36 Volcanic activity in the Lesser Antilles island arc (West Indies) produces large quantities of ash, pumice, and rock that are delivered to the shallow and deep marine envi- ronments of the western Caribbean Sea and eastern Atlantic Ocean. On the island of Montserrat, in the northern part of the Lesser Antilles, Soufrière Hills volcano has erupted frequently since 1995 (Figure 1). About 1.1 km 3 of andesitic magma (Wadge et al., 2010) has erupted, and much of this material has been transported into the ocean as pyroclastic ﬂows—hot avalanches of rocks, ash, and gas that travel at speeds in excess of 160 km per hour (Wadge et al., in press). In addition, mud ﬂows (lahars) carrying volcanic debris wash into the ocean during periods of intense rain. High-resolution bathymetric mapping around Montserrat revealed the importance of volcanic collapses that generate large landslides, known as debris avalanches, as a critical mechanism for transporting large amounts of volcanic material into the marine environment (Deplus et al., 2001; Lebas et al., 2011). Debris avalanches can trig- ger signiﬁcant tsunamis, and contribute to the geological hazards associated with this dynamic boundary. e current volcanic episode includes an eruption on December 26, 1997, that devastated the southwest ﬂanks of Soufrière Hills volcano and razed two villages, sweeping the houses and their contents into the sea. E/V Nautilus investigated the eﬀects of both the recent inﬂux of volcanic material into the sea from the eruption and larger debris avalanche events that took place in the recent geologic past. Eﬀects from discharge of volcanic ﬂows into the sea were found to be localized and related to the ﬂows’ intensity/ concentration. A major dome collapse (the largest of any historical dome collapse worldwide) in July 2003 initiated a submarine pyroclastic ﬂow (Troﬁmovs et al., 2006). Observations of carbonate shelf blocks on the surface of these deposits indicate that the shelf was also destabilized by this event. In the area oﬀshore of St. Patrick’s village, which was destroyed by the 1997 eruption, few eﬀects could be seen in shallow water (100–200 m). Dense colonies of whip corals (Stichopathes sp.) occupy the marine slopes, indicat- ing that volcanic ﬂows had lile impact just oﬀshore of the village despite the devastating eﬀect on land (Figure 2a). It is likely that the energetic ﬂows were too dilute to form high-concentration ﬂows that continued downslope into the marine environment. In contrast, only a few hundred meters along the coast toward the capital city of Plymouth, the shallow seaﬂoor has been swept clean of most marine organisms. ey have been replaced by coarse deposits of volcanic ash and boulders (Figure 2b), and repeated lahar deposits over the last 18 years have formed a signiﬁcant shallow-water deltaic fan. ese observations may oﬀer insight into rates of recovery of marine ecosystems as deep as 1,000 m following extreme geological disturbances. Previous work identiﬁed at least ﬁve major debris avalanches around Montserrat, although the ages and sources are poorly constrained (Le Friant et al., 2004). ROV dives focused on sampling and observing individual blocks in the deposits to facilitate correlations with land- based sequences and estimation of the units’ ages. East of Impact of Volcanic Eruptions on the Seaﬂoor Around Montserrat, West Indies By Steven Carey, Katherine L.C. Bell, Stephen Sparks, Adam Stinton, Jesse Ausubel, Brennan T. Phillips, Nicole A. Raineault, Nam Siu, Christina Fandel, Omari Graham, Hannah Ramsingh, Ruth Blake, Steven Auscavitch, Amanda W.J. Demopoulos, and Katherine Rodrigue Figure 1. Map of the northern Lesser Antilles island arc showing the location of Montserrat island. Inset photo is an explosive eruption of Soufrière Hills volcano, located in the southern part of Montserrat. 36