We investigate the shape and the size of the current head formed when a viscous liquid driven by gravity spreads on a horizontal smooth substrate. A characteristic roll-shaped current head is observed during the experiments, which evolves towards a wedgelike shape when the (decreasing) capillary number Ca goes below the unity. The lower part of the advancing roll observed when Ca much greater than 1 may be described as half a cusped entrance of rile free liquid surface, centered on the spreading surface. The size of the roll structure during this stage is proportional to the square of the front velocity which, in turn, is determined by the global dynamics of the flow.
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