The island of Milos in Greece is well known for its beautiful scenery.
One of its prominent features is the Sarakiniko Beach, whose thick white rocks formed through
highly explosive volcanic eruptions as almost the entire island is volcanic in origin.
However, the volcano which caused the creation of this unusual landscape is by no means extinct
but rather is still active.
Looking around the island there are a number of spots in the landscape where volcanic gasses
rise out of the ground, or bubbles rise to the surface just off the coast from submarine
fumaroles.
And, in 140 CE, a volcanic eruption was witnessed by Roman residents, leading to the destruction
of a small town near the coastline.
Although the island of Milos is less volcanically active than the island of Santorini, it could
still produce a similar repeat of that Roman era disaster.
The volcanic island of Milos is located in south central Greece, where it is 150 kilometers
south-southeast of the city of Athens.
While it might initially look like this island contains the remains of an ancient caldera,
this is not the case.
Rather, the water filled "U" shaped section represents a tectonic graben, aka a low point
caused by two large faults which run adjacent to the edge of the bay.
Volcanic activity over a timespan of several million years formed vents which were centered
to the east and west of this bay, thus creating the island's modern shape.
The island of Milos is part of the Aegean volcanic arc which also contains the volcanoes
Methana, Santorini, and Nisyros.
It exists due to a tectonic plate collision more than 150 kilometers southwest of the
island where the African plate is subducting underneath the Aegean Sea plate.
The melted material from this collision then migrates upwards until it erupts onto the
seafloor, forming a chain of shallow submarine volcanoes.
Volcanic activity at Milos began 3.3 million years ago when a variety of unusually viscous
rhyolite magma erupted onto the seafloor at depths of approximately 300 meters.
Although some explosive activity occurred, it was largely suppressed by water pressure
at this depth.
Over tens of thousands of years a series of rhyolite lava domes grew on the ocean floor
and overlapped one another, forming the beginnings of the Kimlos island which is located northeast
of Milos.
The construction of the island of Milos began 3.08 million years ago when a similar series
of submarine vents erupted onto the seafloor.
Over the next several hundred thousand years several dozen vents erupted in the same region,
forming much of what is now the western half of Milos.
Around 2.6 million years ago, a cluster of highly explosive eruptions occurred at shallow
depths to the east, ejecting large volumes of white tephra into the air.
Much of this tephra settled back to the slopes of the existing volcanic edifice, forming
a thick bed of material which eventually became Sarakiniko Beach.
For context, large rhyolitic eruptions often leave behind large volumes of white tephra
that is primarily composed of pumice.
Take for example the similarities the tephra layer has to the deposits left from the caldera
forming rhyolite eruptions of Mount Churchill in Alaska.
Due to a combination of volcanic activity and magmatic uplift, the volcano permanently
broke the ocean surface around 1.4 million years ago.
The two islands later connected, forming the modern U shaped Milos.
In the last 1 million years, eruptions have almost universally occurred on the eastern
side of the island.
One of these eruptions formed a beautiful cluster of polygonal columns shown here.
Since then, volcanic activity has been largely phreatic in nature, constructing a series
of tuff rings.
One such 1700 meter wide tuff ring on the south of the island formed in a series of
highly explosive eruptions between 110,000 and 60,000 years ago.
The only historical eruption occurred in 140 CE when a volume of magma caused a large chunk
of groundwater to flash to steam and explode.
This created a pyroclastic flow which raced towards the coastline, burning several buildings.
These buildings would later be buried by lahar deposits up to 4 meters deep.
Although an eruption is unlikely for the immediate future, if one were to occur it would almost
certainly be phreatic and occur in the region which I have outlined on screen.
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