Sustainability of groundwater in Mali,West Africa

The following paper describes the goals and some preliminary work in the Bani sustainability study, an ongoing project in Mali, West Africa. Rural communities in Mali are increasingly relying on hand-pumps, which tap groundwater resources, as a means of obtaining potable water. The long-term sustainable yield of groundwater resources is not known but can be evaluated in sustainability study. In 2005, a groundwater sustainability study was established along the Bani River of Mali. The Bani study collected groundwater levels that were used in a conceptual groundwater flow model—the Bani model—to develop an understanding of current aquifer conditions and to make limited predictions of sustainability under various future scenarios. The Bani model showed the climatic parameters of recharge (derived from precipitation) and evapotranspiration to influence simulated groundwater levels and groundwater volume available, while increased pumping rates, due to population growth, showed little effect. When considered in the context of the actual Bani sustainability study area, the change in groundwater levels resulting from climatic parameters may have negative implications, especially during several consecutive years of decreased precipitation, such as drought, or if downward trends anticipated for precipitation continue.     

Households’ experience of local government during recovery from cyclones in coastal Bangladesh: resilience,equity, and corruption

Households’ links with local Government provide important support for disaster resilience and recovery on the Bangladeshi coast. Few previous studies of disaster resilience and recovery have explored how linking social networks—and in particular local government—contribute. Using household surveys, focus groups, and key informant interviews, we examine strengths and weaknesses of local government’s contribution, using two cyclone-affected coastal villages as case studies. The findings show that local government provides important support, for example relief distribution, livelihood assistance, and reconstruction of major community services. However, patronage relationships (notably favouring political supporters) and bribery play a substantial role in how those responsibilities are discharged. The equity and efficiency of these contributions to recovery are markedly diminished by corruption. Reducing corruption in UP’s contributions to disaster recovery could significantly improve resilience; however, general reform of governance in Bangladesh would needed to bring this about.     

Mechanisms for transition in eruptive style at a monogenetic scoria cone revealed by microtextural analyses (Lathrop Wells volcano, Nevada, U.S.A.)

Explosive activity at Lathrop Wells volcano, Nevada, U.S.A. originated with weak Strombolian (WS) eruptions along a short fissure, and transitioned to violent Strombolian (VS) activity from a central vent, with lava effusion during both stages. The cause for this transition is unknown; it does not reflect a compositional change, as evidenced by the consistent bulk geochemistry of all the eruptive products. However, comparison of agglutinate samples from the early, WS events with samples of scoria from the later, VS events reveal differences in the abundance and morphology of groundmass phases and variable textures in the rims of olivine phenocrysts. Scanning electron microscope (SEM) examination of thin sections from the WS samples show euhedral magnetite microlites in the groundmass glass and olivine phenocrysts show symplectite lamellae in their rims. Secondary ion mass spectrometry (SIMS) depth profiles of these symplectites indicate they are diffusion-controlled. The calculated D_Fe-Mg allows an estimation of the oxygen fugacity (fO₂) and indicates an increased fO₂ during eruption of the WS products. Conversely, the VS samples show virtually no magnetite microlites in the groundmass glass, a lack of symplectites in the olivines, and a lower calculated fO₂. These microtextural features suggest that the Lathrop Wells trachybasalt experienced increased oxidation during WS activity. As magma ascended through the original fissure, exsolved bubbles were concentrated in the wider part(s) (the protoconduit) and this bubble flux drove convective circulation that oxidized the magma through exposure to atmosphere and recirculation. This oxidation resulted in groundmass crystallization of magnetite within the melt and formation of symplectites within the olivine phenocrysts. Bubble-driven convection mixed magma vertically within the protoconduit, keeping it fluid and driving Strombolian bursts, while microlite crystallization in narrower parts of the fissure helped to focus flow. Development of a central conduit increased the magma ascent velocity (due to a greater product volume in the later eruptive stages) and caused the shift in eruption intensity. Consequently, variations in microtextures of the Lathrop Wells products reveal how a combination of fluid dynamic and crystallization processes in the ascending magma resulted in different styles of activity while the products maintained a consistent bulk composition.     

Fundamental changes in the activity of the natrocarbonatite volcano Oldoinyo Lengai, Tanzania

On September 4, 2007, after 25 years of effusive natrocarbonatite eruptions, the eruptive activity of Oldoinyo Lengai (OL), N Tanzania, changed abruptly to episodic explosive eruptions. This transition was preceded by a voluminous lava eruption in March 2006, a year of quiescence, resumption of natrocarbonatite eruptions in June 2007, and a volcano-tectonic earthquake swarm in July 2007. Despite the lack of ground-based monitoring, the evolution in OL eruption dynamics is documented based on the available field observations, ASTER and MODIS satellite images, and almost-daily photos provided by local pilots. Satellite data enabled identification of a phase of voluminous lava effusion in the 2 weeks prior to the onset of explosive eruptions. After the onset, the activity varied from 100 m high ash jets to 2–15 km high violent, steady or unsteady, eruption columns dispersing ash to 100 km distance. The explosive eruptions built up a ∼400 m wide, ∼75 m high intra-crater pyroclastic cone. Time series data for eruption column height show distinct peaks at the end of September 2007 and February 2008, the latter being associated with the first pyroclastic flows to be documented at OL. Chemical analyses of the erupted products, presented in a companion paper (Keller et al. 2010), show that the 2007–2008 explosive eruptions are associated with an undersaturated carbonated silicate melt. This new phase of explosive eruptions provides constraints on the factors causing the transition from natrocarbonatite effusive eruptions to explosive eruptions of carbonated nephelinite magma, observed repetitively in the last 100 years at OL.     

Catastrophic rock avalanche 3600 years BP from El Capitan,Yosemite Valley,California

Large rock slope failures from near‐vertical cliffs are an important geomorphic process driving the evolution of mountainous landscapes, particularly glacially steepened cliffs. The morphology and age of a 2·19 × 10⁶ m³ rock avalanche deposit beneath El Capitan in Yosemite Valley indicates a massive prehistoric failure of a large expanse of the southeast face. Geologic mapping of the deposit and the cliff face constrains the rock avalanche source to an area near the summit of ～8·5 × 10⁴ m². The rock mass free fell ～650 m, reaching a maximum velocity of 100 m s^?1, impacted the talus slope and spread across the valley floor, extending 670 m from the base of the cliff. Cosmogenic beryllium‐10 exposure ages from boulders in the deposit yield a mean age of 3·6 ± 0·2 ka. The ～13 kyr time lag between deglaciation and failure suggests that the rock avalanche did not occur as a direct result of glacial debuttressing. The ～3·6 ka age for the rock avalanche does coincide with estimated late Holocene rupture of the Owens Valley fault and/or White Mountain fault between 3·3 and 3·8 ka. The coincidence of ages, combined with the fact that the most recent (AD 1872) Owens Valley fault rupture triggered numerous large rock falls in Yosemite Valley, suggest that a large magnitude earthquake (≥M7.0) centered in the south‐eastern Sierra Nevada may have triggered the rock avalanche. If correct, the extreme hazard posed by rock avalanches in Yosemite Valley remains present and depends on local earthquake recurrence intervals. Published in 2010 by John Wiley & Sons, Ltd.     

板块边界观测数据管理计划

第一章 执行概况 板块边界观测计划（PBO）是地球透镜计划（EarthScope）的一部分,将在5年内建立875个连续的全球定位系统（CGPS）、174个钻孔应变仪（BSM）和5个激光应变仪（LSM）,以研究贯穿美国西部的活动板块边界的变形。另外,将用有100台接收机的PBO组合装置接收测量的GPS数据（SGPS）,并且从第2”年开始,把目前美国西部地球物理观测网络中的225个CGPS站吸收到PBO网络中。     

Evaluating suitability of a tephra dispersal model as part of a risk assessment framework

In volcanic risk assessment it is necessary to determine the appropriate level of sophistication for a given predictive model within the contexts of multiple sources of uncertainty and coupling between models. A component of volcanic risk assessment for the proposed radioactive waste repository at Yucca Mountain (Nevada, USA) involves prediction of dispersal of contaminated tephra during violent Strombolian eruptions and the subsequent transport of that tephra toward a hypothetical individual via surface processes. We test the suitability of a simplified model for volcanic plume transport and fallout tephra deposition (ASHPLUME) coupled to a surface sediment-transport model (FAR) that calculates the redistribution of tephra, and in light of inherent uncertainties in the system. The study focuses on two simplifying assumptions in the ASHPLUME model: 1) constant eruptive column height and 2) constant wind speed and direction during an eruption. Variations in tephra dispersal resulting from unsteady column height and wind conditions produced variations up to a factor of two in the concentration of tephra in sediment transported to the control population. However, the effects of watershed geometry and terrain, which control local remobilization of tephra, overprint sensitivities to eruption parameters. Because the combination of models used here shows limited sensitivity to the actual details of ash fall, a simple fall model suffices to estimate tephra mass delivered to the hypothetical individual.     

Shallow plumbing systems for small-volume basaltic volcanoes

Eruptive dynamics in basaltic volcanoes are controlled, in part, by the conduit geometry. However, uncertainties in conduit shape and dike-to-conduit transition geometry have limited our predictive capability for hazards assessments. We characterize the subvolcanic geometry of small-volume basaltic volcanoes (magmatic volatile-driven eruptions, 0.1 to 0.5 km³) based on a synthesis of field studies of five basaltic volcanoes exposed to varying degrees by erosion and exhibiting feeder dikes, conduits, and vent areas ≤250 m depth. Study areas include East Grants Ridge (New Mexico, USA), Basalt Ridge, East Basalt Ridge, Paiute Ridge, and Southeast Crater Flat (Nevada, USA). Basaltic feeder dikes 250 to 100 m deep have typical widths of 4–12 m, with smooth host-rock contacts (rhyolite tuff). At depths less than 100 m, heterogeneities in the host rock form preferential pathways for small dike splays and sills, resulting in a 30-m effective width at 50 m depth. The development of a complex conduit at depths less than 70 m is reflected in bifurcating dikes and brecciation and incorporation of the country rock. The overall zone of effect at depths less than 50 m is ≤110 m wide (220 m elongated along the feeder dike). Based on comparisons with theoretical conduit flow models, the width of the feeder dike at depths from 250 to 500 m is expected to range from 1 to 10 m and is expected to decrease to about 1–2 m at depths greater than 500 m. The flaring shape of the observed feeder systems is similar to results of theoretical modeling using lithostatic pressure-balanced flow conditions. Sizes of observed conduits differ from modeled dimensions by up to a factor of 10 in the shallow subsurface (<50 m depth), but at depths greater than 100 m the difference is a factor of 2 to 4. This difference is primarily due to the fact that observed eroded conduits record the superimposed effects of multiple eruptive events, while theoretical model results define dimensions necessary for a single, steady eruption phase. The complex details of magma-host rock interactions observed at the study areas (contact welding, brecciation, bifurcating dikes and sills, and stoping) represent the mechanisms by which the lithostatic pressure-balanced geometry is attained. The similarity in the normalized shapes of theoretical and observed conduits demonstrates the appropriateness of the pressure-balanced modeling approach, consistent with the conclusions of Wilson and Head (J Geophys Res 86:2971–3001, 1981) for this type of volcano.     

Period–colour and amplitude–colour relations in classical Cepheid variables – V. The Small Magellanic Cloud Cepheid models

Period–colour (PC) and amplitude–colour (AC) relations at maximum, mean and minimum light are constructed from a large grid of full amplitude hydrodynamic models of Cepheids with a composition appropriate for the Small Magellanic Cloud (SMC). We compare these theoretical relations with those from observations. The theoretical relations are, in general, in good agreement with their observational counterparts, though there exist some discrepancy for short period  (log [ P ] < 1)  Cepheids. We outline a physical mechanism which can, in principle, be one factor to explain the observed PC/AC relations for the long and short period Cepheids in the Galaxy, Large Magellanic Cloud (LMC) and SMC. Our explanation relies on the hydrogen ionization front (HIF)–photosphere interaction and the way this interaction changes with pulsation period, pulsation phase and metallicity. Since the PC relation is connected with the period–luminosity (PL) relation, it is postulated that such a mechanism can also explain the observed properties of the PL relation in these three galaxies.     

Visible and near-infrared spectrophotometry of the Deep Impact ejecta of Comet 9P/Tempel 1

We have obtained optical spectrophotometry of the evolution of Comet 9P/Tempel 1 after the impact of the Deep Impact probe, using the Supernova Integral Field Spectrograph (SNIFS) at the UH 2.2-m telescope, as well as simultaneous optical and infrared spectra using the Lick Visible-to-Near-Infrared Imaging Spectrograph (VNIRIS). The spatial distribution and temporal evolution of the “violet band” CN (0-0) emission and of the 630 nm [OI] emission was studied. We found that CN emission centered on the nucleus increased in the 2 h after impact, but that this CN emission was delayed compared to the light curve of dust-scattered sunlight. The CN emission also expanded faster than the cloud of scattering dust. The emission of [OI] at 630 nm rose similarly to the scattered light, but then remained nearly constant for several hours after impact. On the day following the impact, both CN and [OI] emission concentrated on the comet nucleus had returned nearly to pre-impact levels. We have also searched for differences in the scattering properties of the dust ejected by the impact compared to the dust released under normal conditions. Compared to the pre-impact state of the comet, we find evidence that the color of the comet was slightly bluer during the post-impact rise in brightness. Long after the impact, in the following nights, the comet colors returned to their pre-impact values. This can be explained by postulating a change to a smaller particle size distribution in the ejecta cloud, in agreement with the findings from mid-infrared observations, or by postulating a large fraction of clean ice particles, or by a combination of these two.