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About this book

Volcanoes have terrified and, at the same time, fascinated civilizations for thousands of years. Many aspects of volcanoes, most notably the eruptive processes and the compositional variations of magma, have been widely investigated for several decades and today constitute the core of any volcanology textbook. Nevertheless, in the last two decades, boosted by the availability of volcano monitoring data, there has been an increasing interest in the pre-eruptive processes related to the shallow accumulation and to the transfer of magma approaching the surface, as well as in the resulting structure of volcanoes. These are innovative and essential aspects of modern volcanology and, as driving volcanic unrest, their understanding also improves hazard assessment and eruption forecasting. So far, the significant progress made in unravelling these volcano-tectonic processes has not been supported by a comprehensive overview.
This monograph aims at filling this gap, describing the pre-eruptive processes related to the structure, deformation and tectonics of volcanoes, at the local and regional scale, in any tectonic setting. The monograph is organized into three sections (“Fundamentals”, “Magma migration towards the surface” and “The regional perspective”), consisting of thirteen chapters that are lavishly illustrated. The reader is accompanied in a journey within the volcano factory, discovering the processes associated with the shallow accumulation of magma and its transfer towards the surface, how these control the structure of volcanoes and their activity and, ultimately, improve our ability to estimate hazard and forecast eruption.
The potential readership includes any academic, researcher and upper undergraduate student interested in volcanology, magma intrusions, structural geology, tectonics, geodesy, as well as geology and geophysics in general.

Table of Contents

Frontmatter

1. Volcanoes and Volcanic Activity

Abstract
Volcanoes are an astonishing manifestation of the activity of planets and their satellites, as observed in active and/or fossil examples on Earth, Mars, Venus, Mercury, the Moon and the Jovian satellite Io. On Earth, volcanoes are one of the most impressive evidence of the same imbalance in energy that is also driving plate tectonics. Active volcanoes have terrified and at the same time fascinated populations and civilizations for thousands of years.
Valerio Acocella

2. Crustal Deformation

Abstract
As discussed in Chap. 1, volcano-tectonics focuses on the stress-deformation relationships related to volcanic activity, at the local and regional scale. While Chap. 1” has introduced volcanoes and their activity, this second chapter provides complementary introductory knowledge, summarizing the stress-deformation relations affecting the crustal rocks and completing the fundamentals section of the book.
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3. The Rise of Magma Through the Crust

Abstract
After the fundamentals summarized in Chaps. 1 and 2, this chapter introduces the second and main part of the book. This part, from this chapter to Chap. 9, focuses on the general path followed by magma in passing through the crust, ideally consisting of its rise, shallow accumulation, shallow transfer and eruption.
Valerio Acocella

4. Magma Emplacement and Accumulation: From Sills to Magma Chambers

Abstract
The previous chapter has discussed the rise of magma throughout the crust. This fourth chapter focuses on the arrest, emplacement and accumulation of magma. These are indeed primary and widespread processes at volcanoes, as most of the rising magma remains stalled in the crust, with only a fraction being erupted (approximately one tenth; e.g., Shaw 1985; White et al. 2006). Moreover, the accumulated magma may develop magma chambers, whose dynamics can be detected to define the state of active volcanoes, also providing a warning for forecasting any impending eruption.
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5. Calderas

Abstract
After having described magma chamber formation and growth in Chap. 4, this fifth chapter considers the surface processes resulting from the dynamics of magma chambers, including magma accumulation on the long- and short-term, and rapid magma withdrawal and eruption. The rapid withdrawal of magma may develop a caldera. Calderas often represent the surface expression of long-lived and large magmatic reservoirs, which may be responsible for the most destructive eruptions.
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Chapter 6. Volcano Flank Instability and Collapse

Abstract
After having discussed magma chamber formation and dynamics in the previous two chapters, in this chapter the focus is on the shallower volcano-tectonic processes related to the instability and collapse of the flanks of volcanic edifices. Flank instability and collapse is in fact, together with caldera formation (considered in the previous chapter), a first-order process affecting the shape of a volcanic edifice and, in turn, controlling shallow magma propagation, which is the topic of the next chapter.
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Chapter 7. Shallow Magma Transfer

Abstract
This chapter focuses on the processes controlling the shallow transfer of magma below and within volcanic edifices. As such, it builds on the knowledge of the previous chapters, which considered the general mechanisms for the rise of magma in the crust (Chap. 3), its arrest and the development of magma chambers nucleating magma-filled fractures (Chap. 4), and the important topographic variations induced by calderas (Chap. 5) and sector collapse (Chap. 6). At the same time, shallow magma transfer generates signals detected by monitoring systems (Chap. 8), which can be used to understand the state of active volcanoes and ultimately improve eruption forecasting (Chap. 9).
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8. Volcano Monitoring

Abstract
This chapter focuses on the monitoring techniques and signals associated with the volcano-tectonic processes presented in Chaps. 37 occurring at the volcano scale, with the aim to understand unrest and, ultimately, forecast eruptions, which are topics of Chap. 9. Volcano monitoring data are indeed essential to understand the real-time structure, dynamics and state of active volcanoes, which is a pre-requisite for hazard assessment, eruption forecasting and, ultimately, risk mitigation.
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9. Unrest and Eruption Forecasting

Abstract
The shallow accumulation and/or transfer of magma commonly result in anomalous geodetic, geophysical or geochemical activity of the volcano, named unrest, which is detectable through a monitoring system. At closed conduit volcanoes, every eruption is preceded by unrest. However, not all unrest culminates into eruption, as unrest may also vanish back into quiescence. Therefore, deciphering the monitoring signals captured during unrest is probably the main challenge for volcanology. This in fact allows not only understanding magmatic processes, but also forecasting impending eruptions and the possible location for the opening of vents. The recent boost in the quantity and quality of monitoring data, based on key multi-parameter sets, significantly contributes to face this challenge towards enhanced understanding and more accurate and reliable eruptive forecast: the future for this exciting field looks definitely promising.
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10. Volcanoes and Plate Tectonics

Abstract
This chapter introduces the third part of the book, presenting the regional tectonic frame of volcanoes. In this third part the previously described volcano-tectonic processes are considered at a wider scale, highlighting the interaction of the volcanoes with the regional tectonic context. The focus here is on how the tectonic setting may affect the location, distribution, style, type and frequency of volcanic activity, on both the longer-term (i.e., thousands to millions of years) and, as suggested by recent studies, the shorter-term (i.e., years or less, as in the co- and post-seismic cycles of regional earthquakes). The change in scale in this part of the book permits to appreciate first-order magmatic processes related to plate-tectonics mechanisms, in an exciting journey around key regions of our planet. This journey allows explaining the major differences among the volcanic provinces, as well as showing how magma plays a leading role not only in promoting intra-plate processes but, quite unexpectedly, also in shaping plate boundaries.
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11. Volcanoes at Divergent Plate Boundaries

Abstract
This chapter focuses on divergent plate boundaries, that is where two lithospheric plates drift away from each other. Plate divergence may occur on continental, transitional and oceanic lithosphere, with spreading rates varying over nearly 2 orders of magnitude, from a few mm/year to ~15 cm/year. Except for the continental and oceanic boundaries characterized by the lowest bound of spreading rates, divergent plate boundaries are commonly associated with widespread magmatic activity.
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12. Volcanoes Along Convergent Plate Boundaries

Abstract
This chapter focuses on the tectono-magmatic relationships along convergent plate boundaries characterized by subduction: these boundaries are the sites of the largest earthquakes and eruptions and constitute the most active, unstable and hazardous areas on Earth. Volcanic arcs are the surface manifestation of the magmatic activity resulting from plate convergence. As anticipated in Chap. 10, their structural setting may vary significantly, mainly depending on the velocity and angle of convergence between the subducting and overriding plates.
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13. Hot Spots

Abstract
Hot spots are the surface expression of plumes of hotter and lighter material upwelling from the Earth’s mantle. The current number of hot spots is estimated to range between 45 and 70: these are mostly in intraplate settings, especially on oceanic lithosphere, and along divergent plate boundaries. Neglecting hot spots along divergent boundaries and shaped by the related far-field tectonics (as with Afar and Iceland, described in Chap. 11), oceanic hot spot volcanoes show a considerable variability in distribution, evolution and activity, as at Hawaii, Galapagos, Easter Island, Reunion, Canary Islands and Azores. This results from the different mantle plume properties (plume configuration and productivity) and local tectonic context (age of the intruded oceanic lithosphere, rate of plate motion, pre-existing structures), which make each hot spot distinctive. Despite this variability, most oceanic hot spot volcanoes also display recurrent structural features, which include overlapping mafic edifices with summit calderas, radial volcanic rift zones and flank instability. Then, there is the less common and more evolved volcanism derived from continental hot spots, of which Yellowstone is the most dramatic example and, at the same time, quite distinct from other less productive continental cases, as for instance Tibesti. All these characteristics make hot spots widely different, stimulating from structural and magmatic perspectives and complicating established models.
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Backmatter

Additional information