Tim Davies

Spreading of rock avalanche debris by mechanical fluidization

SummarySpreading of Rock Avalanche Debris by Mechanical FluidizationTwo hypotheses for the motion of large rock avalanches (sturzstroms) are examined: (a) that sturzstrom deposits result from the spreading of a mass of debris in a fluidised state under the influence of gravity, and (b) that the debris becomes fluidised because of the existence of a high shear rate in the basal region. The first hypothesis is supported by data describing the length of sturzstrom deposits, and the second is shown to be in agreement with simple laboratory tests, with the grain-flow theory of Bagnold and with the characteristic features of sturzstrom deposits.

Ultrafiltration with size-exclusion liquid chromatography for high yield isolation of extracellular vesicles preserving intact biophysical and functional properties

UNLABELLED Extracellular vesicles (EVs) are natural nanoparticles that mediate intercellular transfer of RNA and proteins and are of great medical interest; serving as novel biomarkers and potential therapeutic agents. However, there is little consensus on the most appropriate method to isolate high-yield and high-purity EVs from various biological fluids. Here, we describe a systematic comparison between two protocols for EV purification: ultrafiltration with subsequent liquid chromatography (UF-LC) and differential ultracentrifugation (UC). A significantly higher EV yield resulted from UF-LC as compared to UC, without affecting vesicle protein composition. Importantly, we provide novel evidence that, in contrast to UC-purified EVs, the biophysical properties of UF-LC-purified EVs are preserved, leading to a different in vivo biodistribution, with less accumulation in lungs. Finally, we show that UF-LC is scalable and adaptable for EV isolation from complex media types such as stem cell media, which is of huge significance for future clinical applications involving EVs. FROM THE CLINICAL EDITOR Recent evidence suggests extracellular vesicles (EVs) as another route of cellular communication. These EVs may be utilized for future therapeutics. In this article, the authors compared ultrafiltration with size-exclusion liquid chromatography (UF-LC) and ultra-centrifugation (UC) for EV recovery.

Determining rheological parameters of debris flow material

Abstract A 2.0 m diameter steel 30° inverted cone-and-plate viscometer/rheometer was designed, constructed, and used to test the behaviour of coarse-grained debris flow materials. A 1: 5 scale model machine was also constructed and used to test the internal flow dynamics of the viscometer/rheometer and to obtain results for fluids, grain-fluid mixtures, and debris flow fines. For fluids and grain-fluid mixes, our results were similar to those obtained earlier using standard viscometric systems. Derived rheological parameters for debris flow materials and clay slurries agreed well with those determined from calculation, direct measurement, and field observation. Apparent viscosities were shear-rate dependent, extremely sensitive to water content, and as high as 6000 Pa·s. Instantaneous stresses within shearing debris flow material varied over a wide range. Debris flow materials with bimodal grain-size distributions had a dilatant plastic rheology. Those with a low content of coarse material and unimodal grain-size distribution, or exceptionally high fines content, had a plastic or viscoplastic rheology.

Large debris flows: A macro-viscous phenomenon

SummaryField observations from a variety of sources suggest that destructive debris flows occur when the density of the fluid-solid mixture exceeds about 1.5 T/m3, and that their destructive ability is due to their pulsing nature and to their ability to carry large boulders.If debris flows are treated as a macroviscous flow of large stones in a slurry of fine solids in water, several of their obvious characteristics (boulder transport, deep bed erosion, intermittent jamming) can be explained. Further, the amplification and translation in a main channel of random surges due to jamming in tributaries explains the regular, large pulses in Chinese debris flows as a roll-wave phenomenon.

Effects of debris on ice-surface melting rates: an experimental study

Here we report a laboratory study of the effects of debris thickness, diurnally cyclic radiation and rainfall on melt rates beneath rock-avalanche debris and sand (representing typical highly permeable supraglacial debris). Under continuous, steady-state radiation, sand cover >50mm thick delays the onset of ice-surface melting by >12 hours, but subsequent melting matches melt rates of a bare ice surface. Only when diurnal cycles of radiation are imposed does the debris reduce the longterm rate of ice melt beneath it. This is because debris >50 mm thick never reaches a steady-state heat flux, and heat acquired during the light part of the cycle is partially dissipated to the atmosphere during the nocturnal part of the cycle, thereby continuously reducing total heat flux to the ice surface underneath. The thicker the debris, the greater this effect. Rain advects heat from high-permeability supraglacial debris to the ice surface, thereby increasing ablation where thin, highly porous material covers the ice. In contrast, low-permeability rock-avalanche material slows water percolation, and heat transfer through the debris can cease when interstitial water freezes during the cold/night part of the cycle. This frozen interstitial water blocks heat advection to the ice-debris contact during the warm/day part of the cycle, thereby reducing overall ablation. The presence of metre-deep rock-avalanche debris over much of the ablation zone of a glacier can significantly affect the mass balance, and thus the motion, of a glacier. The length and thermal intensity of the diurnal cycle are important controls on ablation, and thus both geographical location and altitude significantly affect the impact of debris on glacial melting rates; the effect of debris cover is magnified at high altitude and in lower latitudes.

The October 1999 Mt Adams rock avalanche and subsequent landslide dam‐break flood and effects in Poerua river, Westland, New Zealand

Abstract On 6 October 1999 a very large (c. 10–15 million m3) rock avalanche from Mt Adams blocked the Poerua River 11 km upstream from the SH6 road bridge on the West Coast of the South Island. The 120 m high rock debris dam impounded a lake with a volume of 5–7 million m3before it overtopped on 7 October. The short survival time of landslide dams in rivers in Westland and around the world suggested a high probability of rapid dam failure and flooding downstream. This was confirmed when the dam breached 6 days later on 12 October 1999, during the first significant rain after the landslide occurred. The resulting dam‐break flood deposited considerable coarse gravel from the landslide in the valley downstream of the dam, and (mostly fines) on the alluvial fan below the Poerua gorge exit. The flow inundated farmland in the upper Poerua valley, but otherwise was largely confined to the river channel and did little damage at the time, mainly because of significant flow attenuation (c. 50% or greater) and sediment deposition on the alluvial fan below the gorge exit. Subsequently the remnant lake has been infilled, and c. 75% of the dam material has been transported downstream during floods. About 1.7 million m3 of alluvium has been deposited in the river channel and across farmland between the gorge exit and the SH6 bridge, changing the rivers course and causing lateral erosion of older terraces. These effects are continuing and will cause ongoing problems in the future. The rock avalanche and landslide dam failure in the Poerua valley were significant events which have had a profound local geomorphic impact. The landslide and subsequent downstream effects are typical landscape‐forming events. These events and the resulting community response to them have provided valuable information on the hazards, effects, and management of future landslide‐dam failures in Westland. Increased resources within local authorities for hazard assessments and response planning during such events would reduce the risk from dam‐break floods in the future, especially following the next Alpine Fault earthquake, when further landslide dam failures are expected.

Rockslides and Their Motion

The motion of landslides sourced from mostly bedrock (called rockslides) is controlled by the phenomenon of grain flow, and the frictional resistance of the constituent rock grains and their interstitial fluids. Modern understanding of grain-flow dynamics recognises that the important interactions between grains are irregularly distributed within the grain mass, with fortuitous alignments of grains carrying most of the stress in “force chains”, while other grains are only weakly stressed. In rapidly shearing grain flows, under substantial confining stress, force-chain stresses rise high enough to crush grains. Such comminuting grain flows develop a distinctive grain-size distribution that is fractal over many orders of magnitude of grain size down to sub-micron sizes. In the moment of crushing, grains are not solids, and behave as high-pressure fluids. As the grain fragments are injected into lower pressure surroundings, they behave as would any other fluid, lowering the effective stress on other grains, and thereby lowering frictional resistance to flow. We show how this affected the blockslide component of New Zealand’s prehistoric giant Waikaremoana rockslide; New Zealand’s Falling Mountain rock avalanche triggered by an earthquake in March 1929; and a small prehistoric New Zealand rockslide that was too small to be a comminuting grain flow, but which fell on and mobilized a fine, saturated substrate. We use grain-flow dynamics to explain the motion of these rockslides determined through field studies and physical and numerical modeling.

Assessment of rainfall-generated shallow landslide/debris-flow susceptibility and runout using a GIS-based approach: application to western Southern Alps of New Zealand

Rainfall-triggered shallow slope failures are very common in the western Southern Alps of New Zealand, causing widespread damage to property and infrastructure, injury and loss of life. This study develops a geographic information system (GIS)-based approach for shallow landslide/debris-flow susceptibility assessment. Since landslides are complex and their prediction involves many uncertainties, fuzzy logic is used to deal with uncertainties inherent in spatial analysis and limited knowledge on the relationship between conditioning factors and slope instability. A landslide inventory was compiled using data from existing catalogues, satellite imagery and field observations. Ten parameters were initially identified as the most important conditioning factors for rainfall-generated slope failures in the study area, and fuzzy memberships were established between each parameter and landslide occurrence based on both the landslide inventory and user-defined functions. Three output landslide susceptibility maps were developed and evaluated in a test area using an independent population of landslides. The models demonstrated satisfactory performance with area under the curve (AUC) varying from 0.708 to 0.727. Sensitivity analyses showed that a six-parameter model using slope angle, lithology, slope aspect, proximity to faults, soil induration, and proximity to drainage network had the highest predictive performance (AUC = 0.734). The runout path and distance of potential future landslides from the susceptible areas were also modelled based on a multiple flow direction algorithm and the topographic slope of existing debris-flow deposits. The final susceptibility map has the potential to inform regional-scale land-use planning and to prioritize areas where hazard mitigation measures are required.

A possible coseismic landslide origin of late Holocene moraines of the Southern Alps, New Zealand

Abstract Moraine deposits of the Southern Alps, New Zealand, have been used to infer past climatic regimes, such as the “Little Ice Age”. Recent work has identified four major movements of the Alpine Fault since AD 1200. These earthquakes are inferred to have produced numerous large rock avalanches, some of which must have fallen onto the valley glaciers, with this debris subsequently deposited as terminal moraines. Evidence is presented which suggests that periods of moraine formation follow each of these major earthquakes. Considerable caution must therefore be exercised in inferring past climatic conditions from the size and location of these terminal moraines. These findings have implications for Southern Hemisphere mid‐latitude paleoclimatic reconstruction.

Regional coseismic landslide hazard assessment without historical landslide inventories: A new approach

Currently, regional coseismic landslide hazard analyses require comprehensive historical landslide inventories as well as detailed geotechnical data. Consequently, such analyses have not been possible where these data are not available. A new approach is proposed herein to assess coseismic landslide hazard at regional scale for specific earthquake scenarios in areas without historical landslide inventories. The proposed model employs fuzzy logic and geographic information systems to establish relationships between causative factors and coseismic slope failures in regions with well-documented and substantially complete coseismic landslide inventories. These relationships are then utilized to estimate the relative probability of landslide occurrence in regions with neither historical landslide inventories nor detailed geotechnical data. Statistical analyses of inventories from the 1994 Northridge and 2008 Wenchuan earthquakes reveal that shaking intensity, topography, and distance from active faults and streams are the main controls on the spatial distribution of coseismic landslides. Average fuzzy memberships for each factor are developed and aggregated to model the relative coseismic landslide hazard for both earthquakes. The predictive capabilities of the models are assessed and show good-to-excellent model performance for both events. These memberships are then applied to the 1999 Chi-Chi earthquake, using only a digital elevation model, active fault map, and isoseismal data, replicating prediction of a future event in a region lacking historic inventories and/or geotechnical data. This similarly results in excellent model performance, demonstrating the models predictive potential and confirming it can be meaningfully applied in regions where previous methods could not. For such regions, this method may enable a greater ability to analyze coseismic landslide hazard from specific earthquake scenarios, allowing for mitigation measures and emergency response plans to be better informed of earthquake-related hazards.