Hawaii Volcano Blog

Eruption Update: Kīlauea Calming Down

October 4, 2021, 7:06 PM HST
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IMG_4403Kilauea Eruption Sept. 29, 2021
Kilauea Eruption Sept. 29, 2021. PC: USGS

Kīlauea volcano continued erupting as of Monday, Oct. 4, 2021.

At approximately 3:21 p.m. HST on Sept. 29, 2021, an eruption began within Halemaʻumaʻu crater, within Kīlauea’s summit caldera in Hawai‘i Volcanoes National Park. The USGS Hawaiian Volcano Observatory (HVO) elevated Kīlauea’s volcano alert level to WARNING and its aviation color code to RED to assess the intensity of eruptive activity and identify associated hazards.  

Vigorous fountaining — with bursts up to 50 to 60 meters (164 to197 feet) — produced significant amounts of pumice, Peleʻs hair, and fragments of volcanic glass that were deposited in areas downwind along the rim and beyond Halemaʻumaʻu crater.

Over the past several days, a thick layer (approximately 27 meters or 89 feet) of molten lava has accumulated as a lava lake at the base of the crater, partially drowning the vents resulting in subdued fountaining.

During the same time, the amount of sulfur dioxide (SO2) emitted has dropped from 85,000 tons per day (one metric ton equals 2,200 pounds) to 12,000 tons a day. Although the amount of gas and volcanic particle production has decreased since the eruption onset, they both remain significant local hazards within the plume. Concentrations of SO2 at the vents remain high (likely over 100 parts per million or ppm) and significantly elevated (5-10 ppm) at stations a few kilometers (a couple of miles) southwest of Halemaʻumaʻu.


The eruption is currently confined to Halemaʻumaʻu crater, within Hawai‘i Volcanoes National Park.  HVO does not see any indication of activity migrating elsewhere on Kīlauea volcano  and expects the eruption to remain confined to the summit region.


HVO is lowering Kīlauea’s volcano alert level to WATCH and its aviation color code to ORANGE, reflecting the less-hazardous nature of the ongoing eruption. 

It is unclear how long the current eruption will continue. Kīlauea summit eruptions over the past 200 years have lasted from less than a day to more than a decade. This ongoing eruption is similar to the most recent Kīlauea eruption, which was also confined to Halemaʻumaʻu crater and generated a lava lake. The most recent eruption lasted approximately five months, from December 2020 to May 2021. 

HVO is in constant communication with the National Park Service and Hawai‘i County Civil Defense and other agencies responsible for public safety. 

Hazard Analysis


This new eruption at Kīlauea’s summit is occurring within a closed area of Hawaiʻi Volcanoes National Park. Therefore, high levels of volcanic gas and fine volcanic particles are the primary hazards of concern, as these hazards can have far-reaching effects downwind.

Large amounts of volcanic gas — including carbon dioxide (CO2) and sulfur dioxide (SO2) — are continuously released during eruptions of Kīlauea volcano. Concentrations of SO2 can be much greater than recommended exposure levels on Halemaʻumaʻu rim and extending several kilometers downwind. Exposure to these elevated SO2 levels is considered hazardous and may cause breathing difficulties. Additional hazards include Pele’s hair and other lightweight volcanic glass fragments from the lava fountains that can be entrained in the plume and fall several kilometers (miles) downwind of the fissure vents.

Strong winds may waft lighter particles to greater distances and impact surrounding communities. Residents should minimize exposure to fine volcanic particles, which can cause skin and eye irritation.  As the SO2 plume moves away from the vent, it reacts in the atmosphere to create the visible haze known as vog (volcanic air pollution) that has been observed downwind of Kīlauea. Vog creates the potential for airborne health hazards to residents and visitors, damages agricultural crops and other plants, and affects livestock. 

For more information on gas hazards at the summit of Kīlauea see: https://pubs.er.usgs.gov/publication/fs20173017. 

Vog information can be found at https://vog.ivhhn.org/.  

Other significant hazards also remain around Kīlauea caldera from Halemaʻumaʻu crater wall: ground instability, ground cracking, and rockfalls can be enhanced by earthquakes within the area closed to the public. This underscores the extremely hazardous nature of Kīlauea caldera rim surrounding Halemaʻumaʻu crater, an area that has been closed to the public since late 2007.  

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