Peter J. Talling¹, Gareth Keevil¹

(1) Bristol University (Centre for Environmental and Geophysical Flows), Bristol, United Kingdom

ABSTRACT: Channels and Lobes Formed by Subaerial Mud-flows: Analogs for Submarine Fans

Subaerial mud-flow systems fed by mud-volcanoes near Maranello in Northern Italy show remarkable similarities with submarine channels and lobes. The mud-flows are 20-metres long and fed by a continuous series of mud-pulses from the caldera. On steep slopes adjacent to the caldera the mud-flows erode into the substrate forming a 'canyon'. There is a down-flow transition, as gradients decrease, to a depositional leveed channel that progressively aggrades above its surroundings. The very first flow in new mud-flow system (after caldera breaching) forms a mud-sheet. The much narrower leveed channel is progressively built-up above this sheet, which is analogous to a 'HARP' in submarine systems. The leveed channel narrows significantly with time, and its position remains stable. Bends do not rotate and migrate in a down-flow direction. Such channel behaviour, which differs significantly from that of river channels, characterises submarine channels (e.g. Peakall et al., Jour. Sed. Res. 2000). Most strikingly, the mud-flow systems have an abrupt down-flow transition from a single stable channel to sheet-flow that forms a topographic lobe. The origin of the channel-lobe transition is enigmatic, as it does not coincide with a measurable slope-break, and is the subject of ongoing laboratory experiments. The rheology of the mud-flows closely approximates a Bingham plastic with a small yield strength. Sandy submarine mass-flows are predicted to have a similar rheology if they contain only a few percent of mud. The mud-flow systems thus provide unique insights into the evolution and sub-seismic scale geometry of submarine channels.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado