The 1 MA evolution of constructive and destructive processes at the island arc volcano of Montserrat

Abstract

Montserrat is a small island arc volcano in the Caribbean island arc. The island comprises three main volcanic centres: Silver Hills, active between 2.5-­1 Ma; Centre Hills, active between ~1 to 0.5 Ma; and the Soufrière Hills-­South Soufrière Hills volcanic complex, active from ~0.3 Ma. Here an extensive (> 1 Ma) and detailed stratigraphic record is compiled for Montserrat using both the subaerial and submarine (in the form of three International Ocean Drilling Program cores) records. This combined record gives valuable insight into the evolution of volcanic and mass-wasting processes at Montserrat, and may be useful for future hazard mitigation.
The stratigraphic record shows that eruptive styles, volcanic intensity and mass-­wasting processes have varied through time. Dome-­style eruptions have dominated the past 1 Ma of volcanic activity at Montserrat. At the older edifice of Centre Hills, regular large-­magnitude explosive eruptions (represented by >1m thick pumiceous sequences onshore) also occurred, but such explosive eruptions are rare at the younger Soufrière Hills-­South Soufrière Hills volcanic complex.
Periods of heightened volcanic activity occurred between 1.1-­0.9 Ma, 0.3 Ma, and 0.2-­0.1 Ma. Another period of increased volcanism may have also occurred at
~0.5±0.2 Ma. These coincide with periods of increased, mass-­wasting, identified at 1.1-­0.9 Ma, 0.6-­0.5 Ma, 0.3 Ma, and 0.2-­0.1 Ma and suggest that increased volcanic activity may facilitate mass-­wasting processes. This may be due to increased deposition of material on the island flanks, or increased seismic activity that can trigger collapses.
The ages of the largest landslide deposits (volumes >0.3 km3) observed offshore of Montserrat also coincide with periods of faster sea-­level rises. Analysing the global database, large landslides coincide with rapid sea-­level rise at other island arc volcanoes, but not at ocean islands. The reason for this difference in behavior is unclear, but maybe associated with differences in island composition and size, or tectonic regimes.

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