The South Aegean Active Volcanic Arc

This book is a collection of 22 selected papers from the homonymous Conference held in September 2003 Milos, Greece. The aim of the conference was to serve as a forum for the presentation and constructive discussion of the state-of-the-art and emerging issues on the South Aegean Volcanic Arc. In the first part of the book the tectonic- geodynamic setting and the present upper mantle structure of the Aegean area are discussed. It includes an interesting interpretation of data on the spatial distribution of intermediate focal depth earthquakes, fault plane solutions and deep velocity structures, to further investigate active tectonics related to the deep structure of the southern Aegean volcanic arc. The second part deals with general volcanological, petrological and tectonic characteristics of the SAAVA presenting an extensive review of volcanological, chemical, isotope and tectonic data, using a large amount of new field and laboratory data. Interesting conclusions are presented regarding the present volcanic associations, the volcanic fields location and shape in respect to the large tectonic lineaments and the plate motions, the source of the SAAVA parental magmas. Presented in the third part is an extensive review on the volcanic hazard assessment and the monitoring state of the SAAVA centers. Seismic and geodetic monitoring of the Santorini volcano and the recent (1995-1998) crisis of Nisyros volcano are presented and discussed. The last part deals with hydrothermal deposits and processes in the SAAVA, as well as products and processes in adjacent areas with a particular interest and significance that link them to the SAAVA processes. *Systematic re-evaluation on the geodynamic and tectonic setting of the Aegean active volcanic centers *Thorough review with new data and ideas on the magma source region, the magma differentiation processes in both the deep and shallow levels, and the volcanological processes related both to the magma composition and storage depth as well as to the tectonic regime of the volcano growth area *Up to date estimation of the volcanic hazard in the Aegean area, and a detailed presentation of the present state and the monitoring efforts of the South Aegean active centers

This book presents the first compilation of scientific research on the island of Nisyros, involving various geoscientific disciplines. Presenting a wealth of illustrations and maps, including a geological map of the volcano, it also provides valuable insights into the geothermal potential of Greece. The island of Nisyros is a Quaternary volcano located at the easternmost end of the South Aegean Volcanic Arc. The island is nearly circular, with an average diameter of 8 km, and covers an area of approximately 42 km2. It lies above a base of Mesozoic limestone and a thin crust, with the mantle-crust transition located at a depth of approximately 27 km. The volcanic edifice of Nisyros comprises a succession of calc-alkaline lavas and pyroclastic rocks, as well as a summit caldera with an average diameter of 4 km. Nisyros marks the most recent volcano in the large prehistoric volcanic field between Kos-Yali-Strongyli-Pyrgousa-Pachia-Nisyros, where the largest eruption (“Kos Plateau Tuff”) in the history of the eastern Mediterranean devastated the Dodecanese islands 161,000 years ago. Although the last volcanic activity on Nisyros dates back at least 20,000 to 25,000 years, it encompasses an active hydrothermal system underneath the volcano with temperatures of roughly 100°C at the Lakki plain, the present-day caldera floor and 350°C at a depth of 1,550 m. A high level of seismic unrest, thermal waters and fumarolic gases bear testament to its continuous activity, which is due to a large volume of hot rocks and magma batches at greater depths, between 3,000 and 8,000 m. Violent hydrothermal eruptions accompanied by major earthquakes occurred in 1873 and 1888 and left behind large, “world-wide unique” explosion craters in the old caldera. Through diffuse soil degassing, the discharge of all hydrothermal craters in the Lakki plain releases 68 tons of hydrothermal-volcanic derived CO2 and 42 MW of thermal energy per day. This unique volcanic and hydrothermal environment is visited daily by hundreds of tourists.

In the region comprising Turkey and Greece, people have been using water from geothermal sources for bathing and washing of clothes since ancient times. This region falls within the Alpine-Himalayan orogenic belt and hence is a locus of active volcanism and tectonism and experiences frequent seismic events. This volcanic and tectonic activity has given rise to over 1500 geothermal springs. Its importance was recognized decades ago and the geothermal water is now being utilized for district heating, industrial processing, domestic water supply, balneology and electric power generation. The geothermal potential in this region is large. In Turkey alone it is estimated to be more than 31500 MWt while the proven potential is 4078 MWt. At present 2084 MWt is being utilized for direct applications in Turkey and 135 MWt in Greece. In Turkey electricity is produced for 166 MW installed capacity, whereas in Greece geothermal energy is presently not used for electricity production despite its potential. This book discusses the geochemical evolution of the thermal waters and thermal gases in terms of the current volcano-tectonic setting and associated geological framework that makes the region very important to the geothermal scientific community. The book explains, in a didactic way, the possible applications, depending on local conditions and scales, and it presents new and stimulating ideas for future developments of this renewable energy source. Additionally, the book discusses the role(s) of possible physicochemical processes in deep hydrothermal systems, the volatile provenance and relative contributions of mantle and crustal components to total volatile inventories. It provides the reader with a thorough understanding of the geothermal systems of this region and identifi es the most suitable solutions for specifi c tasks and needs elsewhere in the world. It is the fi rst time that abundant information and data from this region, obtained from intensive research during the last few decades, is unveiled to the international geothermal community. Thus, an international readership, in the professional and academic sectors, as well as in key institutions that deal with geothermal energy, will benefit from the knowledge from geothermal research and experiences obtained from the Aegean Region.

The Hiroshi Wakita Volume II is a collection of original papers regarding the role of terrestrial fluids in earthquake and volcanic processes. This Pure and Applied Geophysics volume provides the results of recent studies on terrestrial fluids involved in both processes. This special publication honors Hiroshi Wakita for his scientific contributions. The volume should be useful for both active researchers in this field and for graduate students alike.

This memoir synthesizes all the data from the Cambridge, Bristol and Clermont groups, and integrates data from other research groups on the caldera volcanoes of Santorini. It provides interpretations of the tectonic and magmatic evolution of Santorini. The volcanic field has been remapped and a picture of cyclic volcanic activity and magmatic evolution has emerged from this work.