Analysis of thunderstorm and lightning activity associated with sprites observed during the EuroSprite campaigns: Two case studies

During the summers of 2003 to 2006 sprites were observed over thunderstorms in France by cameras on mountain tops in Southern France. The observations were part of a larger coordinated effort, the EuroSprite campaigns, with data collected simultaneously from other sources including the French radar network for precipitation structure, Meteosat with images of cloud top temperature and the Météorage network for detection of cloud-to-ground (CG) flash activity. In this paper two storms are analyzed, each producing 27 sprite events. Both storms were identified as Mesoscale Convective Systems (MCS) with a trailing stratiform configuration (ST) and reaching a maximum cloud area of ~ 120,000 km². Most of the sprites were produced while the stratiform area was clearly developed and during periods of substantial increase of rainfall in regions with radar reflectivity between 30 and 40 dBZ. The sprite-producing periods followed a maximum in the CG lightning activity and were characterized by a low CG flash rate with a high proportion of + CG flashes, typically around 50%. All sprites were associated with + CGs except one which was observed after a − CG as detected by the Météorage network. This − CG was estimated to have − 800 C km charge moment change. The peak current of sprite-producing + CG (SP + CG) flashes was twice the average value of + CGs and close to 60 kA with little variation between the periods of sprite activity. The SP + CG flashes were further characterized by short time intervals before a subsequent CG flash (median value < 0.5 s) and with clusters of several CG flashes which suggest that SP + CG flashes often are part of multi-CG flash processes. One case of a lightning process associated with a sprite consisted of 7 CG flashes.     

Patterns of faunal extinction and paleoclimatic change from mid-Holocene mammoth and polar bear remains, Pribilof Islands, Alaska

Qagnaxˆ Cave, a lava tube cave on St. Paul Island in the Pribilofs, has recently produced a mid-Holocene vertebrate faunal assemblage including woolly mammoth, polar bear, caribou, and Arctic fox. Several dates on the mammoth remains converge on 5700 ¹⁴C yr BP. These dates, ~ 2300 yr younger than mammoth dates previously published from the Pribilof Islands, make these the youngest remains of proboscideans, and of non-extinct Quaternary megafauna, recovered from North America. Persistence of mammoths on the Pribilofs is most parsimoniously explained by the isolation of the Pribilofs and the lack of human presence in pre-Russian contact times, but an additional factor may have been the local existence of high-quality forage in the form of grasses enriched by nutrients derived from local Holocene tephras. This interpretation is reinforced by stable carbon and nitrogen isotope values obtained from the mammoth remains. The endpoint of mammoth survival in the Pribilofs is unknown, but maybe coterminous with the arrival of polar bears whose remains in the cave date to the Neoglacial cold period of ~ 4500 to 3500 ¹⁴C yr BP. The polar bear record corroborates a widespread cooling of the Bering Sea region at that time.     

A feasible methodology for landslide susceptibility assessment in developing countries: A case-study of NW Nicaragua after Hurricane Mitch

In October 1998, Hurricane Mitch triggered a large number of landslides (mainly debris flows) in Honduras and Nicaragua, resulting in a high death toll and in considerable damage to property. In recent years, a number of risk assessment methodologies have been devised to mitigate natural disasters. However, due to scarcity of funds and lack of specialised personnel few of these methodologies are accessible to developing countries. To explore the potential application of relatively simple and affordable landslide susceptibility methodologies in such countries, we focused on a region in NW Nicaragua which was among the most severely hit during the Mitch event. Our study included (1) detailed field work to produce a high-resolution inventory landslide map at 1 : 10,000 scale, and (2) a selection of the relevant instability factors from a Terrain Units Map which had previously been generated in a project for rural development. Based on the combination of these two datasets and using GIS tools we developed a comparative analysis of failure-zones and terrain factors in an attempt to classify the land into zones according to the propensity to landslides triggered by heavy rainfalls. The resulting susceptibility map was validated by using a training and a test zone, providing results comparable to those reached in studies based in more sophisticated methodologies. Thus, we provide an example of a methodology which is simple enough to be fully comprehended by non-specialised technicians and which could be of help in landslide risk mitigation through implementation of non-structural measures, such as land planning or emergency measures.     

Sensitivity analysis of seismic hazard for the northwestern portion of the state of Gujarat, India

We test the sensitivity of seismic hazard to three fault source models for the northwestern portion of Gujarat, India. The models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years. These recurrence intervals imply that large earthquakes occur on one of these faults every 266–533 years, similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the New Madrid region in the central United States. If one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults, the peak ground accelerations (PGA; horizontal) and 1-Hz spectral acceleration ground motions (5% damping) are greater than 1 g over a broad region for a 2% probability of exceedance in 50 years' hazard level. These probabilistic PGAs at this hazard level are similar to median deterministic ground motions. The PGAs for 10% in 50 years' hazard level are considerably lower, generally ranging between 0.2 g and 0.7 g across northwestern Gujarat. Ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals. These higher ground motions are mainly caused by the application of intraplate attenuation relations, which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies. For sites in Bhuj and Ahmedabad, magnitude (M) 7 3/4 earthquakes contribute most to the PGA and the 0.2- and 1-s spectral acceleration ground motion maps at the two considered hazard levels.     

Characterization of model evaporitic environments through the study of lipid components

A saline circuit has been studied as a model of coastal evaporite system. The lipid composition of diverse salt ponds encompassing calcite, gypsum and halite domains has been determined. Most of the lipid materials has been found in the carbonate samples and is related to algal/cyanobacterial debris. Lipids in the gypsum domain are of heterotropic microbialorigin and extreme halophilic bacteria constitute the main lipid contribution in the halite samples. n-Alkane distributions with high predominance of n-docosane constitute a previously described feature of sedimentary evaporitic conditions that is charateristics of the intermediate calcite/gypsum samples. In the calcite domain, the presence of C20 highly branched isoprenid olephines, tetrahymanol and the large amounts of phytol constitute likely precursors of lipids usually found in evaporitic environments (i.e. C20 highly branched isoprenoid alkanes, gammacerane and high phytane/pristane ratios). Their occurence point to dehydration and hydrogenations as two main diagenetic processes leading to the formation of “evaporitic molecular markers”.     

Spatio-temporal analysis of rockfall pre-failure deformation using Terrestrial LiDAR

We present a long-term spatio-temporal analysis of rock slope evolution using a Terrestrial LiDAR aiming to improve our understanding of the link between pre-failure deformation and the spatial prediction of rockfalls. We monitored the pilot study area located at the Puigcercós cliff (Catalonia, Spain) over a period of 1,705 days and detected the deformation of nine different cliff regions together with a high rockfall activity. An exact match was observed between the progressively deformed areas and the regions recently affected by three of the highest magnitude rockfall events, demonstrating a causal relationship between pre-failure deformation and rockfall occurrence. These findings allowed us to make a forward spatial prediction of future failures, hypothesizing a high probability of failure in the six remaining regions. We observed an exponential acceleration of the deformation close to failure, in accordance with tertiary creep theory. However, the temporal analysis of the deformed areas showed a complex and variable behavior, so no exact prediction of the date of failure can yet be made. Our findings have broadened our understanding of the pre-failure behavior of rockfalls and have clear implications for the future implementation of early warning systems.     

Cold seeps in Monterey Bay, California: Geochemistry of pore waters and relationship to benthic foraminiferal calcite

An extensive geochemical and biogeochemical examination of CH₄ seeps in the Clam Flats area of Monterey Bay provides insight into the character of relationships between seep geochemistry and benthic foraminiferal geochemistry. The area is characterized by sulfide-rich fluids. Sulfide increases are associated with large increases in alkalinity, as well as small decreases in dissolved Ca and Mg. In addition, only small increases in NH₄ are observed, but values of δ¹³C of dissolved inorganic C are as low as −60‰ at shallow depths (<3 cm). These observations indicate that all these processes are related to the bacterial oxidation of CH₄, which is transported upward by slow seepage of pore fluids. The geochemistry of the pore fluids should be relevant to the geochemistry of the carbonate tests of living and dead foraminifera. However, a profound disequilibrium of approximately an order of magnitude occurs between the δ¹³C values of stained (cytoplasm-containing) foraminiferal carbonate and the C isotope values of ambient pore water dissolved inorganic C. Reasons are unclear for this isotopic disequilibrium, but have important implications for interpretations of foraminiferal carbonate as a paleoenvironmental proxy. Much fine scale work is needed to fully understand the relationships between the biogeochemistry of benthic foraminifera and the geochemistry of the pore waters where they live.     

Integrated Landslide Susceptibility Analysis and Hazard Assessment in the Principality of Andorra

In the paper we present the procedure for hazard assessment that has been used to prepare the landslide hazard map of the Principality of Andorra at 1:5,000 scale. The main phases of the hazard assessment are discussed. Susceptibility analysis has involved the location of the potential slope failures, and the estimation of both landslide volume and runout distance. In the susceptible areas, landslide magnitude and frequency has been determined in order to produce the Hazard Zoning Map. Data required for hazard assessment have been introduced into a GIS or derived directly from available Digital Terrain Models. Data handling and treatment with the GIS has allowed the performance of the landslide hazard assessment and mapping in a fast and reproducible way.     

Holocene hydro-climatic change and effects on carbon accumulation inferred from a peat bog in the Attawapiskat River watershed,Hudson Bay Lowlands,Canada

Multiple proxies from a 319-cm peat core collected from the Hudson Bay Lowlands, northern Ontario, Canada were analyzed to determine how carbon accumulation has varied as a function of paleohydrology and paleoclimate. Testate amoeba assemblages, analysis of peat composition and humification, and a pollen record from a nearby lake suggest that isostatic rebound and climate may have influenced peatland growth and carbon dynamics over the past 6700 cal yr BP. Long-term apparent rates of carbon accumulation ranged between 8.1 and 36.7 g C m^? 2 yr^? 1 (average = 18.9 g C m^? 2 yr^? 1). The highest carbon accumulation estimates were recorded prior to 5400 cal yr BP when a fen existed at this site, however following the fen-to-bog transition carbon accumulation stabilized. Carbon accumulation remained relatively constant through the Neoglacial period after 2400 cal yr BP when pollen-based paleoclimate reconstructions from a nearby lake (McAndrews et al., 1982) and reconstructions of the depth to the water table derived from testate amoeba data suggest a wetter climate. More carbon accumulated per unit time between 1000 and 600 cal yr BP, coinciding in part with the Medieval Climate Anomaly.