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The Geological History of Deep-Sea Volcanoes

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The Geological History of Deep-Sea Volcanoes or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The approval portionthe ofwith any articlepermitted only photocopy by is of machine, reposting, this means or collective or other redistirbution This article has This been published in MOUNTAINS IN THE SEA BY HUBERT STAUDIGEL And DAVID A. CLAGUE Oceanography THE GEOLOGICAL HISTORY journal of The 23, Number 1, a quarterly , Volume OF DEEP-SEA VOLCANOES BIOSPHERE, O HYDROSPHERE, ceanography S And LITHOSPHERE ociety. © INTERACTIONS The 2010 by O ceanography ceanography O ceanography ceanography S ociety. ociety. A ll rights reserved. S ociety. ociety. S end all correspondence to: [email protected] or Th e [email protected] to: correspondence all end P ermission is granted to copy this article for use in teaching and research. article for use research. and this copy in teaching to granted is ermission O ceanography ceanography S ociety, ociety, PO Box 1931, R epublication, systemmatic reproduction, reproduction, systemmatic epublication, R Emergence of a submarine volcano near Nukualofa, Tonga, March 18, 2009. The eruption ockville, MD 20849-1931, column displays two very characteristic features for shallow-submarine eruptions, base surges (light colored) that spread out horizontally at the base and “cocks’ tail” tephra jets that emerge from the center of the column. Photo credit: Dana Stephenson/Getty Images USA . 58 Oceanography Vol.23, No.1 AbSTRACT. The geological evolution of seamounts has distinct influence on their to science and society. They have rich interactions with the ocean, their hydrology, geochemical fluxes, biology, resources, fisheries (Pitcher et al., 2010), are marine- and geohazards. There are six geological evolutionary stages of seamounts: (1) small biological and microbiological hotspots seamounts (100–1000-m height), (2) mid-sized seamounts (>1000-m height, > 700-m (Danovaro et al., 2009; Emerson and eruption depth), (3) explosive seamounts (< 700-m eruption depth), (4) ocean islands, Moyer, 2010), and have a significant (5) extinct seamounts, and (6) subducting seamounts. Throughout their lifetimes, geochemical impact, with chemical fluxes seamounts offer major passageways for fluid circulation that promotes geochemical that allow mantle-derived materials to exchange between seawater and the volcanic oceanic crust, and seamounts likely interact with the hydrosphere (Fisher host significant microbial communities. Water circulation may be promoted by and Wheat, 2010). Hence, seamounts hydrothermal siphons in conjunction with the underlying oceanic crust, or it may are key points of intersection among the be driven by intrusions inside seamounts from Stage 2 onward. Geochemical fluxes biosphere, hydrosphere, and lithosphere, are likely to be very large, primarily because of the very large number of Stage 1 and they are globally relevant. seamounts. Intrusive growth of seamounts also initiates internal deformation that In this paper, we explore how ultimately may trigger volcano sector collapse that likely peaks at the end of the main seamounts grow, collapse, and age, volcanic activity at large seamounts or islands. Explosive activity at seamounts may and how these processes interact with begin at abyssal depth, but it is most pronounced at eruption depths shallower than the hydrosphere and impact biological 700 m. Wave erosion inhibits the emergence of islands and shortens their lifespans processes. The reader is referred to earlier before they subside due to lithosphere cooling. Once volcanism ends and a seamount reviews by Batiza and White (2000), is submerged, seamounts are largely unaffected by collapse or erosion. Throughout Schmidt and Schmincke (2000), and a their histories, seamounts offer habitats for diverse micro- and macrobiological recent monograph (Pitcher et al., 2007). communities, culminating with the formation of coral reefs in tropical latitudes. Geological hazards associated with seamounts are responsible for some of the largest DEFINIng A SEAMOUNT natural disasters recorded in history and include major explosive eruptions and large- There is no uniform definition for the scale landslides that may trigger tsunamis. term seamount that equally satisfies all scientific disciplines. Definitions reflect InTRODUCTION in height and does not offer any topo- diverse interpretative perspectives and Seamounts are the least explored major graphic detail below this scale. This state disciplinary approaches that can be quite morphological features on Earth. of exploration reveals nothing about specific to the needs of a particular scien- Hundreds of thousands of them are a seamount’s geology. In fact, this lack tific community (see Box 1 on page 20 dispersed through the ocean basins, with of detail would be considered entirely of this issue [Staudigel et al., 2010a]). less than 0.1% known from any direct unacceptable for topographic features We use here a definition that centers observation such as an echosounding, on land, effectively all of which are on seamounts as isolated geological or any kind of sampling. Most of what now sampled and mapped by direct features on the seafloor. Seamounts are we know about seamounts comes from measurements with a resolution better typically volcanoes that form on top of satellite observations that sense them than 30 m in vertical and 100 m in the oceanic crust with their own central indirectly from the centimeter-size horizontal dimensions. Seamounts are magma supply and hydrothermal system. deflections they impose on sea surface the last major frontier in our exploration This simple distinction can become more topography (e.g., Wessel et al., 2010). of Earth’s surface. complex when isolated volcanoes form This indirect method reliably identi- The minimal level of seamount explo- right on the mid-ocean ridge axis, such fies only features larger than 1500 m ration contrasts with their significance as Axial Seamount on the Juan de Fuca Oceanography March 2010 59 Ridge (see Spotlight 1 on page 38 of this easily from the processes involved in oceanic intraplate volcanoes (OIVs) issue [Chadwick et al., 2010a]). seamount formation (see Koppers and are formed by decompression melting Isolated volcanoes on the seafloor Watts, 2010). It may bulge upward of mantle materials that buoyantly rise come in a range of sizes whereby the from the buoyancy of rising mantle or in upward convective flow and/or in smallest ones are typically referred to due to heating of the lithosphere from response to plate extension and thin- as abyssal hills and the larger ones as below. However, as soon as a seamount ning. Subduction zone volcano magmas seamounts. We use 100 m as the tallest has reached a critical size, subsidence are commonly formed by the lowering abyssal hill and smallest seamount, becomes the dominant vertical force, of the melting point of the sub-arc following a definition of Schmidt and caused by the bending of the oceanic mantle due to addition of volatiles from Schmincke (2000). By this definition, crust into the mantle as it yields to the descending slab. These different seamounts may form in any tectonic the seamount load (Watts, 2001). For melting processes have a profound setting; they may have conical, flat- example, data from drowning coral impact on the chemistry of seamount topped, or complex shapes; and they terraces on Hawai`i suggest a subsid- rocks and the chemical evolution of may or may not have carbonate or ence rate of 2.6 mm yr-1 for the Island the volcanoes formed. sedimented caps. We also include of Hawai`i (Moore and Fornari, 1984; Seamounts close to MORs and in OIV oceanic islands in our definition of a Moore et al., 1996). However, on a much settings erupt mostly basaltic (tholeiitic seamount, considering them as very longer time scale extending millions of and alkalic) magmas, whereas subduc- large seamounts that breached the sea years, seamounts also subside owing to tion zone volcanics are predominantly surface. Viewing islands as a subgroup the cooling of the lithosphere they are composed of calc-alkaline (andesitic or of seamounts is unusual because most built upon. Most seamounts are formed arc-theoleiitic) magmas. All seamount views focus on the distinct nature within a few hundred kilometers of rocks are formed by mantle melting of islands in terms of their volcanic mid-ocean ridges at roughly 2.5-km processes that involve smaller degrees features, subaerial weathering, and water depth. These seamounts will of melting than are characteristic for land-based biology (see Gillepsie and subside with the underlying cooling the generation of the oceanic crust Clague, 2009). However, our grouping lithosphere to about 5-km water depth itself. As a result, their incompatible makes sense from a geological point of within 60 million years and possibly element abundances may be an order of view in which volcanic islands are the down to 10-km depth when they arrive magnitude higher, and seamount fluxes summit regions of very large seamounts at subduction zones. This journey from of these elements may dominate global that are temporarily exposed above sea mid-ocean ridge to subduction zone may mantle fluxes even though seamounts are level. Most oceanic islands start out as involve thousands of kilometers of hori- substantially less voluminous than the seamounts and turn back into seamounts zontal displacement. For example, the elongated volcanoes forming the MORs toward the ends of their life cycles. majority of
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