Susceptibility of mid‐ocean ridge volcanic islands and seamounts to large‐scale landsliding

Abstract

[1] With a view to assessing the incidence of large-scale landsliding, a morphologic database was created for volcanic islands and seamounts on young oceanic lithosphere. The database included 44 mid-ocean ridge seamounts, Jasper seamount and the islands of Ascension, Bouvet, Guadalupe, and several of the Galapagos and Azores Islands, supplemented with published reports from a further five volcanic edifices. The data reveal that major landslides are common on edifices taller than 2500 m but are rare in shorter edifices, implying a threshold of instability at around 2500 m. A number of causes of this threshold are discussed. For example, many structures taller than 2500 m are, or were originally, volcanic islands, and therefore their flanks probably include extensive weak hyaloclastite built up from lava-sea interactions around coasts. Compaction of hyaloclastites in larger edifices lead to regions of low permeability, which may help to explain the more deeply seated slope failures. It is intriguing that the threshold also coincides with the edifice height at which volcanic ridges become observable, a stage at which dike intrusion is probably common because slope oversteepening or excess pore pressure associated with dike intrusions have been proposed elsewhere as landslide triggers. The current indications of landsliding reveal no observable relation to rainfall, as landslides occur equally in wet and dry climates, and no relation to tectonic setting, as there are relatively few major landslides in the seismically active Azores group.INDEX TERMS: 3035 Marine Geology and Geophysics: Midocean ridge processes; 3022 Marine Geology and Geophysics: Marine sediments-processes and transport; 8499 Volcanology: General or miscellaneous; KEYWORDS: landslides, volcanic debris avalanche, slope stability, multibeam sonar, side-scan sonar Citation: Mitchell, N. C., Susceptibility of mid-ocean ridge volcanic islands and seamounts to large-scale landsliding,

Coastal evolution on volcanic oceanic islands: A complex interplay between volcanism, erosion, sedimentation, sea-level change and biogenic production

“…Modern examples include those on Madeira Island (Brum da , El Hierro in the Canaries (Masson, 1996), Guadalupe off Mexico, and Isabela in the Galápagos (Mitchell, 2003). However, failure may not always generate embayments; the westerly flank of La Palma shows more of a convex-seawards coastline and a debris cone on the submarine slope of the island (Urgeles et al, 1999) and the slump system of Kīlauea (Hilina) has been continually overlain by new lavas (e.g.…”

“…An aseismic movement of the Hilinia Slump system has been recorded with continuous GPS measurements and linked with a major rainfall event (Cervelli et al, 2002) so pore pressures are clearly important. Also suggesting links with pore pressure, Quidelleur et al (2008) put forward evidence for incidences of landslides occurring during glacial-induced eustatic sea-level change and Mitchell (2001Mitchell ( , 2003 outlined a transition in the morphology of edifices at > 2000 m height that may have a pore-pressure origin amongst other possibilites. Concerning links to intrusions, Clague and Denlinger (1994) suggested that the high density and weak rheology of hot olivine cumulates may contribute to the movement of the Hilina slump.…”

“…Large volume, catastrophic lateral flank collapses may remove huge volumes from island edifices, dramatically changing coastal outlines and reseting marine erosion (Mitchell, 2003). Small, either gradual or catastrophic, mass movements are simultaneously one of the most effective mechanisms of cliff erosion and an important source of coarse sediment (Griggs and Trenhaile, 1994;Bird, 2008;Trenhaile, 2011).…”

“…Gravitational mass wasting at different scales contributes significantly to coastal regression (Holcomb and Searle, 1991;Mitchell, 2003). Large volume, catastrophic lateral flank collapses may remove huge volumes from island edifices, dramatically changing coastal outlines and reseting marine erosion (Mitchell, 2003).…”

A review of marine geomorphometry, the quantitative study of the seafloor

“…McArthur et al, 2010;Brown et al, 2011;Harris and Baker, 2012;Rengstorf et al, 2012;Lecours et al, 2015b) already summarized the extent to which many of these techniques have been employed in habitat mapping studies, and many of these techniques have yet to be employed in other contexts. (2003) Mitchell (2003) Mitchell (2004) Mitchell (2005) been useful in determining the key processes constructing and modifying volcano flanks and specifying the conditions that lead to slope instability (Mitchell, 2003;Mitchell et al, 2002;Stretch et al, 2006). Initially, the techniques of general geomorphometry used in the study of submarine landscapes were less numerous and varied than those used in the study of subaerial landscapes.…”