From May to August 2018, the Kilauea volcano erupted, sending millions of cubic tons of lava into the ocean.

A massive algae bloom was subsequently seen on the ocean surface. Measuring more than 100 miles long and 20 miles across, it was so large that it could be seen from space.

However, the volcanic eruption was not the direct cause of the massive bloom, as lava does not contain nitrates.

To find out the cause, between 13th to 17th July 2018, researchers were at the vicinity where the lava entered the water, to test the water chemistry and access the biological response to the lava flowing into the ocean.

They saw that the waters where the lava entered the ocean had turned green, signifying the presence of large amounts of chlorophyll. They discovered that the waters contained higher-than-normal nitrate levels, silicic acid, iron and phosphate.

It turned out that the nitrogen was likely to have come from the deep ocean, due to the entry of lava into the water. The hot lava forced an upwelling of colder, deep ocean water, which carried nitrogen and other particles upward toward the surface.

The large amount of nitrogen, which is a natural fertiliser for plants, subsequently caused the algae bloom. The findings of the research was published in the Science journal.

“The expedition in July 2018 provided a unique opportunity to see first-hand how a massive input of external nutrients alters marine ecosystems that are finely attuned to low-nutrient conditions,” said co-author Sam Wilson, from the University of Hawaii’s Mānoa Center for Microbial Oceanography: Research and Education.