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International audience[1] The 1997 Boxing Day collapse, a remarkable feature of the ongoing eruption of Soufrière Hills on Montserrat, has prompted new interest in the study of volcano stability in the Lesser Antilles. Building on a few cases documented in the literature, we have now identified at least 47 flank collapse events on volcanoes of the Caribbean arc where this type of behavior is characteristic and repetitive. About 15 events occurred on active volcanoes within the last 12,000 years. In the northern part of the arc, flank collapses are repetitive, do not exceed 1 km 3 in volume, occur in all directions, and are promoted by intense hydrothermal alteration and well-developed fracturing of the summit part of the edifices. In contrast, infrequent but large sector collapses, with volumes up to tens of km 3 , are typical of the southern volcanoes. They are always directed to the west as a result of the high overall slopes of the islands toward the deep back-arc Grenada Basin. Because Caribbean islands are small, a large part of the resulting debris avalanches have flowed into the sea thus contributing voluminous and sudden inputs of volcaniclastic sediments to the Grenada Basin. Deposits from such submarine flows have been identified during the recent AGUADOMAR and CARAVAL oceanographic cruises and traced to their source structures on land. Edifice collapses have a major influence on subsequent volcanic activity but also are of high concern because of their tsunamigenic potential

Significance Based on ice core archives of sulfate and tephra deposition, one of the largest volcanic eruptions of the historic period and of the past 7,000 y occurred in A.D. 1257. However the source of this “mystery eruption” remained unknown. Drawing on a robust body of new evidence from radiocarbon dates, tephra geochemistry, stratigraphic data, a medieval chronicle, this study argues that the source of this eruption is Samalas volcano, part of the Mount Rinjani Volcanic Complex on Lombok Island, Indonesia. These results solve a conundrum that has puzzled glaciologists, volcanologists, and climatologists for more than three decades. In addition, the identification of this volcano gives rise to the existence of a forgotten Pompeii in the Far East.