When hot lava from a volcanic eruption invades a forest, often the lava does not overthrow the larger trees, but flows around them. The moisture in the tree cools the lava in contact with the trunk and a hard exterior shell is formed. As the lava drains away, only the solidified “lava trees” are left standing. The tremendous heat burns away the wood inside and a hollow cast in the shape of the original tree is left behind. In some cases, the tree can remain standing and stays for years as a black charred skeleton, and in rare cases, some trees even survive and continue to grow after the eruption.

The best example of lava trees are found on the island of Hawaii, in southeast of Pāhoa in the Puna District. Here, an entire forest of ohi'a trees were engulfed in molten lava up to 11 feet deep, when the Kilauea volcano erupted in 1790. Trees that were surrounded by the molten lava cooled the lava that coated them, while the heat of the lava caused the tree to burn to ash. Soon after a nearby fissure opened in the ground allowing the molten lava to drain away back into the earth. But the lava surrounding the trees had already cooled and started to harden and remained above ground as monuments to the trees that once stood in the same spot.

Forest of lava trees resulting from eruption of a 1-km-line of vents east of Pu‘u Kahaualea. The bulbous top of each lava tree marks the high stand of the lava flow as it spread through the trees. As the fissure eruption waned, the flow continued to spread laterally; its surface subsided, leaving pillars of lava that had chilled against tree trunks. Spattering is from fissure out of view to the left. Note blob of spatter adhering to the top of the stripped ‘ohi‘a tree (Photo by J.D. Griggs, USGS / Text from Pacific Island Parks)