Among the dry mountains of Oaxaca, Mexico, there is a huge formation that looks like a waterfall flowing down a cliff. White and cream-colored streaks cover the rock surface, while the long folds descending down the cliff make it look as if the water suddenly froze in place.
But the waterfall at Hierve el Agua is not actually flowing.
Because what we are looking at is not water.
It is rock.
The famous “petrified waterfalls” of Hierve el Agua were formed by calcium carbonate deposits left behind by mineral-rich spring water over a very long period of time. Water still reaches the surface today, and thin new mineral layers can continue to form, slowly changing this unusual geological landscape.
Located about 70 kilometers east of Oaxaca City, Hierve el Agua is remarkable not only for its two large petrified waterfall formations, but also for its mineral springs, pools, terraces, and ancient water channels.
So how can water build rock? Why does this place look like a frozen waterfall? And if “Hierve el Agua” means “the water boils,” is the water actually boiling?
The answer is hidden in the long journey of groundwater through the rocks beneath the mountains.
What Is Hierve el Agua?
Hierve el Agua is a group of natural travertine formations located in the state of Oaxaca in southern Mexico.
Its most striking features are the massive white mineral formations that extend down the side of the cliffs and resemble large waterfalls. Because of their appearance, they are commonly described as “petrified waterfalls.”
But there is no ancient waterfall here that suddenly turned into stone.
The waterfall-like appearance is the result of mineral deposition.
Carbonate-rich water emerges from natural springs and flows across the rock surface. As it moves, it leaves behind calcium carbonate. Over time, countless thin layers of mineral deposits accumulate on top of one another.
These deposits form curtains, steps, ridges, and long vertical patterns on the cliff face.
From a distance, the rock looks like water flowing downward.
According to official Oaxaca tourism information, Hierve el Agua contains two major petrified waterfall formations, approximately 30 meters and 12 meters high.
Behind these formations lies a deep valley, making the white cliffs appear even more dramatic when viewed from a distance.
What Does “Hierve el Agua” Mean?
In Spanish, “Hierve el Agua” literally means:
“The water boils” or “boiling water.”
The name can easily make people think that Hierve el Agua is a place of extremely hot geothermal springs.
But the water is not boiling in the normal sense.
At some of the spring outlets, gas bubbles rise through the water and create a surface that looks as if it is boiling.
This bubbling appearance is one of the reasons the place became known as Hierve el Agua.
So the word “boiling” should not be understood as water reaching temperatures close to 100°C.
What makes the water geologically important is not mainly its temperature.
It is its chemical composition.
How Did Hierve el Agua Form?
The story of Hierve el Agua begins with rainwater.
Some of the rain that falls on the surrounding mountains flows across the surface, while some of it seeps underground through fractures and porous rocks.
As the water moves through soil and rock, it interacts with carbon dioxide.
CO₂ dissolving in the water helps produce a weak carbonic acid.
This slightly acidic water can react with carbonate-bearing rocks underground.
As a result, calcium and bicarbonate ions become dissolved in the groundwater.
So when the water eventually returns to the surface, it is not simply ordinary water.
It carries dissolved minerals with it.
When this mineral-rich groundwater reaches the surface through fractures and natural springs, the surrounding conditions change.
Pressure decreases.
The water comes into contact with the atmosphere.
Some of the dissolved carbon dioxide escapes.
As CO₂ is lost, calcium carbonate becomes less soluble and begins to precipitate from the water.
The process can be simplified with this reaction:
Ca²⁺ + 2HCO₃⁻ → CaCO₃ + CO₂ + H₂O
The CaCO₃, or calcium carbonate, produced by this process is the main material that builds the formations at Hierve el Agua.
A single drop of water leaves behind only an extremely small amount of mineral.
But when this process happens again and again for very long periods of time, the result becomes much larger.
One layer forms.
Then another layer forms on top of it.
Then another.
Over time, thin mineral coatings can grow into massive carbonate deposits several meters thick.
The petrified waterfalls of Hierve el Agua are the spectacular result of this slow and continuous process.
What Is Travertine?
One of the most important words for understanding Hierve el Agua is travertine.
Travertine is a type of carbonate rock that commonly forms when mineral-rich spring water deposits calcium carbonate at the surface.
When groundwater reaches the surface, it can begin to lose carbon dioxide.
This chemical change encourages calcium carbonate to precipitate from the water.
The deposition does not occur only around the spring itself.
As long as the water continues to flow, minerals can continue to accumulate along its path.
Travertine may therefore form around:
- spring outlets,
- small channels,
- pool edges,
- sloping surfaces,
- terraces,
- and cliff faces.
At Hierve el Agua, the movement of water over the edge of the cliffs was especially important.
As water repeatedly followed similar pathways, calcium carbonate built up along those routes.
Over time, these deposits developed into large rock curtains descending down the cliff.
This is why the formations look so much like frozen waterfalls.
Is Hierve el Agua Really a “Petrified Waterfall”?
“Petrified waterfall” is an impressive name, but geologically it can be slightly misleading.
It should not be imagined as a huge waterfall that once flowed normally and then suddenly turned into stone.
The actual process is almost the opposite.
The rock that looks like a waterfall was slowly built by mineral-rich water itself.
For this reason, a more precise geological description would be:
a large travertine formation shaped like a waterfall.
The term “petrified waterfalls” is still widely used because it describes the appearance of the formations very well.
Cascada Grande and Cascada Chica
Hierve el Agua has two main petrified waterfall formations.
Cascada Grande
As the name suggests, Cascada Grande is the larger and more dramatic formation.
Mineral deposits extend down the cliff in long vertical bands.
In some areas, the carbonate forms thin curtain-like surfaces. In others, it creates thick ridges and bulging mineral deposits.
From far away, Cascada Grande can easily look like a giant mass of water falling down the cliff.
But when viewed more closely, the surface is clearly made of mineral layers.
Cascada Chica
The smaller formation is closer to the upper area where many of the springs and pools are located.
This area is also associated with a section known as El Anfiteatro, or The Amphitheatre.
The springs, small pools, and travertine surfaces found here provide a good opportunity to see that Hierve el Agua is not only an ancient formation.
Mineral deposition can still occur in areas where water continues to flow.
Official Oaxaca sources describe the two main formations as approximately 30 meters and 12 meters high.
How Did the Pools at Hierve el Agua Form?
The turquoise and greenish pools at the top of Hierve el Agua are almost as famous as the petrified waterfalls themselves.
Travertine deposition does not only create vertical cliff formations.
When mineral-rich water flows over flat or gently sloping ground, calcium carbonate can gradually build small natural barriers.
Water can then collect behind these mineral edges.
Over time, this process may create travertine pools and terraces.
The upper area of Hierve el Agua contains natural formations, but some sections have also been modified and used by people in the past.
For this reason, it is not accurate to describe every visible pool as completely untouched and purely natural.
Even so, the carbonate crusts around the pools and the continuing mineral deposition are direct signs of the natural geological process.
The blue-green appearance of the water can also be influenced by several factors, including water depth, mineral surfaces on the bottom, sunlight, and reflections from the surrounding environment.
Why Are the Rocks White, Yellow, and Orange?
Pure calcium carbonate is usually white or very light in color.
This is why much of Hierve el Agua appears white, cream, or pale gray.
But natural spring water does not contain only one chemical element.
Different minerals and trace elements can become incorporated into the deposits.
Iron-bearing compounds, for example, can create yellow, brown, or orange tones on the rock surface.
The appearance of the travertine can also change depending on where the water flows, whether the surface is wet or dry, biological activity, and the age of the mineral deposit.
This is why travertine formations are rarely completely uniform in color.
Different flow paths may create lighter and darker bands across the same cliff face.
Is Hierve el Agua Still Forming Today?
Yes.
One of the most interesting things about Hierve el Agua is that the geological system is not completely inactive.
In areas where spring water still flows, calcium carbonate can continue to precipitate and form new mineral layers.
This does not mean that visitors can actually watch the rock grow in front of their eyes.
Geological change is often extremely slow compared with a human lifetime.
But over years, centuries, and longer periods, very thin mineral coatings can build into significant rock formations.
In this sense, Hierve el Agua is not simply an ancient geological structure.
It is a place where the process of rock formation itself can still be observed.
Is Hierve el Agua Volcanic?
Because of its unusual appearance, Hierve el Agua is sometimes associated with volcanic activity or lava flows.
But the waterfall-like rock formations are not frozen lava.
They are mainly travertine structures created by carbonate minerals deposited from spring water.
This distinction is important.
Lava forms when molten rock cools and solidifies.
Travertine forms through a completely different process:
water → dissolved minerals → chemical change → carbonate precipitation → rock accumulation
So to understand the “waterfalls” of Hierve el Agua, we need to look at groundwater chemistry rather than magma.
The Similarity to Cave Stalactites
One easy way to understand the formation of Hierve el Agua is to think about stalactites inside a limestone cave.
In caves, mineral-rich water drips from the ceiling.
As the water loses CO₂, it can leave behind very thin layers of calcite.
When this process continues for a long time, stalactites slowly grow.
The basic chemistry at Hierve el Agua is similar.
But the environment is very different.
Instead of occurring on the ceiling of a dark cave, the process happens in the open air across a large cliff.
Because of this, the mineral deposits form broad surfaces, terraces, channels, and waterfall-shaped rock curtains rather than narrow cave stalactites.
Where Geology and Human History Meet
Hierve el Agua is not only a geological site.
Permanent water sources would have been extremely valuable to people living in this dry mountainous landscape.
Ancient terraces and channel systems have been identified around Hierve el Agua.
For many years, these structures were interpreted as evidence of early agricultural irrigation.
However, archaeological research has also produced other interpretations.
Some researchers have suggested that parts of the channel system may have been used to evaporate mineral-rich water and possibly produce salt or other mineral products.
This means the archaeological system at Hierve el Agua is interesting not only because of its age and engineering, but also because its original purpose is still discussed.
One thing is clear:
The natural springs and the geology of the area strongly influenced how people used this landscape.
Hierve el Agua has also been considered an important place in the history and cultural landscape of the Zapotec people.
Why Is Hierve el Agua Geologically Important?
Travertine formations are not unique to Hierve el Agua.
Other famous places around the world, such as Pamukkale in Turkey, are also known for large carbonate deposits formed by mineral-rich spring water.
What makes Hierve el Agua especially striking is the shape of its travertine.
Here, carbonate deposition preserved the pathways of flowing water so clearly that the resulting rock genuinely resembles a waterfall.
Several geological processes can also be observed within one landscape:
- groundwater circulation,
- water-rock interaction,
- mineral dissolution,
- CO₂ loss,
- calcium carbonate precipitation,
- travertine formation,
- surface water flow,
- erosion,
- and human use of geological resources.
For this reason, Hierve el Agua is much more than a beautiful natural landscape.
It is an open-air example of how water chemistry can slowly build rock over time.
Frequently Asked Questions About Hierve el Agua
Is Hierve el Agua a real waterfall?
No. The large waterfall-shaped formations are made mainly of travertine created by the precipitation of calcium carbonate from mineral-rich spring water.
Why is Hierve el Agua called a petrified waterfall?
The travertine layers extend down the cliff and look like a waterfall frozen in place. The term describes their appearance, but an actual waterfall did not suddenly turn into stone.
How was Hierve el Agua formed?
Mineral-rich groundwater rises to the surface through natural springs. As the water loses carbon dioxide, calcium carbonate precipitates. Over long periods of time, these deposits build large travertine formations.
What kind of rock is Hierve el Agua made of?
The main formations are composed largely of calcium carbonate-rich travertine.
Is the water at Hierve el Agua actually boiling?
No. Although the name “Hierve el Agua” means “the water boils,” the bubbling appearance should not be confused with water actually boiling at very high temperatures.
Is Hierve el Agua still growing?
In areas where mineral-rich water continues to flow, new calcium carbonate can still be deposited. This means parts of the geological system are still active today.
Where is Hierve el Agua?
Hierve el Agua is located in the state of Oaxaca, Mexico, near San Lorenzo Albarradas and approximately 70 kilometers east of Oaxaca City.
Conclusion
At first glance, Hierve el Agua looks like a waterfall.
But when we look at the geology, the story becomes much more interesting.
Rainwater enters the ground, moves through the rocks, interacts with minerals, and eventually returns to the surface carrying dissolved calcium and bicarbonate.
When the water reaches the surface, the conditions change.
Carbon dioxide escapes.
Calcium carbonate begins to precipitate.
One drop of water leaves behind almost nothing.
But when the same process continues for thousands of years, those tiny mineral deposits can reshape an entire cliff.
The great stone curtains of Hierve el Agua are the result of this slow accumulation.
It is not an ancient waterfall that suddenly froze into stone.
What is more remarkable is that the water itself built the rock that now looks like a waterfall.
