Search results for "LCA"
showing 10 items of 1995 documents
Tectonic evolution of the Sierra Maestra Mountains, SE Cuba, during Tertiary times: From arc-continent collision to transform motion
2008
Abstract A structural study was carried out along the southern Sierra Maestra mountain range, SE Cuba. This was aimed to monitor the effects of Paleogene island arc formation and collision due to convergence of the Caribbean and North American plates and subsequent Neogene disruption of the arc by initiation of the North Caribbean Transform Fault. In the Sierra Maestra two different and unrelated volcanic arcs are exposed, one of Cretaceous age (pre-Maastrichtian) and the other of Paleogene age, the latter forming the main expression of the mountain range. The volcanic arcs are overlain by Middle–Upper Eocene siliciclastic, carbonate and terrigenous rocks. Six distinct phases of deformation…
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…
Tarsius tumpara: A New Tarsier Species from Siau Island, North Sulawesi
2008
Abstract: A new, critically endangered species of tarsier, one of the world's 25 most endangered primates, is described from the remote island of Siau, North Sulawesi, based on distinguishing characteristics of the tail tuft, pelage coloration, skull, and vocalizations. Siau is part of the Sangihe Island chain, a volcanic arc composed of islands that rise from the ocean floor. There is a single previous record of a tarsier from Siau; a skull in the Dresden Museum that Meyer (1897) classified with tarsiers from Sangihe Island as Tarsius sangirensis. Sangihe and Siau Islands are geologically separated by about 60 km of ocean that greatly exceeds 1,000 m in depth. Genetic data for the new spec…
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…
The Problem of Volcanic Unrest: The Campi Flegrei Case History
1996
Campi Flegrei is one of the most densely populated active volcanic areas of the world. It consists of a complex structure with a multicollapse caldera and many postcaldera, explosive, mostly monogenetic vents. The last eruption was in 1538 (Mt. Nuovo). Progressive reduction of eruption energy has accompanied migration of the vents toward the center of the caldera. Campi Flegrei activity is fed by a shallow magma chamber in which trachybasaltic magma undergoes cooling and fractionation, producing trachytic residual melt that is periodically tapped and erupted to the surface. The depth of the chamber is estimated, from petrological and active and passive seismic data, to be about 4 km beneath…