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How Volcanoes Work: a 25 Year Perspective 1888 2013

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How Volcanoes Work: a 25 Year Perspective 1888 2013 How volcanoes work: A 25 year perspective 1888 2013 CELEBRATING ADVANCES IN GEOSCIENCE Katharine V. Cashman† and R. Stephen J. Sparks School of Earth Sciences, University of Bristol, Bristol BS81RJ, UK Invited Review ABSTRACT eruption triggers. Finally, we look at eruptions Hawaiian volcanism is associated with the themselves, from the ascent of magma through eponymous Hawaiian eruptive style, which is Over the past 25 years, our understanding the crust to the physical controls on eruption dominated by fl uid lava fl ows. Lava fl ows often of the physical processes that drive volcanic styles and generation of eruptive products. We emerge directly from dike-fed fi ssure systems; eruptions has increased enormously thanks recognize that it is impossible to do justice to all for this reason, shield volcanoes tend to be to major advances in computational and of these topics—or all of the scientists who have elongated along the fi ssure direction. Hawai- analytical facilities, instrumentation, and col- contributed to the contemporary understanding ian shield volcanoes are built of stacks of these lection of comprehensive observational, geo- of volcanism—in a single article. In this regard, fl ows; their low slopes refl ect both the fl uidity physical, geochemical, and petrological data we note that a thorough review of the fi eld was of the initial lava and the tendency for lava fl ows sets associated with recent volcanic activity. completed in 2000 with the publication of the En- to thicken (because of cooling, crystallization, Much of this work has been motivated by the cyclopedia of Volcanoes (Sigurdsson et al., 2000). and associated increases in viscosity) with trans- recognition that human exposure to volcanic port distance from rift zone vents (e.g., Katz and hazard is increasing with both expanding VOLCANIC ERUPTIONS— Cashman, 2003). An unprecedented look at populations and increasing reliance on infra- AN OVERVIEW the structure of Hawaiian volcanoes has been structure (as illustrated by the disruption provided by a 15-yr-long drilling project that to air traffi c caused by the 2010 eruption of Volcanoes vary greatly in morphology, evolu- recovered core from Hawaii’s Mauna Loa vol- Eyjaf jallajökull volcano in Iceland). Reducing tion, eruptive styles, and behaviors as a conse- cano to a depth of ~3500 m, which represents vulnerability to volcanic eruptions requires a quence of the wide variety of tectonic settings, an ~700 k.y. history of the Hawaiian plume thorough understanding of the processes that melt production rates, magma compositions, and (Stolper et al., 2009). Not surprisingly, given govern eruptive activity. Here, we provide eruption conditions that they represent. Here, the proximity of the drilling site to the current an overview of our current understanding we introduce common volcanic landforms, to- shoreline, subaerial lavas represent only a small of how volcanoes work. We focus particu- gether with the eruption styles responsible for fraction of the core samples, with most of the larly on the physical processes that modulate their formation. Because magma composition volcanic sequence represented by subaqueous magma accumulation in the upper crust, is an important control on eruptive style, we hyaloclastites and pillow basalts. transport magma to the surface, and control separate discussions of mafi c and intermediate/ From a hazards perspective, an important eruptive activity. silicic volcanism. discovery about Hawaiian volcanism has been the recognition that Kilauea volcano has expe- INTRODUCTION Mafi c Volcanoes rienced periods of highly explosive activity in addition to the effusive eruptions of the past Volcanic eruptions are a spectacular manifesta- Mafi c volcanoes vary greatly in scale and few centuries (Fiske et al., 2009). Episodes tion of a dynamic Earth. They not only link deep construction style. The iconic basaltic landform of explosive activity are particularly frequent Earth (the geosphere) to the hydrosphere, atmo- is a shield volcano, such as those that comprise during times immediately following summit sphere, and biosphere but also affect human popu- the Hawaiian Islands, United States (Fig. 1A). caldera formation (Swanson, 2008; Swanson lations: ~600 million people live close enough to Shield volcanoes are constructed primarily by et al., 2012). Summit calderas in mafi c shield an active volcano to be affected by eruptions, and successive lava fl ows and are commonly char- volcanoes form by rapid drainage of magma civilization itself could be threatened by the larg- acterized by relatively low slopes. Other mafi c from summit storage regions to fl ank vents (e.g., est explosive eruptions that have occurred in Earth volcano morphologies include the “inverted Gudmundsson, 1987). In Hawaii, this drainage history. The core questions of volcanology focus soup bowl” shape of Galapagos volcanoes; allows access of groundwater to the magmatic on how volcanoes work, that is, how magma steep-sided cones, like Pico volcano in the system, which may fuel the high explosivity ob- forms and moves to the surface, and how the spe- Azores and Kluchevskoi in Kamchatka; fi s- served in postcaldera periods. cifi c properties of the magma, and the lithosphere sure volcanoes in tectonic rifts such as Iceland, Stromboli volcano, Italy (Fig. 1B), is the through which it moves, control eruptive activity. where they may be associated with a central sub- type location for the Strombolian eruption style, Here, we review progress that has been made on sidence caldera; tuja volcanoes erupted under ice which is characterized by frequent (often sev- this core topic over the past quarter century. To or in shallow-marine environments; mid-ocean eral per hour) small explosions that have been provide a context, we start by reviewing volcanic ridges with morphologies that refl ect spreading attributed to the rise and bursting of large indi- landforms and associated styles of eruptive activ- rate; and fi elds of monogenetic volcanoes, each vidual gas bubbles (e.g., Vergniolle and Jaupart, ity. We then describe our current understanding of related to a single eruptive episode. These land- 1986). Stromboli thus represents an “open-sys- magma storage regions (magma chambers) and forms refl ect a range in eruptive styles, the most tem” volcano, that is, a volcano where gases can common of which are reviewed next (see also move freely through the system. In fact, Strom- †E-mail: [email protected] Francis et al., 1990). boli typically produces ~105 times more gas GSA Bulletin; May/June 2013; v. 125; no. 5/6; p. 664–690; doi: 10.1130/B30720.1; 18 fi gures. 664 For permission to copy, contact [email protected] © 2013 Geological Society of America How volcanoes work A B C D Figure 1. Photographs of mafi c volcanic landforms. (A) Mauna Loa shield volcano, United States; (B) Stromboli strato- volcano, Italy; (C) Paricutin cinder cone, Mexico; (D) Colli Albani mafi c caldera complex, Italy, viewed from Rome. than can be accounted for by the magma ejected face; whether this characteristic requires inter- generation of large mafi c ignimbrite deposits is beyond the vent (e.g., Harris and Ripepe, 2007). action with external water sources remains a curious from several perspectives, including the However, Stromboli can also produce lava fl ows matter of debate (e.g., White and Ross, 2011). mechanisms by which large volumes of mafi c and “paroxysmal” eruptions, as demonstrated in Improving our understanding of small mafi c (and very low viscosity) magma accumulate in 2002–2003 and 2007 (e.g., Ripepe et al., 2005; eruptions is important because cities such as the upper crust (rather than rise to the surface Calvari et al., 2008; Scandone et al., 2009). This Auckland, New Zealand, Bend, Oregon, and in small batches) and maintain sustained ex- variability in eruption style derives from the Mexico City, Mexico, are constructed within plosive activity (rather than losing volatiles and complex structure of the magma storage and active cinder cone fi elds. changing to effusive eruption styles). transport system, and the resulting alternation More important for hazards, and more puz- Another exciting advance in mafi c vol canism between near-surface and deep controls on erup- zling from the perspective of physical vol- over the past few decades has come from the tive activity. canol ogy, is the recent documentation of highly oceans. Studies of submarine volcanism in- Cinder cone fi elds characterize regions of ac- explosive eruptions from mafi c volcanic cen- creased with the advent of the RIDGE program tive extension and transtension (Fig. 1C). Here, ters. Widespread tephra deposits from mafi c of the 1980s and 1990s, which greatly enhanced ascent and eruption of small mafi c magma volcanoes were fi rst recognized from eruptions our understanding of processes occurring in mid- batches produce a spectrum of eruptive styles of Masaya, Nicaragua (Williams, 1983; Bice, ocean-ridge environments. Mid-ocean ridges are from fi ssure-fed Hawaiian lava fl ows to Strom- 1985). Interest in mafi c Plinian eruptions re- sites of frequent volcanic activity that is typically bolian bubble bursts to explosive gas-charged vived with documentation of a mafi c Plinian manifested as fi ssure-generated lava fl ow erup- violent Strombolian eruptions to passive lava eruption from Etna volcano in 122 B.C. (Coltelli tions of varying intensities (e.g., Rubin et al., effu sion. Hawaiian-style eruptions are domi- et al., 1998) and has led to numerous detailed 2012). These eruptions can be monitored where nated by lava fl ows, Strombolian-style eruptions fi elds studies of mafi c explosive volcanism (for ocean-based hydrophone networks are suffi - produce small scoria cones and/or lava fl ows, example, Cas and Giordano, 2006; Pérez and ciently dense to record T-phase seismicity asso- and violent Strombolian eruptions produce sub- Freundt, 2006; Costantini et al., 2010). Most ciated with magma migration to the surface (e.g., stantial tephra sheets.
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