Tsunamis are usually caused by either an underwater earthquake or a meteor slamming into an ocean or sea.  About 10,000 years ago it is believed that massive meteor crashed into the Indian Ocean, sparking a mega-wave.  These tsunamis wrecked havoc across the coast of Africa, leaving wedge-shaped deposits of sediment in Madagascar.

Signs of an ancient tsunami are not easy to spot, leaving the question wide open as to whether or not the a tidal wave is to blame for the chevrons.  As the waters erode back to ocean, they take with them the evidence of their existence.

Geologist Dallas Abbott states the question quite well:  “While most researches have assumed that the sand in the dues was transported inland by the wind, we instead have proposed that the deposits are from a mega-tsunami event.”

Abbott presented her evidence and new theory at the American Geophysical Union meeting in San Francisco.  Presenting 22 samples from two distinct dunes in Madagascar showing high levels of carbonate, that were dated to around 10,000 years ago, Abbot and her colleagues contened the notion of wind carriage.

Madagascar Chevrons
Madagascar Chevrons. Image: Google Earth

The source of the carbonate is primarily from marine microfossils, lending credibility to the researchers new theory.  Inland deposits such as these support the idea of being deposited by a mega-tsunami.  The cliffs of Madagascar are 175 meters tall, meaning the mega-wave to support this theory would need to be nearly 90 meters.

However Abbott was not met without contention to her interpretation of the evidence she and her team collected.  Carbonate sand is not uncommon in many regions and a different local explanation should not be ruled out.  Joanne Bourgeois, a sedimentary geologist at the University of Washington has a different theory for the wedge-shaped deposits, wind.

She created a model that showed the likely path that giant waves would take if produced by a giant meteor.  She found many variations from where the chevrons are located and where the projections place the deposits to be located.  If a giant wave did produce the deposits they should be perpendicular to the coast, but many are parallel.

In 2009 Bourgeois stated:  “And if it really was from an impact, you should find evidence on the coast of Africa too, since it is so near.”  Recently she updated her stance to National Geographic, “I have no reason to reconsider our analysis.  The evidence is unconvincing for a mega-tsunami hypothesis.”

Meanwhile, Abbott still believes that the age of the fossils support her side of the debate.  “No only that, but if the fossils were blown by wind to their final resting place they would have been powder by the time they landed.”