Sinkholes

Sinkholes are large caverns covered by a one block layer of sand, gravel, or loose dirt. Because all of these blocks are affected by gravity when the player builds or mines one of these block the entire roof of the cavern will collapse bringing the player with it. In all sinkholes will create a sense of caution in the Minecraft world making players be extra careful where they build their creations.

Loose dirt is just a block that looks like dirt but is affected by gravity