Tree mold
From Conservapedia
Fluid basaltic lava may preserve the shapes of trees and other objects by solidifying around them. Tree molds are formed when lava surrounds a tree, chills against it, and then drains away. The standing structure left behind is often called a lava tree.
Tree trunks engulfed and incinerated by lava leave cylindrical hollows, or tree molds, where lava solidified against them; tree molds often preserve the original surface texture of the tree. Tree molds are found within standing lava trees and on the surfaces of lava flows. They are common in pahoehoe flows and occasionally found in `a`a flows.[1]