The U.S. Geological Survey said with sulfur dioxide emissions at Kilauea drastically lower than they have been for decades, it has turned its attention to measuring another gas — carbon dioxide.

“Carbon dioxide (CO2) is a significant volcanic emission, along with the familiar sulfur gases, water vapor, and trace amounts of other gases, such as hydrogen chloride, hydrogen fluoride, and helium,” said the USGS in a recent Volcano Watch post. “What’s important about CO2 specifically is that it can give clues about the depth of magma.”

More specifically, data on the CO2/SO2 ratio can be an indication of magma depth and allow scientists to document changes “that could eventually indicate an increased likelihood of renewed activity at Kilauea.”

In order to get accurate measurements of the ratio, which is tricky, due to large and variable amount of CO2 that already exists in the atmosphere as well as limited access, scientists have installed multi-gas sensors at the Kilauea summit, and are using gas sensors mounted on unmanned aerial systems, or drones, to collect data.

When magma is deeper, as is the case now, there is enough pressure to keep the SO2 dissolved. As magma rises to shallower depths, pressure lessens and different gases, including sulfur dioxide, are able to escape along the way, leading to vog.

Carbon dioxide, on the other hand, can escape even when the magma is deep, and Kilauea is currently producing significant amounts of CO2.

So the higher the CO2/SO2 ratio, the deeper the magma is. Measuring this ratio over time can help indicate whether the magma is once again rising through the system, scientists said.

Some sulfur dioxide is still present at Kilauea, along with hydrogen sulfide, which causes a rotten egg smell.

The USGS Hawaiian Volcano Observatory also published a new post today saying that the answer to how long it takes for new lava flows to solidify depends on various factors, including initial eruptive temperatures, thickness of the flow, heat loss from both the top and bottom of a flow, in addition to air temperature, rainfall and wind.

“Preliminary analyses of the 2018 LERZ eruption flow thicknesses, suggest that the average flow thickness is around 33 to 50 feet,” said USGS. “Based on the cooling rate calculation, it could take roughly eight months to 1.5 years for flows of these thicknesses to solidify.”

Even thicker flows of 65 to 100 feet thick could take 2.5 to six years to solidify, while the thickest lower East Rift Zone flow on land, about 180 feet thick, may take roughly 20 years to completely solidify.

In the meantime, the USGS’s weekly report says Kilauea is not erupting, and rates of seismicity, deformation, and gas release have not changed significantly over the past week. Kilauea has been relatively quiet since September 2018.