Distal ash hurricane (pyroclastic density current) deposits from a ca. 2000 yr BP Plinian-style eruption of Mount Pelee, Martinique: Distribution, grain-size characteristics, and implications for future hazard

摘要

Plinian-style activity has not occurred on any volcano in the Lesser Antilles since European settlement; however, pumice-rich deposits from this eruptive style are found throughout the Lesser Antilles, and such eruptions were witnessed by pre-Columbian Native American populations. One of these eruptive events from Mount Pelee on Martinique, occurring between 1800 and 2200 yr B.P., produced pumice-and-ash flow deposits that followed the main drainage channels on the volcano, ash hurricane deposits that both mantle the volcano's flanks (slopes up to 25 degrees) and extended at least 20 km from the crater. We examined the latter in the context of modern developments in understanding transport and depositional mechanics of pyroclastic density currents. Based on grainsize analysis, they are subdivided into proximal and distal deposits. The distal deposits become progressively more depleted in fines and enriched in crystals with distance from the crater. We conclude these are deposits of dilute, or inertia-dominated pyroclastic overcurrents, which decoupled from their underflows as they surmounted the topographic barrier formed by the older Pitons du Carbet volcanic center. A combination of topography and ingestion of air and water vapor from tropical vegetation perhaps caused the considerable expansion and liftoff, and resulting extreme crystal enrichment. Their areal distribution suggests much of the northern half of Martinique must have been severely affected, and the zone of devastation extended at least to the northern outskirts of the capital Fort-de-France, although their final runout distance may have extended significantly further south. Major coignimbrite plumes dispersing ash and aerosols over thousands of kilometers would today pose hazards to aviation.