The Sequential fragmentation/transport theory (SFT), applied to grain size analysis of the deposits from the 1723 and 1963-65 Irazú volcano eruptions, showed an appreciable number of cases with positive dispersion, usually associated to particle aggregation. A new fractal dimension is proposed here to explain them as a secondary fragmentation process. This leads to a new fractal model of volcanic eruptive process, where the Hurst Coefficient and the power law exponent are included. Dispersion values near zero suggest the existence of lava pools. Results deduced from the model agree well with field observations.

Fragmentacion/Transporte secuencial; Coeficiente de Hurst; exponente de ley de potencias; modelo fractal volcánico; volcán Irazú; Costa Rica