Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/7891
AuthorsCagnoli, B.* 
Manga, M.* 
TitleVertical segregation in granular mass flows: A shear cell study
Issue Date2005
Series/Report no./32 (2005)
DOI10.1029/2005GL023165
URIhttp://hdl.handle.net/2122/7891
Keywordspyroclastic flows
vertical segregation
Subject Classification04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism 
AbstractNon-fluidised, dry granular mass flows are obtained with rock fragments located on a rough rotating disk. In these flows that develop a quasi-rigid upper layer and a basal layer of colliding particles, dense clasts sink whereas light ones rise when surrounded by particles with intermediate density. Our experiments demonstrate that the presence of a quasi-rigid upper layer in granular mass flows does not prevent vertical segregation and that the formation of coarse-tail grading in pyroclastic flows does not require fluidising gases. High-speed videos reveal that vertical segregation in granular mass flow of rock fragments is generated by inertia differences between segregating clasts and matrix when they are both pushed upward by collisions with the basal layer. Coarse-tail grading occurs because the average segregation velocity of smaller clasts is smaller than that of larger clasts.
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