Explosive volcanism (VEI 6) without caldera formation: insight from Huaynaputina volcano, southern Peru

Through examination of the vent region of Volcán Huaynaputina, Peru, we address why some major explosive eruptions do not produce an equivalent caldera at the eruption site. Here, in 1600, more than 11 km³ DRE (VEI 6) were erupted in three stages without developing a volumetrically equivalent caldera. Fieldwork and analysis of aerial photographs reveal evidence for cryptic collapse in the form of two small subsidence structures. The first is a small non-coherent collapse that is superimposed on a cored-out vent. This structure is delimited by a partial ring of steep faults estimated at 0.85 by 0.95 km. Collapse was non-coherent with an inwardly tilted terrace in the north and a southern sector broken up along a pre-existing local fault. Displacement was variable along this fault, but subsidence of approximately 70 m was found and caused the formation of restricted extensional gashes in the periphery. The second subsidence structure developed at the margin of a dome; the structure has a diameter of 0.56 km and crosscuts the non-coherent collapse structure. Subsidence of the dome occurred along a series of up to seven concentric listric faults that together accommodate approximately 14 m of subsidence. Both subsidence structures total 0.043 km³ in volume, and are much smaller than the 11 km³ of erupted magma. Crosscutting relationships show that subsidence occurred during stages II and III when ∼2 km³ was erupted and not during the main plinian eruption of stage I (8.8 km³). The mismatch in erupted volume vs. subsidence volume is the result of a complex plumbing system. The stage I magma that constitutes the bulk of the erupted volume is thought to originate from a ∼20-km-deep regional reservoir based on petrological constraints supported by seismic data. The underpressure resulting from the extraction of a relatively small fraction of magma from the deep reservoir was not sufficient enough to trigger collapse at the surface, but the eruption left a 0.56-km diameter cored-out vent in which a dome was emplaced at the end of stage II. Petrologic evidence suggests that the stage I magma interacted with and remobilized a shallow crystal mush (∼4–6 km) that erupted during stage II and III. As the crystal mush erupted from the shallow reservoir, depressurization led to incremental subsidence of the non-coherent collapse structure. As the stage III eruption waned, local pressure release caused subsidence of the dome. Our findings highlight the importance of a connected magma reservoir, the complexity of the plumbing system, and the pattern of underpressure in controlling the nature of collapse during explosive eruptions. Huaynaputina shows that some major explosive eruptions are not always associated with caldera collapse. Editorial responsibility: J Stix     

Carboxylic acid distribution patterns of temperate C3 and C4 crops

Agricultural grasses cover a major part of the land surface in temperate agro-ecosystems and contribute significantly to the formation of soil organic matter. Crop-derived lipids are assumed to be responsible for fast carbon turnover in soils. Differences in lipid distribution patterns between crops following C₃ and C₄ photosynthesis pathways have rarely been described, but could be useful for source apportionment of crop-derived input into soils or sediments. The distribution of long chain n-carboxylic acids (C₂₂, C₂₄, C₂₆) reveals significant differences between crop plants following either the C₃ or the C₄ photosynthetic carbon fixation pathway. The plant compartments leaves, stems and roots of C₄ plants contain relatively large proportions (> 40%) of n-C₂₄ carboxylic acid when compared to C₃ plants. These reveal larger relative proportions of n-C₂₂ and n-C₂₆ acids, whose relative abundance is subject to change between different plant compartments and during the growing season. The carboxylic acid ratio [CAR = n-C₂₄/(n-C₂₂ + n-C₂₆) carboxylic acids] provides distinct ratios for C₄ (> 0.67) and C₃ crops (< 0.67) and can thus be used as a molecular marker for the differentiation of crop plant biomass. In combination with the bulk stable carbon isotopic composition (δ¹³C) the CAR can be used as a tool for the estimation of the C₄ derived carbon proportion in soils or sediments.     

Thermal history and exhumation of the Northern Apennines (Italy): evidence from combined apatite fission track and vitrinite reflectance data from foreland basin sediments

ABSTRACT Apatite fission track ages of 20 samples collected from turbidite successions deposited in foreland basins adjacent to the Northern Apennines range between ∼3 and ∼10 Ma. The youngest fission track ages are concentrated in a NW–SE elongated belt, which approximately runs through the centre of the study area, while gradually increasing ages are distributed towards the south-western and north-eastern borders. Integration of apatite fission track data and published vitrinite reflectance values indicate this region of the Apennines experienced continuous but variable exhumation starting from ∼14 Ma. The extent of exhumation and uplift range between 5 and 6 km at the south-western and north-eastern borders of the study area, and ∼7 km in the central part. Exhumation was driven mainly by erosion, with minor faulting in response to structural readjustment related to differential exhumation. Regional exhumation and erosion are interpreted as the result of isostatic rebound following crustal thickening in the lower part of the orogen.     

Mechanisms for ground-surface fracturing and incipient slope failure associated with the 2001 eruption of Mt. Etna, Italy: analysis of ephemeral field data

During the July–August 2001 eruption of Mt. Etna development of extensional fractures/faults and grabens accompanied magma intrusion and subsequent volcanic activity. During the first days of the eruption, we performed an analysis of attitude, displacement and propagation of fractures and faults exposed on the ground surface in two sites, Torre del Filosofo and Valle del Leone, located along the same fracture system in the region surrounding the Valle del Bove depression on the eastern flank of Mt. Etna. Fractures and faults formed as the consequence of a shallow intruding dyke system that fed the several volcanic centres developed along the fracture system. The investigated sites differ in slope attitude and in geometrical relationships between fractures and slopes. In particular, the fracture system propagated parallel to the gentle slope (<7° dip) in the Torre del Filosofo area, and perpendicular to the steep slope (25° dip) in the Valle del Leone area. In the Torre del Filosofo area, slight graben subsidence and horizontal extension of the ground surface by about 3 m were recorded. In the Valle del Leone area, extensional faulting forming a larger and deeper graben with horizontal extension of the ground surface by about 10 m was recorded. For the Valle del Leone area, we assessed a downhill dip of 14° for the graben master fault at the structural level beneath the graben where the fault dip shallows. These results suggest that dyke intrusion at Mount Etna, and particularly in the region surrounding the Valle del Bove depression, may be at the origin of slope failure and subsequent slumps where boundary conditions, i.e. geometry of dyke, slope dip and initial shear stress, amongst others, favour incipient failures.     

Investigating soil moisture feedbacks on precipitation with tests of Granger causality

Granger causality (GC) is used in the econometrics literature to identify the presence of one- and two-way coupling between terms in noisy multivariate dynamical systems. Here we test for the presence of GC to identify a soil moisture (S) feedback on precipitation (P) using data from Illinois. In this framework S is said to Granger cause P if F(P_t|Ω_t−Δt)≠F(P_t|Ω_t−Δt−S_t−Δt) where F denotes the conditional distribution of P, Ω_t−Δt represents the set of all knowledge available at time t−Δt, and Ω_t−Δt−S_t−Δt represents all knowledge except S. Critical for land–atmosphere interaction research is that Ω_t−Δt includes all past information on P as well as S. Therefore that part of the relation between past soil moisture and current precipitation which results from precipitation autocorrelation and soil water balance will be accounted for and not attributed to causality. Tests for GC usually specify all relevant variables in a coupled vector autoregressive (VAR) model and then calculate the significance level of decreased predictability as various coupling coefficients are omitted. But because the data (daily precipitation and soil moisture) are distinctly non-Gaussian, we avoid using a VAR and instead express the daily precipitation events as a Markov model. We then test whether the probability of storm occurrence, conditioned on past information on precipitation, changes with information on soil moisture. Past information on precipitation is expressed both as the occurrence of previous day precipitation (to account for storm-scale persistence) and as a simple soil moisture-like precipitation-wetness index derived solely from precipitation (to account for seasonal-scale persistence). In this way only those fluctuations in moisture not attributable to past fluctuations in precipitation (e.g., those due to temperature) can influence the outcome of the test. The null hypothesis (no moisture influence) is evaluated by comparing observed changes in storm probability to Monte-Carlo simulated differences generated with unconditional occurrence probabilities. The null hypothesis is not rejected (p>0.5) suggesting that contrary to recently published results, insufficient evidence exists to support an influence of soil moisture on precipitation in Illinois.     

Deformation patterns in a high-viscosity lava flow inferred from the crystal preferred orientation and imbrication structures: an example from Salina (Aeolian Islands,southern Tyrrhenian Sea,Italy)

Shape-preferred orientation and imbrication structures of crystals have been measured on samples representative of the base, centre and top of a highly viscous lava flow on Salina (Aeolian Islands, southern Tyrrhenian Sea). The data allow zones with different deformation patterns to be identified. In the base and top of the flow, deformation leads to the development of discrete preferred orientation and imbrication of the elongate crystals. The sense of shear is right-lateral at the base and left-lateral at the top of the flow. Shear strain can be estimated by the analysis of crystal preferred orientation. Deformation increases from the flow centre to the outer, more viscous boundary layers. Random orientation of crystals in the inner zone supports the presence of plug flow in a pseudoplastic lava. The textural features of the studied lava may be related to different mechanisms (i.e. lateral expansion). We conclude that the observed crystal alignments and imbrication structures may be related to a plug flow moving between two non-deforming walls. The walls are represented by the solidified, broken upper and basal crust of the flow. The low shear strain values calculated in the outer margins of the flow are indicative of the last deformation event. Crystal preferred orientation and imbrication structures may be related to the occurrence of velocity gradients existing between the inner zone of the flow and its solidus or near-solidus outer margins.     

Resonant Fly-by Missions to Near Earth Asteroids

The authors here propose a mission scenario, aimed at close exploration of a Near-Earth Asteroid, exploiting low-V resonant trajectories. These trajectories allow repeated fly-bys of a chosen target. A selection procedure, which has been used to find some interesting mission opportunities in the 2005-2015 time frame, is described and the corresponding detailed mission profiles are derived, using an indirect optimization method.     

Characterizing and Predicting Traffic Accidents in Extreme Weather Environments

Motorists are vulnerable to extreme weather events, which are likely to be exacerbated by climate change throughout the world. Traffic accidents are conceptualized in this article as the result of a systemic failure that includes human, vehicular, and environmental factors. The snowstorm and concurrent accidents that occurred in the Northeastern United States on 26 January 2011 are used as a case study. Traffic accident data for Fairfax County, Virginia, are supplemented with Doppler radar and additional weather data to characterize the spatiotemporal patterns of the accidents resulting from this major snowstorm event. A kernel density smoothing method is implemented to identify and predict patterns of accident locations within this urban area over time. The predictive capability of this model increases over time with increasing accidents. Models such as these can be used by emergency responders to identify, plan for, and mitigate areas that are more susceptible to increased risk resulting from extreme weather events.     

Kinematic significance of mingling-rolling structures in lava flows: a case study from Porri Volcano (Salina, Southern Tyrrhenian Sea)

 A basaltic andesite lava flow from Porri Volcano (Salina, Southern Tyrrhenian Sea) is composed of two different magmas. Magma A (51 vol.% of crystals) has a dacitic glass composition, and magma B (18 vol.% of crystals), a basaltic glass composition. Magma B is hosted in A and consists of sub-spherical enclaves and boudin-like, banding and rolling structures (RS). Four types of RS have been recognized: σ–type;δ–type; complex σ-δ–types and transitional structures between sub-spherical enclaves and rolling structures. An analysis of the RS has been performed in order to reconstruct the flow kinematics and the mechanism of flow emplacement. Rolling structures have been selected in three sites located at different distances from the vent. In all sites most RS show the same sense of shear. Kinematic analysis of RS allows the degree of flow non-coaxiality to be determined. The non-coaxiality is expressed by the kinematic vorticity number Wk, a measure of the ratio Sr between pure shear strain rate and simple shear strain rate. The values of Wk calculated from the measured shapes of microscopic RS increase with increasing distance from the vent, from approximately 0.5 to 0.9. Results of the structural analysis reveal that the RS formed during the early–intermediate stage of flow emplacement. They represent originally sub-spherical enclaves deformed at low shear strain. At higher strain, RS deformed to give boudin-like and stretched banding structures. Results of the kinematic analysis suggest that high viscosity lava flows are heterogeneous non-ideal shear flows in which the degree of non-coaxiality increases with the distance from the vent. In the vent area, deformation is intermediate between simple shear and pure shear. Farther from the vent, deformation approaches ideal simple shear. Lateral extension processes occur only in the near-vent zone, where they develop in response to the lateral push of magma extruded from the vent. Lateral shortening processes develop in the distal zone and record the gravity-driven movement of the lava. The lava flow advanced by two main mechanisms, lateral translation and rolling motion. Lateral translation equals rolling near the vent, while rolling motion prevailed in the distal zones. Received: 6 November 1997 / Accepted: 29 November 1997     

Biochemical indicators of contaminant exposure in spotted pigfish (Orthopristis ruber) caught at three bays of Rio de Janeiro coast

The initial sampling in the Marine Monitoring Program (MOMAM), coordinated by the Ministry of Marine Affairs (IEAPM), was performed along the southeast coast of Brazil. Orthopristis ruber samples were collected at Guanabara, Sepetiba and Ilha Grande Bays. Microsomal CYP1A levels and cytosolic cholinesterase (ChE), catalase (CAT) and glutathione S-transferase (GST) activities were measured in the liver of these fish according to established procedures. CAT activity and CYP1A content were significantly higher (P < or = 0.05) in fish caught at Guanabara Bay, which might be due to higher levels of peroxisome proliferators and Ah receptor agonists, respectively, at this site compared to the other sites. Also, lower GST activity was observed in fish from this site, which may possibly be related to the presence of oxidative-stress inducing compounds.