Prehistoric Stratigraphy of the Soufrière Hills–South Soufrière Hills Volcanic Complex, Montserrat, West Indies

Bioclastic flow deposits offshore from the Soufrière Hills volcano on Montserrat in the Lesser Antilles were deposited by the largest volume sediment flows near this active volcano in the last 26 kyr. The volume of these deposits exceeds that of the largest historic volcanic dome collapse in the world, which occurred on Montserrat in 2003. These flows were most probably generated by a large submarine slope failure of the carbonate shelf comprising the south‐west flank of Antigua or the east flank of Redonda; adjacent islands that are not volcanically active. The bioclastic flow deposits are relatively coarse‐grained and either ungraded or poorly graded, and were deposited by non‐cohesive debris flow and high density turbidity currents. The bioclastic deposit often comprises multiple sub‐units that cannot be correlated between core sites; some located just 2 km apart. Multiple sub‐units in the bioclastic deposit result from either flow reflection, stacking of multiple debris flow lobes, and/or multi‐stage collapse of the initial landslide. This study provides unusually precise constraints on the age of this mass flow event that occurred at ca 14 ka. Few large submarine landslides have been well dated, but the slope failures that have been dated are commonly associated with periods of rapid sea‐level change.

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“…Similarly, studies of the stratigraphy on land (Harford et al. , 2002; Smith et al. , 2007; Le Friant et al.…”

Section: Discussionmentioning

confidence: 99%

Evidence for carbonate platform failure during rapid sea-level rise; ca 14 000 year old bioclastic flow deposits in the Lesser Antilles

Trofimovs¹,

Fisher

MacDonald³

et al. 2009

Sedimentology

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“… Comparison of dated subaerial sequences of Soufrière Hills and South Soufrière Hills [ Harford et al ., ; Smith et al ., ], tephrochronology from the south east offshore of Montserrat [ Trofimovs et al ., ] and from the south west offshore of Montserrat [ Le Friant et al ., ; Cassidy et al ., , also Cassidy et al, submitted manuscript, 2014], including the tephrochronology from this study. Average global sea level curve from Lea et al .…”

Section: Discussionmentioning

confidence: 99%

“…Arguably, the most complete offshore data set now comes from the island of Montserrat in the Lesser Antilles. This offshore data set complements unusually detailed subaerial observations of the 1995‐recent eruption of the Soufrière Hills volcano [ Druitt and Kokelaar , ; Wadge et al ., ], subsurface magmatic system [e.g., Paulatto et al ., ], and older eruption record [ Harford et al ., ; Smith et al ., ], thereby providing a benchmark data set for the evolution of a volcanic island.…”

Section: Introductionmentioning

confidence: 99%

Late Pleistocene stratigraphy of IODP Site U1396 and compiled chronology offshore of south and south west Montserrat, Lesser Antilles

Wall-Palmer

Coussens

Talling

et al. 2014

Geochem Geophys Geosyst

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Marine sediments around volcanic islands contain an archive of volcaniclastic deposits, which can be used to reconstruct the volcanic history of an area. Such records hold many advantages over often incomplete terrestrial data sets. This includes the potential for precise and continuous dating of intervening sediment packages, which allow a correlatable and temporally constrained stratigraphic framework to be constructed across multiple marine sediment cores. Here we discuss a marine record of eruptive and masswasting events spanning 250 ka offshore of Montserrat, using new data from IODP Expedition 340, as well as previously collected cores. By using a combination of high-resolution oxygen isotope stratigraphy, AMS radiocarbon dating, biostratigraphy of foraminifera and calcareous nannofossils, and clast componentry, we identify five major events at Soufriere Hills volcano since 250 ka. Lateral correlations of these events across sediment cores collected offshore of the south and south west of Montserrat have improved our understanding of the timing, extent and associations between events in this area. Correlations reveal that powerful and potentially erosive density-currents traveled at least 33 km offshore and demonstrate that marine deposits, produced by eruption-fed and mass-wasting events on volcanic islands, are heterogeneous in their spatial distribution. Thus, multiple drilling/coring sites are needed to reconstruct the full chronostratigraphy of volcanic islands. This multidisciplinary study will be vital to interpreting the chaotic records of 3000Geochemistry, Geophysics, Geosystems PUBLICATIONS submarine landslides at other sites drilled during Expedition 340 and provides a framework that can be applied to the stratigraphic analysis of sediments surrounding other volcanic islands.

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“…1). Montserrat is an ideal region for this type of study, because the surrounding seafloor has been extensively surveyed (Le Friant et al, 2004, 2009Lebas et al, 2011;Watt et al, 2012a,b) and cored (Trofimovs et al, 2006(Trofimovs et al, , 2008(Trofimovs et al, , 2013Le Friant et al, 2008, 2009Cassidy et al, 2013Cassidy et al, , 2014, and the subaerial record of volcanism and igneous geochemistry is particularly wellconstrained (Rea, 1974;Roobol and Smith, 1998;Harford et al, 2002;Zellmer et al, 2003;Smith et al, 2007;Cassidy et al, 2012). This earlier work has shown that marine volcaniclastic sedimentation around Montserrat encompasses a rich array of processes, and that the identification of tephra fall deposits within the stratigraphy is not a trivial task.…”

Section: Page |mentioning

confidence: 99%

“…Most recently, this activity has originated from the currently active Soufrière Hills (282 ka -present), Page | 16 with an interlude of volcanism at South Soufrière Hills (SSH) (128 -131 ka) (Harford et al, 2002). The subaerial record of volcanism at these two centres suggests eight active episodes, dating from 174 ka (Rea, 1974;Roobol and Smith, 1997;Harford et al, 2002;Smith et al, 2007;Cassidy et al, 2013). Studies of the history of Montserrat volcanism using submarine deposits have only been undertaken recently (Le Friant et al, 2008;Trofimovs et al, 2010Trofimovs et al, , 2013Cassidy et al, 2013Cassidy et al, , 2014.…”

Section: Montserrat: the Natural Laboratorymentioning

confidence: 99%

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

Cassidy

Watt

Palmer

et al. 2014

Earth-Science Reviews

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Detailed knowledge of the past history of an active volcano is crucial for the prediction of the timing, frequency and style of future eruptions, and for the identification of potentially at-risk areas. Subaerial volcanic stratigraphies are often incomplete, due to a lack of exposure, or burial and erosion from subsequent eruptions. However, many volcanic eruptions produce widelydispersed explosive products that are frequently deposited as tephra layers in the sea. Cores of marine sediment therefore have the potential to provide more complete volcanic stratigraphies, at least for explosive eruptions. Nevertheless, problems such as bioturbation and dispersal by currents affect the preservation and subsequent detection of marine tephra deposits.Consequently, cryptotephras, in which tephra grains are not sufficiently concentrated to form layers that are visible to the naked eye, may be the only record of many explosive eruptions.Additionally, thin, reworked deposits of volcanic clasts transported by floods and landslides, or during pyroclastic density currents may be incorrectly interpreted as tephra fallout layers, leading to the construction of inaccurate records of volcanism. This work uses samples from the volcanic island of Montserrat as a case study to test different techniques for generating volcanic eruption records from marine sediment cores, with a particular relevance to cores sampled in relatively proximal settings (i.e. tens of kilometres from the volcanic source) where volcaniclastic material may form a pervasive component of the sedimentary sequence. Visible volcaniclastic deposits identified by sedimentological logging were used to test the effectiveness of potential alternative volcaniclastic-deposit detection techniques, including point counting of grain types (component analysis), glass or mineral chemistry, colour spectrophotometry, grain size measurements, XRF core scanning, magnetic susceptibility and X-radiography. This study demonstrates that a set of time-efficient, non-destructive and high-spatial-resolution analyses (e.g. XRF core-scanning and magnetic susceptibility) can be used effectively to detect potential cryptotephra horizons in marine sediment cores. Once these horizons have been sampled, microscope image analysis of volcaniclastic grains can be used successfully to discriminate between tephra fallout deposits and other volcaniclastic deposits, by using specific criteria Page | 3 related to clast morphology and sorting. Standard practice should be employed when analysing marine sediment cores to accurately identify both visible tephra and cryptotephra deposits, and to distinguish fallout deposits from other volcaniclastic deposits.

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Prehistoric Stratigraphy of the Soufrière Hills–South Soufrière Hills Volcanic Complex, Montserrat, West Indies

Cited by 24 publications

References 15 publications

Evidence for carbonate platform failure during rapid sea-level rise; ca 14 000 year old bioclastic flow deposits in the Lesser Antilles

Evidence for carbonate platform failure during rapid sea-level rise; ca 14 000 year old bioclastic flow deposits in the Lesser Antilles

Late Pleistocene stratigraphy of IODP Site U1396 and compiled chronology offshore of south and south west Montserrat, Lesser Antilles

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

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