curiously, the same influences that created the mousterian pluvial also appear to have brought it to a close. in the period of its fullest development, c. 30 to 18 kybp, the laurentide ice sheet not only covered an enormous geographic area, but increased its altitude to 1750 meters (more than 1 mile). it generated its own long term weather patterns, which affected the jet stream passing over the north american continent. the jet stream effectively split in two, creating a new dominant weather pattern over the northern hemisphere that brought harsher conditions to several regions (including parts of central asia and the middle east) — changes that included an end to the mousterian pluvial and a return to a more arid climate in northern africa.