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VOLCANISM AND PETROGENESIS

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Versione italiana
Academic year
2015/2016
Teacher
MASSIMO COLTORTI
Credits
6
Didactic period
Primo Semestre
SSD
GEO/07

Training objectives

The course is aiming at giving to the master student the chanche to deepen his/her knowledge on fundamental aspects of the volcanology nd its relationships with the petrological mechanisms which generates magmas. More in detail the student could:

- Know the various kind of volcanoes and their distribution over the terrestrial globe;

- Evaluate their hazard in relation to distribution and position with resepct to Plate Tectonics;

- Know the tools that allow us to estimate the intensive parameters (T, P, fO2, XH2O, etc.) of a magmatic system;

- Know the dynamics within the magma chamber or the feeding system and how they control the eruptive mechanisms and their hazard;

- Know the distribution and the kind of volcanoes in Italy;

- Evaluate the hazard and the risk in relation to value and vulnerability of the human constructions and resilience of the territory, a concept that can be extended also to other non-vulcanic geological events;

- Know the meaning of precursor signals and how they can be used in the monitoring system;

- How it could be possible to prevent and foreseen the set up of a volcanic crisis.



At the end of the course the student:

- Would be acquainted with the compositions of the most common magmas and ho their chemical-physical features may control the hazard of an eruptive event also as function of geological and geographical position;

- Which are the factors that favor the formation of a magma chamber and a close or open feeding system;

- Delineate future eruptive scenario and hazard related to single eruptive manifestations that could be mitigated with specific, single intervention;

- Which are the Italian volcanoes and which are the eruptive scenario foreseen for them.

These knowledge represent the essential expertise of a geologist who wants enter in the wide and multifaceted volcanological world, both for the aim of a correct scientific dissemination and for the inclusion in research centers devoted to the study and monitoring of the volcanoes in Italia and abroad.

Prerequisites

To the master student that approach this teaching is required a deep knowledge of magma petrology and their chemical-physical characteristics that is normally acquired through the courses of Petrography, Petrology and Geochemistry.

Side by side to the Petrology teaching the student would apply in this course the fractionation model for the estimate of the volumes of magmas erupted from the volcano or intruded underneath it, as well as the thermo-barometric tools to estimate its T, fO2 and XH2O conditions using composition and zoning of the phenocrystals.

This to the end of better delineate the kind of the feeding system located beneath the volcano, the most probable expected eruptive scenario and the kind of manifestations that may occur. Of large use would also be the assimilation of the course named “Chemical Analyses of Geomaterial”” where the student will acquire the knowledge of the most used instruments to obtain geochemical data, which are their limits and potentialities. Of some use could also be some concepts regarding dynamics of fluids taken from the teaching of Sedimentology.

Course programme

The teaching is mainly developed with theoric lessons for a total of about 6 CFU, that is 48 h. At the beginning the most important topics of the magmatic petrology will be summarized, such as:

a) Magma classification : modal and normal analyses, saturation and underasaturation of magmas, double triangle of Streickeisen, TAS and diagrams for discriminate serial affinity (AFM, K2O vs SiO2; Na2O vs K2O, etc);

b) Physical-chemical features of magmas: temperature, density, chemical composition and viscosity. Major and trace elements. Compatible and incompatible elements;

c) Few issues about analytical methodologies: X-ray fluorescence (XRF), Electron Microprobe (EMP), Inductively-coupled plasma mass spectrometer (ICP-MS) also equipped with Laser ablation (LAM-ICP-MS). Ion microprobe (SIMS).



This summary is developed aiming at homogenize the cultural background of every students and verify their knowledge level taking also into account the Bachelor from which they come from. This part will be extended over about 1 CFU. Afterwards the course carry on with:



d) Magma uprising from the mantle to the surface: thermic and compositional anomalies, dihedral angle, migration mechanisms of magmas, porous flow vs fracturing (0,25 CFU);

e) Structure of magmatic liquids, network-forming and network-modifying elements, role of the volatiles and degree of polymerization, chemical and thermic diffusion coefficients (0,5 CFU);

f) Hints of magmatic dynamic modelling; convective currents in laminar or turbulent mode, Rayleigh and Reynolds numbers. Settling velocity, Stokes law. Conditions and velocity of magma cooling (0,25 CFU);

g) Magmatic differentiation: crystal growth, nucleation and crystal growth velocity, role of volatiles, crystallization in open or closed system, effusive and intrusive rock textures (0,5 CFU);

h) Magma chamber: layered complex, kind of layering and mechanisms for their formation. Dynamics of fluids within the magma chamber, dynamic (convective) or static (in situ) models, double diffusive process (0,5 CFU);

i) Volcanic forms and lava flows: Shield and strato-volcanoes, Flat top volcanoes. Craters and calderas. Necks, spine and plugs. Subaerial and submarine (pillow) basic lava flows, intermediate and acid lava flows. Domes and domo-lavas (0,5 CFU);

j) Eruption classification following Walker (1980): effusive and explosive eruptions, freato-magmatic explosions, eruptions in subaerial or submarine environments, plinian eruptions. Volcanic Explosivity Index (VEI) (0,5 CFU);

k) High and shape of the eruptive plinian or hydromagmatic column. Piroclastic deposits, eruptive sequences and genetic mechamisms. Lahars and mod flows. Epiclastites vs piroclastites (0,5 CFU);

l) Volcanic Hazard and Risk: topographic, geomorphological and petrographical elements to evaluate the volcanic hazard. Anthropic factors to define the risk. Precursor phenomena, monitoring systems and active volcanic surveillance, geophysical, geochemical and topographic parameters. Scientists and decision-makers relationships (0,5 CFU);

m) Regional volcanology: volcanic events in the Italian geological history. Active volcanoes in Italy: Evolution history, predicted eruptive scenarios, hazard and risk t Vesuvio, Phlegrean Fields, Stromboli and Etna (1 CFU).

Didactic methods

The teaching is mainly developed through theoric lessons. During the lessons transparencies and slides are projected to allow the student to better follow the treated issues. The theoric issues are continuously compared with volcanic events occurred in Italy and abroad. All the petrographic and petrological topics learned by the student are revisited within a volcanological framework and their outcome and importance deepened in the light of this re-visitation.

The teacher keep inviting the students to download photos of films (beside scientific materials such as article from review and text book also in English) for a more concrete treating of the topic. They are continuously stimulated to assume an active part to the lessons with a critical and mature attitude. Volcanoes, volcanic forms, lava flows pyroclastic deposits and depositional sequences are shown by means of slides and films of volcanic outcrops all over the world.

Excursions made up a fundamental step to an adequate development of the volcanological background of the students and represents the most appealing part. To this aim along the years several volcanological excursions have been organized both in Italy and abroad, such as, for example: Sicily (Etna and Eolian islands), Canary Islands (Tenerife), Hungary (Balaton lake) and Iceland. Due to obviously time constrains these excursions cannot be counted within the course, but they can be included in F credits. To avoid interferences with other courses the excursions are usually held outside the lesson period, as for example during Easter holidays, or in conjunction with 23rd or 25th of April, 1st of May or 2nd of June, or during the summer (compulsory for Iceland).

Learning assessment procedures

The examination consists in an oral test during which the teacher ask questions to verify not only the basic knowledge and the acquisition of the most important notions of Volcanism and Petrogenesis but overall the attitude of the students to link data, processes and modelling and to be able to develop an autonomous reasoning over complex situations. Photos of volcanoes or volcanic forms are sometime shown to provide the trigger to an interpretation theory.

Reference texts

Cas R.A.F., Wrigth J.V., 1987. Volcanic successions. Allen & Unwin, London.
Malooe, S. 1983. Principles of igneous petrology. Sprinter-Verlag, Berlin.
Scandone R., Giacomelli L. 1998. Vulcanologia. Liguori ed.
H.-U. Schmincke. 2004. Volcanism. Sprinter-Verlag, Berlin.