SIMPLE STOCHASTIC MODELING OF THE ERUPTION HISTORY OF A BASALTIC VOLCANO - NYAMURAGIRA, ZAIRE

Three simple models of the behavior of a series of basaltic eruptions have been tested against the eruptive history of Nyamuragira. The data set contains the repose periods and the volumes of lava emitted in 22 eruptions since 1901. Model 1 is fully stochastic and eruptions of an y volume with random repose intervals are possible. Models 2 and 3 are constrained by deterministic limits on the maximum capacity of the ma gma reservoir and on the lowest drainage level of the reservoir respec tively. The method of testing these models involves (1) seeking change points in the time series to determine regimes of uniform magma suppl y rate, and (2) applying linear regression to these regimes, which for models 2 and 3 are the deterministic limits to those models. Two chan ge points in the time series for Nyamuragira, in 1958 and 1980, were d etermined using a Kolmogorov-Smirnov technique. The latter change invo lved an increase in the magma supply rate by a factor of 2.5, from 0.5 5 to 1.37 m3s-1. Model 2 provides the best fit to the behavior of Nyam uragira with the ratio of variation explained by the model to total va riation, R2, being greater than 0.9 for all three regimes. This fit ca n be interpreted to mean that there is a deterministic limit to the el astic strength of the magma reservoir 4-8 km below the summit of the v olcano.