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