What Made These Perfectly Shaped Hills? | Weird Places
The Chocolate Hills of Bohol, Philippines are so perfectly shaped that local legends say they were crafted by giants. Geologists can't agree exactly what happened, but the answer might be as simple as limestone, water, and wind.
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Sources: https://docs.google.com/document/d/e/2PACX-1vQLJrBzxhCteR_ZHshgEJU__ASLsjGf4RTMYlnHDeH5QEv3po0kKmvHyJTRguxnwWXGcXaDS97zLo3B/pub
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Video Transcript
You'd be forgiven for thinking that you are currently looking at a picture of precisely formed chocolate truffles.
That is, until you notice the trees at their base.
These are the Chocolate Hills of Bajal, an island in the central Philippines.
It's one of the most striking karst landscapes in the world, which means it is formed from the erosion of limestone.
That's not unusual on its own.
Fifteen to twenty percent of Earth's surface has limestone beneath it.
But what sets the Chocolate Hills apart is their weirdly perfect symmetry.
And also that I want to eat them.
And while their formation has baffled residents and geologists alike,
the secret of the hills might be surprisingly simple.
[♪ OUTRO MUSIC ♪, thanks for watching!]
Bajal is home to 1,176 chocolate hills.
They're not all identical.
Most are 30 to 50 meters, while the largest is 120 meters tall.
They don't always look like chocolate.
The name comes from the brown color the grasses turn during the dry season, from February
to April each year.
Again, don't eat grass.
The rest of the time, they're a lush green, thanks to the tremendous amount of rain brought
by the monsoons.
Their striking appearance and symmetry have given rise to many local legends about how they formed.
One tells the story of two giants fighting, hurling humongous handfuls of mud at each other.
The mud balls that fell to the ground became the hills.
Another, less violent version says the hills are the tears of a giant mourning the loss of his human lover.
And these hills have inspired equally wide-ranging theories among geologists.
From each hill being a small volcano coated in chalk, to the domes being formed by ancient sea currents.
In fact, if you read about the Chocolate Hills online,
you're probably going to see a bunch of these ideas.
But scientists now know the evidence doesn't support them.
You're telling me that there's incorrect information on the internet?
The truth is, these unique formations are an example of a very common geological process—
the erosion of limestone.
Most of the islands of the Philippines are formed from the remnants of an ancient mountain range.
This gives the area a base of relatively tough metamorphic rocks, like gneiss and schist.
60 million years ago, these mountains had long since eroded down,
and this base of hard rock formed the bottom of a shallow sea.
And then, a coral reef started to grow in this sea.
And slowly, layer upon layer built up,
and these generations of coral were all made of calcium carbonate.
And you can find remnants of this ancient reef today.
The Chocolate Hills have fossils of coral, mollusks, algae, and plankton.
Eventually, the movement of tectonic plates pushed the seafloor down,
and nearby islands up.
Erosion of these islands buried the reef under layers of sediments like shale,
and it lithified, turning into solid limestone.
Seven million years ago, more tectonic forces pushed all these layers
up to the surface and erosion began, grinding the shale.
down to expose the limestone beneath.
Limestone erodes in a unique way, in a process known as carstification.
That is the tendency for limestone to erode into these dramatic features.
