Brad Scott, GNS Science Volcanologist
This post was originally published by GeoNet.
Following the 9 December devastating eruption at Whakaari/White Island we have put together some information about the island.
New Zealand’s most active volcano Whakaari/White Island is currently New Zealand’s most active volcano, it has been since an eruptive episode started in 1976. It was in almost continuous eruption from 1976-2000 and numerous explosive eruptions impacted the entire Main Crater floor area. A second eruptive episode started in 2011 and continues today. Whakaari/White Island is a cone volcano and has built up a typical-looking volcanic cone from many small but locally significant eruptions over a long period. The cone rises about 900m above the local sea floor but most of the cone is below sea level.
Eruption styles at Whakaari/White Island
Whakaari/White Island is a wet volcano with a crater lake and typically has explosive eruptions. These occur with little-to-no warning, and often impact the Main Crater floor area. These explosions eject hot rocks (cannonball-like projectiles), ash clouds and surges (pyroclastic density currents).
What is a phreatic eruption?
A phreatic eruption is driven by superheated steam and gas. Often this steam and gas builds up behind a rock and mineral seal and when the strength of that seal is exceeded by the gas pressure, an explosive eruption can occur. The gas driving the eruption likely comes from a deeper source of magma, but the magma itself is not directly involved. Phreatic eruptions can also occur when hot magma comes into contact with cold ground water, but we don’t believe this is the situation at Whakaari/White Island.
Danger to coastal communities
Whakaari/White Island lies about 50 km from the North Island coast so there is an extremely low likelihood of any effects from the eruption on the mainland. If there were any effects, the most likely are fine ash falls (like pollen) and the smell of volcanic gas, which are more likely to just be a nuisance.
Communicating the volcano’s status
In New Zealand we use the NZ Volcanic Alert Level System to communicate the level of activity at the active volcanoes in New Zealand. Information about the level of activity is posted to our website, app and social media by way of Volcanic Alert Bulletins. The NZ Volcanic Alert Level System has 6 steps. Level 0 is a quiet volcano where no activity is occurring. Levels 1 and 2 relate to ‘volcanic unrest’, this is when we detect changes at the volcano (earthquakes, ground movement or gas emissions etc.) that indicate a change in status. This may be an increase or decrease in activity. Alert Levels 3, 4 and 5 relate to small, medium and large eruptions and the likely area affected. An eruption can occur from any level with no warning, and the levels may not move in sequence as activity can change rapidly.
Is it unusual to go from Level 2 to an eruption?
An eruption can occur at any Volcanic Alert Level (Level 1 or Level 2). There are also times when the volcano is raised to Level 2 with no subsequent eruption.
In 1914 a landslide destroyed a mining village and killed 10 workers on the Main Crater floor. There was no eruption related to this landslide.
Over the next 24 hours we estimate an equal likelihood of either no eruption or a smaller/similar sized eruption that would impact the Main Crater floor. There is a high level of uncertainty associated with this estimate. We also estimate that the least likely scenario is a larger eruption.
Current eruption information
- Eruption occurred 2.11pm NZST 9 December 2019 – it was a short-lived event, of 1-2 minutes duration
- The eruption has impacted the Main Crater floor area. Ash and debris cover the crater floor
- The eruption created a steam and ash column to 12,000 ft (3-4km) above the island
- We raised the Volcanic Alert Level to Level 2 from Level 1 on November 18 to reflect heightened activity at the island
- Monitoring equipment on the island is still functional and providing near real time data
- While we have seen a steady decline in activity, there remains significant uncertainty about any future activity
- The Volcanic Alert Level remains at Volcanic Alert Level 3 (minor volcanic eruption)
- During the eruption, the Volcanic Alert Level was at Level 4 (moderate volcanic eruption)
- The Volcanic Alert Level relates only to volcanic activity, and not impact. Even small eruptions can have devastating impacts, as is the case with this eruption
- We will continue to closely monitor Whakaari/White Island
- GeoNet has been continuously monitoring Whakaari/White Island for many years. It is New Zealand’s most active volcano
- GNS Science experts are providing update information to both national and regional responding agencies
- GNS Science’s role is to advise responding stakeholder agencies
- We are updating the public (and media) via Volcanic Alert Bulletins