I'm in Sicily.

I'm having a great meal, as usual, but this show is not going to be about food, it's going to be about geology because in my opinion, the geology of Sicily is every bit as tasty as the food.

Sicily rises in the heart of the Mediterranean Sea.

The entire Mediterranean region has long been gripped by powerful geologic forces, literally squeezing it from all sides.

[Thunder] At the crossroads of this earthly fury is Sicily, ground zero for the head-on collision of two tectonic plates, the African and Eurasian plates.

Millions of years of this relentless collision have forged a dynamic island graced with alluring rocks, transformed by people into marvelous works of art and architecture.

We're in Sicily, where Africa literally meets Europe, geologically.

So this is "Doug's Geology Journal."

Let's go explore this unique, incredible island.

♪ ♪ Announcer: Funding for this program was provided by the National Science Foundation.

♪ Doug: The island of Sicily is 10,000 square miles in size, or 26,000 square kilometers, about the size of the state of Massachusetts.

It's only a few miles, a 30-minute ferry ride, across the Strait of Messina to mainland Italy and the rest of the European continent.

To the south, the African continent is 90 miles away across the Mediterranean, but geologically there is no separation between Africa and Europe on Sicily.

I'll draw you a picture to show you how Sicily straddles two tectonic plates, the Eurasian and African plates, where they have been crashing head-on for over 60 million years.

The collision is forcing the African Plate to subduct below the Eurasian Plate, slowly crumpling the seafloor upward.

Eventually, a chunk of the seafloor has emerged to become land, and that chunk is the island of Sicily.

So, much of Sicily is made of rocks that were once part of the seafloor.

Not all of it, though, as we'll see later in the show.

But mostly, Sicily's rocks are limestone, which formed from the accumulation of sea creatures that left their skeletons to pile up on the seabed.

Today, limestone is seen in massive rock formations and cliffs all over the island.

Wow!

Ho ho.

The edge of Sicily.

That's a long way down to the Tyrrhenian Sea.

Looks like about 400 feet.

So, this is all limestone, beautiful limestone rocks.

And if you pick one up-- this rock, limestone is a very heavy rock.

Sicily's limestone has served its inhabitants exceedingly well through the ages, perhaps nowhere as well as in this gorgeous coastal town.

I'm in the town of Cefalù on the north coast, and right behind the town is a giant chunk of limestone, rising up about 800 feet.

This beautiful sheer-sided limestone was a very important piece of the people's existence here for centuries.

So I'm just going to climb up the rock and go up to the top.

Here we go.

This rock, or mountain, is called Rocca di Cefalù, and climbing its steep trails is a fun thing to do.

But long ago, the climb was often done for sheer survival.

So this huge limestone mountain next to Cefalù was a great benefit to the people in one big way, and that was protection.

There were lots of raids through the centuries against the people of Cefalù, and they would just come up here, and they could sustain themselves during a siege for a long, long time because they built a settlement up here.

One of the ancient structures they built up here is thought to be the oldest in Sicily.

This is the Temple of Diana, and it's built out of limestone blocks without mortar.

And you can see the incredible amount of fossils in these blocks.

It was built about 3,000 years ago, and here it stands today.

And there have been tons of earthquakes through the millennia, so it's kind of a testament to how durable limestone is as a building material.

All over Sicily, ancient, sturdy limestone buildings and works of art are a feast for the eyes.

This amazing cathedral in downtown Palermo is made out of limestone, just like most of the buildings in Palermo and in this whole western part of Sicily, because that's the rock they had to work with.

It's pretty interesting because you go to other parts of Sicily, there's different kinds of rock and the buildings there are made out of that kind of rock, and I'll tell you what that kind of rock is when we go there.

But let's not go there quite yet.

First, let's make a must-see stop in southern Sicily on the Eurasian Plate, which is the plate we've been on so far.

This is called the Valley of the Temples, but that name is not quite right because, actually, all these temples are built on a plateau.

The plateau is made out of limestone-- surprise, surprise.

[Chuckles] And so are the temples themselves.

Right next to the Valley of the Temples, the town of Agrigento was actually built on the same limestone rock layer, but the town is higher up because the rock layer was shoved up and over the rocks below it by tectonic forces, which bent the limestone upward.

Geologists call this a thrust sheet, or a nappe.

[Sighs] Ahh.

If you don't mind, I need a nap.

But, actually, I already have a nappe.

I'm sitting on a nappe.

This entire town of Agrigento is built on a nappe, spelled n-a-p-p-e.

The two plates that are coming together under Sicily are compressing the Earth's crust and making it bow up here, and they put Agrigento right at the top of this nappe.

So I'm going to take a nap on this nappe.

So, buonanotte.

The colliding plates created nappes all over Sicily, especially inland.

Let's take a look at a few on the European Plate.

If you go inland, first of all, you're going to be on an incredible winding road, and, second of all, you're going to come to a lot of limestone cliffs, like the one behind me here.

[Thunder] Oh!

That is incredible.

There's a huge thunderstorm behind that hill town over there.

That town is Calascibetta.

It's one of the hill towns in central Sicily built on a nappe.

Right across the valley is another hill town called Enna.

This unique geologic situation led to the area's selection as a geopark.

The concept of a geopark was created to protect geologic landscapes that are of incredible and unique value.

A geopark is an international designation.

It's a UNESCO designation, a very special one.

So this whole area is a geopark, and it's being protected as one, hopefully, forever.

The Rocca di Cerere Geopark is one of two in Sicily.

The other geopark protects another thrust-up limestone mountain range, where fine hiking trails beckon.

I was so excited to be here that I set off immediately for the outback, but I forgot something important... a camera.

The Madonie Mountains, or Madonia Mountains, are the highest range in Sicily.

And it's all limestone, beautiful limestone rocks.

As you hike around in this range, it isn't long before you notice something strange about the rocks.

When you get up here, it's just rubble.

There's little rocks, medium-sized rocks, but there's no giant outcrops, there's no walls of rock anywhere.

One reason for that is because as the mountains rose up, strong tectonic forces, fractured the limestone and made it vulnerable to being torn to rubble by erosion as the mountains grew.

If you glance down and take a look at the rubble, you'll discover that this is not just any rubble.

I'm at the top of the mountain now, 6,200 feet.

There's fossils everywhere.

There are a lot of corals and things that came from the bottom of the sea.

And there's so many that I'll just bend down.

I'll close my eyes.

I'm going to bend down, pick something up.

And look at that.

That's just crazy.

There's these beautiful fossils in it.

And now for something completely different and un-limestone-like.

The Madonie Mountains are the highest mountain range in Sicily, but the highest single mountain is nearly twice as high.

That's because it's an active volcano, Mount Etna.

OK... Doug, voice-over: It's possible to get close to the top, which is 11,000 feet, or 3,300 meters, if you're lucky.

This is the Funivia.

It goes quite a ways up but nowhere near the top.

I'll still have to walk.

Here we go.

Etna is a very unusual volcano.

[Rattling] It's an unusual-- Etna's a very strange volcano because it erupts both basaltic lava, basalt, and ash, whatever mood it's in.

So all of a sudden, we're in the clouds.

It's snowing.

Wow.

It just popped through.

I think we're going to be good.

Wow.

OK.

But I started noticing more and more hikers retreating as the snow and fog thickened.

I wondered how much further I could go.

So now I'm up about 9,000 feet, yeah, and it's snowing.

It's kind of like hail, actually.

So what about Etna's erupting both lava and ash?

One theory says that it's because the subducting African Plate has developed a big tear where it bends down under the Eurasian Plate.

This allows magma from below the crustal plates to rise up through the tear and get to the surface quickly, erupting as lava.

But normally when volcanoes sit over subduction zones, the magma is created within the plates, where it is mixed with crustal materials, including water, making it erupt with lots of ash.

By now, the snow and fog on Mount Etna was so thick that hikers could be mistaken for ghosts floating in the murk.

Filming the summit was hopeless.

Well, that didn't work.

Too snowy up there.

We'll try tomorrow.

The next morning, I woke up lucky.

From my hotel room in the town of Taormina, I could see Etna, perfectly cloudless, and it was even erupting.

So I'm going up today again.

It's a beautiful day, so this is going to work today.

It's so exciting.

Today's eruption was lava, erupting from several of Etna's summit craters, but only the smoke was visible in daylight.

It's very active up there.

It's actually erupting right now.

Mount Etna is very young geologically.

It's only 500,000 years old.

And when it started its life, it was on the seafloor, so all of this land was under the sea, and it built up the mountain over 500,000 years, and now it's at 11,000 feet more or less.

So that's very fast growth.

It's going to be snowing here in about an hour, just like it was yesterday, but we're good.

We got up there and saw it in the sun, saw the entire volcano erupting.

What more could you ask for in life?

Whoo!

But I couldn't pass up climbing a volcanic cone rising on Etna's flank before leaving the mountain.

This little miniature volcano on the side of Mount Etna had erupted ash, like this.

It was an explosive eruption, and now Mount Etna is mainly erupting lava.

It still erupts ash, but it's more lava than ash being erupted by the volcano.

Etna is a strange volcano, indeed, and it is fitting that the northeast corner of Sicily, where Etna rises, is also very strange.

Geologically, that is.

This is where the city of Messina hugs the coast and where you take the ferry across the Strait of Messina to mainland Italy.

Messina is sitting on a very unusual part of Sicily, geologically.

This part of the crust was not formed anywhere near here.

It was formed as part of the island of Sardinia, which is way north of the Tyrrhenian Sea.

And then tectonic forces rafted it down here over millions of years, and tacked that part of the crust onto Sicily.

So let me draw you a picture to show you how that worked.

About 10 million years ago, pieces of the Eurasian Plate broke off from Sardinia and migrated southeast.

These chunks of the earth's crust, which geologists call exotic, included what was about to become the foot of the Italian mainland.

Eventually, the chunks wedged into an opening between the Italian mainland and Sicily.

This intense crustal juggling forged a mountainous region in northeastern Sicily from Messina to the coastal town of Patti, which is infamous for a geological byproduct of all of this activity.

[Bells ringing] It's 6:00 in Patti on the North Coast, and I'm right outside the cathedral.

Patti sits on the boundary between the main bulk of the island and the chunk of the island that it formed way up as part of Sardinia and rafted its way down here and stuck itself onto the island.

So because of all that movement, tectonically, there are a lot of earthquakes here, very active seismically.

In fact, this is the most seismically active part of Sicily.

Patti's cathedral, originally built in the 11th century, was destroyed in an earthquake in the 1600s and rebuilt using not only limestone but a different rock, one that I told you I'd show you that is particular to this region.

This Cathedral is built from basalt from Mount Etna's lava and limestone.

It's a beautiful combination.

Not far from Patti, the town of Taormina, perched high above the sea, is also on the exotic piece of crust from Sardinia.

This chapel was built inside a cave in those tough, far-traveled rocks, giving it lots of protection from earthquakes, but the nearby city of Messina, though also on the exotic crust, is built on a veneer of loose coastal sediments.

So the city suffered severe damage when the magnitude 7.0 Messina earthquake struck in 1908.

Besides earthquakes, Messina is also well known to geologists for another reason.

Six million years ago, an almost unfathomable geologic event occurred.

And that's when the Mediterranean Sea dried up.

The drying event was called the Messinian salinity crisis, named after Messina, where evidence for the drying was first discovered.

What happened was plate tectonics had moved Spain and Africa close enough together that it actually closed off the opening between the Atlantic Ocean and the Mediterranean Sea.

And so the Mediterranean Sea dried up.

It looked like Death Valley in California, where you just look out across a white salt pan.

The seabed remained mostly dry for about 600,000 years.

And then another amazing geologic event happened.

The barrier holding back the Atlantic Ocean broke.

So water from the Atlantic flooded back into the Mediterranean dry seabed and filled it back up again.

The refilling of the Mediterranean took a few months to a few years, which was extremely fast.

New layers of sediments piled up on the seabed.

And over the next five million years, the sedimentary rock formation made of limestone and clay was pushed up out of the sea by tectonic forces in southern Sicily.

This beautiful, extremely bright white rock formation is called the Turkish Steps, and they're called that because Turkish pirates and other pirates actually used this spot here to go up the steps and maraud and raid.

But what created the steps here?

It has to do with variations in the hardness of the alternating layers.

Over geologic time, this made some layers erode faster than others, creating a stunning stairway up the cliff face.

The Messinian salinity crisis left another dramatic legacy in Sicily, one that has been indispensable for people and for the tastiness of the food, salt.

This is a salt mine out at the western edge of Sicily, near the town of Trapani.

And this is a place where they first started mining salt.

It was a great choice, as the Mediterranean Sea became a lot saltier after it dried up and refilled.

The Mediterranean Sea is a wonderful place to get salt because it's very, very salty.

It's one of the saltiest seas in the world.

And this salt mine started 2700 BC or so by the Phoenicians, so that's 4,000 to 5,000 years of salt production right here.

So far in this show, all the places we have visited are on the European Plate, because the bulk of Sicily sits on top of it.

But now it's time to go to the African Plate, which can be seen in the southeast corner of Sicily and in one other tiny spot along the coast to the west, which is fully occupied by the city of Sciacca.

All these people are coming out of Sciacca, and real quickly, they'll go on to the European Plate.

So I'm going to try to sneak around this corner and go to the African Plate.

Kind of hard, though.

Really narrow.

Here we go.

Whoo!

Whoo!

Ta-da.

Ha ha!

But let's go to the main chunk of the African Plate in Sicily, to the coastal city of Siracusa, where erosion sliced off a chunk of limestone to create an island called Ortigia.

Ortigia has very narrow, winding streets and alleyways, so finding things is kind of tricky sometimes.

There's a spring in the city here that I've got to show you, so let's go this way.

It's really easy to find.

It shouldn't be any problem finding my way through here.

I'm pretty sure it's this way.

Hi, kitty.

I'm looking for the Fountain of Arethusa, a freshwater spring, for centuries, the main source of water for the city.

For sure, this is it.

Almost there.

No problem.

I think this is it.

Ah.

Hey!

There it is.

That was easy.

[Chuckles] And the spring is still active today.

Going Inland from Ortigia, the African Plate is rugged limestone with green fields and olive plantations.

Beautiful hill towns are plentiful, some on thrust-up nappes, like the ones we saw on the Eurasian Plate.

The hill town of Caltagirone is near rich clay deposits, and it is one of Sicily's most important ceramic centers.

Ceramic tiles adorn this stairway, built in the 1600s.

Every step has had a different pattern on the tiles.

So these steps were created centuries ago.

And the tiles on the steps were made from clay from the African Plate here.

From Caltagirone, we continue to explore the African Plate, which features limestone plateaus pushed up out of the sea by the collision of the African and Eurasian plates.

For our last stop in Sicily, we descend into a hauntingly beautiful canyon, wherein lies the Necropolis of Pantalica.

These are tombs.

These are ancient burial chambers that people cut into this limestone rock, and they actually started cutting into this rock here about 3,500 years ago.

Must be a couple hundred tombs up there on that sheer cliff.

It's incredible.

I don't know how they got up there to chisel out the chambers, but they did.

Incredible, a word that comes to mind so often when exploring beautiful, rugged Sicily, where you are treated to a gorgeous island served up on two tectonic plates, where earthly shifts crunched the planet's crust together and created a masterpiece out of limestone and hardened lava, sourced from the bottom of the sea and slowly cooked to perfection over millions of years.

♪ ♪