CO<Subscript>2</Subscript> and He degassing at El Chichón volcano,Chiapas, Mexico: gas flux,origin and relationship with local and regional tectonics

During 2007–2008, three CO₂ flux surveys were performed on El Chichón volcanic lake, Chiapas, Mexico, with an additional survey in April 2008 covering the entire crater floor (including the lake). The mean CO₂ flux calculated by sequential Gaussian simulation from the lake was 1,190 (March 2007), 730 (December 2007) and 1,134 g m⁻² day⁻¹ (April 2008) with total emission rates of 164 ± 9.5 (March 2007), 59 ± 2.5 (December 2007) and 109 ± 6.6 t day⁻¹ (April 2008). The mean CO₂ flux estimated from the entire crater floor area was 1,102 g m⁻² day⁻¹ for April 2008 with a total emission rate of 144 ± 5.9 t day⁻¹. Significant change in CO₂ flux was not detected during the period of survey, and the mapping of the CO₂ flux highlighted lineaments reflecting the main local and regional tectonic patterns. The ³He/⁴He ratio (as high as 8.1 R _A) for gases in the El Chichón crater is generally higher than those observed at the neighbouring Transmexican Volcanic Belt and the Central American Volcanic Arc. The CO₂/³He ratios for the high ³He/⁴He gases tend to have the MORB-like values (1.41 × 10⁹), and the CO₂/³He ratios for the lower ³He/⁴He gases fall within the range for the arc-type gases. The high ³He/⁴He ratios, the MORB-like CO₂/³He ratios for the high ³He/⁴He gases and high proportion of MORB-CO₂ (M = 25 ±15%) at El Chichón indicate a greater depth for the generation of magma when compared to typical arc volcanoes.     

Geochemical evidence of the renewal of volcanic activity inferred from CO<Subscript>2</Subscript> soil and SO<Subscript>2</Subscript> plume fluxes: the 2007 Stromboli eruption (Italy)

On 27 February 2007, a new eruption occurred on Stromboli which lasted until 2 April. It was characterized by effusive activity on the Sciara del Fuoco and by a paroxysmal event (15 March). This crisis represented an opportunity for us to refine the model that had been developed previously (2002–2003 eruption) and to improve our understanding of the relationship between the magmatic dynamics of the volcano and the geochemical variations in the fluids. In particular, the evaluation of the dynamic equilibrium between the volatiles (CO₂ and SO₂) released from the magma and the corresponding fluids discharged from the summit area allowed us to evaluate the level of criticality of the volcanic activity. One of the major accomplishments of this study is a 4-year database of summit soil CO₂ flux on the basis of which we define the thresholds (low–medium–high) for this parameter that are empirically based on the natural volcanological evolution of Stromboli. The SO₂ fluxes of the degassing plume and the CO₂ fluxes emitted from the soil at Pizzo Sopra la Fossa are also presented. It is noteworthy that geochemical signals of volcanic unrest have been clearly identified before, during and after the effusive activity. These signals were found almost simultaneously in the degassing plume (SO₂ flux) and in soil degassing (CO₂ flux) at the summit, although the two degassing processes are shown to be clearly different. The interpretation of the results will be useful for future volcanic surveillance at Stromboli.     

Analysis of the liquefaction phenomena in the village of Vittorito (L��Aquila)

This paper describes a case-history of liquefaction occurred near the village of Vittorito after the April 6, 2009 L’Aquila earthquake (moment magnitude M_w = 6.3), approximately 45 km far from the epicentre. In the document, first, an estimation of the seismic motion in the area has been made. Thereafter, the performed geotechnical investigation is described, followed by the application of some fast assessment criteria for the occurrence of liquefaction, recently proposed by the new Italian Building Code. A careful assessment of all the parameters involved in conventional Seed and Idriss (1971) liquefaction analyses is considered. The cyclic resistance ratio CRR is evaluated by cone penetration tests CPT and by in situ seismic dilatometer tests SMDT; in the latter case CRR is evaluated by different empirical correlations with shear wave velocity V_s and horizontal stress index K_D. Analytical data confirmed the observed occurrence of the liquefaction in Vittorito, even if the acceleration field in the area, produced by the L’Aquila earthquake, was very low.     

The Ricker Hills Tillite provides evidence of Oligocene warm-based glaciation in Victoria Land, Antarctica

The relationship between the Ricker Hills Tillite (RHT), which represents the northernmost outcrop of lithified continental glacial deposits in Victoria Land, is discussed with respect to the glacial landscape assemblage of the Ricker Hills, a nunatak at the internal border of the Transantarctic Mountains. A warm-based ice sheet deposited the tillite and induced syn- to post-depositional glacial deformation under wet conditions both of the tillite and of the bedrock. The thickness of the ice sheet on the nunatak is estimated to have been 600 m, at most. The area had been deeply eroded before deposition of the RHT as documented by the low elevation of tillite outcrops located in overdeepened depressions of the nunatak. Micropaleontological analysis evidences only the presence of Permian to Jurassic palynomorphs. X-ray diffraction and SEM–EDS analyses of clay minerals in the RHT indicate continental chemical weathering under wet conditions after the RHT deposition. As documented by clay mineral assemblage variation in CRP drillholes, the progressive cooling of the Antarctic continent allowed chemical weathering in “warm” conditions until the Late Oligocene period in southern Victoria Land, leading to a chronological constrain for RHT deposition. Conservatively estimating the sea level to have been between the tillite outcrops and the erosional trimline limiting horns in the Ricker Hills, at the time of RHT deposition, we suggest that the maximum uplift of the area would not have exceeded 900–1500 m since at least Late Oligocene.     

Estimation of net theoretical excavation rates in concrete and sandstone

Abstract

The estimation of excavation rates in specific geological and geotechnical conditions is one of the most delicate aspects for mining and geotechnical operations particularly offshore. Many models have been developed to study the effectiveness of a drilling tool in contact with the ground. In this article, the results of laboratory cutting tests on concrete specimens are shown. The comparison of the results of laboratory tests with different predictive models, helped to identify the most representative models. The models were then used to study in more detail, the effectiveness of the excavation tools through a parametric analysis. The research helped to define how to obtain rubrics, which can estimate the theoretical net cutting production of an excavation machine, when the power of its engines is known, or to evaluate, when the requested net cutting production is available, the power that the cutting machine must have. The findings were also applied to a sandstone previously investigated. The results are based on theoretical models and cannot be used on geomaterials with the same (or similar) geotechnical properties.     

Emergence and evolution of active and ephemeral regions: Comparison between observations and models

This work aims to describe some aspects relevant to the emergence of magnetic structures on the solar surface. Using high resolution photospheric and chromospheric data, besides than EUV images acquired by space telescopes, the dynamics of rising flux tubes is studied. It is shown that, for both long-lived and short-lived magnetic regions, the flux tubes are initially characterized by a high rising velocity, which eventually decreases as the region develops. Other results concern the timeline of the active regions appearance in the atmospheric layers and the asymmetries in plasma downflows between preceding and following legs of the flux tubes. These results are briefly discussed in the light of most recent models.     

Imaging DOAS for volcanological applications

The simultaneous quantitative determination of two-dimensional bromine monoxide (BrO) and sulphur dioxide (SO₂) distributions in volcanic gas plumes is described. Measurements at the fumarolic field on the island Vulcano (autumn 2004) and in the plume of Mt. Etna volcano (spring 2005) were carried out with an Imaging DOAS instrument. The SO₂ fluxes of several fumaroles were estimated from two-dimensional distributions of SO₂. Additionally, the first two-dimensional distributions of BrO within a volcanic plume were successfully retrieved. Slant column densities of up to 2.6 × 10¹⁴ molecules per square centimetre were detected in the plume of Mt. Etna. The investigation of the BrO/SO₂ ratio, calculated from the two-dimensional distributions of SO₂ and BrO, shows an increase from the centre to the edge of the volcanic plume. These results have significance for the involvement of ozone during BrO formation processes in volcanic emissions.