Page 94 - Caldera Volcanism Analysis, Modelling and Response
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Pyroclastic Density Currents 69
Figure 5 Example of deposits (a) and mechanisms of particle support and segregation (b) for
a £ow-boundary zone dominated by granular £ow regime.
Currents dominated by granular temperatures are also called non-cohesive
debris flows (Postma, 1986). They can be classified as: (i) true grainflows, in which
the interstitial fluid has a negligible effect on the physical state of the granular mass;
and (ii) modified grainflows (Lowe, 1982), in which the physical characteristics
of the moving granular mass are modified by the intergranular fluid (Iverson
and Vallance, 2001). The wide spectrum of PDCs contains both end-members,
