random sand mass appearing

I was playing as usual around my base camp area, all nicely landscaped and neatly organised, noticed a huge wall of sand and sandstone had generated randomly (savanna biome!) upon investigating I realise it is around 16x16x18 spanning above and underground and was sloped off behind in a quarter pyramid fashion. Very confused I spent around 45 minutes trying to level it off. Exited game, logged in yesterday and there it is again! Regenerated, not only that, across the river into desert biome another much larger looking mass has also generated, again sand on top of sandstone, again 16x16x18 (ground level, hard to establish any changes below ground as already on a desert biome) again the same type of ascending shape....this is very frustrating and perplexing