Age and petrology of the Late-Pleistocene brown tuffs on Lipari,Italy

Late-Pleistocene volcanic products on Lipari consist mainly of pyroclastic surge deposits (Monte Guardia sequence) and fine-grained brown tuffs. Radiometric age determination on carbon from thin soils at the top of the tuffs indicate that they have several ages of emplacement ranging from more than 35,000 to 16,800 years ago. Chemical and microprobe data on glass and mineral fragments from these tuffs show that they belong to a shoshonite or high-K series. This composition is compatible with an origin related to the magma system of Vulcano, but not with the magma system on Lipari. These tuffs have a widespread distribution on several of the Aeolian islands as well as on the northern part of Sicily. They have features typical of ash-flow tuffs of hydromagmatic origin. We propose that they originated from submarine eruptions from the Vulcanello vent before this volcano emerged above sea level.     

Hazard map of El Chichón volcano,Chiapas, México: Constraints posed by eruptive history and computer simulations

El Chichón volcano consists of a 2-km wide Somma crater compound cone 0.2 Ma old with peripheral domes with a central crater reactivated several times during the Holocene. The most recent eruption at El Chichón occurred from March 28 to April 4, 1982, resulting in the worst volcanic disaster during historical times in Mexico, killing more than 2000 people and destroying nine towns and small communities. The volcanic hazard map of El Chichón is based on detailed field work that documented twelve eruptions during the last 8000 years, and computer simulations. To validate the results, computer simulations were first performed over pre-1982 topography mimicking the extent of the actual deposits produced and afterwards run over post-1982 topography. These eruptions have produced pyroclastic fall, surge, flow and lahar deposits. Pyroclastic flows have different volumes and Heim coefficients varying from 0.2 (pumice flows), to 0.15 (block-and-ash flows) and 0.10 (ash flows). Simulations using FLOW3D and TITAN2D indicate that pumice flows and block-and-ash flows can fill the moat area and follow main ravines up to distances of ca. 3 km from the crater, with no effect on populations around the volcano. On the other hand, more mobile ash flows related to column-collapse events can reach up to 4 km from the vent, but will always follow the same paths and still not affect surrounding populations. The energy-cone model was used to simulate the outflow of pyroclastic surges based on the 1982 event (H/L = 0.1 and 0.2), and shows that surges may reach some towns around the volcano.     

Evaluation of the Titan2D two-phase flow model using an actual event: Case study of the 2005 Vazcún Valley Lahar

Titan2D is a depth-averaged, thin-layer computational fluid dynamics (CFD) code, suitable for simulating a variety of geophysical mass flows. Titan2D output data include flow thickness and flow momentum at each time step for all cells traversed by the flow during the simulation. From this information the flow limit, run-out path, flow velocity, deposit thickness, and travel time can be calculated. Results can be visualized in the open-source GRASS GIS software or with the built-in Titan2D viewer. A new two-phase Titan2D version allows simulation of flows containing various mixtures of water and solids. The purpose of this study is to compare simulations by the two-phase flow version of Titan2D with an actual event. The chosen natural flow is a small ash-rich lahar (volume 50,000 m³–70,000 m³) that occurred on 12 February 2005 in the Vazcún Valley, located on the north-east flank of Volcán Tungurahua, Ecuador. Lahars and pyroclastic flows along this valley could potentially threaten the 20,000 inhabitants living in and near the city of Baños. A variety of data sources exist for this lahar, including: post-event meter-scale topography, and photographic, video, seismic and acoustic flow monitoring (AFM) records from during the event. These data permit detailed comparisons between the dynamics of the actual lahar and those of the Titan2D simulated flow. In particular, detailed comparisons are made between run-up heights, flow velocity, inundation area, and flow thickness. Simulations utilize a variety of data derived from field observations such as lahar volume, solid to pore-fluid ratio and pre-event topography. Titan2D is important in modeling lahars because it allows assessment of the impact of the flows on buildings and infrastructure lifelines located near drainages that descend from volcanoes.     

Modelling the effects of fire and rainfall regimes on extreme erosion events in forested landscapes

Existing models of post-fire erosion have focused primarily on using empirical or deterministic approaches to predict the magnitude of response from catchments given some initial rainfall and burn conditions. These models are concerned with reducing uncertainties associated with hydro-geomorphic transfer processes and typically operate at event timescales. There have been relatively few attempts at modelling the stochastic interplay between fire disturbance and rainfall as factors which determine the frequency and severity with which catchments are conditioned (or primed) for a hazardous event. This process is sensitive to non-stationarity in fire and rainfall regime parameters and therefore suitable for evaluating the effects of climate change and strategic fire management on hydro-geomorphic hazards from burnt areas. In this paper we ask the question, “What is the first-order effect of climate change on the interaction between fire disturbance and storms?” The aim is to isolate the effects of fire and rainfall regimes on the frequency of extreme erosion events. Fire disturbance and storms are represented as independent stochastic processes with properties of spatial extent, temporal duration, and frequency of occurrence, and used in a germ–grain model to quantify the annual area affected by extreme erosion events due to the intersection of fire disturbance and storms. The model indicates that the frequency of extreme erosion events will increase as a result of climate change, although regions with frequent storms were most sensitive.     

A simple two‐parameter model for scaling hillslope surface runoff

The objective of this research was to develop and parameterise a physically justified yet low‐parameter model to quantify observed changes in surface runoff ratios with hillslope length. The approach starts with the assumption that a unit of rainfall‐excess runoff generated at a point is a fraction β of precipitation P (m) which travels some variable distance down a slope before reinfiltrating, depending on the local rainfall, climate, soils, etc. If this random distance travelled Y is represented by a distribution, then a survival function will describe the probability of this unit of runoff travelling further than some distance x (m). The total amount of per unit width runoff Q (m²) flowing across the lower boundary of a slope of length λ (m) may be considered the sum of all the proportions of the units of rainfall excess runoff integrated from the lower boundary x = 0 to the upper boundary x = λ of the slope. Using these assumptions we derive a model Q(λ) = βPμλ/(μ + λ), (μ > 0, 0 ≤ β ≤ 1, λ ≥ 0) that describes the change in surface runoff with slope length, where μ (m) is the mean of the random variable Y. Dividing both sides of this equation by Pλ yields a simple two‐parameter equation for the dimensionless hillslope runoff ratio Q_h(λ) = βμ/(μ + λ). The model was parameterised with new rainfall and runoff data collected from three replicates of bounded 2 m wide plots of four different lengths (0.5, 1.0, 2.0 and 4.0 m) for 2 years from a forested SE Australian site, and with 32 slope length–runoff data sets from 12 other published studies undertaken between 1934 and 2010. Using the parameterised model resulted in a Nash and Sutcliffe statistic between observed and predicted runoff ratio (for all data sets combined) of 0.93, compared with –2.1 when the runoff ratio was fixed at the value measured from the shortest plot. Copyright © 2014 John Wiley & Sons, Ltd.     

Seasonal variability in heat-related mortality across the United States

This study examines the seasonal variability in the heat mortality relationship across 29 US metropolitan areas from 1975 to 2004 to discern the seasonal cycle of the health risk from anomalously high temperatures (relative to the time of season). Mortality data for the 30-year period are standardized to account for population trends and overall seasonal and interannual variability. On days when a city experienced an “oppressive” air mass, mean anomalous mortality was calculated. Results show that while the greatest overall health impact is found mid-summer in many locations due to the peak frequency of hot weather occurring at this time, the relative increase in acute mortality on oppressive air mass days is actually just as large in spring as it is in summer, and in some cases is larger. Late summer and autumn vulnerability to anomalously warm or hot days is much less significant than spring days in all areas except along the Pacific coast. Results show significant spatial variability, with the most consistent results across the more ‘traditionally’ heat vulnerable areas of the Midwestern and northeastern US, along with the Pacific Coast. Elsewhere, the seasonal cycle of the correlation between anomalously high temperatures and human health is more ambiguous.     

Impact of an unsealed forest road stream crossing: water quality and sediment sources

Turbidity monitoring and rainfall and runoff simulation experiments were conducted at a newly constructed unsealed road stream crossing to determine the quantity and sources of sediment entering the stream. Continuous measurements of turbidity and estimation of total suspended solids (TSS) concentration upstream and downstream of the stream culvert were taken over a 5 month period. There was a statistically significant difference in turbidity and TSS downstream of the crossing during baseflow conditions, but the quality of the water column remained good during non‐rain periods. Rainfall events comprised around 20% of the observation period and led to decreases in water quality downstream of the crossing. Water quality could be considered as degraded for 10% of the observations. This was during a period when the rainfall was 65% of the long‐term average. Calculated suspended sediment loads were 0·78 t upstream and 2·77 t downstream, an increase of 3·5. It was estimated that at least 2–3 t of bedload material was also added to the stream during the crossing construction and from subsequent erosion. This material is a deposit on the cobble stream bed, and is most likely to degrade aquatic ecosystem values. Rainfall and runoff simulation revealed the principal sediment sources to be a fillslope that contributed coarse bedload material through rill erosion and unprotected toe scour, and the unmetalled road verge that provided fines. Although the quality of water column was good for the majority of the observations, the new Australian and New Zealand Water Quality Guidelines for Fresh and Marine Waters suggest this site exceeded ‘trigger levels’ that would warrant further investigation for both the water column and the bed deposits. Copyright © 2002 John Wiley & Sons, Ltd.     

Sedimentary basins of the atlantic margin of North America

Scismic exploration has identified eight distinct basin structures along the North American Atlantic continental margin forming a chain of elongate depocenters parallel to the continental slope and interrupted by transverse basement arches and impinging oceanic fracture zones. From south to north these are: South Florida—Bahamas Basin bounded on the north by Peninsular Arch and Bahama Escarpment fracture zone; Blake Plateau Basin with Cape Fear Arch and the impinging Great Abaco and Blake Spur fracture zones; Baltimore Canyon Trough bounded by the Long Island Platform and impinging Kelvin fracture zone; Georges Bank Basin with the bounding Yarmouth Arch; Scotian Shelf Basin with Scartarie and Canso Ridges and impinging Newfoundland Ridge fracture zone; Grand Banks Troughs and the intervening horst ridges; and the East Newfoundland Basin separated by Cartwright Arch and the impinging Gibbs fracture zone from the Labrador Shelf Basin.All the basins are characterized by great depths to basement filled with from 7 to 14 km of possible Triassic, Jurassic, Cretaceous and Tertiary sediments. Basement faulting controls the basins' boundaries and the faults have affected the overlying sediments. The major boundary faults of the basins undoubtedly formed during the initial rifting of the Atlantic margin in the Jurassic or perhaps Triassic. However, throughout the Mesozoic and Cenozoic these basement faults have moved in response to different orientations of stress and strain rates produced by continued spreading of the Atlantic Ocean. As a result, the basement faults of the Atlantic Margin were apparently influenced by at least three different local stress systems, spatially overlapping but temporally independent. These are the east—west extensional Atlantic Ocean stress system, the northwest—southeast extensional White Mountain stress system, and the north-south extensional Labrador Sea stress system.Some consequences of this basic tectonic setting were differential cross-strike tilts of the basin blocks with each basin moving somewhat independent of its neighbor. The resulting buildup of the basins' sedimentary geometries reflect these tectonic tilts and varying strain rates. Correlations are found between changes in orientation and rates of Atlantic sea-floor spreading with observed major sedimentary events such as progradations, planar bedding episodes, reef platform development, regressive hiatuses, and transgressions. An understanding of this marginal geosyncline could yield a model with predictability.     

Nekton of new seagrass habitats colonizing a subsided salt marsh in Galveston Bay, Texas

Subsidence and erosion of intertidal salt marsh at Galveston Island State Park, Texas, created new areas of subtidal habitat that were colonized by seagrasses begining in 1999. We quantified and compared habitat characteristics and nekton densities in monospecific beds of stargrassHalophila engelmanni and shoalgrassHalodule wrightii as well as adjacent nonvegetated substrates. We collected 10 replicates per habitat type during April, July, October, and December 2001. Most habitat characteristics varied with season. Water temperature, salinity, and dissolved oxygen were similar among habitat types. Turbidity and depth were greatest inH. engelmanni beds and least inH. wrightii beds.H. engelmanni exhibited shorter leaves and higher shoot density and biomass core⁻¹ thanH. wrightii. Densities of almost all dominant species of nekton (fishes and decapods) were seasonally variable, all were higher in seagrass habitats than in nonvegetated habitats, and most were higher in one seagrass species than the other. Naked gobyGobiosoma bosc, code gobyGobiosoma robustum, bigclaw snapping shrimpAlpheus heterochaelis, and blue crabCallinectes sapidus, were most abundant inH. engelmanni. Brown shrimpFarfantepenaeus aztecus, brackish grass shrimpPalaemonetes intermedius, and daggerblade grass shrimpPalaemonetes pugio were most abundant inH. wrightii. PinfishLagodon rhomboides and pink shrimFarfantepenaeus duorarum were equally abundant in either seagrass. Most dominant nekton varied in size by month, but only two (L. rhomboides andC. sapidus) exhibited habitat-related differences in size. Nekton densities in these new seagrass habitats equaled or exceeded densities associated with historical and current intertidal smooth cordgrassSpartina alterniflora marsh. Continued seagrass expansion and persistence should ensure ecosystem productivity in spite of habitat change.