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1 Department of Geology, University of Luton, Luton, LU1 3JU, UK
2 Planetary Image Centre, University College London, 33/35 Daws Lane, Mill Hill, London, NW7 4SD, UK
3 Department of Geography, University of Liverpool, Liverpool, L69 3BX, UK
The Lahar Facies of Mt Vulture, which forms a broad apron around the base of the cone, is composed predominantly of mass-flow deposits. There is a spectrum of lithological types ranging from monolithologic units which may be of a primary pyroclastic flow origin and are composed entirely of juvenile material, to polylithologic deposits, containing a range of clast types, interpreted to be cold debris-flow deposits. Some debrisflow deposits show evidence of being hot on emplacement. Debris-flow deposits are interbedded with lapilli-fall layers and lava flows suggesting formation contemporaneous with eruptive activity. Some debris-flow deposits travelled no more than 3 km from their source. Many flows were apparently non-erosive, although there is one example where a debris-flow eroded clasts from the top of a lava flow. The presence of fractured ‘jigsaw’ blocks and large fragile blocks of pyroclastic material rules out turbulent flow and high shear for much of the transport prior to emplacement. Multiple grading and abundant development of reverse grading with large lava blocks rafted on, or protruding through, the upper surface of flow units implies that the lahars were high-concentration, high-strength flows in which differential shearing produced discontinuous multiple grading. Locally, individual debris-flow deposits have convex upper surface profiles with internal grading paralleling the surface, strongly supporting a conclusion that these debris-flow deposits were emplaced en masse.
