the formation of the modern andes began with the events of the triassic and jurassic when pangea begun to break up and several rifts developed. it was during the cretaceous period that the andes began to take their present form, by the uplifting, faulting and folding of sedimentary and metamorphic rock of the ancient cratons to the east. the rise of the andes has not been constant and different regions have had different degrees of tectonic stress, uplift, and weathering.