Transport and deposition of subaerial pyroclastic flows and surges

Abstract

In this chapter we examine more closely the transportational and depositional processes associated with pyroclastic flows and surges (Ch. 5). Both are a type of flow, one at the dilute, low particle concentration end of the spectrum and the other at the highly concentrated end. It is shown that there is a broad spectrum of pyroclastic flow types, and that the flow mechanics can vary, as do the resultant facies. The roles of fluidisation and turbulence are evaluated. The anatomy of pyroclastic flows is also examined, and consideration is given to the characteristic depositional processes associated with the head, body and trailing cloud. We similarly look in detail at the flow and depositional mechanics associated with surges, and consider the differences between wet and dry surges. Finally, we look at the possible relationships and differences between pyroclastic flows and surges.