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 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 dyke 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.
N. C. Mitchell,
Susceptibility of Mid-Ocean Ridge Volcanic Islands and Seamounts to Large-Scale Landsliding, J. Geophys. Res., 2003 (DOI: 10.1029/2002JB001997)..