The death of Lake Chad

Earlier I posted about the later years of Sahara. I am now reading Lewis Dartnell's Origins. With that, let's talk about the early years.

If Egypt is the Nile's gift, the Sahara is the monsoons' curse. When they falter, the region dries out: so Dartnell, 72. Also, per p. 105: by 6 mya the old Tethys had become a literal "Mediterranean", an almost landlocked salt lake, open only to the west - and ever shrinking. Meanwhile the Alps and other European mountains arose, to weaken the north winds; and, between this newly re-occidented ocean and the rest of Africa, the Atlas mountains rose up to block what was left. Given the prevailing winds of that latitude, the only moisture the Sahara region could get, was from the east.

Gibraltar closed off 6-5.5 mya. The western Med turned into a salt plain; the eastern Med, into a big Dead Sea. But this mattered little to North Africa; the passage reopened 5.3 mya. What mattered more: the Rift formed to Africa's east 5.5-3.7 mya (p. 11). This blocked all but the mightiest monsoons.

We know there was enough Sahara dust to blanket the Canary Isles 4.8 mya. That delay looks, to me, like the death of Lake Chad.

I think that the Wet Sahara depended on Lake Chad, much as the Garamantes would depend on their wells. The lake effect watered the surrounding sahel and small forests; the (seasonal) monsoons watered the lake. Without the monsoons, Chad was and is a fossil.