The phrase "hot lava" refers to molten rock that is very hot and flowing like a liquid. It is used to describe something dangerous or intense, often in a playful way. Full definition
If the thought of hot lava and ash doesn't scare you off, it's currently available for rent as a vacation home. (newatlas.com)
My kids are always playing hot lava with our pillows, so I'm sure they'd love these! (munchkinsandmoms.com)
Sometimes they break through, or sometimes, I've found, they can lay dormant for a really long time, bubbling like hot lava underneath volcanic crust. (mindbodygreen.com)