scholarly journals Granulometric investigations of snow avalanches

2009 ◽  
Vol 55 (193) ◽  
pp. 829-833 ◽  
Author(s):  
Perry Bartelt ◽  
Brian W. McArdell
Keyword(s):  
Granule Size ◽  
Depositional Environments ◽  
Vertical Shear ◽  
Size Distributions ◽  
Size Segregation ◽  
Surface Shear ◽  
Natural Sediment ◽  
Near Surface ◽  
Sediment Size ◽  
Log Normal

AbstractAvalanche deposits consist of rounded granules composed of aggregates of snow and ice particles. The size of the granules is related to vertical shear gradients within the flow; studying the granule-size distribution may be useful in understanding the flow and stopping of avalanches. We applied a sediment-size sampling method to measure snow granule-size distributions at different depositional environments on two dry and two wet avalanche deposits at three field sites. The granule-size distributions are approximately log-normal, similar to many natural sediment deposits. The median granule size in the wet and dry avalanches varies between 65 and 162 mm. Wet avalanches tend to produce more large granules than dry avalanches, indicating both smaller flow velocities and near-surface shear gradients. Granule size is similar in frontal lobes and levee deposits, suggesting that levee formation occurs independently of the size segregation at the avalanche front.

Characteristics of Oil Droplets Stabilized by Mineral Particles: The Effect of Salinity

2003 ◽  
Vol 2003 (1) ◽  
pp. 963-970 ◽  
Author(s):  
Ali Khelifa ◽  
Patricia Stoffyn-Egli ◽  
Paul S. Hill ◽  
Kenneth Lee
Keyword(s):  
Droplet Size ◽  
Size Distributions ◽  
Oil Droplets ◽  
Natural Sediment ◽  
Mineral Particles ◽  
Sediment Size ◽  
Maximum Value ◽  
Seawater Salinity ◽  
Droplet Size Distributions ◽  
Oil Type

ABSTRACT The influence of salinity on the characteristics of oil droplets stabilized by mineral particles (oil-mineral aggregates – OMA) was studied in the laboratory using three different oils and a natural sediment. Size and concentration of oil droplets associated with negatively and positively buoyant OMA were measured by image analysis using epi-fluorescence microscopy. Results showed that the median droplet size increases rapidly from about 5 μm at zero salinity to double at salinity close to 1.2 ppt; decreases dramatically to about 5 μm at salinity 3.5 ppt and then increases slightly to 6 μm at the seawater salinity. The concentration of oil droplets also increases sharply when the salinity increases from zero to a critical aggregation salinity Scas, after which it stabilizes at its maximum value. The concentration of mineral-stabilized droplets is strongly affected by oil type at any salinity. When normalized to its maximum value, the concentration of droplets correlates well with normalized salinity S/Scas. A relationship is derived to predict the effect of salinity on the concentration of mineral-stabilized droplets. Size distributions of oil droplets follow similar trends, but their magnitudes depend on salinity and oil type. Self-similarity in droplet size distributions was shown when the data were plotted using normalized variables N/Nt and D/D50, where N is the number of droplets of diameter D, Nt is the total number of droplets and D50 the median size of the droplets. With these normalized variables, oil droplet size distributions measured in this study and those measured in field and laboratory under various conditions by different investigators fit the same curve regardless of the formation conditions of the droplets. A function is derived to calculate normalized cumulative size distributions of oil droplets.

Evolution of the Velocity Structure in the Diurnal Warm Layer

2020 ◽  
Vol 50 (3) ◽  
pp. 615-631 ◽  
Author(s):  
Kenneth G. Hughes ◽  
James N. Moum ◽  
Emily L. Shroyer
Keyword(s):  
Wind Speed ◽  
Velocity Structure ◽  
Heat Fluxes ◽  
Vertical Shear ◽  
Scaling Analysis ◽  
Wind Component ◽  
Surface Shear ◽  
Near Surface ◽  
Wind Speeds ◽  
Sea Surface Temperature Anomalies

AbstractThe daily formation of near-surface ocean stratification caused by penetrating solar radiation modifies heat fluxes through the air–sea interface, turbulence dissipation in the mixed layer, and the vertical profile of lateral transport. The transport is altered because momentum from wind is trapped in a thin near-surface layer, the diurnal warm layer. We investigate the dynamics of this layer, with particular attention to the vertical shear of horizontal velocity. We first develop a quantitative link between the near-surface shear components that relates the crosswind component to the inertial turning of the along-wind component. Three days of high-resolution velocity observations confirm this relation. Clear colocation of shear and stratification with Richardson numbers near 0.25 indicate marginal instability. Idealized numerical modeling is then invoked to extrapolate below the observed wind speeds. This modeling, together with a simple energetic scaling analysis, provides a rule of thumb that the diurnal shear evolves differently above and below a 2 m s−1 wind speed, with limited sensitivity of this threshold to latitude and mean net surface heat flux. Only above this wind speed is the energy input sufficient to overcome the stabilizing buoyancy flux and thereby induce marginal instability. The differing shear regimes explain differences in the timing and magnitude of diurnal sea surface temperature anomalies.

Benthic foraminiferal zonation in deep-water carbonate platform margin environments, northern Little Bahama Bank

1988 ◽  
Vol 62 (01) ◽  
pp. 1-8 ◽  
Author(s):  
Ronald E. Martin
Keyword(s):  
Deep Water ◽  
Benthic Foraminifera ◽  
Carbonate Platform ◽  
Sedimentary Facies ◽  
Depositional Environments ◽  
Near Surface ◽  
Sediment Gravity Flows ◽  
Gravity Flows ◽  
Platform Margin ◽  
Water Carbonate

The utility of benthic foraminifera in bathymetric interpretation of clastic depositional environments is well established. In contrast, bathymetric distribution of benthic foraminifera in deep-water carbonate environments has been largely neglected. Approximately 260 species and morphotypes of benthic foraminifera were identified from 12 piston core tops and grab samples collected along two traverses 25 km apart across the northern windward margin of Little Bahama Bank at depths of 275-1,135 m. Certain species and operational taxonomic groups of benthic foraminifera correspond to major near-surface sedimentary facies of the windward margin of Little Bahama Bank and serve as reliable depth indicators. Globocassidulina subglobosa, Cibicides rugosus, and Cibicides wuellerstorfi are all reliable depth indicators, being most abundant at depths >1,000 m, and are found in lower slope periplatform aprons, which are primarily comprised of sediment gravity flows. Reef-dwelling peneroplids and soritids (suborder Miliolina) and rotaliines (suborder Rotaliina) are most abundant at depths <300 m, reflecting downslope bottom transport in proximity to bank-margin reefs. Small miliolines, rosalinids, and discorbids are abundant in periplatform ooze at depths <300 m and are winnowed from the carbonate platform. Increased variation in assemblage diversity below 900 m reflects mixing of shallow- and deep-water species by sediment gravity flows.

scholarly journals Seismic Risk Assessment of Chania, Greece, Using an Integrated Computational Approach

2021 ◽  
Vol 11 (23) ◽  
pp. 11249
Author(s):  
Ioannis Koutsoupakis ◽  
Yiannis Tsompanakis ◽  
Pantelis Soupios ◽  
Panagiotis Kirmizakis ◽  
SanLinn Kaka ◽  
...  
Keyword(s):  
Seismic Risk ◽  
Seismic Vulnerability ◽  
Risk Model ◽  
Soil Classification ◽  
Velocity Model ◽  
Surface Shear ◽  
Near Surface ◽  
Effective Decision Making ◽  
Ground Motion Scenarios ◽  
The City

This study develops a comprehensive seismic risk model for the city of Chania, in Greece, which is located ina highly seismic-prone region due to the occurrenceof moderate to large earthquakes because of the nearby major subduction zone between African and Eurasian tectonic plates. The main aim is to reduce the seismic risk for the study area by incorporating the spatial distribution of the near-surface shear wave velocity model and the soil classification, along with all possible seismic sources, taking into account historical events. The study incorporates and correlates various ground motion scenarios and geological fault zones as well as information on existing buildings to develop a seismic risk model using QuakeIST software, and then the seismic hazard and a realistic prediction of resulting future adverse effects are assessed. The developed model can assist the municipal authorities of Chania to be prepared for potential seismic events, as well as city planners and decisionmakers, who can use the model as an effective decision-making tool to identify the seismic vulnerability of the city buildings and infrastructure. Thus, this study enables the implementation of an appropriate and viable earthquake-related hazards strategy to mitigate damage and losses in future earthquakes.

Sign in / Sign up

Export Citation Format

Share Document