Tree-like shapes of sea-penetrating lava flows

What is it about?

When lava goes from land into water, the behaviour of the lava is difficult to monitor, as these areas are typically dangerous and the water becomes clouded by particles. We used a sonar over the bows of a local coastal research vessel in the Azores to image the shapes of lava flows where lava had gone into the sea. We typically found the lava to form branching patterns, much like trees. The branching may result from the effects of rapid cooling on the lava, which we suggested leaves the outer (tough) strong layer of the lava thin in places where it is easily broken.

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Photo by Toby Elliott on Unsplash

Photo by Toby Elliott on Unsplash

Why is it important?

Multibeam sonar data collected around coastlines revealed dendritic shapes of lava flows penetrating the sea. By analogy with how pahoehoe lava typically develops in dendritic patterns, we suggested this implies repeated breakouts of the submarine flows to cause the branchings. This in turn may imply that submarine flow involves localised weakness of the outer visco-elastic layer of the lava, perhaps caused by irregular rapid cooling by seawater penetrating cracks.