Dirt pile?

[LunaCat]

I'm on an island I see a pile of dirt but I can't use a shovel on it. Is it there for looks?

[Weaver]

if its an actual dirt pile it should have a slight glow to it like all items you can interact with. If its not glowing and looks like a giant ball of dirt, that's a bugged buried treasure and you need to use the metal detector to "find" it.

[❃ Galiäna Krüger ❃]

There's two types of dirt piles, one that's small and glow white light inside caves they are dirt pile that can be dig using shovel and you will find dirt pile for crop lot and sometimes other material (stone, nail, hinge, scrap, metal ore) and the other is the large dirt pile left over after you locate a treasure spot by using metal detector and dig corresponding site to cause a giant pile of dirt after you grabbed the treasure.

If its latter you probably played with someone who used a metal detector and dug up a treasure without you knowing and you lack the knowledge of that's why you don't know what it is for, or you simply forgotten about it after you travel to the island recently but not far enough (beyond 1000 but no further than 2000) the giant dirt pile will remain.