This book consists of four parts. The first part (part. I) deals with magmas, the conditions of their genesis, and their ascent and evolution within the crust. We firstly present the main types of primary magmas, including the relevant petrological and geochemical characteristics of each type : mid-oceanic ridge basalts, intraplate basalts, mantle-derived andesites (boninites), and rhyolitic magmas resulting from crustal melting (examplified by the Macusani ignimbrites from Peru). Then we consider the different processes of magma transport in the crust, at both microscopic and macroscopic scales, and we look at some of the physical properties that are relevant to their rheological behaviour (viscosity, tensile strength). Thereafter we present some aspects of the magma storage and evolution in the crust. This includes the major petrological processes of magmatic differentiation (crystal fractionation, magma mixing, contamination) as well as some insights into the geometry and tructure of magmatic transport and storage systems under volcanoes. We address also the use of short-lived radioactive disequilibria in the study of magma storage and dynamics.
In part II, J.e consider volcanic gases and primary volcanicproducts (lava flows and
domes, pyroclastic deposits). We also address the varied eruptive mechanisms that
produce the observed variety of volcanic products. Volcanic gases have variable composition and emission rate from which we learn about magmatic processes in general, and about the current activity of a give~volcano. Lavas have variable geometry, morphology, internal structure, mobility and flow behaviour, which depend on physical and chemical properties of magmas, on environmental factors (e.g. subaerial or subaqueous emplacement) and on effusion rate. Pyroclastic products are erupted as pyroclast-gas mixtures fragmented then accelerated by decompression, either at depth or at the Earth's surface. Explosive eruptions need exsolution of magmatic gases (magmatic eruptions) and/or interaction of magma with ground or external water (hydrovolcanic eruptions). Phreatic eruptions are a particular kind of eruption in which steam is explosively decompressed but no magma is erupted. Upon eruption, pyroclastic products may be emplaced as pyroclastic fall, flow or surge deposits.
In part III, we firstly document the main types of volcanoes and volcanic systems. This includes monogenetic volcanoes (scoria cones, maars, tuff-rings and tuff-cones) as exemplified by the Chaine des Puys field, stratovolcanoes with emphasis on the wide-world andesitic ones, basaltic shield volcanoes, flood basalt plateaux, ubmarine seamounts and ridges, and large calderas. Volcanoes and volcanic ystems are described in their form, internal structure and their temporal evolution in response to the magmatic and structural evolution of the system. We then address" ome of the major tools currently used in studying modem and ancient volcanic systems : mapping and remote sensing in volcanic areas, datation of volcanic rocks by geochronological methods, geophysical investigation of the internal structure and plumbing system of volcanoes by seismic, gravity, magnetic and electric methods.
Part IV finally addresses volcanic hazards and the geophysical and geochemical monitoring of active volcanoes. General concepts and methods guiding the hazards assessment and zonation are firstly presented, then applications are given to the french active volcanoes of the Lesser Antilles arc (Montagne Pelee, Soufriere of
Guadeloupe) and Reunion (Piton de la Foumaise). Monitoring of active, potentially hazardeous volcanoes is conducted by the mean of various instrumental methods, some being commonly used almost as a matter of routine, other ones being as yet in a pioneering stage of development. These methods are presented in their basic principles and with examples of application to selected volcanoes. These are the seismic, ground deformation, volcanomagnetic, gravity, electric, geochemical and remote-sensing monitoring. The logistical aspects of the implementation of monitoring equipments and permanent or mobile networks are finally discussed, along with the current state of the art in short-term prediction of volcanic eruptions.

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