Minor eruption at White Island, alert level raised, New Zealand

A minor eruption occurred at New Zealand's White Island (Whaakari) about 09:50 UTC on April 27, 2016 (21:50 NZST), GeoNet reports. 

As a consequence of this activity, the Volcanic Alert Level was raised to Level 3 (out of 5 / Minor volcanic eruption) and lowered to 2 (Moderate to heightened volcanic unrest) after new observations. Aviation Colour Code was raised to Orange. 

No further eruptive activity has been observed since yesterday. Seismic activity remains low and new gas emission data show a SO₂ (sulphur dioxide) flux level similar to that prior to the eruption. 

Wednesday's eruption, accompanied by a moderately elevated seismic activity, deposited material over the north side of the crater floor and up onto north crater wall.

GNS volcanologists flew over White Island on April 28 to assess the impacts of the eruption. A dark-green ash deposit from the eruption covers at least 80% of the floor of Main Crater, and up the sides of the crater wall on both the north and south sides.

At a distance of 500 m (0.3 miles) from the eruption site the ash deposit is about 5 mm (0.2 inches) thick. The green color is due to minerals on the ash.

Ash covering monitoring station at White Island – April 28, 2016. Credit: GeoNet

Image credit: GeoNet

There is currently no indication that activity may be building up at White Island. However, GNS Science staff will not be visiting the main crater floor until further notice due to the heightened state of volcanic unrest.

As reported yesterday, GNS volcanologist Brad Scott visited the volcano last week and confirmed the White Island's Crater Lake level has dropped 2 m (6.5 feet) in the last two weeks. The lake was at about the same level it was in 2014. The drop in water level of the Crater Lake has revealed several islands or crater outlines and the lake temperature has increased 2 ºC (35.6 ºF), from 56 to 58 ºC (132.8 to 136.5 ºF) since February 2016.

White Island volcano before Wednesday's eruption – April 2016. Credit: GeoNet

Scott noted there has been a small decrease in the temperature of the hottest fumarole, from 169 to 161 ºC (336.2 to 321.8 ºF) since February. The SO₂ gas output has ranged between 90 and 480 tons per day (1.0 to 5.5 kg per second) of gas during the last five weeks. These are typical values for White Island.

Geological summary

Uninhabited 2 x 2.4 km White Island, one of New Zealand's most active volcanoes, is the emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The 321-m-high island consists of two overlapping andesitic-to-dacitic stratovolcanoes; the summit crater appears to be breached to the SE because the shoreline corresponds to the level of several notches in the SE crater wall. Volkner Rocks, four sea stacks that are remnants of a lava dome, lie 5 km NNE of White Island. 

Intermittent moderate phreatomagmatic and strombolian eruptions have occurred at White Island throughout the short historical period beginning in 1826, but its activity also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced rapid changes in crater floor topography. The collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. (GVP)

Featured image: An ash eruption from White Island on February 12, 1977 is viewed from off the NE coast. The eruption column originates from the Christmas Crater vent, formed the previous year, shortly after the start of the eruption on December 18. The first 20th century eruption of White Island to produce new magmatic material took place a month after the date of this photo. Intermittent phreatomagmatic eruptions continued until late 1981. Photo by Simon Nathan, 1977 (GeoNet)