Page 92 - Caldera Volcanism Analysis, Modelling and Response

Pyroclastic Density Currents 67

Figure 4 Example of deposit (a) and mechanisms of particle support and segregation (b) for
a £ow-boundary zone dominated by £uid escape regime.

development of an effective fluid-escape regime. Deposits of PDCs dominated
by fluid-escape regimes are fines-rich and usually show poor or absent grading
of large, heavy clasts. Upward increases in concentration of large pumice
and/or lighter clasts can occur due to floating processes related to density contrasts