Sedimentological and geochemical evidence for multistage failure of volcanic island landslides: A case study from Icod landslide on north Tenerife, Canary Islands

Abstract

[1] Volcanic island landslides can pose a significant geohazard through landslide-generated tsunamis. However, a lack of direct observations means that factors influencing tsunamigenic potential of landslides remain poorly constrained. The study of distal turbidites generated from past landslides can provide useful insights into key aspects of the landslide dynamics and emplacement process, such as total event volume and whether landslides occurred as single or multiple events. The northern flank of Tenerife has undergone multiple landslide events, the most recent being the Icod landslide dated at $165 ka. The Icod landslide generated a turbidite with a deposit volume of $210 km 3 , covering 355,000 km 2 of seafloor off northwest Africa. The Icod turbidite architecture displays a stacked sequence of seven normally graded sand and mud intervals (named subunits SBU1-7). Evidence from subunit bulk geochemistry, volume, basal grain size, volcanic glass composition and sand mineralogy, combined with petrophysical and geophysical data, suggests that the subunit facies represents multistage retrogressive failure of the Icod landslide. The basal subunits (SBU1-3) indicate that the first three stages of the landslide had a submarine component, whereas the upper subunits (SBU4-7) originated above sea level. The presence of thin, non-bioturbated, mud intervals between subunit sands suggests a likely time interval of at least several days between each stage of failure. These results have important implications for tsunamigenesis from such landslides, as multistage retrogressive failures, separated by several days and with both a submarine and subaerial component, will have markedly lower tsunamigenic potential than a single-block failure.

Key Future Directions For Research On Turbidity Currents and Their Deposits

“…However, not every major earthquake appears to produce a widespread sediment flow (Völker et al 2011;Sumner et al 2013b), and there is a need for more studies of the seafloor where it is known that a major earthquake occurred. Turbidites can record the emplacement dynamics of submarine landslides, and suggest that some volcanic island collapses occur in multiple stages over a prolonged period (Hunt et al 2011). There is a need for long-term, well-dated sequences of turbidites to analyze the recurrence times of such hazards.…”

“…There is currently vigorous debate over the extent to which turbidites can be used as a record of major earthquakes (e.g., Goldfinger 2011;Atwater et al 2014), and why some major earthquakes fail to produce extensive slope failure and widespread turbidites (Sumner et al 2013b;Völker et al 2012). Recent work on volcanic island landslides suggests that they can occur in multiple prolonged stages, as shown by associated turbidites with numerous subunits (Hunt et al 2011), thereby reducing tsunami magnitude.…”

Construction of volcanic records from marine sediment cores: A review and case study (Montserrat, West Indies)

“…As well as forming debris avalanche or debris flow deposits, such events can evolve into poorly-sorted, mud-rich debris flows, or turbidity currents via flow dilution (c.f. Mulder & Cochonat 1996;Ilstad et al, 2004;Bryn et al, 2005), and may appear in marine sediments as thick (up to several metres; Rothwell et al, 1992), coarsegrained and far-reaching turbidites (>1000 km; Rothwell et al, 1992;Piper et al, 1999;Fine et al, 2005), with significant basal erosion (Garcia 1996;Wynn and Masson 2003;Masson et al, 2006;Hunt et al, 2011). Although widespread, the distribution of these deposits is ultimately subject to topographic controls, in contrast to tephra fallout deposits.…”

“…In proximal subaqueous environments, volcaniclastic-grains may be a common sediment type. Such environments are often sedimentologically and tectonically active, and discrete volcaniclastic deposits may be produced through a host of processes other than tephra fallout, including mass-flow or turbidite deposits derived from pyroclastic density currents, subaerial or submarine volcanic landslides, floods or lahars, or the reworking of submarine slope sediment (Boygle, 1999;Schneider et al, 2001;Gudmundsdóttir et al, 2011;Hunt et al, 2011;Schindlbeck et al, 2013). Additionally, multiple discrete deposits may have similar chemical compositions, because they are derived from the same magmatic system, meaning that glass or mineral analyses are less useful for inter-core correlations although note that such problems may also be relevant, but under-appreciated, for the correlation of widespread distal deposits, cf.…”

“…In making such reconstructions, it is important that explosive eruption deposits are correctly identified, and can be discriminated from volcaniclastic sediments deposited via other mechanisms (e.g. Ruddiman and Glover, 1972;Schneider et al, 2001;Trofimovs et al, 2006;Manville et al, 2009;Hunt et al, 2011) If this can be achieved, and if these tephra deposits are preserved within an environment of continuous sediment accumulation, then subaqueous sediment cores can be used to produce explosive eruption records that are more complete, and which have better age-constraints, than those typically derived from subaerial deposits. Marine and lacustrine sediments can thus provide a medium by which to assess the periodicity of eruptions and potential hazards posed by volcanoes, across a range of temporal and spatial scales (McGuire et al, 1997;Pyle et al, 2006;Carel et al, 2011;Kutterolf et al, 2008Kutterolf et al, , 2013Watt et al, 2013;Van Daele et al, 2014).…”