I don't know what the other earthworks are like, but that particular one is only about a foot high and 5-6 feet wide. It looks like one run over with a plough would pretty much wipe it out. It might be drainage related? Or somebody dug it to put a pipe in but never finished the job?
It was only because it was in an area with a lot of round barrows that I posted it in the first place.
-Chris