COARSE-TAIL VERTICAL AND LATERAL GRADING IN PYROCLASTIC FLOW DEPOSITSOF THE LATERA VOLCANIC COMPLEX (VULSINI, CENTRAL ITALY) - ORIGIN AND IMPLICATIONS FOR FLOW DYNAMICS

Citation
Dm. Palladino et Ga. Valentine, COARSE-TAIL VERTICAL AND LATERAL GRADING IN PYROCLASTIC FLOW DEPOSITSOF THE LATERA VOLCANIC COMPLEX (VULSINI, CENTRAL ITALY) - ORIGIN AND IMPLICATIONS FOR FLOW DYNAMICS, Journal of volcanology and geothermal research, 69(3-4), 1995, pp. 343-364
Citations number
38
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
0377-0273
Volume
69
Issue
3-4
Year of publication
1995
Pages
343 - 364
Database
ISI
SICI code
0377-0273(1995)69:3-4<343:CVALGI>2.0.ZU;2-N
Abstract
Coarse-tail vertical and lateral grading are common features of pyrocl astic flow deposits of the Latera Volcanic Complex (Vulsini Volcanoes, central Italy), and are described for four representative flow units. Lithic clasts show normal vertical and lateral grading in all four un its. Pumice clasts show reverse vertical and lateral grading within th ree flow units; normal vertical and lateral grading of scoria clasts h as been observed in one flow unit. The origin of vertical and lateral grading of lithic and pumice clasts is related to mechanisms operating during the transport process within the high particle concentration b asal avalanche of pyroclastic flows. Vertical grading results from the balance between gravitational and dispersive forces, and is transferr ed to a lateral grading by vertical velocity gradients within a nontur bulent flow zone of pyroclastic Bows. The pyroclastic flows are modele d as Bingham-type fluids, a framework that explains some of the basic deposit features even though it is a highly simplified treatment of th e flows. Plug flow zones in the flows were a relatively minor part of their thicknesses. Evidence for the flows having had high densities, p robably within a factor of two of the final deposit density, is presen ted. Finally, their origin by ''single pulse'' or ''progressive format ion'' is discussed.