On March 21st, 2022, the alert level of Mount Ruapehu in New Zealand was raised from 1 to
2, corresponding to a change from green to yellow.
This change was made due to it showing signs of activity as increased temperatures were
detected at its summit crater lake along with high levels of volcanic earthquakes.
Ruapehu is the most active volcano on the north island of New Zealand, as it has erupted
42 times since 1950.
Between 1889 and 2007 an eruption occurred like clockwork about once every two years.
However, since 2007, it has not produced a single eruption, representing the longest
absense of eruptive activity since 1889.
So, is Ruapehu going to erupt?
Was is the significance of its raised alert level?
This video will answer these two questions and discuss the ongoing seismic unrest.
The Ruapehu volcano is located in the south central section of the North Island of New
Zealand, where it is 230 kilometers north-northwest of Wellington.
This volcano exists due to an unusual geologic setting.
To the east of the North Island is a tectonic plate boundary, where the Pacific Plate is
colliding with the Australian plate.
Some of the subducted crust from this collision then melts and migrates upwards, resulting
in a series of volcanoes.
However, in this section of New Zealand, subduction has been ongoing for long enough that it caused
a section of overlying crust to thin.
As a result, hot material from the mantle rushed upwards to fill the empty space, resulting
in a rift zone.
This rift zone is referred to as the Taupo Volcanic Zone, and is slowly spreading apart
to the east and west, allowing for magma to intrude into the crust and erupt onto the
surface.
At Ruapehu, this process has been ongoing for 200,000 years, which over time constructed
the island's tallest active volcano.
Since a magma chamber is still ever present, residual heat and gasses from this molten
material is transferred upwards and released at a series of fumaroles and hot springs.
The main site of this activity is the volcano's central crater lake.
Thus, by monitoring the temperature, pH, and amount of gas around the lake, it can be determined
if the volcano is showing signs of unrest.
A higher temperature indicates more activity.
At Ruapehu, its crater lake commonly produces 1 to 6 month long cycles where its temperature
varies from 20 to 40 degrees Celsius.
One such heating trend unexpectedly began on March 13th, and its temperature has since
increased from 28 to 31 degrees Celsius.
On its own, this isn't all that notable, as typically temperatures above 42 to 45 degrees
Celsius are best indicative of an imminent eruption.
However, this increase in crater temperature simultaneously occurred alongside a large
increase in volcanic earthquakes.
These earthquakes are caused by the movement of volcanic gasses underlying the summit.
Taken into account the amount of gas and associated heat indicated by the earthquakes there is
a potential problem.
The crater lake is heating up at a much slower rate than it should be.
This suggests that a partial blockage exists underneath the lake.
Given sufficient time, enough heat and combustible gasses could build at this blockage until
it becomes too great, exploding upwards in a volcanic eruption.
With all of this being said, an eruption is not imminent as one is not even certain in
the first place.
In the last several years, Ruapehu has on multiple occasions been placed on a raised
alert level due to a similar sequence of events.
While this week's increase in activity is slightly unusual, it does not standout as
truly noteworthy.
The local volcanologists I spoke with had the same opinion, as they thought an eruption
was unlikely at this time.
Of course, volcanic eruptions triggered by steam explosions are incredibly difficult
almost downright impossible to predict, as seen for example with the deadly eruption
of White Island in 2019.
Thus, with the raised alert level present a phreatic eruption could theoretically occur
with little or no warning while it remains.
However, in all likelihood nothing will occur.
With this being said, I would advise staying at least 2 kilometers away from its crater
lake as this represents the outer boundary of where bombs of lava have reached during
historical eruptions.
Thanks for watching!
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