Lava Tree State Monument is a public park located 2.7 miles southeast of Pāhoa in the Puna District on the island of Hawaii. It preserves lava molds of the tree trunks that were formed when a lava flow swept through a forested area in 1790. The lava covered the trees from bottom to top. As the lava drained away and the moisture inside the trees cooled the lava, a hard exterior shell was formed. Many of the trees are covered in moss, others have fallen to the ground and others remain standing for years as black charred skeletons.
Pretzelpaws at the English language Wikipedia [GFDL or CC-BY-SA-3.0], via Wikimedia Commons
By Sean A. Clevenger – Own work, CC BY-SA 3.0, Link
By Sean A. Clevenger – Own work, CC BY-SA 3.0, Link
Inside view of lava tree with moss
By Sean A. Clevenger – Own work, CC BY-SA 3.0, Link
Large lava tree that fell and broke apart
By Sean A. Clevenger – Own work, CC BY-SA 3.0, Link
By Sean A. Clevenger – Own work, CC BY-SA 3.0, Link
e MORFES 
Never heard of this. So, I DID learn something new today!