Just one scar out of hundreds, stretched across the land of Madagascar, that presents proof of immense undertakings upon the land went on in ancient times. https://satellites.pro/Madagascar_map#-18.249298,45.172305,17 . This one measured across is 80 ft. I can not say for sure how they are made , except guessing they might have just pulled heavy rocks over the land , but at times it looks different . So many questions created in end toward how this shaped the country.