Hawaiian Volcano Update: Kīlauea’s SW Rift Intrusion Wanes
After last week’s ramping up of earthquakes, seismicity peaked at the end of last week coincident with a massive intrusion around the Koaʻe Fault Zone above Kīlauea’s Southwest Rift Connector, and has since dropped off significantly across the volcano. The USGS Hawaiian Volcano Observatory recorded more than 3,000 earthquakes in total during the event, lowering the alert levels from WATCH/ORANGE to ADVISORY/YELLOW on Saturday morning. They report GPS receivers on the Southwest Rift moving laterally up to 8 inches or 20 cm, and upwards up to 20 inches or 50 cm, as their models “suggest an accumulation of as much as 40 million cubic yards (30 million cubic meters) in the region to the southwest of the caldera during this event.” If this estimate holds, that exceeds each of the three eruptions in 2023, and approaches the volume erupted during the 5-month eruption from December 2020 to May 2021, largely during a shorter period of approximately 3 days.
Ground tilt monitors, which at first showed swelling of the southwest caldera and Halemaʻumaʻu at alternating rates, dropped steeply following the progression of earthquakes and magma down the Southwest Rift. Halemaʻumaʻu began to re-inflate after about a day, only to resume deflating over the last two days. The southwest caldera area around Sand Hill has continued to sag ever since the peak of the intrusion, although at slowing rates, suggesting magma continues to leave this area and enter the Southwest Rift. The southwestern south flank of the volcano briefly activated following the migration of earthquakes down the rift, which may prove significant in the future but for now appears to have passed. These numerous but smaller quakes pose little risk to local settling within the Hilina Slump itself, although activation of the deeper faults beneath Kīlauea could eventually lead to the magnitude of shaking required for concern.
Closer to the surface, USGS-HVO crews have discovered new ground cracks in the area of the Twin Pit Craters on the Southwest Rift, in Hawaiʻi Volcanoes National Park’s Kaʻū Desert. They extend “tens of meters in length and centimeters (inches) in width, formed in loose Keanakākoʻi tephra along the Maunaiki trail.” As the activity remained beneath the surface despite the upheaval, gas emissions remain at background levels for the volcano around 70 tonnes of SO2 per day, but still can affect sensitive individuals downwind. Maunaloa remains relatively quiet with few earthquakes, with slowing inflation as it recharges with magma, and remains at the lowest USGS warning level.
