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Nava Fedaeff
Steam has been observed to rise from the warm surface of the crater lake, and increased gas emissions have raised the mountain’s volcanic alert rating to level two.
The higher alert level and increased activity in Mount Ruapehu’s crater lake are not an indication that an eruption will occur, but it is possible.
The crater lake, Te Wai ā-moe, warmed to 43 degrees Celsius on Monday, prompting GeoNet to improve its Volcanic Alert Level (VAL).
Alert level 2, indicating moderate to intense volcanic disturbances, remains in place.
That means that volcanic disturbances mean that hazards can occur on or near the active volcano. It has the potential to explode with little to no warning.
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An eruption can include explosions, flying rocks, rapidly moving hot ash clouds, lava flows and domes, landslides, volcanic gases, lightning, or earthquakes.
“The Volcanic Alert Level reflects the current level of volcanic upheaval or activity and is not a forecast of future activity,” read a statement from Michael Rosenberg, volcanologist on duty at GeoNet.
GNS Science / Supplied
A GNS Science technician takes measurements in the crater lake of Mount Ruapehu as part of regular monitoring of the volcano (FILE).
How often does the lake get hot?
The crater lake has warmed like this many times before without causing an eruption, often fluctuating between 15 ° C and 45 ° C throughout the year.
Rises above 45 ° C can cause a rash, but is not guaranteed.
Te Wai ā-moe warmed from 24 ° C to around 40 ° C in February this year, and in April 2019 it reached 42 ° C. The highest temperature ever recorded at the lake was 60 ° C in 1968 .
The alert level in the area has not risen to level 2 since 2016, when the lake warmed to 46 ° C. The alert remained in place for four months at the time.
When did it last erupt?
The last eruption was on September 25, 2007. The explosive eruption lasted about 7 minutes and caused ash, rocks, and water to spread over the summit area.
It produced lahars, mud streams caused by lake water that is projected onto ice and snow, in two valleys, including the Whakapapa ski field.
There was no large amount of ash, unlike the 1996 eruption.
What are scientists looking for to cause a change in alertness?
Rising lake temperatures, an increase in short-lived pulsating volcanic tremors, and gas leakage prompted the alert level change on Monday.
The aviation color code has also changed from green to yellow, indicating signs of elevated disturbances.
An exclusion zone, which stretches 2 km around the top of the mountain, has made the area off-limits for guided walks. The Tongariro Alpine Crossing is not affected and remains open, confirmed the Department of Conservation (DOC).
RNZ
There is a two-kilometer exclusion zone around Mount Ruapehu’s crater lake, Te Wai a-moe, after GeoNet raised its volcanic alert level.
“The Tongariro National Park is an active volcanic area, so eruptions can occur with little or no warning. The closer people are to the park’s active volcanic vents, the greater the risk, ”said DOC Tongariro Operations Manager Connie Norgate.
A recent gas flight showed that the lake was “well mixed” with some flow over the outlet. Gas production had increased due to warming, with the highest amounts of carbon dioxide and sulfur gases recorded in the last 20 years, according to GeoNet.
There has also been an increase in energy input into the lake in the last month, around 200 megawatts to 400 MW.
What happens next
GNS Science and the National Geohazards Monitoring Center are monitoring the volcano for more signs of activity.
It is monitored by a network of seismic and acoustic sensors, GPS receivers and sensors on the lake, as well as visits to the area and flights.
If unrest continues to increase and the probability of an eruption increases, the summit danger zone, a radius of 3 km from the lake, may be closed.
