Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODPExpedition 340

Abstract

IODP Expedition 340 successfully drilled a series of sites offshore Montserrat, Martinique and Dominica in the Lesser Antilles from March to April 2012. These are among the few drill sites gathered around volcanic islands, and the first scientific drilling of large and likely tsunamigenic volcanic island-arc landslide deposits. These cores provide evidence and tests of previous hypotheses for the composition and origin of those deposits. Sites U1394, U1399, and U1400 that penetrated landslide deposits recovered exclusively seafloor sediment, comprising mainly turbidites and hemipelagic deposits, and lacked debris avalanche deposits. This supports the concepts that i/ volcanic debris avalanches tend to stop at the slope break, and ii/ widespread and voluminous failures of preexisting low-gradient seafloor sediment can be triggered by initial emplacement of material from the volcano. Offshore Martinique (U1399 and 1400), the landslide deposits comprised blocks of parallel strata that were tilted or microfaulted, sometimes separated by intervals of homogenized sediment (intense shearing), while Site U1394 offshore Montserrat penetrated a flat-lying block of intact strata. The most likely mechanism for generating these large-scale seafloor sediment failures appears to be propagation of a decollement from proximal areas loaded and incised by a volcanic debris avalanche. These results have implications for the magnitude of tsunami generation. Under some conditions, volcanic island landslide deposits composed of mainly seafloor sediment will tend to form 420Geochemistry, Geophysics, Geosystems PUBLICATIONS smaller magnitude tsunamis than equivalent volumes of subaerial block-rich mass flows rapidly entering water. Expedition 340 also successfully drilled sites to access the undisturbed record of eruption fallout layers intercalated with marine sediment which provide an outstanding high-resolution data set to analyze eruption and landslides cycles, improve understanding of magmatic evolution as well as offshore sedimentation processes.

Permeability and pressure measurements in Lesser Antilles submarine slides: Evidence for pressure‐driven slow‐slip failure

“…Le Friant et al . [] make similar arguments, and note that the relatively intact, small‐offset nature of marine deposits found in submarine slides offshore Montserrat indicates possible slow‐slip deformation. If the pressure‐driven slow‐slip hypothesis is correct, one might anticipate finding elevated fluid pressures in deep marine sediment in submarine slides that facilitate progressive downslope failure.…”

Construction and destruction of Mont Pelée volcano: Volumes and rates constrained from a geomorphological model of evolution

“…In contrast to eruptive volumes that are estimated for individual eruptions, our construction volumes are calculated for long time intervals and reflect the ability for volcanic activity to construct relief. Also, our construction rates integrate only proximally erupted material because tephra tends to be dispersed into the atmosphere over long distances and some pyroclastic material is deposited directly into the ocean [ Le Friant et al , , ]. Furthermore, erupted volumes are often expressed as dense rock equivalent (DRE) to take into account the compaction of the material and can vary by 2 orders of magnitude when considering pyroclastic material.…”

“…Because of these failures, the volcano's volume is calculated incorrectly if one considers only the present topography. Accordingly, the offshore record, which preserves a number of units missing on land [ Boudon et al , ; Le Friant et al , ], must be taken into account. A total of 54 eruptions have been identified for the last 9 ka (Global Volcanism Program), but the volumes of only 24 eruptions totaling approximately 3.35 km 3 have been estimated (Large Magnitude Explosive Volcanic Eruptions database of the Volcano Global Risk Identification and Analysis Project).…”

Rapid onset of mafic magmatism facilitated by volcanic edifice collapse

“…IODP Expedition 340 collected sediment cores to depths of up to 200 m from four sites around Montserrat [ Le Friant et al ., ]. The samples studied here come from Sites U1394 and U1395, SE of Montserrat (Figure ).…”