Ongoing monitoring at Ruapehu, including a Crater Lake visit to measure the lake temperature and collect water samples, data from airborne gas measurements and seismic activity, have shown declines in the recent measurements. This indicates that the current period of elevated unrest is passing.

The Crater Lake temperature has now dropped to around 23 to 25 °C, having ranged from 34 to 37 °C since October 2007. The latest measurement was 23.3 °C (July 15). The airborne gas plume measurements which had shown significant increases after April 2008 now show that SO₂ and CO₂ gas emissions have decreased to the typical background levels for Ruapehu.

Results from the Crater Lake chemistry are also indicative of cooling in the vent area. The slight increase in the level of volcanic tremor we previously reported has also declined to typical background levels.

These observations are consistent with the volcano-hydrothermal system now cooling. The current phase of volcano unrest appears to be over, however Ruapehu remains an active volcano. Future eruptions may occur without warning.

The Volcanic Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest).

Brad Scott
Volcano Surveillance Co-ordinator

* Previously known as Science Alert Bulletin and Scientific Alert Level.

Ongoing monitoring at Ruapehu, including a Crater Lake visit to measure the lake temperature and collect water samples, data from airborne gas measurements and seismic activity have continued to show variations.

The airborne gas plume measurements show the SO₂ emission has gradually increased since last year’s eruption and the CO₂ flux has varied. The emission rates of both SO₂ and CO₂ gases have shown significant increases since April 2008, being about ten times above the typical background. Our latest measurements on June 12 remains high.

The Crater Lake temperature has remained elevated and fluctuates between 34 and 37 °C. The latest measurement was 35.2 °C (June 12). Sustained heat from depth is required to keep the temperature this high for this length of time. It is believed that the source of this heat is magma within the volcano conduit. This magma is also producing the higher than normal gas flow and other chemical changes in the lake.

The slight increase in the background level of volcanic tremor we previously reported has now declined to typical background levels.

These observations remain consistent with the volcano-hydrothermal system responding to recent eruptions and ongoing interaction with magma in the volcano conduit. The volcano remains in a state of unrest and the possibility of further activity remains at the volcano. If further eruptions occur, they may occur without warning.

The Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest) and will continue to be re-assessed regularly.

Brad Scott
Volcano Surveillance Co-ordinator

The earthquake on Friday has been followed by many aftershocks (several hundreds) and the larger ones have been felt on the Bay of Plenty coast. Monitoring of the volcano since Friday has established that there has been no immediate significant response from the volcano. Starting Sunday morning, and lasting through to Monday we have recorded volcanic tremor and some volcanic earthquakes; these continue intermittently. Volcanic seismicity, including weak volcanic tremor and volcanic earthquakes, are common at White Island. Gas monitoring has not shown any change in gas flux.

White Island is an active volcano and eruptions can occur at any time without warning. As a consequence of this earthquake sequence the eruption hazard at the island may have increased above the normal levels. However as we have not recorded any significant changes over the last few days, it would appear the volcano is returning to a normal quiescent state. Normal cautions should be applied when visiting the volcano.

The Alert Level for White Island remains at Alert Level 1; there is no significant change in volcanic activity on the island.

Brad Scott
for Duty Volcanologist

This morning's earthquake was a tectonic-type earthquake, and these are common in the outer Bay of Plenty. We are recording many aftershocks following this event. The level of ground shaking may have produced some landslides, but we are not aware of any at this time from viewing the camera images. There has been no immediate response from the volcano though the large number of aftershocks means that any seismic response may be difficult to see for several hours.

We will continue to monitor the earthquake activity and, conditions permitting, make a monitoring flight to assess the volcanic gas output. If the volcano responds there is likely to be an increase in gas output and/or an increase in volcano seismic activity.

White Island is an active volcano and there is always a level of hazard associated with it. Moderate-sized tectonic earthquakes are also common events in the outer Bay of Plenty and historically no connection has been demonstrated between them. However as a consequence of this earthquake the eruption hazard at the island may have increased above the normal levels and we would recommend no visits to the island for the next 48 - 72 hours as a precautionary measure.

The active crater at White Island is now occupied by a crater lake, ponding in the crater that formed during eruptions in the 1970s – 1990s. The last eruption at White Island, in 2000, occurred from a vent that is now beneath the lake. Recent volcanic seismicity has included weak volcanic tremor and low frequency volcanic earthquakes, both of which are common at White Island.

The Alert Level for White Island remains at Alert Level 1; there is no significant change in volcanic activity on the island.

Brad Scott
Duty Volcanologist

Data from the airborne gas measurements, seismic activity and Crater Lake temperature have continued to show variations since the September 25 2007 eruption.

The airborne gas plume measurements show the SO₂ flux has gradually increased since last year’s eruption and the CO₂ flux has varied. However the fluxes of both SO₂ and CO₂ gases have shown significant increases in our latest measurements (April 4 and May 7), being about ten times above the typical background.

The Crater Lake temperature has remained elevated and fluctuates between 34 and 36.8 °C. The latest measurement was 34.4 °C (April 26). Sustained heat from depth is required to keep the temperature this high for this length of time. It is believed that the source of this heat is magma within the volcano conduit. This magma is also producing the higher than normal gas flow and chemical changes.

The slight increase in the background level of volcanic tremor has continued, as have some short periods of stronger volcanic tremor. However volcanic tremor and changes in the level of tremor are very common at Ruapehu.

These observations are consistent with the volcano-hydrothermal system responding to recent eruptions and ongoing interaction with magma in the volcano conduit. The volcano remains in a status of unrest and the possibility of further activity remains at the volcano. If further eruptions occur, they may occur without warning. GNS Science will be making further observations this week.

The Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest) and will continue to be re-assessed regularly.

Brad Scott
Volcano Surveillance Co-ordinator

Data from the Crater Lake sampling, seismic activity and airborne gas measurements have continued to show a change since the September 25 eruption.

The airborne gas plume measurements show the SO₂ flux has increased since last year’s eruption. CO₂ flux has varied, but has shown increases recently, while H₂S gas has become measurable since March 2008.

The lake chemistry shows increased Mg/Cl ratios since the September eruption, with variable sulphate and relatively constant chloride concentrations. Chemical equilibrium relationships amongst gases discharging from the volcano suggest that temperatures are increasing in the hydrothermal system at depth.

The Crater Lake temperature rose in response to the eruption by about 20 °C and reached a peak of 37.5 °C by December 21 2007. Since then it has remained elevated and fluctuated between 34 and 36.8 °C. Sustained heat is required to keep the temperature this high for this length of time. It is believed that the source of this heat is the magma that is producing the higher than normal gas flow and chemical changes.

There has been a small increase in the background level of volcanic tremor and some short periods of stronger volcanic tremor. However volcanic tremor and changes in the level of tremor are very common at Ruapehu.

Since September 2007 magma has started to degas more than is normal at Ruapehu and this is carrying with it additional heat which is keeping the temperature of Crater Lake hot. It is not clear if these changes are signs that further eruptions will occur. If further eruptions do occur, they may occur without any warning.

The Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest) and will continue to be re-assessed regularly.

Brad Scott
Volcano Surveillance Co-ordinator

Accompanying the rise in lake level has been a drop in lake temperature from 63 °C to 53 °C, which reflects the lake’s greater volume. The lake colour has also changed from a turbid grey to a light green, reflecting less suspended sediment.

Fluctuations in the level of the lake at White Island, together with its temperature and sometimes colour, are common and reflect several factors including changes in the volcanic steam and gases entering the lake and variations in rainfall.

White Island’s crater lake occupies a crater that formed during eruptions in the 1970s – 1990s. The last eruption at White Island, in 2000, occurred from a vent that is now beneath the lake.

No other significant changes have been observed at the White Island and normal monitoring, including the lake level, is continuing unchanged.

The Alert Level for White Island remains at Alert Level 1; there is no significant change in volcanic activity on the island.

Steven Sherburn
Duty Volcanologist

The Volcanic Alert Level remains at Level 1 (some signs of unrest).

Since our last update (1 November 2006) elevated volcanic earthquake activity has continued at Ngauruhoe. The number of events per day has typically ranged between 5 and 30 earthquakes per day. This activity started in late May 2006 and the largest earthquakes are about magnitude 1.5. Observations suggest that the earthquakes continue to occur within about 1 km of the surface beneath the volcano's northern flank.On January 6 the number of events started to increase and by 9 - 10 January there were up to 80 per day, decreasing slightly since then. The magnitudes of the larger events ranged between M 1.2 and 1.5.

In response to these changes we have visited the volcano. Measurements of volcanic gas concentrations, temperatures and soil gas flux were made at the summit area of Ngauruhoe on 17 January. These data have not changed since the unrest began in late May 2006, and are similar to measurements made in 2006 - 7. The maximum fumarole temperature near the summit remains about 86 °C.

We have also installed 3 portable seismographs to collect more data on the continuing earthquakes.

We have recorded no other signs of unrest at Ngauruhoe, and have no evidence that an eruption is imminent. We will continue to monitor as necessary.

Brad Scott
Duty Volcanologist

As part of the routine monitoring, GNS scientists have analysed fumarole temperature and gases, and measured gas flux through the soil. Gas concentrations in the steam plume were also measured more frequently in response to the earthquakes. Temperatures of the fumaroles are well within the typical ranges for those measurements (100 - 120 °C). Soil gas levels are lower than levels recorded in the last 6 months, but are within the longer term ranges. The gas flux quantified by plume measurement of SO₂, CO₂ and H₂S gas show minor increases, but again are typical of the last two years. The crater lake has changed colour markedly, and vigorous upwelling and low-level geysering have been observed. Nevertheless, the lake’s level does not appear to have changed significantly. The lake temperature has decreased from 67 to 64 °C. Some tall steam plumes have also been observed on fine days, as atmospheric conditions allow plumes to form.

Since the November earthquakes we have also recorded some weak volcanic tremor and rare small volcanic earthquakes.

Recent monitoring indicates some minor changes to the volcano-hydrothermal system. Such changes are not uncommon in this type of system and serves to remind us this is an active volcano.

The Alert Level for White Island remains at Alert Level 1; there is no significant change in volcanic activity on the island.

Michael Rosenberg
GeoHazards Duty Volcanologist

Associated activity at White Island volcano is unchanged as a result of the earthquakes. Tremor levels at the volcano are similar to those recorded over the past few months and visual observations via remote cameras indicate no change in hydrothermal activity. While monitoring indicates no apparent changes to the volcanic system, local and regional earthquake activity may have perturbed the hydrothermal system. Such changes could destabilise the hydrothermal system resulting in local steam explosions with no warning.

The Alert Level for White Island remains at Alert Level 1; there is no significant change in volcanic activity on the island.

Arthur Jolly
Duty Volcano Seismologist

Data from Crater Lake sampling and airborne surveys to analyse gases in the volcanic plume have shown a response to the eruption on September 25, as has the seismic activity recorded by the GeoNet equipment.

The Crater Lake temperature has risen slightly (13 to 19 °C), the SO₂ flux has shown no change, while the CO₂ flux has increased slightly. The lake chemistry shows a slight increase in magnesium, while there is little change in chloride concentrations. There has been a small increase in the background level of volcanic tremor, but almost no volcanic earthquakes. These observations are consistent with the volcano's hydrothermal system responding to an eruption through it. The hydrothermal system has not stabilised as yet and the possibility of further activity remains at the volcano. Any further eruptions may also occur without warning.

The Department of Conservation in conjunction with GNS Science has developed guidelines for access to the mountain and maps showing areas at risk from volcanic activity. Visitors are encouraged to follow these. View Map Here

The Alert Level is now reduced to Level 1 (departure from typical background surface activity, signs of unrest) and will continue to be re-assessed regularly.

Brad Scott
Duty Volcanologist

Analysis of water samples taken on Friday September 28 shows that there has been no major change in the chemistry of the crater lake. A slight increase in magnesium is consistent with vent fluids being injected into the lake after the eruption.

An airborne survey to analyse gases in the volcanic plume was flown earlier today. Preliminary analysis of the data suggests that the fluxes of sulphur dioxide and carbon dioxide from the volcano are low; this means that there is probably no new magma at shallow depths in the volcano.

Seismicity has remained low since the eruption on September 25; the only significant event over the last week has been a smaller volcanic earthquake on Saturday September 29.

We advise people to follow Department of Conservation guidelines for access to the mountain.

The Alert Level remains at 2 (minor eruptive activity) and will continue to be re-assessed regularly.

Further observations and images are available.

We advise people to follow Department of Conservation guidelines for access to the mountain.

The Alert Level remains at 2 (minor eruptive activity) and will be re-assessed on a daily basis.

Craig Miller
Duty Volcanologist

A gas monitoring flight was also conducted this morning to measure any gas that may be associated with the eruption. Preliminary results indicate that only small amounts of SO₂ gas are present (~13 tonnes/day). No other volcanic gases were detected.

Indications from further analysis of the geological and seismic data are that the blast had a strong directionality to it. Most of the erupted material was directed northward towards the Whakapapa ski field, over the summit plateau.

We cannot rule out the likelihood of a future eruption and lahars at Mt Ruapehu in the next few weeks and as such people should follow Department of Conservation guidelines for access to the mountain. Any future eruption may also be strongly directional towards the summit plateau and hence the risk for that area remains high.

So far all evidence indicates that the eruption was hydrothermal in nature with no involvement of magmatic material.

The alert level remains at 2 (minor eruptive activity) and will be re-assessed on a daily basis.

Further observations and images are available.

Craig Miller
Duty Volcanologist

Visual observations of the lake level indicate that it is 2 - 3m below overflow, this indicates that approx 500,000 cubic metres of water was ejected from the lake during the eruption.

There is a strong up-welling from the northern vent under the lake and some sulphur slicks on the lake surface. These are fairly typical phenomena observed at the crater lake following hydrothermal activity.

There is a well-defined and fairly narrow apron of ballistic fall (rocks) to the north of the lake. Most of the ejecta comprised lake floor sediments, some crystalline rocks (altered) and abundant sulphur. So far there is no evidence of fresh magmatic material in the ejecta.

A volcanic gas measuring flight planned for today was postponed due to the strong winds, however data obtained from a gas detection satellite (AURA-OMI) shows no gas signature following the eruption.

These observations suggest that the eruption was most likely hydrothermal in nature, confirming the initial interpretation of the event.

Evidence gathered yesterday indicates that the lahar down the Whangaehu was larger than initially thought, but still much smaller than the March 2007 dam-break lahar.

Monitoring equipment at Dome Shelter was also not as badly damaged as initially thought and seismic data from one of the two systems is continuing to flow, although the data are rather noisy. We are currently relying on nearby monitoring stations to provide us with full seismic monitoring of Ruapehu.

The Alert Level remains at 2 and will be re-assessed on a daily basis.

Craig Miller
Duty Volcanologist