New Observations on a Classic Eruption: Mount Pelée Martinique, May 8, 1902

Mount Pelée in Martinique W.I. is the type locality where pelean eruptions were first described during the catastrophic eruption of 1902 which destroyed the city of St-Pierre, killing ~28,000 people (Alfred Lacroix, 1904). The continuing expansion of a pre-existing quarry by the company Sablière de Fond-Canonville to the south of the Tombeau des Caraibes (but north of Rivière Claire), has exposed a new rock-face, which, during February of 2001, was more than 275 meters long. More than 35m of vertical stratigraphy was exposed, comprising deposits of the nuée ardentes from both the 1902 and 1929 eruptions. In total, ~15m of 1902 and ~20m of 1929 deposits were newly exposed (separated by a well-defined orange-brown paleosol). Extensive photographic work was done to record the exposed surface during February/March of 2001. The major units were recorded and correlated within vertical cross-sections from previous studies. The oldest unit exposed in the outcrop (U1) is a 2-meter thick black scoriaceous agglomerate altered to pink material in its upper part. This unit corresponds to the deposit from the destructive May 8, 1902 eruption. Compared with the 1929 dome material, U1 has, respectively, less SiO2 (57.5 vs. 62.1), less K2O (0.78 vs. 1.02) and more Fe2O3 (8.1 vs. 6.45) all in wt. %. Microscopic observations of the major rock types, the 1902 black scoria of May 8, and the grey andesite of 1929, provide evidence for magma mixing. Mixing textures are present in both the 1902 and 1929 deposits (two different types of volcanic glass were found coexisting in the same sample). Preliminary observations made on etched surfaces of plagioclase phenocrysts using the Nomarski Differential Interference Contrast technique show that the plagioclase crystals are intricately zoned (oscillatory, normal) and indicate a complex mixing history.