Landslides and spreading of oceanic hot-spot and arc shield volcanoes on Low Strength Layers (LSLs): an analogue modeling approach
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Subaerial
Shield volcano
Slumping
ABSTRACT Continuous seismic profiles from the upper continental slope east of North Islands, New Zealand, show that surface sediment 10–50 m thick has slumped down bedding planes sloping at 1°–4°. There are four slumps, the Kidnappers Slump which has an area of 250 km 2 , the Paoanui Slump of 80 km 2 , a small slump of only several square kilometers and a slump of undetermined extent. All occurred during the last 20,000 years in Last Glacial Age sediments. A glide plane is exposed at the head of each slump and beds are thrust or contorted at the toe of some slumps. Slumping was probably caused by the failure of loosely packed sandy silt during major earthquakes.
Slumping
Bed
Slope failure
Silt
Bedding
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Abstract A large submarine slump covers more than 150 km2 of a gentle (1 W) slope offshore of Eureka, Calif. We have conducted a detailed geologic and geotechnical investigation of the slump and the surrounding area to delineate the geometry of the slump, determine its cause, and quantitatively evaluate the sediment properties that led to the failure. Our study included an effort to test procedures for using short-core samples in such an evaluation. Cyclic and static triaxial and one-dimensional consolidationtests were performed on gravity-core samples from both within and outside the slump; all samples showed some degree of overconsolidation. We used a normalizedstrength- parameter approach to estimate the strength at the failure surface below the level of sampling. A stability analysis based on a pseudo static infinite-slope model shows the slump probably to be earthquake induced. This analysis also gave values of the sedimentparameters leading to failure at the slump site and to stability at surrounding sites. Owing to the complex variation in sediment properties, subtle changes in properties may determine the stability or failure of thesediment mass. Introduction Slumping (defined as rotational movement along a discrete failure surface) is common to many continental margins of the world and can be an important mechanism of downslope sediment transport (Cook and others, 1981). With the expanded economic exploitation of offshore areas, mass transport of sediment by slumping and other means has become an important consideration in engineering design. Because of the hazard that such mass transport poses to engineering structures, a need exists both for identification of active or potential sediment failures and for quantitative assessment of the potential formovement. Both a geologic and geotechnical (soil mechanics) approach to the study of submarine slumps is important for complete assessment. Interpretive sub bottom acoustic profiling and side-scan sonography are required for identification of zones of past and present instability, whereas measurements of sediment strength and other characteristics are needed to diagnose failure mechanisms and stability factors. From a combined approach, an understanding of submarine mass transport can be obtained. Studies conducted in 1977 and 1978 by the U.s. Geological Survey identified several large areas of unstable sediment, including the one discussed herein, on the continental margin off northern California (Field and others, 1980). In 1979, a combined geologicgeotechnica 1 a na lysis of a large slump a nd the surrounding sea-floor west of Eureka, Calif. was conducted. The study was designed to evaluate the geometry of the slump, the mechanism of failure, and the relative stability of adjacent areas.
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Slope failure
Mass movement
Seabed
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Abstract Subaerial volcaniclastic deposits are produced principally by volcanic debris avalanches, pyroclastic density currents, lahars, and tephra falls. Those deposits have widely ranging geomorphic and sedimentologic characteristics; they can mantle, modify, or create new topography, and their emplacement and subsequent reworking can have an outsized impact on the geomorphic and sedimentologic responses of watersheds surrounding, and channels draining, volcanoes. Volcaniclastic deposits provide a wealth of information about eruptive histories, volcanic processes, and landscape responses to eruptions. The volcanic processes that produce these deposits, and consequently the character and sedimentary structures of the deposits themselves, are influenced by initiation mechanism. Deposit preservation is affected by deposit magnitude, texture, and composition, depositional environment, and climate regime. Innovative analyses of deposits from several modern eruptions and advancements in physical and numerical modelling have vastly improved our understanding of volcanic processes, interpretations of eruptive histories, and recognition of the hazards posed by volcanic eruptions. This contribution highlights and summarizes major advances that have occurred in the past few decades in understanding of volcaniclastic deposits and linkages with volcanic processes.
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Lahar
Peléan eruption
Volcanic ash
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Subaerial
Pyroclastic fall
Submarine volcano
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Climate change is increasing the frequency and intensity of thermokarst, but the influences of regional climate and physiography remain poorly understood. Retrogressive thaw slumping is one of the most dynamic forms of thermokarst and affects many areas of glaciated terrain across northwestern Canada. In this study, we used airphotos and satellite imagery to investigate the influence of climate and landscape factors on thaw slump dynamics. We assessed slump size, density, and growth rates in four regions of ice-rich terrain with contrasting climate and physiographic conditions: the Jesse Moraine, the Tuktoyaktuk Coastlands, the Bluenose Moraine, and the Peel Plateau. Observed increases in: (1) the area impacted by slumps (+2 to +407%), (2) average slump sizes (+0.31 to +1.82 ha), and (3) slump growth rates (+169 to +465 m2 yr−1) showed that thermokarst activity is rapidly accelerating in ice-rich morainal landscapes in the western Canadian Arctic, where slumping has become a dominant driver of geomorphic change. Differences in slump characteristics among regions indicate that slump development is strongly influenced by topography, ground ice conditions, and Quaternary history. Observed increases in slump activity occurred in conjunction with increases in air temperature and precipitation, but variation in slump activity among the four regions suggests that increased precipitation has been an important driver of change. Our observation that the most rapid intensification of slump activity occurred in the coldest environment (the Jesse Moraine on Banks Island) indicates that ice-cored landscapes in cold permafrost environments are highly vulnerable to climate change.
Thermokarst
Slumping
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Late Pleistocene pyroclastics, ejected from the Meerfelder maar in the western Eifel, are underlain by a podsol profile developed in coarse sand. The undersurface of the very first volcanic layer shows an irregular pattern of globular and lobate mounds separated by differently formed depressions. The internal structure is characterized by an uneven textural distribution. It is thought that the observed features point to an initial deposition of a hot muddy mass of low viscosity.
Subaerial
Deposition
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Slumping
Dimensionless quantity
Concrete slump test
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