eli5 if deserts used to be wet where did all the water go?

Question

and why is there still a little bit in oases

In: 8

Answer 1

I could be wrong, but iirc deserts like the great Basin desert in Utah/Idaho/Nevada in the western United States used to be a giant inland Sea formed by the melting of glacial ice sheets which used to cover huge swaths of Canada and the Northern U.S during the last Ice Age. Since these glaciers were not renewable reserves, then once they melted, that was it. The great basin filled with water and the weather patterns/rain shadow from the Sierra Nevada/Cascade mountain ranges did not provide enough rainfall to replenish the lake, so over thousands of years it evaporated, leaving only the Great Salt Lake and Utah Lake as the last surviving (and rapidly drying; thanks climate change and 20 yrs of drought) remnant.