As you approach Hierve el Agua you would be forgiven for thinking that you are about to witness close up one of nature’s magnificent sites – that of a large, full flowing waterfall. However, closer inspection would reveal to you that what you thought was water cascading down the side of a hill is something else entirely.
Very much of the beaten track and little visited the waterfall is in fact a natural formation of rock. In Spanish the name means the water boils but it looks more as if it has been frozen – perhaps there was some irony on the lips of the person who gave the place its name. Later, however, we will discover the reason for the name.
Just over 70 kilometers from Oaxaca City in the eponymous state, the closest town to Hierve el Agua is San Lorenzo Albarradas which only has a population of a little over two thousand people. When you drive up the unpaved road which leads to the site you eventually come across two rock shelves. The shelves are home to fresh water springs.
However, the water in the springs is over saturated with minerals, particularly calcium carbonate. This is found in rock all over the world and, additionally is the primary constituent of marine organism shells, pearls and snail shells.
Below these pools the formations of white rock spill down the mountainside, looking very much like a waterfall. The water drips continuously through the cliffs (not, as you might expect, from the top) and loses the minerals on its way towards the ground. They are deposited on to the side of the mountain – in a very similar way that stalactites are formed in caves.
The very name stalactite comes from the Greek work to drip, so imagine a slow but steady millennia long process of dripping. As the saturated water comes in to contact with air then the reaction that created it goes in to reverse and the calcium carbonate is deposited on the side of the mountain.
Although you would not drink this water as it is, it is considered beneficial to swim in it, so although the smaller pools along the cliffs are natural, two artificial pools have been created for that purpose. The larger of the artificial pools is very close to the cliff edge, even though there is no danger at all – unless you purposefully put it in your path.
As you can imagine, the rock formations of Hierve el Agua took many thousands of years to get to what we see today. After all, each of the cliffs is over fifty meters from the floor of the valley – that is a long way down. Eventually they may reach the ground at the bottom but at the moment one formation goes down 12 meters and the larger one 30.
They have names which translate as small waterfall and, you guessed it, large waterfall. Although misnomers, they are often referred to as salt waterfalls or petrified waterfalls. The water comes, at a temperature of about 27C, through cracks in the rock on the cliff.
The calcium carbonate is what gives the falls their near white color but there are a host of other minerals such as barium and iron in the rock – around 5 percent. The local rainwater passes underground and it absorbs carbon dioxide. The result is that molecules of carbonic acid are formed in the water. This comes in to contact with marble (still underground) and that reaction creates the calcium bicarbonate.
The name of the place – the water boils – comes from the fact that when the water comes up through the springs then it bubbles. It is thought that the Zapotec people, who lived in the area two and a half thousand years ago, held the place in great reverence. They irrigated the surrounding land from the cliffs and created a system which is unique in Mexico.