What you are looking at is the single tallest sea stack on the planet.
Known as Ball's Pyramid, it is taller above the ocean's surface than it is wide.
And standing at 572 meters or 1,877 feet in height, this island portion of New South Wales
in Australia with its dark black and gray coloration is clearly volcanic in origin.
It might thus seem difficult to believe, but a mere 3.5 million years ago this jagged sea
stack was not visible as instead it was buried underneath layers of volcanic rock.
At the time there was instead a much larger lush and green island measuring 21.6 kilometers
long and 10.2 kilometers wide.
In a manner of speaking, at the time this fascinating feature used to look somewhat
like the island of Faial in the Azores.
Yet, with Lord Howe Island to the north, and a chain of older and younger volcanic features
to the north and south of these two ancient volcanoes there is clear cut evidence of how
they originated.
Much like the Hawaiian Island chain, Ball's Pyramid and Lord Howe Island formed not due
to plate subduction but rather an unusually warm spot in the earth's mantle known as a
hotspot.
This hotspot suddenly appeared 28 million years ago around the same time that 4 other
low intensity mantle plumes were moving underneath eastern Australia and the adjacent ocean.
These other hotspots would go on to figuratively move in a south-southwest direction as they
did not move but rather the overlying Indo-Australian tectonic plate moved to the north-northeast.
The first eruption of the Lord Howe hotspot occurred 28 million years ago, eventually
creating a submarine volcano now known as the Horsehead Seamount which rose over 2,000
meters above the ocean floor.
Moving at a rate of 69.5 kilometers every 1 million years, this hotspot continued to
produce scattered seamounts and volcanic islands over the next 20 million years.
Eventually, it reached the site of the modern Lord Howe Island, which also began initially
erupting as a submarine volcano.
This submarine volcano began erupting basaltic lava 7 million years ago, which starting at
a depth of 2000 meters produced abundant clasts of pillow basalt.
However, eruptions at this region were surprisingly frequent and within 200,000 years it had reached
the ocean surface, explosively erupting and forming a brand new volcanic island.
After a small ash plateau was created, lava flows covered this.
Over the next 300,000 years, this feature continued to grow a lush green island which
was settled by many birds and forests.
During this time, it even developed a several kilometer wide caldera as the island expanded
to be about the modern size and height of the Cerro Azul shield volcano in the Galapagos
Islands.
As eruptive activity from Lord Howe island waned, the hotspot was now centered 30 kilometers
to the south-southeast.
6.5 million years ago, a new submarine volcano erupted, often coloring the regional ocean
a cyan blue as this volcano continued to grow.
Over time, this smaller volcano reached the ocean surface around 6.35 million years ago,
and just like Lord Howe Island, grew to be lush and with a profile instantly recognizable
as a shield volcano, even including a small summit caldera.
This small caldera was supplied molten rock from an at depth magma chamber which had the
shape of an inverted wedge.
This represented the figurative neck of the volcano which included its magma conduit to
its central vents.
Reaching a height of 1200 meters, lava continued to erupt from Balls Pyramid Island, which
caused flows of black lava to roll over some surface vegetation.
However, this volcanism would not last, and eventually Balls Pyramid shifted to a weaker
post shield stage volcanism, causing its caldera to disappear.
Eruptions eventually ceased altogether as the hotspot shifted further southward.
Over the next 6 million years, the outer edges of the island eroded away and the entire mass
slightly subsided into the ocean.
The island continued to shrink until only the hardest volcanic rock remained, that within
the volcanic neck.
This is now what we see at Balls Pyramid as much like Nihoa it is a highly eroded remnant
of a now almost completely submerged extinct volcano.
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