Liquid may give strong cohesion properties to a granular medium, and confers a solid-like behavior. We study the evolution of a fixed aggregate of wet granular matter subjected to a flow of dry grains. In the confined geometry of a thin cell, the aggregate is hold by the walls, and the dry matter flowing around will pull grains out of the aggregate. Thus, by granular erosion, the shape of the interface is modified. Image treatment allows us to retrieve the interface of the wet area, and analyze the phenomenon. Two different configurations are set up for erosion study. In a rotating drum, we follow the diameter of a circular aggregate remaining at the center. This provides an erosion rate, related to the liquid and grains physical properties. In an open cell between vertical plates, we can form a heap-shaped aggregate. Then, with a funnel of constant outlet, we inject dry grains, flowing on top of the cohesive heap. We observe destabilization of an initial flat profile in certain conditions. The coupling between the flow stress and the shape of the heap creates periodical structures, which propagate to the top through the erosion process.