In the North Island of New Zealand, adjacent to the city of Taupo, is a well known volcano
which goes by the same name.
This supervolcano is responsible for the most consistently large volcanic eruptions on the
island, and also the planet's most recent true supereruption.
Although this massive lake filled volcano has not erupted since 260 CE, it will eventually
erupt again.
Evidence of its continuous shallow magma chamber can be found via a series of geothermal vents
emitting volcanic gasses to the north of its primary caldera, most notably at the Craters
of the Moon geothermal site.
However, fumaroles are not the only evidence that this volcano is still quite active.
Approximately once every 9 years, a series of earthquake swarms often accompanied by
ground deformation occurs, hinting at the movement of magma at depth.
While not as pronounced as previous episodes, a series of earthquake swarms began around
the eastern part of Lake Taupo beginning on April 28th and continuing to the present.
During this timespan a total of 85 volcanic earthquakes have occurred, which is more than
3 times the average background rate at this volcano.
These earthquakes have been centered in two clusters, one in the east central section
of Lake Taupo and another centered near the geothermal field to the north.
These quakes occurred at between 3 and 16 kilometers in depth, with the highest magnitude
quake being a mere 3.6.
The highest magnitude quakes were centered in the eastern section of Lake Taupo and were
almost certainly magmatic in origin.
For context, Lake Taupo is a volcanic complex which has been erupting intermittently for
about 300,000 years.
It exists due to an offshore plate boundary where the Pacific plate is subducting underneath
the Australian plate.
Since this subduction has been ongoing for such a long time, it thinned a large section
of crust, causing it to slowly spread apart in what is known as a rift zone.
Volcanoes such as Ruapehu and Taupo formed within this rift zone, which is spreading
apart by about a centimeter each year.
Although Taupo has produced numerous lava dome forming eruptions, it has also produced
some of the planet's largest recent explosive eruptions.
Its largest known eruption occurred 26,500 years ago and ejected 1,170 cubic kilometers
of volcanic rock.
Pyroclastic flows from this eruption wiped out life over a wide swath of the north island,
burying some areas in more than 200 meters or 660 feet thick of ash.
Due to the large amount of ejected material from this eruption, part of the underlying
magma chamber was now empty which caused the ground to collapse downwards like a sinkhole
and form a massive caldera.
This caldera forms the majority of the modern Lake Taupo's outline.
In the last 10,000 years, Taupo has erupted 21 times, with two such eruptions being an
order of magnitude larger than the deadly 1886 eruption of Tarawera.
The larger of these two formed a second smaller caldera in 233 CE, and produced pyroclastic
flows which burned everything in an 80 kilometer radius, even travelling up the summit of Tongariro.
After another much smaller eruption 27 years later, the volcano has not erupted since.
While it has been a lengthy period of time since its last eruption, this does not increase
the odds of an eruption in the near future.
In the last 12,000 years, Taupo has gone as much as 3030 years between individual eruptions.
At the present, Taupo still has a large magma chamber, totaling 250 cubic kilometers of
material which is a mixture of both basalt and rhyolite.
The ongoing earthquake swarm is occurring at the edges of the largely rhyolitic magma
due to a slow and steady influx of material.
This magma over time increases the pressure within the system, eventually triggering a
rock failure or slip at an adjacent fault line, thus triggering an earthquake.
The current earthquake swarm appears to be caused by largely horizontal movement of magma,
as there was no discernible recent ground uplift when checked from satellite.
This is in contrast to several other episodes of volcanic uplift in the last 140 years.
As a result, there is no reason to worry about the current earthquake swarm.
Just like the Yellowstone supervolcano, Taupo produces both hydrothermal and magmatic earthquakes
of which 4,200 have occurred in the last 10 years.
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