GeoNet reported that a low-level eruption at Whakaari/White Island was ongoing through 12 September, confirmed by data from webcams, overflights, and satellite images. Sulfur dioxide emissions recorded during a 5 September overflight were some of the highest during the previous 20 years. The rate of emissions was lower during an 11 September overflight; though emissions were variable the total gas output remained at higher than normal levels. The vent area appeared slightly larger on 11 September.

The plumes were darker and higher based on webcam images on 11 September, suggesting a substantially higher ash content; less ash was present in the plumes on 12 September. According to the Wellington VAAC ash-and-gas plumes rose 0.9 km (3,000 ft) a.s.l. and drifted E and SE during 13-14 September. The gas-and-ash plumes had been rising a few hundred meters to 1 km above the volcano and drifting tens of kilometers downwind. The plumes were sometimes tracked as far as 100 km downwind, and occasionally the plumes had passed over land. Ash fell as far as 3 km from the island. The Volcanic Alert Level remained at 3 (on a scale of 0-5) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological Summary. The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

Sources: GeoNet, Wellington Volcanic Ash Advisory Center (VAAC)