On the Big Island of Hawaii, the towering Mauna Kea volcano is truly an impressive sight
to behold.
If you were to measure Mauna Kea from its starting point on the ocean floor, it would
not only be the tallest volcano but also tallest mountain on the planet, rising a total of
33,496 feet from the ocean floor.
It was so tall that during the last ice age, its summit area even contained glaciers!
However, while many people think that Mauna Kea is a dormant volcano, it could also be
described as active as it has erupted several times during the Holocene period, the last
of which occurred in a cluster of several eruptions between 4,000 and 6,000 years ago.
To further prove this, I have outlined the areas which were covered in lava flows and
ash from the Mauna Kea volcano in the last 10,000 years.
With this being said, despite 5,000 years being a long time, Mauna Kea is likely to
erupt again at some point in the future, perhaps distant future, as two other active volcanoes
which have not erupted in a similar timespan are the Crater Lake volcano in Oregon and
Carrizozo volcano in New Mexico.
The Mauna Kea volcano is the oldest still active volcano on the Big Island of Hawaii,
encompassing a little less than one quarter of the island's area above sea level.
You might note that this volcano somewhat looks similar to Hualalai, as just like that
volcano Mauna Kea does not currently have a caldera.
Although the exact age of Mauna Kea is unclear, it likely began forming somewhere between
800,000 and 1 million years ago.
Its initial activity began with effusive eruptions of basalt composition lava on the deep seafloor,
which created numerous rounded clasts of lava referred to as pillow basalt.
After reaching the surface more than 100,000 years after its first eruption, the main phase
of shield building volcanic activity began.
During this period, numerous lava fountains and spatter cones were generated through effusive
volcanism whose's yearly rate in terms of volume of erupted material was about half
as much as Kilauea's average yearly rate during the last 200 years.
Eventually, three rift zones developed allowing for more distant flank eruptions to more commonly
occur.
One rift zone went towards the south-southeast, one towards the east-northeast, and one towards
the west-northwest.
This caused Mauna Kea's edifice to become somewhat elongated along those three rifts
in a highly rounded triangle like shape.
By 250,000 years ago, more than 90% of Mauna Kea's modern edifice had been constructed.
Volcanism thereafter shifted to a post shield phase.
This caused eruptions to be slightly more explosive but more importantly produce more
viscous lava which in turn created a steeper slope on the volcano.
The boundary between the shield building and post shield lavas can be easily spotted on
Mauna Kea's flanks due to an abrupt change in slope.
While the eruptive rate of the volcano declined during this period to one tenth of what is
was during its shield building phase, numerous cinder cones were constructed and the summit
of Mauna Kea grew in height.
During this period, several glaciers expanded and retreated on Mauna Kea's summit, which
smoothed some of the local topography.
Beginning around 65,000 years ago and continuing to 4,000 years ago, almost all of Mauna Kea's
eruptions were more explosive creating black tephra deposits visible from satellite and
creating the majority of cinder cones which dot its summit, flanks, and three rift zones.
One of these cinder cones, erupted approximately 4,000 years ago.
This eruption's original magma chamber may have led to the formation of an evolving pit
crater which reached the surface sometime between 2015 and 2016.
Although Mauna Kea will erupt again, this is statistically less likely to occur than
100 future eruptions of Mauna Loa happening first.
With this being said, if an eruption was to occur it would likely originate at one of
three rift zones, creating slow moving lava flows but unlike many other Hawaiian eruptions,
depositing at least a dusting of ash across sections of the Mauna Kea volcano, perhaps
within 5 to 6 miles of an erupting vent.
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