Application of sequential fragmentation/transport theory to deposits of 1723 and 1963-65 eruptions of Irazú volcano, Costa Rica. Negative dispersion case

Abstract

Sequential fragmentation/transport theory (SFT) was used to analyze tephra deposits of the two main recent explosive eruptions from Irazú volcano, the 1723 and 1963-65 events. The final results provide a new way to analyze fragmentation and transport processes, which fix well with the field observations made by Alvarado (1993). A new way to process fragmentation/transport revealed 4 phi ranges that can be associated to initial volcanic fragmen- tation. The SFT fragmentation coefficient method is expanded to include all 5 subpopulations, allowing to compare the 1723 and 1963-65 events. SFT interpretation of 1723 eruptions is in good agreement with the volcanological des- cription of such explosive events, whereas SFT points to a more complex 1963-65 eruption, probably due to volcanic recycling and sedimentary reworking as it is observed in the field.