This Is What Happens When Lava Meets The Sea

This is a close-up of the very newest land in Hawaii, fresh lava dripping into the sea to build out a new layer of basalt on this island volcano. The ropey texture of the flow is a consequence of its chemistry, the same geochemistry behind the slow, oozing eruptions characteristic of the tropical paradise.

Top image: Fresh lava building out new land for the island of Hawaii. Extracted from video by Kawika Singson

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Lava pouring into the ocean and flashing the ocean into steam at Hawaii Volcanoes National Park. Image credit: Mbz1

Geology is an odd mix of incredibly slow processes over hugely long periods of time, and abrupt, immediate changes happening right now. While Canada and Australia vie for the title of who has the oldest rock from when the Earth's crust was still hot and young, Hawaii and other island volcanoes are in a constant competition for the freshest, newest rock around. When the lava meets the sea, it cools quickly while boiling the ocean into steam. This results in a distinctive texture: the quenching produces a glassy outer surface from the lava cooling too quickly for crystal structure to grow. This insulates the inside of the globs, trapping any dissolved gas as bubbles and allowing internal microcrystal growth from the slightly slower cooling rate.

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The thick, gooey lava is quickly quenched by the sea, while the fresh, hot rock boils the ocean into steam. Screenshot from video by Kawika Singson

Hawaii is a hot spot volcano, one of the rare volcanoes disassociated from tectonic boundaries. While the exact nature of hot spots or mantle plumes are under constant academic research and debate, the hand-wavy true-enough-for-now version is that these volcanoes are the surface expression of a particularly hot spot in the underlaying mantle that melts the crust. Because this particular hot spot is out in an ocean it melts the oceanic crust into silica-poor magma. This mafic lava allows gas to escape easily, resulting in burbling, gentle eruptions with small lava fountains and creeping lava flows building into gently-curved shield volcanoes. This is unlike volcanoes fed by the silica-rich magmas of continental plates that produce violently dramatic eruptions from steeply conical stratovolcanoes like Krakatoa and Mount Saint Helens.

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The mafic lava produces characteristically dark basaltic rock at this island volcano. Image credit: aprilandrandy

In this video from February 2013, photographer Kawika Singson brought his camera up close and personal with where the lava meets the sea. In doing so, he demonstrated the daring that volcanoes bring out in people: along with the direct risk of being burned by splashing globs of melty rock, he was close enough to be broiled by steaming seawater and to choke on any poisonous gasses accompanying the eruption. The video also highlights another hazard associated with volcanoes: when new rock is formed by this globby, sloppy process of endless layers, the end result is weak rocks that can fail into massive landslides with very little provocation.

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For more on Hawaiian eruptions, you might be interested in how lava impacts their roadworks and subdivisions.

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