Volcano Watch: Replacing Mauna Loa’s carbon dioxide; replacing destroyed station

On the night of Nov. 27, 2022, when lava poured out over the floor of Moku‘āweoweo, Mauna Loa’s summit caldera, it was still many hours away from reaching infrastructure. Or “most” infrastructure.

The next day the lava blocked the access road to the Mauna Loa NOAA observatory. But well before it got there, it destroyed the Hawaiian Volcano Observatory’s summit gas measuring station, which occurred less than 10 minutes after the eruption began.

The station measured four gases— sulfur dioxide (SO₂), carbon dioxide (CO₂), hydrogen sulfide (H₂S) and water vapor — as well as meteorological parameters including wind speed and fumarole (small gas vent) temperature.

As part of the observatory’s monitoring network, the station was installed to provide alerts about any changes in gas concentrations or the temperature at the site. Had the station survived, it would have given the observatory a rich dataset regarding the chemistry of any eruptive gases blown toward it.

Carbon dioxide can be indicative of deep magma recharge, either before or after an eruption.

For example, at Kīlauea, a decrease in the proportion of carbon dioxide relative to sulfur dioxide over a few months was a clue hinting at the eventual onset of Kīlauea’s 2008 to 2018 summit eruption.

At Mauna Loa, the NOAA observatory has a long history of measuring atmospheric carbon dioxide. Volcanic carbon dioxide is removed from their long-term atmospheric dataset, though that removed data can in turn be used to study Mauna Loa’s carbon dioxide emissions.

A study published in 2001 by a NOAA observatory scientist — using data from the 1950s through the 1990s, which covers the periods after the 1950, the 1975, and the 1984 eruptions— showed that most carbon dioxide there has been released after each of those eruptions.

That study also showed a small increase in carbon dioxide emission from Mauna Loa in the 1990s, when there was no eruption. It’s possible that this carbon dioxide pulse was related to a deep magma intrusion that didn’t make it to the surface.

There was no increase in carbon dioxide emission detected before the 2022 eruption; however, based on the 2001 NOAA study, we might expect enhanced carbon dioxide degassing now that the eruption is over.

Given the potential for anomalous carbon dioxide emissions before, during and after eruptions, Hawaiian Volcano Observatory is eager to replace the station at Mauna Loa summit as soon as possible.

However, before we can do that, we need to find a new suitable location. The previous station was on the floor of Moku‘āweoweo, where we hoped that it might detect increased degassing before a new eruption, but that location clearly came with a lot of risks.

The initial lava flows from the 2022 eruption destroyed the station, preventing the observatory from getting any data during the ensuing two weeks of the eruption.

This time, the observatory is considering placing a station on the caldera rim, which is close enough to measure carbon dioxide emitted from the caldera during favorable wind conditions. It also is a much safer spot. A new station there should survive future summit activity and provide gas data throughout eruptions.

Earlier in June, observatory gas scientists headed to Mauna Loa’s summit to begin searching for locations where gas might already be leaking out of the ground. They brought with them small, portable versions of the same gas sensors that are part of larger permanent monitoring stations. Visits to other summit locations are planned for later this summer as we continue the hunt for the best spot for the new station.

As you read this, you may be wondering how volcanic carbon dioxide emissions like those at Mauna Loa and Kīlauea compare to other sources of carbon dioxide, such as those from industry. Though volcanoes and their eruptions may seem like they should be big factors in the global carbon dioxide budget, volcanoes release less than 1% of the carbon dioxide emitted by human activities.

Although the amount of carbon dioxide emitted by Mauna Loa may be small in a global view, it could still yield important clues about Mauna Loa’s volcanic processes and future eruptions. Hawaiian Volcano Observatory hopes to find a location for the new gas monitoring station soon and have it installed in the coming months.

In the meantime, the observatory has a similar gas monitoring station high on Mauna Loa’s Southwest Rift Zone, as well as another at Kīlauea summit. Even without the Mauna Loa summit station, the observatory is still keeping an eye on the volcanoes and their degassing.