Palaeolake Mega-Chad: Largest Lake in the World Disappeared, Once Covered 360,000 Square Kilometers in Sahara 6,000 Year Ago

At its peak around 6,000 years ago, Palaeolake Mega-Chad was the largest freshwater lake on Earth, with an area of 360,000 km2. Now today’s Lake Chad is reduced to a fraction of that size, at only 355 km2. The drying of Lake Mega-Chad reveals a story of dramatic climate change in the southern Sahara, with a rapid change from a giant lake to desert dunes and dust, due to changes in rainfall from the West African Monsoon. 

The research, published this week in the journal Proceedings of the National Academy of Sciences of the United States of America confirms earlier suggestions that the climate change was abrupt, with the southern Sahara drying in just a few hundred years.

Part of the Palaeolake Mega-Chad basin that has dried completely is the Bodélé depression, which lies in remote northern Chad. The Bodélé depression is the World’s single greatest source of atmospheric dust, with dust being blown across the Atlantic to South America, where it is believed to be helping to maintain the fertility of tropical rainforests. However, the University of London team’s research shows that a small lake persisted in the Bodélé depression until about 1,000 years ago. This lake covered the parts of the Bodélé depression which currently produce most dust, limiting the dust potential until recent times.

 

The rivers, lake area and catchment area of Lake Megachad overlaid on the DEM of the Chad basin. Lakes are marked in blue, rivers in black and marshlands in green. When rivers flow into sand seas they often disappear in the dunes fields, and thus appear to terminate abruptly. This is probably because the channels are obscured by moving sand. Intermittent channel reaches can often be detected amongst the dunes in both the DEM and Landsat TM imagery suggesting they were once much more extensive 

Credit: King’s College London/ image by Nick Drake

“The Amazon tropical forest is like a giant hanging basket” explains Dr Simon Armitage from the Department of Geography at Royal Holloway. “In a hanging basket, daily watering quickly washes soluble nutrients out of the soil, and these need to be replaced using fertiliser if the plants are to survive. Similarly, heavy washout of soluble minerals from the Amazon basin means that an external source of nutrients must be maintaining soil fertility. As the World’s most vigorous dust source, the Bodélé depression has often been cited as a likely source of these nutrients, but our findings indicate that this can only be true for the last 1,000 years,” he added. 

 

Location of the palaeolake shoreline complexes identified in this research.  

Image by Nick Drake

The field work carried out by Professor Charlie Bristow, Professor Nick Drake and Dr Armitage was made possible by Royal Geographical Society grants for expeditions to Chad in 2005 and northern Nigeria in 2008. Additional sample analyses were funded by the Natural Environment Research Council.

 

 

 

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• Stephen

  Every continent has evidence of large “inland seas” which were left over from the Great Flood about 4300 years ago. This is also when the first historical records appear in every culture – most of which have pagan legends that corroborate the Bible’s account of the Flood. The world’s oceans are remnants of the Flood as well. The Bible is real including the gospel of God’s only Son, Jesus Christ, who gave His life on the cross as full payment for our sins, was buried three days and then resurrected. 2 Peter 3:3-6 “Knowing this first, that there shall come in the last days scoffers, walking after their own lusts, And saying, Where is the promise of his coming? for since the fathers fell asleep, all things continue as they were from the beginning of the creation. For this they willingly are ignorant of, that by the word of God the heavens were of old, and the earth standing out of the water and in the water: Whereby the world that then was, being overflowed with water, perished:”

  Jul 3, 2015, 6:45 am 0 Reply