The purpose of this PhD thesis is to give insights into the dynamics of highly explosive eruptions and on both tephra dispersal and sedimentation, based on the characterization of the erupted material. A systematic and detailed morphological characterization of tephra particles from different eruptions and the calculation of their terminal fall velocity is carried out in order to give new insights in understanding the influence of the morphology of volcanic particles on the settling process. The May 2008 Chaitén eruption has been taken as a case study. The eruption has been studied based on the data collected in the field on January 2009 in order to describe its stratigraphy and to determine the main eruptive parameters (i.e., volume, column height, mass eruption rate). On May 6th the eruption reached its climax producing a tephra layer composed mainly of lithic lapilli and blocks (> 2 mm) and a 19 km high subplinian column. Textural analysis have been carried out on pumice samples produced in this phase and a fractal analysis of the associated ash have also been conducted in order to study the influence of the vescicularity on particle morphology and to get information about the dynamic processes that characterized the eruption.