GeoNet reported that seismic activity at Tongariro remained low during 14-16 August; weather conditions prevented observations of the craters. There were several reports of gas odors on 15 August, particularly from the Manawatu region (S). On 17 August GeoNet noted that although very minor amounts of ash were emitted in the first few days after the eruption, there had been no significant activity since 6 August. Seismic activity had returned to low levels after the eruption. The Alert Level was lowered to 1 (on a scale of 0-5) and the Aviation Colour Code remained at Yellow (second lowest on a four-color scale).

Geological Summary. Tongariro is a large volcanic massif, located immediately NE of Ruapehu volcano, that is composed of more than a dozen composite cones constructed over a period of 275,000 years. Vents along a NE-trending zone extending from Saddle Cone (below Ruapehu) to Te Maari crater (including vents at the present-day location of Ngauruhoe) were active during several hundred years around 10,000 years ago, producing the largest known eruptions at the Tongariro complex during the Holocene. North Crater stratovolcano is truncated by a broad, shallow crater filled by a solidified lava lake that is cut on the NW side by a small explosion crater. The youngest cone, Ngauruhoe, is also the highest peak.

Source: GeoNet