2D-melt percolation models in the partially molten mantle are presented. Previous work has shown that melt solitary waves develop in response to the non-linear dependence of mush permeability to melt concentration. The present study focuses on the wave evolution when the mush viscosity abruptly drops, around a critical concentration fc. 2D-waves develop with a diameter, that shortens as the melt concentration increment for viscosity drop narrows. They are initiated inside 1D-maturing horizontal waves at melt concentration of about 4¿fc. Both 1D- and 2D-waves collect all the melt whose concentration exceeds fc. These features may help to explain the distribution and organization of some melt impregnations observed in mantle outcrops. ¿ 1998 American Geophysical Union