Search results for "Geology"
showing 10 items of 6012 documents
CO2 release to the atmosphere from thermal springs of Sperchios Basin and northern Euboea (Greece): The contribution of “hidden” degassing
2020
Abstract Greece is a region characterised by intense geodynamic activity that favours the circulation of hydrothermal fluids in the crust transporting volatiles from either the deep crust or the mantle to the surface. Elevated heat flow values are detectable at Sperchios Basin and North Euboea (central Greece), two areas defined by a system of deeply rooted extensional faults and Quaternary volcanic activity. This setting contributed to the formation of numerous hydrothermal systems, which are mostly expressed as CO2-rich thermal springs with intense bubbling. The CO2 output from six bubbling pools has been determined by flux measurements with the use of the floating chamber method. The hig…
Pantelleria island (Strait of Sicily): volcanic history and geomorphological landscape
2017
Pantelleria is a volcanic island located in the Strait of Sicily, 95 km far from the Sicilian coastline and 67 km from Cape Bon (Tunisia). The volcanological history of the island begins approximately 324 ka BP and the last eruptive event was a submarine eruption that occurred on 1891 A.D. Eruptive activity was characterized by seven very intense explosive events, the latest being the Green Tuff (44 ka). They have all produced ignimbrite sheets that covered large sectors of the island. The landscape of the island mirrors the variety of the eruptive styles and their interplay with volcano-tectonics. The most evident geomorphological features are represented by: (i) the mantle-like distributi…
Hydrothermal alteration can result in pore pressurization and volcano instability
2021
AbstractThe collapse of a volcanic flank can be destructive and deadly. Hydrothermal alteration is common to volcanoes worldwide and is thought to promote volcano instability by decreasing rock strength. However, some laboratory studies have shown that not all alteration reduces rock strength. Our new laboratory data for altered rhyodacites from Chaos Crags (Lassen volcanic center, California, USA) show that pore- and crack-filling mineral precipitation can reduce porosity and permeability and increase strength, Young's modulus, and cohesion. A significant reduction in permeability, by as much as four orders of magnitude, will inhibit fluid circulation and create zones of high pore fluid pr…
In situ Volcano Monitoring
2015
Abstract During the last couple of decades, volcanology has evolved significantly, allowing for an improved understanding of volcanic processes preceding, accompanying and following eruptive events. Key elements to these achievements are the huge amounts of high quality data being collected by networks of increasingly sensitive instruments deployed at active volcanoes. The diffusion of continuous, precise measurements of: (1) wide-band ground displacement; (2) flux and chemistry of volatile emissions; and (3) the spatio-temporal variations of potential fields (e.g., gravity) now permit imaging the mechanism that controls mass transfer underneath volcanoes to an unprecedented level of detail…
Methanotrophic activity and bacterial diversity in volcanic-geothermal soils at Pantelleria island (Italy)
2014
Abstract. Volcanic and geothermal systems emit endogenous gases by widespread degassing from soils, including CH4, a greenhouse gas twenty-five times as potent as CO2. Recently, it has been demonstrated that volcanic/geothermal soils are source of methane, but also sites of methanotrophic activity. Methanotrophs are able to consume 10–40 Tg of CH4 a−1 and to trap more than 50% of the methane degassing through the soils. We report on methane microbial oxidation in the geothermally most active site of Pantelleria island (Italy), Favara Grande, whose total methane emission was previously estimated in about 2.5 t a−1. Laboratory incubation experiments with three top-soil samples from Favara Gra…
Degassing of trace volatile metals during the 2001 eruption of Etna
2003
This paper provides new data on sulfur, halogens, and minor and trace metal contents in airborne particulate matter from the Mt. Etna volcanic plume. Aerosol samples were collected by conventional filtration techniques before and during the summer 2001 eruption, in order to investigate relations between plume chemistry and volcano dynamics. Data analysis reveals that abundances of trace metals in the plume result from mixing of erosive and volatile components. The former is responsible for the contents of rare earth elements (REE), Ca, Ba, Sr, Ti, Sc, Y, Hf and Th; the latter contributes significantly to the abundance of Cs, Rb, Na and K, probably transported in the plume as metal halides, …
El Lahar Tinguiririca: su significado entre los Lahares chilenos
1982
The Tinguiririca lahar is an example of many similar landforms, which cover large surfaces 60th in andine valleys and the Chilean longitudinal depression. I t is smaller than other ones in Chile, but - at the same time - better conserved, offering good conditions for genetic, kinematic and geochronologic studies, respecting volcanic mudflows. From the genetic and kinematic point of view, the longitudinal lahar profile may be in two parts: a) An upper and middle accumulative area, with concave transverse profile; b) A low accumulative area; whose transverse profile is convexe. These two profiles could be explained by means of braking process in lateral parts, related to central parts, as a f…
Volcanic-gas monitoring
2015
The environmental impact of volcanoes is closely related to the rates, style and chemistry of their gas emissions (Delmelle, 2003). Monitoring the composition and mass flux of volcanic gases is therefore central to understanding how volcanism impacts our planet, on both global and local scales. There are two main modes of volcanic-gas release on Earth (Chapter 14): (i) the impulsive emission of large quantities of gases during episodic, large-scale volcanic eruptions, and (ii) the far more sluggish, but persistent, passive gas release from quiescent or mildly erupting volcanoes. Characterising the chemical composition of impulsive emissions has remained a challenge, and direct measurements …
Chapter 16 Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano
2014
We use volatiles in melt inclusions and nominally anhydrous phenocrysts, with volcanic gas flux and composition, and textural analysis of mafic inclusions to estimate the mass of exsolved vapour prior to eruption at Soufriere Hills Volcano (SHV). Pre-eruptive andesite coexists with exsolved vapour comprising 1.6–2.4 wt% of the bulk magma. The water content of orthopyroxenes indicates a zone of magma storage at pressures of approximately 200–300 MPa, whereas melt inclusions have equilibrated at shallower pressures. Inclusions containing >3 wt% H2O are enriched in CO2, suggesting flushing with CO2-rich gases. Intruding mafic magma contains >8 wt% H2O at 200–300 MPa. Rapid quenching is accompa…
Mobility of plume-derived volcanogenic elements in meteoric water at Nyiragongo volcano (Congo) inferred from the chemical composition of single rain…
2017
The chemical composition of single rainfall events was investigated at Nyiragongo volcano (Democratic Republic of Congo) with the aim of determining the relative contributions of plume-derived elements. The different locations of the sampling sites allowed both plume-affected samples (hereafter referred to as “fumigated samples”) and samples representative of the local background to be collected. The chemical composition of the local background reflects the peculiar geographic features of the area, being influenced by biomass burning, geogenic dust, and biological activity. Conversely, fumigated samples contain large amounts of volcanogenic elements that can be clearly distinguished from th…