Statistical sedimentary aspects of collapsed volcanic edifices along subduction zones.

Using Google Earth imagery and published data on volcanoes worldwide, several examples of volcanic debris avalanche deposits have been compared to characterize the dynamics of mass flow and matrix transformation during climate change. Sedimentological studies of these deposits help to correlate the spatial and temporal distribution of collapsed edifices with the stratigraphy and textural variations of the matrix. Parameters such as percentage of matrix, mean grain size, ratio of matrix sand to gravel and other statistical sedimentary parameters have been calculated to characterize the matrix breccias in relation to the spatio-temporal variability of the mass flow deposits. Factors such as quaternary erosion, nival surface conditions and high intensity rainfall contribute to the transformation of the reworked avalanche deposits into debris flows. The sedimentary characteristics of volcanic debris avalanche deposits are influenced by the profile shape, volcanic area and slope gradient of the collapsed edifices, which are related to the critical stability and quaternary cyclic evolution of the stratovolcanoes. Empirical equations have been developed to propose a co-genetic evolution of avalanche deposits in terms of their spatio-temporal distribution, morphological variations of the collapsed edifices, and climatic changes. Similar correlations between quaternary occurrence, matrix percentage, matrix/gravel ratio, and median grain size show a positive association with the obliquity of the Earth's axis and the precession of the equinoxes. These results highlight the importance of semi-quantitative sedimentological analyses of deposits from collapsed volcanic edifices in refining our understanding of subsequent hazardous flows associated with climate change.