The past 5,000 years of volcanic activity at Mt. Pelee martinique (F.W.I.): Implications for assessment of volcanic hazards

Abstract

The history of Mt. Pelée, Martinique, was subdivided into three stages based on field geology and 14C data. The two first stages constructed an ancient Mt. Pelée and an intermediate cone between 0.4 m.y and 19,500 y.b.p. The third (or present) stage started 13,500 years ago, after a repose of 6,000 years. This paper focuses on the activity of Mt. Pelée during the past 5,000 years as a means to assess and zone volcanic hazards of the 23 magmatic eruptions during the past 5,000 years. The ages of 21 eruptions of this period are based on 75 new 14C dates. The types of phenomena and distribution of pyroclasts relate to four main types of activity: • — The first type consists of pumice-and-ash flows that are not preceded by a Plinian fall. Two eruptions (named P6 and P4) illustrate this type, for which the mixture of gas, ash, and pumice simply overflow the vent and flood several valleys. • — The second type differs from the first by the occurrence of a preliminary moderate Plinian-fall stage. Four eruptions (P5, P31, P2 and P1) illustrate this type. Two eruptions (P3 2 and P3 3) experienced cataclysmic Plinian explosions and pumiceous surges. • — The third type is related to dome growth with the rise of viscous spines and the production of related block-and-ash flows. Five eruptions (1929, Sept. 1902–1904, NPM, NAB 2 and NMP) illustrate this type. • — The fourth type is characterized by violent ejection of more-or-less heterogeneous nuées ardentes. The direction of the blast, dictated by the morphology of the crater, has been towards the south several times at Mt. Pelee. Four eruptions (May 1902, NAB1, NRP2 and NRP3) belong to this type. Future magmatic eruptions at Mt. Pelée will very likely belong to one of these four types. Assessment of hazards at Mt. Pelée is based upon the behavior of the volcano during the past 5,000 years because: (1) recognition of past magmatic eruptions is quite complete and well-dated, and (2) no structural change has occurred in the volcano. A probabilistic and statistical approach has been tentatively followed. Stochastic models of Wickman indicate: (a) the chance that contemporary abnormal seismic and/or phreatic activity at the volcano would signal an impending magmatic eruption is 20 percent, (b) Mt. Pelée exhibits a complex loading-time behavior that may be related to the buffering effect of a magma chamber (time is needed following a single or several closely spaced eruptions to establish conditions to initiate a new eruption), and (c) if the 1929 event can be regarded as the last episode of the major 1902 eruption, the volcano could remain in a dormant stage with respect to magmatic events for another century.