Three distinct regimes of volcanic tremor associated with the eruption of Shishaldin Volcano, Alaska 1999

Tremor signals associated with the eruption of Shishaldin Volcano on 19 and 23 April 1999 were the strongest recorded anywhere in the Aleutian Arc by the Alaska Volcano Observatory (AVO) in its 10-year history. Reduced displacements (D_R) reached 23 cm² on 19 April and 43 cm² on 23 April. During the activity, D_R and spectral data with a frequency resolution of 0.1 Hz were computed and put on the World Wide Web every 10 min. These data are analyzed here. The general temporal patterns of seismicity of these eruption events were similar, but the eruptions and their effects quite different. The 19 April event is known to have culminated in a sub-Plinian phase, which ejected ash to an altitude of 16 km. Despite higher amplitudes and the largest hotspot from satellite data, the 23 April event produced little ash reaching only 6 km altitude. For several hours prior to the sub-Plinian phase on 19 April, tremor with a peak frequency of 1.3 Hz intensified. During the sub-Plinian phase the peak frequency increased to 4-8 Hz. However, in 15 h after the eruption, three episodes of stronger tremor occurred with a lower 1.0-Hz peak, alternating with weaker tremor with a 1.3-Hz peak. These transitions correspond to D_R=~8 cm². Although these strong tremor episodes produced higher D_R levels than the sub-Plinian phase, data from a pressure sensor show that only strong Strombolian explosions occurred. The suite of observations suggests three distinct tremor regimes that may correspond to slug flow, bubbly flow, and sustained strong eruptions, or a cyclic change in source parameters (e.g., geometry, sound speed, or ascent rate). This behavior occurred at Shishaldin only during the April 1999 sequence, and we are not aware of similar behavior at other volcanoes.     

Remote and in situ plume measurements of acid gas release from La Soufrière volcano, Guadeloupe

This paper presents the first remote measurements of La Soufrière gas emissions since the fumarolic and seismic reactivation in 1992. The chemical composition of the plumes has been measured from May 2003 to September 2004 using an Open Path Fourier Transform InfraRed (OP-FTIR) spectrometer, up to 15 m downwind the South Crater. HCl is clearly detected (concentration between 2.4 and 12 ppmv) whereas SO₂ and H₂S generally remain below the detection limit of the OP-FTIR. Direct measurements of SO₂ and H₂S near the South Crater with a Lancom III analyzer show a fast decrease of their concentrations with the distance. Calculated Cl / S mass ratios are high: from 9.4 ± 1.7 at 15 m from the vent to 2.8 ± 0.6 at 140 m. The enrichment in HCl of the gas emitted at La Soufrière, observed since 1998, corresponds to the degassing of a magma enriched in Cl and depleted in S. This result agrees with isotopic measurements which suggest a magmatic origin of the gases. Readjustments inside the volcanic system may have taken place during the seismic activity beginning in 1992 and enhance the transfer of magmatic gases to the summit.     

The influence of a season of extreme wet weather events on exposure of the World Heritage Area Great Barrier Reef to pesticides

The 2010-2011 wet season was one of extreme weather for the State of Queensland, Australia. Major rivers adjacent to the Great Barrier Reef (GBR) were discharging at rates 1.5 to >3 times higher than their long term median. Exposure to photosystem II herbicides has been routinely monitored over a period of up to 5 years at 12 inshore GBR sites. The influence of this wet season on exposure to photosystem II herbicides was examined in the context of this long-term monitoring record and during flood plume events in specific regions. Median exposures expressed as diuron equivalent concentration were an average factor of 2.3 times higher but mostly not significantly different (p<0.05) to the median for the long-term monitoring record. The herbicides metolachlor and tebuthiuron were frequently detected in flood plume waters at concentrations that reached or exceeded relevant water quality guidelines (by up to 4.5 times).     

Dependence of radar quantitative precipitation estimation error on the rain intensity in the Cévennes region,France

Abstract

Radar quantitative precipitation estimates (QPEs) were assessed using reference values established by means of a geostatistical approach. The reference values were estimated from raingauge data using the block kriging technique, and the reference meshes were selected on the basis of the kriging estimation variance. Agreement between radar QPEs and reference rain amounts was shown to increase slightly with the space–time scales. The statistical distributions of the errors were modelled conditionally with respect to several factors using the GAMLSS approach. The conditional bias of the errors presents a complex structure that depends on the space–time scales and the considered geographical sub-domains, while the standard deviation of the errors has a more homogeneous behaviour. The estimation standard deviation of the reference rainfall and the standard deviation of the errors between radar and reference rainfall were found to have the same magnitude, indicating the limitations of the available network in terms of providing accurate reference values for the spatial scales considered (5–100 km²).

Editor D. Koutsoyiannis; Guest editor R.J. Moore

Citation Delrieu, G., Bonnifait, L., Kirstetter, P.-E., and Boudevillain, B., 2013. Dependence of radar quantitative precipitation estimation error on the rain intensity in the Cévennes region, France. Hydrological Sciences Journal, 59 (7), 1300–1311. http://dx.doi.org/10.1080/02626667.2013.827337     

Effects of exposure to petroleum hydrocarbons upon the metabolism of the common sole Solea solea

On December 12th, 1999, the oil tanker Erika sank off the southern coast of Brittany (France), releasing 20000-30000tons of heavy oil in the open sea. Among the affected coastal habitats were important nurseries for numerous flatfish species and particularly for the common sole, Solea solea. To investigate the potential impact of the spill on this economically significant resource, we employed Fry's concept of metabolic scope for activity to assess the deleterious effect of fuel exposure on the functional integrity of juvenile sole. Fish were captured from uncontaminated areas and experimentally exposed to contamination conditions mimicking those encountered during the weeks that followed the Erika spill. Using respirometry techniques we measured basal and active metabolic rates, and calculated aerobic metabolic scope, in control and fuel-exposed sole. We then compared the ability of control and fuel-exposed sole to face an episode of reduced oxygen availability. We found that whereas basal metabolic rate was not altered in fuel-exposed fish, active metabolic rate (-27%), and therefore aerobic metabolic scope, were impacted. These changes in metabolic scope were viewed as indicating changes in fishes' ability to face environmental contingencies. Finally the ability of sole to face an episode of reduced oxygen availability was found to be significantly altered following fuel exposure as indicated by a 65% increase in the critical oxygen level. It is concluded that fuel-exposed sole are functionally impaired and less able to face environmental challenges. The link between these results and the recently reported fall in the abundance of the year class that suffered the Erika oil spill is discussed.     

Classifications of retail stores and shopping centres: some methodological issues

This paper reviews current methods used in classifying retail outlets and areas devoted to retailing, in the geographical and town planning literature. For retail outlets, classifications based upon types of goods sold, and types of shopping trip, are discussed. This is followed by an analysis of modern large store development which reflects property developers' and retailers' concerns. Areas devoted to retail uses are subdivided into unplanned ‘retail areas’ and planned ‘shopping centres’. Traditional classifications based upon central place theory are reviewed for both of these types, and found wanting in the light of recent changes in retail development practice and consumer behaviour. Classifications based upon physical development characteristics and type of shopping trip are recommended. Finally, classifications of urban retail location are examined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Factors affecting rural landholders’ adaptation to climate change: Insights from formal institutions and communities of practice

This study explores the factors affecting rural landholders’ adaptation to climate change from the perspectives of formal institutions and communities of practice. Semi-structured interviews were conducted with formal institutions (e.g. South Australian government agencies) and communities of practice (e.g. farm systems groups) within two natural resource management regions in South Australia. Both groups noted that rural landholders autonomously adapt to a variety of risks, including those induced by climate variability; however, the types and levels of adaptation varied among individuals as a result of variety of barriers to adaptation. The lack of communication and engagement processes established between formal institutions and communities of practice was one major barrier. The paper presents and discusses a model for transferring knowledge and information on climate change among formal institutions, communities of practice, trusted individual advisors and rural landholders, and for supporting the co-management of climate change across multiple groups in rural agricultural areas in Australia and elsewhere.     

The radiocarbon budget for Mono Lake: an unsolved mystery

Since 1957 the ¹⁴C/C ratio of the dissolved inorganic carbon in Mono Lake has risen by about 60‰. The magnitude of this increase is about four times larger than that expected from the invasion of bomb-produced¹⁴C from the atmosphere. We have eliminated the following explanations: (1) measurement error, (2) an unusually high physical exchange rate for non-reactive gases, (3) inorganic enhancement of the CO₂ exchange rate, and (4) biological enhancement of the CO₂ exchange rate. Clandestine disposal of waste radiocarbon remains a dark-horse explanation.In the course of our investigations we have uncovered evidence for at least one episodic input of radiocarbon-free carbon to the lake over the last 1000 years. We speculate that this injection was related to a hydrothermal event resulting from sublacustrine volcanic activity.     

Influence of injection conditions on field tracer experiments

Calibration of ground water transport models is often performed using results of field tracer experiments. However, little attention is usually paid to the influence, on resulting breakthrough curves, of injection conditions and well-aquifer interactions, more particularly of the influence of the possible trapping of the tracer in the injection wellbore. Recently, a new mathematical and numerical approach has been developed to model injection conditions and well-aquifer interactions in a very accurate way. Using an analytical solution derived from this model, a detailed analysis is made of the evolution of the tracer input function in the aquifer. By varying injection conditions from one simulation to another, synthetic breakthrough curves are generated with the SUFT3D ground water flow and transport finite-element simulator. These tests show clearly that the shape of the breakthrough curves can be dramatically affected by injection conditions. Using generated breakthrough curves as "actual" field results, a calibration of hydrodispersive parameters is performed, neglecting the influence of injection conditions. This shows that neglecting the influence of actual injection conditions can lead to (1) errors on fitted parameters and (2) misleading identification of the active transport processes. Conclusions and guidelines are drawn in terms of proposed methodologies for better controlling the tracer injection in the field, in order to minimize risk of misinterpretation of results.     

Influence of the mechanical behaviour of brittle–ductile fold–thrust belts on the development of foreland basins

A two‐dimensional mathematical model considering coupling between a deforming elasto‐visco‐plastic fold–thrust belt, flexural subsidence and diffusional surface processes is solved using the Finite Element Method to investigate how the mechanical behaviour of brittle–ductile wedges influences the development of foreland basins. Results show that, depending mainly on the strength of the basal décollement, two end‐member types of foreland basin are possible. When the basal detachment is relatively strong, the foreland basin system is characterised by: (1) Highly asymmetrical orogen formed by thrusts concentrated in the incoming pro‐wedge. (2) Sedimentation on retro‐side takes place in one major foredeep basin which grows throughout orogen evolution. (3) Deposition on the pro‐side occurs initially in the foredeep, and continues in the wedge‐top before isolated basins are advected towards the orogen core where they become uplifted and exhumed. (4) Most pro‐wedge basins show an upward progression from low altitude, foredeep deposits at the base to high altitude, wedge‐top deposits near the surface. In contrast, when the basal detachment behaves weakly due to the presence of low viscosity material such as salt, the foreland basin system is characterised by (1) Broad, low relief orogen showing little preferential vergence and predominance of folding relative to faulting. (2) Deposition mainly in wedge‐top basins showing growth strata. (3) Many basins are initiated contemporaneously but form discontinuously due to the locus of active deformation jumping back and forth between different structures. Model results successfully reproduce first order observations of deforming brittle–ductile wedges and foreland basins. Moreover, the results support and provide a framework for understanding the existence of two main end‐member foreland basin types, simple and complex, associated with fold–thrust belts whose detachments are relatively strong and weak, respectively.