Last updateFri, 19 Oct 2018 7am

Qanat la Venta 2018 update: It won’t collapse, unless...

If you have a dog-eared copy of the very first version of my book “Outdoors in Western Mexico,” published in 1998, you will find a chapter – deleted in subsequent editions – dedicated to Qanat la Venta, a curious kind of underground aqueduct located ten kilometers west of Guadalajara.

pg8bIt was a system of tunnels we had mistakenly considered for years to be the strangest cave in the world, “with 75 skylight entrances all neatly arranged in a straight line.”

Maybe a year before the publication of that book we brought archaeologist Phil Weigand to the entrance of our mysterious discovery. He took one look and said, “John, your cave is not a cave at all. It’s a man-made structure called a qanat.”

I learned that the original purpose of qanats was to channel water from an underground source through the desert to some spot where water was badly needed. The tunnel was dug by first laying out a straight line route between these two points. Next, workers would dig a series of evenly-spaced vertical access shafts down a precise distance determined by the engineer in charge. Then the holes were connected together underground. The last of these connections – and by far the most dangerous – was to the mother well. If all this was done correctly, the underground channel would have a slope of less than two degrees and the water would slowly make its way down to the far end causing no erosion. All the access holes were then capped with flat rocks, preventing both contamination and evaporation, a serious concern in dry climates.



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