Lava tumuli morphology from Patagonia, Mendoza (Argentina) and Al-Haruj (Libya)

NEMETH K; HALLER MJ; MARTIN U; RISSO C

Zaragoza

Conferencia; 6th International Conference on Geomorphology; 2005

Internationa Association of Geomorphologistst

Compound flows near the vents are characterized by a tube network, skylights, ephemeral vents and tumuli. During discontinuous activity discrete, channel-fed a´a flow units in near-vent often form fan-shaped flow fields that resemble vents effused spatter fed or clastogenic lava. These flows resulted from (a) reconstitution of fountain-generated spatter around vents by syn-depositional agglutination and coalescence, and (b) syn-eruptive collapse of spatter and scoria. In the studied lava shields three types of tumuli have been classified such as (1) lava-coated tumuli, and (2) upper-slope tumuli in near-source regions and (3) flow-lobe tumuli in the distal areas. Flow-lobe tumuli are associated with lava rises of eroded P-type pahoehoe lavas. The flow-lobe tumuli have minor outflows from elongated cracks in large tumuli. Medium size tumuli are cross-like. Dense zone between the upper and lower vesicular zones of tumuli resembles vesicle distribution pattern of P-type flow lobes. The flow lobe tumuli suggest low lava-supply rates (< 5 m3/s). The tube formation is interpreted by sustained but low volume-rates of flow. Flow-lobe tumuli are interpreted to have been supplied with magma from tubes that originate in overflow from and/or through flank fissure connected with the lava lake of shield volcanoes.