Iraquara


The most important limestone karst in Bahia and actually the whole Brazil is found south of the city Iraquara. It is located at the western border of Chapada Diamantina. The limestones under the arid plains are heavily karstified with numerous huge cave systems. The Área de Proteção Ambiental Marimbus-Iraquara (Marimbus-Iraquara Environmental Protection Area) covers the plains with one of the largest karst areas in South America and the highest concentration of caves in Chapada Diamantina. Toca da Boa Vista is the longest cave of Brazil. This karst area has numerous caves, and all of them are quite long. Several caves in this area are probably connected to each other, but the connection has not yet been found. So this is definitely the most important karst area in Brazil.

The reason why this karst area is so important is the hypogene speleogenesis. Normal karst is formed by carbon dioxide from the atmosphere and the soil, which forms a weak acid when it is dissolved in water. This weak acid is now able to react with the limestone and dissolve it. The source of the water and the acid is on the surface, and the karst is consequently called epigenic ("originating from above"). The dolomite in this area is the Salitre Formation, Una Group, which is the Brazilian name of the Ediacaran, of Neoproterozoic Age. The dolomite is about 600 Ma old, which was 25 Million years before the Avalon explosion, an evolutionary event which was the point when complex life started on Earth. As the influence of microorganisms is very important, the sedimentation of limestone at that time was very different from that of the younger limestone deposits of the Mesozoic. The microorganisms, which later reduced the amount of phosphates and sulfur in the loose sediment on the seabed, did not yet exist. As a result, the chemistry of this dolomite is unique, and the high amount of phosphates and sulfur caused a unique process of cave formation. The groundwater releases the phosphates and sulphur, which are then oxidised by microorganisms and form sulphuric acid, which in turn dissolves limestone. This process is called hypogene ("originating from below"), where the acid which dissolves the limestone originates from the underground, the rock itself.

In addition, there is no massive water flow through the caves, no cave river which forms a huge main passage. The cave was created by chemical reaction going on all over the cracks in the rock, the result is an erratic maze and even branches which are crossing but have no connection. This might give you an impression: the cave system has a length of 114 km, the area it covers is only 3 km². And there are numerous such cave systems, currently about half a dozen, with the same morphology. And this morphology of the caves is the reason why it is quite likely that there are connections which have not yet been discovered. Connecting the Toca da Boa Vista with any of those other caves would again make it the longest cave of the Southern Hemisphere.

The climate in this area is semi-arid with less than 500 mm of rain per year, while the average temperature is 28° C. As always, the temperature inside the cave is the average temperature from outside, and the lack of water has more or less stopped any cave development and the growth of speleothems. So the caves are older, originate from a time when the area was much wetter.

It seems there is a sort of cave war going on. While there are several show caves which exist for decades now, some landowners which also have caves on their land started to open them for public tours in the last decade.