Easter Island in the remote Pacific Ocean is well known for its carved stone statues,
called Moai. These statues were carved from both layers of ash called tuff,
and black volcanic rock called basalt. However, many people are not aware that the volcano which
is the source of these rocks is likely still active. The volcano I am referring
to is called Terevaka, which represents the largest of the three volcanoes on the island.
This video will discuss this volcano, and mention what its future hazards are.
Easter island is an island territory of Chile which is located 3500 kilometers or
2200 miles west of mainland Chile. Much like the Hawaiian islands,
this island exists due to a hotspot in the crust. Over many millions of years,
this hotspot has created numerous submarine volcanoes, ranging about 500 kilometers in length
of which Easter Island is the youngest feature. Then, 780,000 years ago, magma related to this
hotspot started to form a new volcano through a series of submarine eruptions.
Eventually, this magma reached the surface, and formed the beginnings of easter island.
This early shield volcano, called Poike, continued to erupt high volumes of basaltic lava for several
hundred thousand years before it went extinct. The second volcano to form was called Rano Kau,
which was also a shield volcano. Located at the southwest tip of Easter Island, this volcano began
forming 760,000 years ago. Numerous effusive and moderately explosive eruptions subsequently built
this volcano to a height of about 300 meters. Then, 400,000 years ago, a large eruption
caused a section of overlying rock to collapse downwards at its summit, thus forming a caldera.
Today, this 1.5 kilometer wide caldera is the site of the largest freshwater lake on Easter Island.
The third volcano to form was called Terevaka, and began forming 380,000 years ago in the north
central part of the island. Eruptions from this volcano were similar to those seen at Kilauea
in Hawaii, and were almost completely absent of explosive activity. During eruptions, lava would
gently erupt out of Terevaka's summit, or out of one of the more than a dozen satellite cones on
its flanks. The orientation of these satellite cones is one reason for the unusual shape of
Easter Island. These satellite cones created a range of structures, ranging from small spatter
cones, to large cinder cones, to tuff rings. Then, 210,000 years ago, a large explosion
occurred on the island, as a freshwater lake on the island suddenly flashed to steam and exploded.
This explosion carved out a 300 meter wide and 80 meter tall ring structure of ash
called a tuff ring. This eruption was notable as it created the feature known as Rano Raraku,
which would later be used as a quarry to produce 95% of the island's famous statues.
Eventually, eruptions moved away from the main summit towards a series of fissure on
the western part of Easter Island. Then, 10,000 years ago, a fountain of lava spewed into the air
5 kilometer south-southwest of Terevaka's summit. Over the course of several months,
an a'a' lava slowly creeped towards the ocean. By the time the eruption had ended, an area of
4 square kilometers had been covered with a fresh layer of volcanic rock. The original vent which
produced this eruption, called Hiva Hiva, now stood at 50 meters tall and 300 meters wide.
Since then, no additional eruptions have been documented on Easter Island. With this being said,
we are certain that the underlying volcanic system is still active. In the early 20th century,
a plume of steam was documented coming from the Rano Kau crater. This photo,
although low resolution, indicates that volcanic gasses and likely lava can still be found in an
underlying magma chamber. If a volcano was to erupt again on easter island, it would occur
on the southwest section of the island. Such an eruption would create a new volcanic cone,
and erupt a river of lava which would flow towards the ocean. As a result, it is quite likely that
the main city on Easter island would experience major damage in the event of a new eruption.
Overall, at least two of the volcanoes on easter island have the potential to produce
a new eruption, which have a 1 in 25,000 chance of occurring in any given year.
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