Chemical alteration of seawater by lava from Kilauea Volcano, Hawaii

Abstract

To examine the chemical alteration of seawater by submarine lava, seawater was sampled at a depth of 21 m east of Kupapau Point, Hawaii, after contact with molten lava from Kilauea Volcano. The warm, mildly acid (pH ∼6.5 at 27°C) hydrothermal solutions are highly enriched in dissolved Si (>40×) and Mn (>400×) relative to ambient seawater. Chloride shows a slight but discernable enrichment in the most altered samples, probably due to boiling and partial phase segregation (steam loss) during heating. Assuming Cl behaves conservatively, Ca and Mg are on the order of 1% depleted in the altered solutions, which we attribute to anhydrite precipitation and secondary silicate formation during the water-rock exchange. Dissolved iron is not enriched in the solutions, although examination of filtered particles suggests that some Fe is mobilized from the basalt. These distinctive chemical changes are consistent with a brief, moderate temperature (<150°C), high water/rock ratio seawater-basalt reaction, and suggest that submarine lava extrusion may constitute a significant input of dissolved Mn and Si, and particulate Fe, to the surrounding seawater.