Abstract : Periglacial geomorphology is one of the oldest branches of climatic geomorphology. After almost a century of research, a morphogenic system has been constructed where mechanical processes of weathering act as exclusive debris producers. Although, over the past decade, this model has been contested. Through an epistemological perspective helped by grids borrowed from the philosophy of sciences, we show that two research programs have insidiously emerged with distinct but complementary objectives : the first one, historically the oldest, deals with models of specific (zonal) processes whereas the second one tries to understand the interaction between specific and non-specific processes and builds a hierarchy of weathering processes. Being positioned in this second perspective, we have studied the impact of biogenic (fungal) processes of weathering on debris production in Iceland and The Faeroes. Fieldwork and laboratory experiments show that cryptoendolithic microorganisms are the first agents of weathering on loose surfaces (moraines, sandur), facilitating, through weathering rind production, the subsequent action of mechanical processes. These weathering rinds appear also as a good dating tool over short time scale (less than 150 years). Finally, regional perspectives of chemical or biochemical weathering of volcanic surfaces show that these processes allow great migrations, temporary (rock coatings) or definitive (oceanic basins), of mineral matter. In this way, chemical and biochemical erosion appears as one of the most important processes in the shaping of humid periglacial landscapes.