The Hawaiian hot spot producing constant, gentle eruptions of low-viscosity mafic lava. For years, the Pu'u 'O'o crater on Kilauea has been flowing south to the coast and ocean, but a new lava flow, Kahauale'a 2, is instead flowing northeast into the forests.

Lava flow from Pu'u 'O'o crater into ohia lehua forests. Photography credit: US Geological Survey/Hawaiian Volcano Observatory

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The behaviour of lava depends on its chemical composition: low-silica content lavas are mafic lavas, while high-silica content lavas are felsic. Mafic lavas are low viscosity, runny fluids that release gas more easily and have consequently gentler eruptions. In contrast, felsic lavas are more viscous and less runny, but trap gas, building pressure into more violent eruptions. The chemical composition is determined by the geological origins of the lavas โ€” the mantle and oceanic crust is mafic, while continental crust is felsic. Consequently, violent eruptions like the infamous Mount Saint Helens are associated with subduction zones, while island volcanoes like Hawaii are generally more beautiful than explosively hazardous.

The Hawaiian chain of island volcanoes. Photography credit: NASA

While mafic lavas are slow-moving, that doesn't mean they're entirely harmless. Lava flows can be incredibly hard to stop or divert (it is possible with epic quantities of sea water, but that's a story for another day), so can cause large amounts of damage. The new flow is not immediately threatening any buildings, but if it continues in the same direction it will eventually reach communities farther to the northeast.

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Eruptions also produce sulfur dioxide gas. This gas reacts with oxygen and water vapor, producing tiny droplets of sulfuric acid: volcanic fog, or vog. The quantity of vog can vary over time โ€” the Kilauea volcano produced an average of 140 metric tons of sulfur dioxide a day in 2003 through 2007, but a relatively colossal 800 metric tons per day in December 2009.

The Kahauale'a 2 lava flow is slowly advancing to the northeast. Photography credit: NASA/EO.

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While the Kilauea lava flows had previously been treading a well-worn path to the sea, this new flow is heading in a new direction. As the lava advances, it burns the forest, producing smoke. The flow is creeping along, only advancing about 600 meters since November. When subterranean pressures change, and the summit inflates, lava surges out of the crater in a new breakout. The breakouts start from the crater, and pushes for some time before advancing the distant flow front.

Head over to the Earth Observatory for an interactive view of the advance between February 2nd and March 11th, or read about the geologic change over time of a volcanic island.