Skip to main content
U.S. flag

An official website of the United States government

February 9, 2023

When Mauna Loa erupted in November 2022 for the first time in nearly forty years, one of the main concerns was the lava and where it would flow. But Mauna Loa didn’t only erupt lava – as with all other volcanic eruptions, many tonnes of volcanic gases were emitted from the active vents.

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. 

Color photograph of eruption plume
Mauna Loa’s Fissure 3 gas plume, with rain clouds, as seen from the Saddle Road on November 29, 2022. The orange-brown tint near the vent is due to scattering by aerosols in the plume. The dark gray clouds are a mix of plume with what are called pyrocumulus clouds, or clouds that the volcano itself generated via the intense heating of the air by the erupting fissure. USGS photo by M. Warren. 

Volcanic gases emitted during eruptions include water vapor, carbon dioxide (CO2), and sulfur dioxide (SO2). During eruptions, the Hawaiian Volcano Observatory (HVO) aims to characterize both the chemistry and amount of gas being emitted. 

SO2 emission rates are a key parameter to measure, as they can be used as a proxy for lava effusion rate and they dictate how much vog, or volcanic air pollution, there is downwind. Typically, we measure SO2 emission rates using a vehicle-mounted ultraviolet spectrometer, which we drive beneath the plume.  

At Kīlauea, because the trade winds tend to blow the summit plume in a single direction, we have a permanent array of spectrometers to measure SO2 there, so we don’t have to do as much driving. Driving on Chain of Craters Road for the Puʻuʻōʻō eruption and on Highway 130 for the 2018 lower East Rift Zone eruption were our common means of measuring the plume in the trade wind direction for these other Kīlauea eruptive sites.  

Mauna Loa, however, at such a high altitude compared to Kīlauea, experiences different wind patterns, and winds were very variable during the eruption. Sometimes measurements of high-altitude plumes can be made relatively easily by flying an airplane or a helicopter beneath the plume instead of driving. However, the Mauna Loa plume had not only high concentrations of gases, but also contained particles, like Pele’s hair, which could adversely affect an aircraft flying under it.  

So what did that mean for the HVO gas crew during the eruption? We had to shift gears and do a whole lot of driving! 

Over the course of the roughly two-week eruption, the winds took the plume in many directions, including over Saddle Road, Ocean View, Pāhala, Puna, Hilo, Kailua-Kona, and Captain Cook. This meant that the HVO gas team drove nearly 3,000 miles (4,800 km) in total! Ultimately, all the driving paid off and we succeeded in measuring emission rates on ten separate days. This allowed HVO to report these emission rates  to the public and to vog forecasters during the eruption. 

Color photograph of volcanic plume
Mauna Loa’s Fissure 3 gas plume as seen from the Saddle Road on December 2, 2022. Winds were from the northeast at the time the photo was taken, and spread the plume over much of the island to the south and west of Mauna Loa summit. USGS photo by P. Nadeau.  

Preliminary data processing suggests that Mauna Loa emitted over two million tonnes (2 Mt) of SO2 between November 28 and December 12. This doesn’t include a large volume of SO2 that satellite images show was emitted with the initial fissure opening overnight between the 27th and 28th of November; we need ultraviolet light to make these driving measurements, which means they can only be conducted during daylight hours.  

Daily emission rates are estimated to have ranged from 200,000 to 500,000 t/d of SO2 early in the eruption and were just over 100,000 t/d later in the eruption. By December 8, emissions had dropped significantly to only about 30,000 t/d. Only about 2,000 t/d were emitted on December 10, and by December 12, emissions were essentially not detectable, even on the ground near the Fissure 3 cone. 

These emission rates are very similar to those measured during the 2018 lower East Rift Zone eruption at Kīlauea, which also emitted SO2 at a rate of nearly 200,000 t/d for a portion of the eruption. The total SO2 emitted by the 2018 eruption was roughly five times more than Mauna Loa’s total, however, owing in part to the longer eruption duration. 

SO2 emission rates reported for the 1984 eruption of Mauna Loa were roughly 100,000 to 200,000 t/d, as derived from satellite data. However, the technology used at the time was not as sophisticated as our modern spectrometers and likely underestimated those emission rates. So Mauna Loa’s 1984 SO2 emissions were probably similar to those in 2022. 

SO2 emission rates at Mauna Loa’s Fissure 3 are down to nearly zero with the eruption being over. Mauna Loa will eventually erupt again and when it does, HVO’s gas team will be in the driver’s seat, ready to do whatever it takes to measure emission rates. 


Volcano Activity Updates


Kīlauea is erupting. Its USGS Volcano Alert level is at WATCH. Kīlauea updates are issued daily.

Kīlauea volcano's summit eruption in Halemaʻumaʻu crater within Hawai‘i Volcanoes National Park continues. Activity is concentrated in a large lava lake in the eastern half of the crater, as well as two smaller locations to the west. Summit tilt has been flat over most of the past week, with deflation over the past day. Summit earthquake activity remains low and eruptive tremor (a signal associated with fluid movement) is present. A sulfur dioxide emission rate of 2,800 tonnes per day was measured on February 6. For Kīlauea monitoring data, see

Mauna Loa is not erupting. Its USGS Volcano Alert Level is at ADVISORY. Mauna Loa updates are issued weekly on Thursdays.

Webcams show no signs of activity on Mauna Loa. Seismicity remains low. Deformation rates show inflation somewhat above background levels, but this is not uncommon following eruptions. Sulfur dioxide (SO2) emission rates are at background levels. For Mauna Loa monitoring data, see:

There were three earthquakes with 3 or more felt reports in the Hawaiian Islands during the past week: a M3.1 earthquake 9 km (6 mi) NE of Pāhala at 32 km (20 mi) depth on Feb. 7 at 8:53 p.m. HST, a M3.2 earthquake 3 km (2 mi) SW of Pāhala at 35 km (21 mi) depth on Feb. 5 at 11:39 p.m. HST, a M3.2 earthquake 10 km (6 mi) NE of Pāhala at 31 km (19 mi) depth on Feb. 5 at 4:30 p.m. HST.

HVO continues to closely monitor the ongoing eruption at Kīlauea, and Mauna Loa.   

Please visit HVO’s website for past Volcano Watch articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake info, and more. Email questions to   

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.

Get Our News

These items are in the RSS feed format (Really Simple Syndication) based on categories such as topics, locations, and more. You can install and RSS reader browser extension, software, or use a third-party service to receive immediate news updates depending on the feed that you have added. If you click the feed links below, they may look strange because they are simply XML code. An RSS reader can easily read this code and push out a notification to you when something new is posted to our site.