flow parallel or oblique to the depth contours, and are laterally constricted along markedly erosional moats aligned parallel to the shelf edge where they increase in flow velocity. The internal geometry and growth patterns of the shelf-edge contourites reflect changes in oceanographic setting affecting the whole Mediterranean Sea. In particular, seismic correlation with published sediment cores documents that these deposits are actively growing and migrating during the present interglacial, implying an enhancement in bottom-water formation during intervals of relative sea-level rise and highstand. Regardless of the specific mechanisms of formation, sediment drifts in both study areas have been affected by widespread thin-skinned mass-wasting events during post-glacial times. Repeated mass-transport processes have affected in particular the downslope flank of the shelf-edge contourite drifts, indicating that these muddy deposits are prone to failure during, or soon after, their deposition.

An experimental study on the cooling mechanism of a shading board in permafrost engineering

Shading boards (SB) were tested on an embankment slope as one of the measures for actively cooling permafrost in roadbed engineering along the Qinghai-Tibet Highway on the Tibet Plateau, China. A series of tests, evaluating the cooling mechanism of SBs, also were conducted in the laboratory that showed that the SB cooled the permafrost by significantly reducing the input of solar radiation onto the side slope surfaces. In these laboratory tests, the radiation intensity was lowered by 85.5%. In addition, the enhanced air convection between the SB and the slope surface removed the heat produced by the secondary radiation from the back side of the board, as well as heat released from the soil. Laboratory tests indicate that the temperature on the slope surface lowered in more degree with the SB can be explained by the “stack effect” triggered between the SB and the slope surface. The accelerated air flow under the SB brings the temperature of the slope surface to ambient air temperature. There was an optimal height of 15 cm for the SB, where the air flow reached its maximum amount and velocity, which means that, in practice, the installed height of the SB should be taken into account. Also, the free flow of the air under the SB should be assured by leaving the space between the SB and the protected surface unblocked. Practical applications of the SB along the Qinghai-Tibet Highway from November 2003 to November 2004 showed that the SB could reduce the annual average surface temperature of the entire embankment side slope by about 3.2 °C compared with the unshaded embankment slope. The maximum reduction was 4 °C. The annual average slope surface temperature under the SB was about 1.5 °C lower than the nearby natural ground surface.

Sedimentological history of Bryant Canyon area, northwest Gulf of Mexico, during the last 135 kyr (Marine Isotope Stages 1–6): A proxy record of Mississippi River discharge

Bryant and Eastern Canyons are located in northwest Gulf of Mexico, and are characterized by a complex sedimentological history related to glacioeustatic cycles, river discharges, and interactions between depositional and halokinetic processes. This study is based on detailed sedimentological analysis from forty-eight long cores from these two canyons. This paper determines the evolutionary history of the canyons and assesses the response of sedimentary processes to morphological, climatic, hydrological, and sea-level changes. During the last glaciation, the upper and middle continental slope was supplied with sediments by low density turbidity currents derived from the depositional segregation (deposition of the coarsest material in the most proximal locations) of large turbidity currents initiated on the outer shelf. The lower continental slope was supplied with sediment by westward flowing bottom currents, originated from the entrainment of the most diluted wash-load and tails of turbidity currents from the Mississippi Fan. Bryant and Eastern Canyon systems were active during the penultimate glaciation, Marine Isotope Stage (MIS) 6, and were supplied with sediments by an ancestral shelf-margin Mississippi River delta. Gravity flows transported enormous amounts of sediment to the continental slope and abyssal plain of the northwest Gulf of Mexico. The sea-level rise at MIS 5 led to confinement of river-sourced sediments to the widespread continental shelf of the northwest Gulf of Mexico, and consequently to the cessation of gravity flows. During the first 40 kyr of MIS 5, salt diapirs transformed the canyons into a network of intraslope basins. The sea level dropped to the mid-shelf during MIS 3 and 4, but never reached the shelf-break, and therefore, river-sourced sediments remained largely confined to the shelf. However, seaward sediment transportation was achieved occasionally through turbidity currents related to sediment failures, storms, and high-river discharges. Four high river discharge events have been identified during this period. The first three were centred at 37, 45, and 53 cal ka BP. The last high river discharge occurred at the end of MIS 3 (29.4-33.2 cal ka BP), and resulted in the deposition of closely-spaced, mud turbidites over the entire continental slope. The Laurentide Ice Sheet (LIS) was restricted north of the upper Mississippi River valley during 60 to ∼ 30 cal ka BP and therefore, the high river discharge events are interpreted as melt-water events, related to brief southward advancements of the LIS, which resulted in the flooding of Mississippi River. The extensive lowering of sea level during the last glacial maximum (MIS 2) resulted in the almost direct discharge of Mississippi River sediments to the upper continental slope leading to the development of abundant turbidity currents. Eleven wet–dry cycles during this period are defined; they probably originated from episodic subglacial melt-water floods, released from southern parts of the LIS. The last deglaciation event is characterized by the development of a major melt water event at 16.5–13 cal ka BP that resulted in the deposition of distinct, organic-rich sediments. At about 13 cal ka BP, the melt water discharges of the LIS in North America switched from the Mississippi River to either the St. Lawrence or Mackenzie River valleys, causing the domination of hemipelagic sedimentation on the continental slope of the northwest Gulf of Mexico. Isotopic data indicate that melt-water discharges returned to the Mississippi River Valley at ∼ 11.4 cal ka BP. The absence of any sedimentological indication on the continental slope of the northwest Gulf of Mexico of the return of the melt-water discharges to the Mississippi River is attributed to the confinement of river-sourced sediments on the continental shelf due to the rise of the sea level.

Late Pleistocene–Holocene stratigraphy and radiocarbon dating of La Malinche volcano, Central Mexico

Previous studies of La Malinche identified and radiocarbon dated several volcanic layers, the youngest of which yielded an age of ca. 7.5 ka. An additional ash fallout layer that crops out at high altitudes was considered the most recent deposit, with an estimated age of 6 ka. In the present work 38 new radiocarbon ages are presented. From these, several date the young ash fallout layer and lie around 3.1 ka. With the aid of these dates a new and comprehensive stratigraphy documenting the Late Pleistocene–Holocene eruptive history of La Malinche is presented. The stratigraphy indicates two main stages of volcanic activity: Pre-Malinche and Malinche. The first undoubtedly comprises the major part of the eruptive history, but its deposits are largely covered by the products of the latter stage, on which this study is focused. The Malinche stage was subdivided into three eruptive periods. Period 1 started with the emplacement of the Huamantla Pumice more than 45 ka ago. This deposit consists of a thick pumice fallout overlain by pyroclastic flow deposits. Subsequently, several episodes of construction and collapse of summit domes occurred. The oldest dome was dated at ca. 45 ka. Period 2 started 21.5 ka ago with the Malinche Pumice I, a widespread pumice fallout covering the entire slopes of the volcano. Pyroclastic flows and lahars related to this eruption were channeled along deep barrancas and reached considerable distances. Deposits produced by partial sector collapse and dated at ca. 20.9 ka, and a pumice-and-ash flow deposit dated at 15.9 ka were also generated during this period. The last period started with the eruption of the Malinche Pumice II, a distinctive fallout deposit overlain by ash flow deposits on the NE slope of the volcano. The age of this pumice layer is estimated between 12 and 9 ka. Formation of block-and-ash flows, lahars and pumice-and-ash flows followed during this period, and peaked in a most intensive episode that was dated at 7.5 ka. After this, a long interval of quiescence was interrupted 3.1 ka ago, with the eruption of an ash fallout accompanied by small pyroclastic flows, whose deposits are the youngest volcanic products recognized at La Malinche. The new stratigraphic findings identify La Malinche as a potentially active and dangerous volcano that could severely affect densely populated areas at its lower slopes. In addition, the results of this work can shed some light on archaeological research that is being carried out in the Puebla–Tlaxcala region.

Slope instability of San Miniato hill (Florence, Italy): possible deformation patterns

The hill of San Miniato (Florence, Italy) has been repeatedly identified in the past as the site of a slow moving, intermittent landslide. Possible hypotheses regarding the mechanisms responsible for past movements and for cracks and fissures present today are formulated based on the comparison of historical information and processed monitoring data. Although it is not possible to completely exclude a large inactive landslide that involves the entire northern slope, it seems more probable that the slide, if it does exist, is no longer active and that present-day damage is due to separate shallow movements concentrated in man-made deposits. This hypothesis can only be verified with a temporal extension of the monitoring activities, necessary in any case for planning possible safeguarding measures for the cultural heritage in the area.

A multi-level filtering approach for fairing planar cubic B-spline curves

In this paper a new approach to the problem of fairing planar B-spline curves is introduced. We propose an algorithm based on a multi-level representation of cubic B-spline curves, which enables the identification of bad control points that need to be faired. The multi-level representation allows splitting a curve into its low resolution and details function parts. The details function permits the formulation of a different approach to the selection of bad control points, differing from others methods that are based on the evaluation of curve and curvature derivatives. Moreover, this new technique leads to an increased interaction with designers that can identify faster the set of bad control points and then operate on them through their level-of-detail (LOD) representation in manner to obtain the expected shape. Hence, designers have more control over the entire slope by thresholding details in several manners fully described in the following chapters. Several numerical examples are presented to validate the effectiveness of this algorithm compared with another technique in (Farin, G., Sapidis, N., 1989. Curvature and the fairness of curves and surfaces. IEEE Computer Graphics and Applications 9 (2), 52–57).

Protection of Shoreline by Using Partial Revetment Structure under Regular and Irregular Waves

In this paper, results obtained from an experimental investigation conducted to determine wave-induced geometric characteristics of shorelines protected by partial revetment structure are presented. The experiments were performed with both regular and irregular waves. The beach sand used in this study had a mean diameter of 0.35 millimeter and a specific gravity of 2.63. The beach had an initial slope of 1 : 5 and was protected by the partial revetment structure. For this purpose, the armor units, mean diameters and specific gravities of which were varied in the range 8.5–67.95 millimeters and 1.81–2.77, respectively, were placed on the wave-breaking area. Different wave groups were generated over an initially flat, partially protected beach, and a number of geometric characteristics of equilibrium beach profiles was determined. Moreover, the static damage of the armor layer was obtained for all test groups. The results of this experimental study were evaluated, and empirical expressions based on the results were formulated to define geometric parameters of equilibrium profile under pure regular waves, pure irregular waves, and regular-irregular waves. The findings showed that the partial revetment structure decreases shore erosion on average 65–70%. Because the sand of the unprotected area spreads over the armor layer, this revetment type does not disturb the beauty of the area and its aesthetics. Moreover, it is a low-cost structure, because the armor layer was placed only within the wave-breaking area, not across the entire slope.

Monitoring and reconstruction of a chairlift midway station in creeping permafrost terrain, Grächen, Swiss Alps

Abstract The midway station of a chairlift located in the ski resort Grachen (Swiss Alps) was originally built in 1997 at 2453 m ASL in alpine permafrost terrain. The chairlift conveys 300,000–330,000 passengers every winter season and constitutes an important link between two cable cars in the ski area. In winter 1997–1998, it became evident that the terrain at the mid-way station was unstable: one of the two concrete foundations started to creep and settle rapidly and cracks formed in the structure. To investigate the properties of the ground, two 25 m boreholes were drilled near the foundations and equipped with inclinometer casings and thermistors. The presence of permafrost with an exceptionally thick active layer and a 20-m talik containing water was confirmed. The horizontal and vertical deformation rates of the ground attained very high values between 2002 and 2003. As a consequence, and in the interest of the safety of the passengers, the original midway station had to be destroyed and a specially developed new station was built in 2003. The excavation trench was lined with insulating material in order to avoid thermal disturbance of the underlying permafrost by hydration heat. The new foundation consists of a concrete T-girder with three point bearings. Repositioning of the entire structure in response to creep is possible, due to the unique character of the structural bearings which can be raised or lowered using hydraulic cylinders and steel plates. The thermal regime of the entire structure, ground temperatures and slope movements continue to be monitored to determine the long-term evolution of the mid-way station.

Soluble Reactive Phosphorus Transport and Retention in Tropical, Rainforest Streams Draining a Volcanic and Geothermally Active Landscape in Costa Rica. : Long-Term Concentration Patterns, Pore Water Environment and Response to ENSO Events

Soluble reactive phosphorus (SRP) transport/retention was determined at four sites in three rainforest streams draining La Selva Biological Station, Costa Rica. La Selva is located at the base of the last remaining intact rainforest transect from 30 m above sea level to 3000 m along the entire Caribbean slope of Central America. Steam SRP levels can be naturally high there due to regional, geothermal groundwater discharged at ambient temperature. Monitoring since 1988 has revealed distinctive long-term differences in background SRP and total P (TP) for three streams in close proximity, and identified the impact of ENSO (El Nino Southern Oscillation) events on SRP-enriched reaches. Mean interannual SRP concentrations (± standard deviation) were 89 ± 53µg/l in the Salto (1988–1996), 21 ± 39µg/l in the Pantano (1988–1998), and 26 ± 35µg/l in the Sabalo (1988–1996). After January, 1997 the separate upland-lowland contributions to discharge and SRP load were determined monthly in the Salto. SRP in Upper Salto was low (19 ± 8µg/l, 1997–2002) until enriched at␣the upland-lowland transition by regional groundwater. Mean SRP concentration in Lower␣Salto (108 ± 104µg/l) was typically highest February–April, the driest months, and lowest July–September, the wettest. SRP concentration was positively correlated to the inverse of discharge in Lower Salto when ENSO data were omitted (1992 and 1998–1999), but not in the Upper Salto, Pantano, or Sabalo. TP was positively correlated to the inverse of discharge in all three streams when ENSO data were omitted. High SRP springs and seeps along the Lower Salto contributed 36% of discharge but 85% of SRP export 1997–2001. Annual SRP flux from the total Salto watershed (1997–2001) averaged 2.9 kg/ha year, but only 0.6 kg/ha year from the Upper Salto. A dye tracer injection showed that pore water environments were distinctly different between Upper and Lower Salto. Upper Salto had high surface water–pore water exchange, high dissolved oxygen, low SRP, and low conductivity similar to surface water, and Lower Salto had low surface water–pore water exchange, low dissolved oxygen, high SRP, and high conductivity reflecting geothermal groundwater influence. SRP export from the Salto was controlled by regional groundwater transfer, which in similar volcanic settings could be a significant P source. However, ENSO events modified the SRP concentration in the Salto suggesting that long-term monitoring is required to understand underlying SRP dynamics and P flux to downstream communities.

Evidence of slope instability in the Southwestern Adriatic Margin

Abstract. The Southwestern Adriatic Margin (SAM) shows evidence of widespread failure events that generated slide scars up to 10 km wide and extensive slide deposits with run out distances greater than 50 km. Chirp-sonar profiles, side-scan sonar mosaics, multibeam bathymetry and sediment cores document that the entire slope area underwent repeated failures along a stretch of 150 km and that mass-transport deposits, covering an area of 3320 km2, are highly variable ranging from blocky slides to turbidites, and lay on the lower slope and in the basin. The SAM slope between 300–700 m is impacted by southward bottom currents shaping sediment drifts (partly affected by failure) and areas of dominant erosion of the seafloor. When slide deposits occur in areas swept by bottom currents their fresh appearence and their location at seafloor may give the misleading impression of a very young age. Seismic-stratigraphic correlation of these deposits to the basin floor, however, allow a more reliable age estimate through sediment coring of the post-slide unit. Multiple buried failed masses overlap each other in the lower slope and below the basin floor; the most widespread of these mass-transport deposits occurred during the MIS 2-glacial interval on a combined area of 2670 km2. Displacements affecting Holocene deposits suggest recent failure events during or after the last phases of the last post-glacial eustatic rise. Differences in sediment accumulation rates at the base or within the sediment drifts and presence of downlap surfaces along the slope and further in the basin may provide one or multiple potential weak layers above which widespread collapses take place. Neotectonic activity and seismicity, together with the presence of a steep slope, represent additional elements conducive to sediment instability and failure along the SAM. Evidence of large areas still prone to failure provides elements of tsunamogenic hazard.