Raiders of the Lost Lake

A lake larger that Lake Superior once brought life to an area of south-central Africa that now hosts only a salty desert. The long-gone Lake Makgadikgadi filled in a huge expanse of northern Botswana near the wildlife paradise of the Okavango Delta, the world’s largest inland river delta.

In its prime, the 90,000 square kilometer (35,000 sq. mi.) lake would have boasted the second largest surface area of any inland body of water after the Caspian Sea.

Prehistoric Africans must have been perplexed when the lake drained away thousands of years ago. Rich fishing and hunting grounds shriveled as the water evaporated or escaped into the Zambezi River.

Nineteenth century European explorers noted the ancient shorelines etched on surrounding hillsides and realized that a massive lake once filled the area. But they didn’t know exactly how large the lake was or what had caused its demise.

More recent geological sleuthing revealed the rise and fall of Lake Makgadikgadi.

The mega lake fluctuated in size between approximately 1.8 million years ago to possibly as recently as 8,500 years ago, until it finally disappeared, Joel Podgorski of the Institute of Geophysics in Zurich, Switzerland told Discovery News. Podgorski’s study of the lake’s ancient boundaries will be published in the October issue of Geology.

Podgorski used magnetic imaging of the lost lake region to determine its ancient shorelines. His study also found a massive lost inland delta, or mega-fan, beneath the vanished lake. A biological paradise, similar to the modern Okavango Delta, may have first been drowned by the mega-lake, then dessicated when the water drained.

Populations of animals in the two small lakes remaining in the Makgadikgadi region may be remnants of the ancient lake’s ecosystem.

“Molecular dating of catfish and crocodiles points to paleo-Lake Makgadikgadi having existed as a connection between now separate populations of these species,” said Podgorski. “One could presume that the lake hosted a sizable wildlife population much as the nearby Okavango Delta does today,” said Podgorski.

Shifts in the Earth’s crust eventually caused the rivers that fed Lake Makgadikgadi to change course. The lower Zambezi River captured the water that once flowed into the mega-lake.

As recently as 1952, earthquakes have altered the flow of rivers in the region. A magnitude 6.7 quake in ’52 changed the water flow in part of the Okavango Delta.

Geologic activity also flattened out the ground beneath the lost lake, making it shallower and hastening its evaporation.

Read more at Discovery News