Page 131 - Volcanic Textures A Guide To The Interpretation of Textures In Volcanic Rocks

Fig. 59 Sedimentary environments and volcanogenic sedimentary facies associations near active volcanoes. The top
frame gives the positions of the schematic sections A-D below. (A) Continental (fluvial and alluvial fan). (B)
Shoreline. (C) Subaqueous shelf. (D) "Deep" subaqueous (lake or ocean), p - pyroclastic deposit; fl - flow; fa -
fallout; wfa - water-settled fallout; rs - resedimented syn-eruptive deposit: t - traction; m - mass-flow. The grain
size subdivisions in (B), (C) and (D) are the same as those shown in (A).

of pumice and scoria have much lower densities than vents for eruptions, although the relationship is not
other non-vesicular clasts of the same size. Facies necessarily simple and direct.
architecture is affected because facies geometry is
complex, and lateral and vertical facies changes are It is important to appreciate that current facies models
abrupt and difficult to predict. Erosion surfaces may be for sedimentary deposits incorporate assumptions
carved by primary pyroclastic flows or surges, or by regarding the type of sediment and supply rate. The
volcanic events, such as steam blasts, that leave no other effects of volcanic events on volcanogenic sedimentary
traces. Facies changes relate ultimately to the source facies have been exploded in the case of an active

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