Posted on Tuesday 17 October 2006

Cenotes are karst formations which occur when underground water etches away at limestone bedrock to form enormous subterranean caverns. Eventually the cavern roofs collapse leaving deep circular rock pools. The word cenote is a Spanish rendering of the Mayan word d'zonot which means literally "a hole in the ground".

In northeastern Mexico, there is a group of five interconnected cenotes, one of which is known as Zacatón. At a depth of 305 metres, it is the deepest in the world and it is also nearly perfectly circular with a diameter of approximately 116 metres. The cenote is primarily of interest to divers who enjoy exploring this seemingly bottomless abyss and it was the scene of the world's deepest cave dive (one which tragically claimed the life of one of the divers who was drowned at a depth of 276 metres).

However, this cenote is also interesting for some notably laputan reasons...

The waters of Zacatón are warm (30 C) and highly mineralised, they also give off a sulphurous odour and while it is still unknown exactly how the islands formed, one theory has it that the vegetation originally colonised rafts of calcium carbonate which had precipitated out of solution and formed a buoyant membrane on the surface.

Other lakes with floating islands have been written about at various times. Athanasius Kircher in the seventeenth century apparently described a group of islands known as the "sixteen little boats" which floated in a lake now known as Lago della Regina near Tivoli. Unfortuantely for me, I wasn't able to find an online version (let alone a translation) of his Latium; id est, Nova & parallela Latii tum veteris tum novi descriptio (1671). However a contemporary of his, Francesco Lana Terzi, had this to say about the islands in his Magisterium naturae, et artis (1684):

"I myself saw several of these islands in a small lake of sulfurous water not far from the Tiber; they were mostly circular or oval, and rose four or six inches above the water. Their surface is flat and grassy, and at the edges of some of them a few larger plants grow, which act as sails, so that even the slightest breeze pushes the islands from one part of the lake to another. The largest of them are a few yards in diameter, yet nonetheless can sustain several men standing upon them."

Even though they don't exist today, the lake is still known in the tourist literature as Lago delle Isole Natanti ("Lake of the Floating Islands").


Fifteen hundred years earlier, the keen eye of Pliny the Younger observed a similar lake. It was known as Lake Vadimon and was the scene a major defeat of the Ethuscans and Gauls in the year 471 BC.

I went up to this lake. It is perfectly circular in form, like a wheel lying on the ground; there is not the least curve or projection of the shore, but all is regular, even and just as if it had been hollowed and cut out by the hand of art. The water is of a clear sky-blue, though with somewhat of a greenish tinge; its smell is sulphurous, and its flavour has medicinal properties, and is deemed of great efficacy in all fractures of the limbs, which it is supposed to heal. Though of but moderate extent, yet the winds have a great effect upon it, throwing it into violent agitation. No vessels are suffered to sail here, as its waters are held sacred; but several floating islands swim about it, covered with reeds and rushes, and with whatever other plants the surrounding marshy ground and the edge itself of the lake produce in greater abundance.

Each island has its peculiar shape and size, but the edges of all of them are worn away by their frequent collision with the shore and one another. They are all of the same height and motion; as their respective roots, which are formed like the keel of a boat, may be seen hanging not very far down in the water, and at an equal depth, on whichever side you stand. Sometimes they move in a cluster, and seem to form one entire little continent; sometimes they are dispersed into different quarters by the wind; at other times, when it is calm, they float up and down separately. You may frequently see one of the larger islands sailing along with a lesser joined to it, like a ship with its long boat; or, perhaps, seeming to strive which shall outswim the other: then again they are all driven to the same spot, and by joining themselves to the shore, sometimes on one side and sometimes on the other, lessen or restore the size of the lake in this part or that, accordingly, till at last, uniting in the centre, they restore it to its usual size.

The sheep which graze upon the borders of this lake frequently go upon these islands to feed, without perceiving that they have left the shore, until they are alarmed by finding themselves surrounded with water; as though they had been forcibly conveyed and placed there. Afterwards, when the wind drives them back again, they as little perceive their return as their departure. This lake empties itself into a river, which, after running a little way, sinks underground, and, if anything is thrown in, it brings it up again where the stream emerges.

—I have given you this account because I imagined it would not be less new, nor less agreeable, to you than it was to me; as I know you take the same pleasure as myself in contemplating the works of nature. Farewell

See also:
The Unusual Cenotes of Tamaulipas
Preliminary Note on the Floating Islands of Zacaton Sinkhole, Mexico