Santorini (Greece): Volcanic Eruptions
1. Define “wonder, ” as in “Geologic Wonder”
a. More than just Beautiful, though that often plays a role in it
b. The natural world (mountains, shorelines, etc.) has long been an
inspiration for artists: painters, musicians, writers….
c. And this course rests upon a premise that when you look at something
with added knowledge about it, it becomes more interesting
i. I could see how baseball might be a painfully slow game to
watch if you weren’t familiar with it.
ii. But I’ve spent so many years of my life playing it, that I watch it
and I see more than the long pauses between pitches; I see the
communication between the pitcher and catcher, the batter
and runners trying to figure that out, and the fielders worrying
about where they will go the moment a ball is hit. There can be
so much going on, even when nothing is happening.
iii. Maybe a better analogy is looking at a person you love. Take a
picture of some random person – one of more than 7 billion on
this planet. They may be pretty, but it won’t mean all that much
to you
1. But take a picture of someone you have known well for
decades, maybe your life’s partner, and you see so much
more, because you know their hopes and fears, their
dreams and struggles, their successes and failures, and
that picture can elicit an intense feeling of love.
iv. The same is true for a mountain. It may be aesthetically
beautiful, but it is just another mountain. But if you know its
history – its formation in the crucible of a massive collision
between ancient continents, its slow and relentless wearing
away under the unforgiving law of gravity for tens of millions
of years – then you begin to see that mountain with the eyes of
a geologist, and it elicits a deep and profound feeling of respect
and of “Wonder.”
d. Another reason that by “Wonder” I don’t just mean beautiful is that it
would just be too arbitrary
i. If you like mountains, like I personally do, you could easily fill
up 36 lectures with beautiful mountains – there are just so
many of them!
ii. But if you like beaches and coastlines, like Margaret does, then
there would be no shortage of spectacular beaches to fill the
course.
2. So, how should I choose what the 36 or so “Geologic Wonders” should be?
There are just so many places to choose from!
a. Decided to give at most one or two lectures on any given geologic
feature or phenomenon, to spread out the lectures across the very
wide array of Earth Science
i. There will be one lecture on waterfalls, one on glaciers, and so
on
b. I have to add that these choices are very arbitrary.
i. There is no consensus as to the Geologic Wonders of the World
ii. There isn’t a list somewhere, like the ancient Seven Wonders of
the World.
iii. – they are only my own choices (though I have gone to experts
I know at many points for advice)
c. So, why should you take my word for it? I have spent a long time
thinking about these things.
i. Have authored or co-written more than 20 science textbooks
from elementary school to graduate school levels
ii. Have led the national Earth Science Literacy Initiative, creating
a list of what every citizen should know about Earth science
iii. Have represented Earth and Space science in the creation of
the nation’s new national K-12 science education standards.
iv. Trust me.
d. Personally, Choosing among the world’s Geologic Wonders has been
very difficult. I confess I agonized for weeks over whether to choose
Iguazu Falls (Argentina) or Victoria Falls as the most spectacular
waterfall. And then there are Angel Falls and Niagara Falls.
i. So, I took the easy way out and came up with a Top 5 list. At
then end of each lecture, I will give you my list of the top
runners-up, sometimes every bit as spectacular as my first
choice!
3. The goal of this course is to help you develop a sense of awe and wonder at
the spectacular world that has formed about us.
a. I hope that you will have the opportunity to travel to some of these
places and see them for yourself!
i. (As they say in Spain, it is not the same thing to speak of bulls
as to be in the ring!)
b. Or, if you have already been to some of them, then for you to be able
see them with new eyes and renew your memories with an increased
sense of appreciation.
c. I confess that I have an ulterior motive as well. I hope that in
marveling at Earth’s Geologic Wonders, you also develop a respect
and appreciation for this unique planet.
i. Humans are intimately connected with Earth
1. We get our resources from it and we are impacted by
natural hazards.
2. But with 7 billion humans on the planet, we are now the
greatest geologic force on Earth’s surface, and we need
to learn our strength and be mindful of it.
ii. I hope that you will begin to see the whole planet with the new
eyes of a geologist.
4. I should also tell you what this course is NOT.
a. It is NOT an introductory geology or Earth Science course. (The
Teaching Company already has those).
i. Now, in explaining how these Geologic Wonders have come to
be, I will be “digging into” many topics that you would find in
one of these courses (Plate tectonics, climate change, Earth’s
evolution, the interconnection of Earth’s many different
systems…)
ii. But, These topics will always be subservient to task at hand of
explaining how these Geologic Wonders have formed, and I
will introduce them and bring them in as they are needed.
iii. There is no course I know of like this taught at any university.
b. This is NOT a course about the “Natural Wonders of the World,”
because this would include living things as well. I would have to
include whale songs, and monarch butterfly migrations.
i. Now, I would definitely want to take such a course on the
“Natural Wonders of the World,” but this is far beyond the
scope of this course.
ii. So, I will not focus on the Great Barrier Reef off the coast of
Australia.
1. But, take a coral barrier reef, bury it for 100 million
years until it turns to limestone, dig it up, and erode it
away into spectacular shapes, and you may have a
Geological Wonder.
2. Life plays a central role in creating the geology of this
planet, so we will certainly spend some time on it.
c. This course will not focus on the ocean, the atmosphere, or other
planets
i. I have tried to focus on places that you could actually go and
visit
1. The deep earth (way down deep) is geologically
wondrous (my own area of research), but you can’t go
there and visit it.
2. The Gulf Stream is remarkable and very important, but
there isn’t much to see there (though there are whole
courses on the ocean!)
3. Geology also includes the study of other planets and
bodies in the solar system, but until we can regularly
hop on a NASA vehicle and visit them, that will be for
another course as well.
5. Last, I tried to choose Geologic Wonders that would have an interesting
STORY to tell, because humans love stories, and they are one of the best
ways, and oldest ways, that we learn about things.
6. And there are few Geologic Wonders with a better story to tell than the
eruption on the island of Santorini, which is the focus of our first lecture:
Volcanic Eruptions
a. 4000 years ago, the Minoan civilization on Crete ruled the eastern
Mediterranean. Their ships controlled trade throughout the region.
b. Their largest city outside of Crete was Akrotiri, on the south side of a
small island of Thera, now called Santorini.
c. If you look at Santorini, it has a very unusual shape: it is basically a
ring of rock. How could such a formation occur? What geologic
process could make this? (I will give you a clue – it is not at all the
same as a
d. At that time, the island consisted of a large, conical volcano that
occupied most of the island.
e. This changed suddenly around 3600 years ago (1600 BCE). An
enormous volcanic eruption occurred, blowing out the entire interior
of the island so that only a ring remains today.
i. Would have spewed ash and dust throughout the region, and
created a devastating ocean tsunami.
ii. The geologic record from Santorini tells a remarkable story
iii. Thin layer of ash, with footprints in it, covered by 60 meters of
volcanic ash.
iv. The enormous blast pulverized and ejected about 60 km3 of
rock
1. For scale, Mt. St. Helens was about 1 km3
2. This is 3x larger than 1883 Krakatoa
v. Akrotiri was destroyed, buried under 200 feet of ash. But no
people were found. Estimates are that they would have only
months to evacuate.
vi. Very different than at Vesuvius, where casts of >1000 bodies
were found, buried in ash. The people here had the chance to
evacuate.
vii. They even took their precious belongings – only one gold
statue was found (under a skeleton in a tomb; someone did try
to “take it with them when they went”).
viii. There is evidence widespread destruction in Crete at that time,
as well as disruption throughout the Mediterranean, even of
widespread fires, and though the Minoans rebuilt, they were
weakened, and within 100-150 years they were overrun by the
Mycenean Greeks.
1. (who, incidentally, stole the Minoan language Linear A
and used it to make the first form of the Greek language
(Linear B)
2. (Linear A remains undeciphered, but if someone could
ever interpret it, we might have the first account of a
volcanic eruption)
f. There are two interesting correlations of events from this time, before
any known written languages
i. 1300 years later, Plato wrote, in the dialogues of Timaeus and
Critias, of the destruction of Atlantis: “But at a later time there
occurred portentous earthquakes and floods, and one grievous
day and night befell them, when the whole body of your
warriors was swallowed up by the earth, and the island of
Atlantis in like manner was swallowed up by the sea and
vanished” [Did I do this in HTEW?]
ii. There are many hypotheses of what may have inspired, but one
is that it was the eruption of Thera.
iii. At roughly the same time, on the other side of the
Mediterranean, the Israelites were leaving Egypt
1. Pillar of smoke and fire; Darkness during the day; Stuff
falling from the sky; the sea opening up (pulling back?)
and then rushing forward
iv. It is possible that the events of this massive eruption not only
changed the course of civilizations there, but provided the
source of two well-known stories from that time, handed down
orally for many hundreds of years: Atlantis and the Exodus.
g. What is the cause of this eruption? Are volcanic eruptions simply
random geologic events? Why here, in this location?
i. For the answer, I need to head back across the Mediterranean
to Africa again. It is, in fact, all Africa’s fault.
ii. As I will discuss more in next lecture (Mount Fujiyama), the
earth’s surface is broken into about a dozen major pieces that
we call tectonic plates.
iii. Thera on a different plate than Africa
iv. Africa rotating counter-clockwise up into Eurasia (causing all
kinds of disruptions)
v. Anatolia (Turkey) is pushed out of the way to the East; pushes
Greece to the southwest; the Greek islands are all volcanoes
that are forming at the boundary between Europe and Africa;
subduction zone volcanoes; water brought down into the
subduction zone causes magma; pressure builds up until an
eruption. Has happened many times before; will happen many
times again!
h. I like starting with this example. Right at the start of civilizations, the
influence of Earth’s geology upon humanity is forcibly and
dramatically demonstrated. These beautiful Greek islands, volcanoes,
only exist because of the plate tectonics of the region: Africa crashing
into Europe, closing up the Mediterranean. But the same forces that
make these beautiful islands can also destroy them; as Plato said, in
“one grievous day and night.”
7. Top 5:
a. Mount Vesuvius, 79 CE (Italy)
i. Birth of Modern Geophysics – eruption described in detail by
Pliny the Younger.
ii. Has come to define an explosive eruption - “Plinian eruption”
iii. First eye-witness description of an eruption: “I cannot give you
a more exact description of its appearance than by comparing
to a pine tree; for it shot up to a great height in the form of a
tall trunk, which spread out at the top as though into
branches. ... Occasionally it was brighter, occasionally darker
and spotted, as it was either more or less filled with earth and
cinders.”
iv. And first description of a tsunami: “the sea seemed to roll back
upon itself, and to be driven from its banks”
v. Has erupted many times – only European mainland eruption
within the past century.
vi. Had only a few years prior been a hiding place for Spartacus
and his army.
vii. Pyroclastic flows and ash falls buried people in-place – more
than 1000 body casts found.
b. Mount Tambora, 1815 (Sumbawa, Indonesia)
i. ~160 km3 of ejecta; largest in recorded human history
ii. eruption directly killed ~70,000; largest in recorded human
history
iii. 1816 = Year Without a Summer (worst famines in Northern
Hemisphere in 19th century)
c. Krakatau, 1883 (Indonesia)
i. Blast heard 5000 km away
ii. ~20 km3 of tephra
iii. killed 40,000 people, most from tsunami
iv. structure before/after is similar to Santorini
v. In the Sumba straits – will eventually connect Sumatra with
Java
d. Laki, 1783 (Iceland)
i. Extended fissure eruption; ejected a great deal of sulfur-based
aerosols
ii. Ben Franklin documented how pale the sun shown in the
summer of 1789 (“Laki haze” from the sulfur dioxide)
iii. Resulting climate change (crop failures in Europe, drought’s in
India, Japan’s worst famine) is responsible for ~6 million
deaths, making it the deadliest volcanic eruption in written
history
e. (Special Mention: Io)
8. Next Lecture: Mount Fujiyama (Japan), and the most spectacular subduction
zone volcanoes
Questions:
1. The Greek islands are currently the location of
volcanoes. Given that Africa is rotating up into Europe
at the rate of about a cm per year, what do you think
will be in the location of Santorini in about 50 million
years?
2. What is the difference between how the famous
eruptions at Santorini and Vesuvius occurred? What
was the result for the people living nearby?