Page 111 - Volcanic Textures A Guide To The Interpretation of Textures In Volcanic Rocks

Fig. 39 Progressive aggradation of a pyroclastic deposit at the base of a stratified, steady pyroclastic flow. The
graph shows a snapshot of the vertical gradients in particle concentration and turbulence above the aggradation
surface. Based on Branney and Kokelaar (1992) and Druitt (1992).

Fig. 40 Schematic graphic logs of three types of primary pyroclastic flow deposits. (A) Block and ash flow deposit,
overlain by co-genetic ash cloud surge and fine grained fallout deposits. Based on Fisher and Heiken (1982). (B)
Scoria and ash flow deposit. Based on Nairn and Self (1978). (C) Pumiceous pyroclastic flow deposit, or
ignimbrite, underlain by co-genetic ground surge deposits and a thin ground layer, and overlain by a co-
ignimbrite fine ash fallout deposit. Based on Sparks et al. (1973). The scale bars in (A) and (B) are about 1 m,
and in (C) 1 to 10 m.

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