F in e p a r tic le s c a r r ie d u p w a r d in te

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Unformatted text preview: e s c a r r ie d u p w a r d , in te r m e d ia te s u s p e n d e d , la r g e p a r tic le s s e ttle L o s s o f g a s a n d fin e p a r tic le s b y e lu tr ia tio n Form the convective cloud so apparent over pyroclastic flows This eventually settles to form the “co-ignimbrite” fall This deposit. In p u m ic e flo w s , flu id iz a tio n r e s u lts in 1 5 - 3 0 % e x p a n s io n o f flo w . 13 Flow Expansion and Levees Active pyroclastic flows are “expanded” relative to are their deposits In other words, there is a large fraction of gas that ultimately escapes Also, coarse particles work to the margins and settle, producing levees. Flow Processes & Deposits “Ground Layer” Effective a surge deposit (the base surge) produced by gas thrusting ahead of main flow body Basal Layer Boundary layer expected from fluid dynamic theory large particles excluded Main body Reverse grading of pumice, which is less dense than matrix Normal grading of lithic fragments, which are more dense. 14...
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