What Are Lava Trees and How Are They Formed?

Lava trees in Hawaii. (Photo: Eduard Moldoveanu/Shutterstock)

The islands of Hawaii are filled with all kinds of volcanic wonders — from the smoking calderas of active volcanoes to the igneous lava tubes forged by ancient eruptions. However, one volcanic feature you may not have heard of is a strange geological formation known as a lava tree (pictured above).

These strange columns are formed when a rush of molten lava makes its way through a forest. Rather than knocking down all the trees in its path, the lava's sudden contact with the tree's trunk allows a thin layer of lava to cool around it. After the initial rush of lava passes and the "tide" goes down, the semi-cooled lava that has accumulated around the doomed tree trunks remains.

In the photo below, captured Jan. 7, 1983, during an eruption at Pu‘u Kahaualea, you can see exactly how one of these lava tree "forests" is formed.

The formation of lava trees east of Pu‘u Kahaualea in Hawaii. (Photo: United States Geological Survey)

As the U.S. Geological Survey points out, "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."

Sometimes the charred skeleton of the tree can remain standing within its igneous cast for many years (and in extremely rare cases, trees have been known to survive and continue to grow). However, the most common scenario is one where the tree catches fire and completely burns up during or shortly after the initial surge of lava. When this happens, it results in a hollowed out trunk, like this:

Inside a lava tree. (Photo: Sean A. Clevenger/Wikimedia)

If you'd like to see these strange fossil-esque formations in person, they are typically found along the slopes of basaltic shield volcanoes that are prone to liquid lava flows. There's a state park you can visit to witness some truly spectacular examples: Lava Trees State Monument.

Located on the Big Island just southeast of the town of Pāhoa, the igneous molds were formed in 1790 after a lava flow barreled through a forest. In the centuries since then, a new forest has sprung up, but the ominous, towering lava trees still stand as reminder of the island's fascinating yet volatile natural history.

A large lava tree in Hawaii. (Photo: Alexey Kamenskiy/Shutterstock)