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Lastarria-Cordon del Azufre complex
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Satellite monitoring of the central Andes situated between Peru and Chile has helped an international team of geologists detect a long wavelength signal over the area's topography.
The area bears 50 active or potentially active volcanoes, spread along a 1500 km-long arc. These volcanic structures mostly rise to between 4000 and 7000 m, are very remote with abrupt slopes, and are often cloaked in snow, making field study extremely difficult.
Now, a team of IRD researchers working in partnership with the University of Chile (Santiago) and the Observatoire de Physique du Globe of Clermont-Ferrand, have focused special attention on the Lastarria-Cordon del Azufre volcanic complex.
In the future, such observation methods could be applied to studying volcanic activity in many regions, like the Andean Cordillera, where access is difficult and thus make the surveillance of volcanic structures as effective as possible.

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The central part of the Andes situated between southern Peru and Chile bears 50 active or potentially volcanoes, spread along a 1500 km-long arc. These volcanic structures mostly rise to between 4000 and 7000 m, are very remote with abrupt slopes and are often cloaked in snow. Few studies have been made on them as such conditions make field surveying extremely difficult. A team of IRD researchers working in partnership with the University of Chile (Santiago) and the Observatoire de Physique du Globe of Clermont-Ferrand  focused special attention on the Lastarria-Cordon del Azufre volcanic complex. With a surface area of 1600 kmē, it is situated in the central Andes Cordillera at the border between Argentina and Chile near Antofagasta.
Research projects on deformations of the earth crust, conducted in this region between 1992 and 2000 by a North American team, had led to the detection of a long wavelength signal over the areas topography, extracted from analysis of data collected by the European Space Agency (ESA) satellite ERS-1. This deformation would correspond to crustal inflation affecting the whole Lastarria-Cordon del Azufre complex. Although this volcano is not considered as active, as the last eruption dates back 9000 years, such inflation could express an underlying activity related to the dynamics of a functioning magma chamber.
IRD geophysicists continued such investigations on the deformations at work in the Lastarria-Cordon del Azufre complex in 2003, by using radar interferometry. This measurement method is based on the superimposition of two satellite radar images of the same geographical area taken at different times. The resulting differential signal between the images, termed the interferogram, provides a way of detecting possible deformation of the earth crust. The value of the wavelength associated with it is proportional to the depth of the source of deformation, down in the lithosphere. For this study, the scientists made use of data acquired by ENVISAT, a satellite ESA launched in 2002. Its ASAR (Advanced Synthetic Aperture Radar) sensor enables it, like its predecessors ERS-l, ERS-2, to perform radar imagery in any weathers. This attribute proves particularly useful for surveillance of the mountainous regions of Latin America.
Between March 2003 and June 2005, ENVISAT recorded a time-series of eight images of the Lastarria-Cordon del Azufre volcanic complex. The IRD team used special software to process the images and obtained 28 interferograms. This data set led to measurement of inflation of about a centimetre affecting the crust over the whole of the area studied . As in the North American study, a long wavelength regional-scale signal was found, covering a surface area of about 45 km long by 35 km wide corresponding to the entire volcanic complex. A short wavelength signal not previously identified was also revealed, but unlike the first, it was located at the smaller scale of the Lastarria volcano only.
Two distinct hypotheses are envisaged to explain the emission of these two wavelengths. As the inflation measured at regional scale corresponds to a long wavelength signal, it has a fairly deep source, estimated by the geophysicists at between 7 and 15 km down. An inflation located at such a depth is highly likely to be generated by magmatic activity. The source of the short wavelength signal, located at about 1000 m beneath the summit of the Lastarria volcano, is more uncertain, however. Indications nevertheless suggest a link with the circulation of hydrothermal fluids.
Future forecasting of the possible evolution of the Lastarria-Cordon del Azufre volcanic complex requires the acquisition of field data to complement the satellite data obtained. GPS measurements especially will enable researchers to check if these inflation effects measured using satellite data effectively correspond to movements of the earth crust. The hope is to obtain further information on changes of mass or density at depth using gravimetry, a geophysical method used for detecting the spatial and temporal variations of the gravity field. Thus, a modification of gravity combined with a displacement of the terrestrial crust could indicate a filling or an emptying of a magma chamber and therefore confirm an underlying volcanic activity. If this turned out to be true, the Lastatria-Cordon del Azufre volcanic complex would be the only area under the Andes where the formation of large magma reservoirs has been demonstrated. In the future, such observation methods could be applied to studying volcanic activity in many regions, like the Andean Cordillera, where access is difficult and thus make the surveillance of volcanic structures as effective as possible.

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RE: Volcanos
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Seismologists on the volcano-rich Kamchatka Peninsula, in Russia's Far East, unveiled Friday the first-ever device for volcanic eruption modelling.
Alexei Ozerov, a senior fellow with the Russian Academy of Sciences' Volcanology and Seismology Institute, said the new device could be used for high-precision modelling of "processes going on inside volcanoes, from the locus of eruptions all the way up to the feeding dykes and the crater."
He presented the 18-meter-tall device at a volcano studies symposium timed to coincide with Volcanologist's Day, which is observed March 30, the anniversary of a 1956 eruption of the Bezymyanny volcano, the first eruption to have been studied by scientists in detail.

"Many physical processes going on at the lower depths have not been quite clear to world science. Until now, that is. As this device will make it possible to get a clearer idea of the nature of these processes and, consequently, to forecast eruptions and their aftermath with greater precision"  - Alexei Ozerov.

Scientists of the Volcanology Institute also used Friday's symposium to report preliminary findings of research into a huge underground volcano in Kamchatka.
The volcano, with an oval crater - or caldera - measuring 35 kilometres, has been dormant since its latest eruption 1.5 million years ago.
Calderas have been the focus of volcanologists' interest for some time, but until now no one has been aware of the existence of such formations in Kamchatka.
The latest eruption of a "super-volcano" occurred some 74,000 years ago in the area of modern-day Sumatra. The average temperature in the northern hemisphere then dropped 21 degrees, resulting, as some scientists contend, in the death of all life in the area.
The Russian Volcanology and Seismology Institute is a successor to the Volcanology Institute of the Soviet Academy of Sciences, set up on the Kamchatka Peninsula in 1962 as the world's first research centre to focus on volcanic studies.

Source Novosti

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The Volcanic Explosivity Index (VEI) was devised by Chris Newhall of the U.S. Geological Survey and Steve Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions.

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Dozens of newly discovered volcanoes in a stretch of the Pacific Ocean pose a major tsunami risk due to the area's seismic instability, an Australian geologist warned on Thursday.

Research teams from the United States, Germany, Australia and New Zealand have discovered 75 previously unknown volcanoes in a 2 000km strip from New Zealand north to Tonga in the past six years, according to Australian National University geologist Professor Richard Arculus.
Previously, only 10 volcanoes were know to exist in the 20 000kmē of seabed.

"It's far more active than previously thought. It's as active as anywhere else on the planet" - Professor Richard Arculus.

The strip of volcanoes posed a major tsunami risk.
On Thursday, Arculus released high-resolution images of the new volcanoes which were created from seabed data complied on an Australian survey vessel in November last year.
Though, more research is needed to determine which of the volcanoes posed significant risks of triggering a tsunami.
40 percent of them were releasing hot water and gas through vents which indicated magma below.

"To a volcanologist, realistically that means all of them are potentially active" - Professor Richard Arculus.

Researchers had targeted the area for investigation because the tectonic plates that comprise the earth's crust are known to be converging north of New Zealand faster than anywhere else on the planet. They are moving at a rate of about 25 millimetres a year.

A tsunami could occur at any time and threaten communities across the Pacific.

-- Edited by Blobrana at 15:17, 2007-03-18

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