A moderate earthquake shook Hawaii overnight as the volcanic eruption at Kilauea’s summit continued. With the eruption somewhat more stable, the USGS and the Hawaii Volcano Observatory (HVO) changed the color code and alert level tied to the ongoing eruption yesterday. With evolving volcanic conditions on the Big Island, residents and visitors are urged to stay vigilant should the eruption or earthquakes take a turn for the worse even if its unlikely in the immediate term.
The U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) recorded a magnitude-4.6 earthquake located east-northeast of Pāhala on Tuesday, October 5, at 8:37 pm local time / 3:37 am ET. The earthquake was centered about 5 miles east-northeast of Pāhala, at a depth of 20 miles. Light shaking, with maximum Intensity of IV on the Modified Mercalli Intensity Scale, has been reported across parts of the Island of Hawai‘i. At that intensity, the USGS says significant damage to buildings or structures was not expected. The earthquake was not strong enough to generate a local tsunami.
According to HVO Scientist-in-Charge, Ken Hon, the earthquake had no observable impact on Mauna Loa and Kīlauea volcanoes. “This earthquake is part of the ongoing seismic swarm under the Pāhala area, which started in August 2019. Webcams and other data streams show no impact on the ongoing eruption at Kīlauea. Please be aware that aftershocks are possible and may be felt. HVO continues to monitor Hawaiian volcanoes for any changes.”
Earthquakes in this swarm occur beneath Kīlauea’s lower Southwest Rift Zone, beneath the town of Pāhala and in an area extending about 6 miles offshore. Most of the earthquakes occur at depths of 15–25 miles. Some scientists hypothesize that earthquakes here are the result of magma movement heading from the Hawaiian Hotspot responsible for the volcanic activity in Hawaii towards the volcanoes on the Big Island. Hawaii’s Big Island is home to three active volcanoes: Kilauea, Mauna Loa, which is the world’s largest active volcano, and Hualalai. Only Kilauea us erupting at this time.
The Volcano Hazards Program Office, through regional groups responsible for volcanoes of concern within their geographic area of concern, is responsible for issuing Aviation Codes and Volcanic Activity Alert Levels. Aviation Codes are green, yellow, orange, or red. When ground-based instrumentation is insufficient to establish that a volcano is at a typical background level of activity, it is simply “unassigned.” While green means typical activity associated with a non-eruptive state, yellow means a volcano is exhibiting signs of elevated unrest above known background levels. When a volcano exhibits heightened or escalating unrest with the increased potential of eruption, it jumps to orange. Finally, when an eruption is imminent with significant emission of volcanic ash expected in the atmosphere or an eruption is underway with significant emission of volcanic ash into the atmosphere, the code becomes red. Volcanic Activity Alert levels are normal, advisory, watch, or warning. As with aviation codes, if data is insufficient, it is simply labeled as “unassigned.” When the volcano is at typical background activity in a non-eruptive state, it is considered normal. If the volcano exhibits signs of elevated unrest above background level, an advisory is issued. If a volcano exhibits heightened or escalating unrest, a watch is issued while a warning is issued when a hazardous eruption is imminent.
With things stabilizing at Kilauea and no signs of an imminent eruption at Mauna Loa, the Alert Levels/Color Codes are at WATCH/ORANGE for Kīlauea and ADVISORY/YELLOW for Mauna Loa at this time.
Lava continues to erupt from multiple vents along the floor and western wall of Halemaʻumaʻu crater. As of yesterday morning, all lava activity is confined within Halemaʻumaʻu in Hawai‘i Volcanoes National Park. Seismicity and volcanic gas emission rates remain elevated. Sulfur dioxide (SO2) emission rates remain high, with preliminary measurements of approximately 7,000 – 9,000 tonnes per day on October 4, 2021.
Lava continues to erupt from multiple vents within Halemaʻumaʻu. The west vent continues to be the most vigorous source, with sustained lava fountain heights of 43–52 feet and bursts up to 66 feet observed. The lava lake has risen to the base of the west vent, around which a spatter rampart is being built. Other vents continue to be active in the southern part of the lake, with sustained lava fountain heights of about 3–16 feet. Due to the location of vents, the lava lake is not level across its surface; areas closer to vents are higher in elevation.
Localized and discontinuous crustal foundering continues; according to USGS, this is a process by which cool lava crust on the surface of the lava lake is overridden by less-dense liquid from below causing the crust to sink into the underlying lake lava.
This new eruption at Kīlauea’s summit is occurring within a closed area of Hawai’i Volcanoes National Park. Therefore, high levels of volcanic gas are the primary hazard of concern, as this hazard can have far-reaching effects down-wind. Large amounts of volcanic gas—primarily water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2)—are continuously released during eruptions of Kīlauea Volcano. As SO2 is released from the summit, it reacts in the atmosphere to create the visible haze known as vog, or volcanic smog, 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.
Additional hazards include Pele’s hair and other lightweight volcanic glass fragments from the lava fountains that will fall downwind of the fissure vents and dust the ground within a few hundred yards of the vents. Strong winds may waft lighter particles to greater distances. USGS and local Civil Defense officials caution that residents should minimize exposure to these volcanic particles, which can cause skin and eye irritation.
Other significant hazards also remain around Kīlauea caldera from Halemaʻumaʻu crater wall instability, ground cracking, and rockfalls that 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.