Kilauea has been erupting continuously since 1983, but in late April and early May 2018 the volcanic eruption took a dangerous new turn.

During the last week of April, the lava lake at Halema‘uma‘u Overlook crater overflowed several times and then began to drain rapidly after the crater floor partially collapsed. Soon after, a swarm of earthquakes spread across Kilauea’s East Rift Zone as magma moved underground. On May 3, 2018, several new fissures cracked open the land surface in the Leilani Estates subdivision, leaking gases and spewing fountains of lava. As of May 7, 2018, slow-moving lava flows had consumed 35 homes in that community of 1,500 people.

In addition to seismic activity and deformation of the land surface, another sign of volcanic activity is increased emission of sulfur dioxide (SO 2 ), a toxic gas that occurs naturally in magma. When magma is deep underground, the gas remains dissolved because of the high pressure. However, pressure diminishes as magma rises toward the surface, and gas comes out of solution, or exsolves, forming bubbles in the liquid magma.

“The process is similar to what happens when a bottle of soda is opened,” explained Ashley Davies, a volcanologist at NASA’s Jet Propulsion Laboratory. “The bubbles of sulfur dioxide and other volatiles, including water and carbon dioxide, begin to rise through the liquid magma and concentrate in the magma closest to the surface, so the first lava to erupt is often the most volatile-rich. There’s usually an increase in sulfur dioxide output right before lava reaches the surface, as the gas escapes from the ascending magma.”

Sensors onboard the Ozone Mapping Profiler Suite (OMPS) sensor on the Suomi NPP satellite have begun to detect signs of activity at Kilauea. The series of images above shows elevated concentrations of sulfur dioxide on May 5, a few days after the new fissures opened up. The second chart (below) underscores the significant natural variability in sulfur dioxide emissions as observed by OMPS over Hawaii between January and May 2018.

“Interpreting the satellite SO 2 data for events like this is complicated because there are multiple SO 2 sources that combine to form the volcanic sulfur dioxide plume. Kilauea volcano has several sources of sulfur dioxide degassing: the summit caldera (a significant source since 2008); the Pu’u ‘O’o vent on the East Rift Zone; and now the new eruption site in Leilani Estates,” said Simon Carn, a volcanologist at Michigan Tech. “It can be very hard to distinguish individual ‘plumes’ from these sulfur dioxide sources with the spatial resolution that we have from OMPS, but we are seeing what seems to be an overall increase that coincides with the latest activity.”

Another satellite-based sensor—the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite—observed SO 2 emissions on on May 6, 2018. When ASTER passed over Hawaii, the largest source of SO 2 appeared to be coming from Kilauea’s summit crater, but there was also a sizable plume streaming southwest from the fissures in Leilani Estates. So far, trade winds have pushed the toxic gas offshore, but Hilo and other communities northwest of Leilani Estates could see air quality deteriorate if the trade winds weaken.

NASA Earth Observatory images by Joshua Stevens, using OMPS data from the Goddard Earth Sciences Data and Information Services Center (GES DISC). Photo courtesy of the U.S. Geological Survey. Story by Adam Voiland, with information from Simon Carn (Michigan Tech), Nickolay Krotkov (NASA Goddard Space Flight Center), Ashley Davies (NASA Jet Propulsion Laboratory), Janine Krippner (Concord University), and Jean-Paul Vernier (NASA Langley Research Center).