Search results for "FEA"
showing 10 items of 4862 documents
The Influence of Floodplains on Mercury Availability
2009
The floodplains of the German river Elbe affect the mercury distribution in the river system in two different ways: they act both as a medium-term sink and as a long-term source. The large amounts of mercury deposited onto the floodplains during annual floodings are first effectively fixed in the soils, rendering them basically unavailable. Sequential extraction experiments reveal that only a small fraction of the mercury (< 3%) is present in available forms, whereas the vast majority is associated with humic substances or present in sulfidic binding forms. After deposition, a small fraction of the total mercury is gradually remobilized into the aqueous phase bound passively to water-solubl…
Geochemistry, geochronology and isotope geology of Nakfa intrusive rocks, northern Eritrea: products of a tectonically thickened Neoproterozoic arc c…
2001
Abstract The north-south-trending Neoproterozoic volcano-sedimentary plutonic associations in northern Eritrea are part of the Nubian Shield. The Nakfa intrusive rocks range in composition from gabbro to syeno-diorite to granite and alkaline syenite and intrude supracrustal rocks of volcanic and sedimentary origin. All granitoid rocks are metaluminous or slightly peraluminous and have typical I-type chemical signatures. The calc-alkaline intrusive rocks and the alkaline syenites have geochemical characteristics (e.g. low Nb values) typical of arc intrusives and plot as volcanic arc granites on various discriminant diagrams. Single zircon evaporation Pb-Pb ages and conventional multigrain U-…
The evolution of a dynamic geological system: the support of a GIS for geochemical measurements at the fumarole field of Vulcano, Italy
1997
The island of Vulcano (Aeolian arc, Southern Italy) has displayed several periods of volcanic unrest since the end of the last eruption (1890). We report here results obtained from a long-term survey concerning variations of both the steam output and the exhaling surface area at the summit crater fumarolic field of La Fossa. The field measurements analysed in a Geographical Information System (GIS) show a highly dynamic volcanic system in which deep variations in the geochemistry and the temperature of the released fluids were accompanied by fluctuations in the mass output of steam and the topography of the crater field. The use of a GIS facilitated digitized reconstructions of maps of the …
The southern margin of the Caribbean Plate in Venezuela: tectono-magmatic setting of the ophiolitic units and kinematic evolution
2002
Abstract The southern Caribbean Plate margin in Venezuela consists of a W–E elongated deformed belt, composed of several tectonic units dismembered along the northern part of the South America continental Plate since the Late Cretaceous. The present review, based on petrology and tectono-magmatic significance of each unit, makes it possible to define the main geotectonic elements and to reconstruct the paleogeographic domains from Late Jurassic to Tertiary: (a) Mid-Ocean Ridge Basalt (MORB) proto-Caribbean oceanic basin (Loma de Hierro Unit); (b) oceanic plateau (Dutch and Venezuelan Islands basement); (c) rifted continental margin (Cordillera de La Costa and Caucagua–El Tinaco Units) with …
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…