On the big island of Hawaii, three of its volcanoes are well known.
The most active of these is the Kilauea volcano, which has been near constantly erupting since
historical record keeping began.
In contrast, the much larger Mauna Loa shield volcano is also well known as its edifice
encompasses the majority of the big island, and it last erupted in 1984.
Also well known is Mauna Kea, which is the tallest volcano in the Hawaiian islands, and
contains a well known astronomy observatory on its summit.
However, the big island also contains a fourth volcano which is largely forgotten about by
tourists, Hualalai.
When you fly into the big island, the runway you land on is built over a lava flow from
this volcano which was emplaced in 1801.
Although it has not erupted since, the area is now heavily populated, meaning a future
eruption could spell disaster for the area.
So, just how active is Hualalai?
What areas are most at risk?
This video will answer these two questions and discuss this fascinating volcano.
The Hualalai volcano encompasses 7% of the Big Island's landmass and encompasses the
central western coastline of the island.
Specifically, its tallest point is located 9 miles or 14.5 kilometers east-northeast
of the city of Kona.
The Hualalai volcano began forming 600,000 years ago at a time when the big island of
Hawaii looked very different as both the Mauna Kea and Kohala volcanoes were near constantly
erupting.
At the time, magma from the underlying hotspot intruded into the crust and erupted onto the
ocean floor, producing layers of a new submarine shield volcano.
Over hundreds of thousands of years, layer after layer of basaltic lava piled on top
of one another, and continued to climb towards the ocean surface.
This stage of volcanic activity deposited so called "pillow basalts" as named due to
the numerous rounded clasts which look similar to pillows.
Then, 300,000 years ago, lavas from Hualalai reached the surface, and began constructing
a new island.
It did not take long for this island to merge with the volcanic edifice to the north, thus
joining it with the larger island.
As the volcano grew larger and larger, magma began intruding underneath Hualalai in dikes
which faced in a northwest to southeast orientation.
This pushed up the overlying crust, creating a series of cracks and forming a rift zone.
This rift zone would go on to produce thousands of eruptions, and may have even contained
a summit caldera at one time.
Occasionally, a flank eruption would occur, building a satellite vent out of small volumes
of ash and lava in what is termed a cinder cone.
These cinder cones only became more frequent when the main phase of shield volcano related
activity ended.
Hualalai entered a postshield phase of activity around 150,000 years ago where new eruptions
became infrequent but when they do occur often produce alkali rich rocks and a'a' or blocky
lava flows.
One of these cinder cones produced an unusual type of lava known as trachyte 100,000 years
ago, and can be found at the location marked on screen.
More recent volcanic activity has been defined by basaltic lava flows which began near the
summit and flowed towards the coastline.
The last of these occurred from 1800 to 1801, and produced two distinct lava flows; one
in each year.
On average, Hualalai seems to produce an eruption about once every 200 to 300 years.
While the last eruption occurred in 1801, this does not necessarily indicate that it
is overdue.
The chance of a new eruption remains the same each year, and there have been closely spaced
eruptions such as in 1784, and 1800 to 1801.
In 1929, an intrusion of magma occurred underneath the volcano, producing a series of large magnitude
6 earthquakes, but this ended without an eruption.
With this being said, the odds of Hualalai producing a new eruption in the next century
are about 40%.
While such a new eruption could initially have a minor explosive component as magma
interacts with abundant groundwater, it would quickly transition to a primarily effusive
eruption.
Such a new eruption would generate a slow moving a'a' lava flow, which would slowly
creep towards the coastline and add new land to the island.
While a new lava flow could occur anywhere on its edifice, it is most likely to affect
an area between the 1800 era lava flow to the north and the Kona International Airport
to the south.
As a result of these hazards, the US Geological Survey designated Hualalai as a high threat
volcano.
I hope that you enjoyed this video.
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