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Dr. Dean W. Blinn

Montezuma Well

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The story of Montezuma Well starts about 12 million years ago when the Verde Valley was covered by a large shallow lake 27 miles long and 15 miles wide. Lake Verde was full of tiny floating plants which, while they produced food, caused dissolved limestone to form minute crystals. These crystals slowly sank to the bottom of the lake and over several million years accumulated into thick layers of limestone rock. About 2 million years ago Lake Verde eroded away the volcanic dam at its southern end and the gigantic lake dried up.

Scientists think that an underground stream dissolved away some of the softer limestone deep under the ground and formed caverns below the surface of the Verde Valley. Over the years, churning water carved these underground caves larger and larger. Along various points of the underground stream, water would come to the surface and form a spring. Over several million years these springs deposited large quantities of salts, called travertine, around their openings. As the salts accumulated, large circular mounds were formed like the one surrounding the Well (see photograph on cover). As recently as 11,000 years ago, the roof of one of the underground caverns supporting a heavy travertine spring mound may have gradually crumbled into a sunken pool and hence MONTEZUMA WELL was formed!

Presently, Montezuma Well is located at an elevation of 3,681 ft. (1,122m) in the Upper Sonoran desert of Arizona. The terrestrial vegetation on the outside rim of the Well is adapted to the dry climate of the Verde Valley and includes juniper and acacia trees as well as assorted grasses, hedgehog and prickly pear cactus plants, and the exotic joint-fir, Ephedra, from which the nerve stimulant ephedrine is extracted.

Montezuma Well is 368 ft. (112m) across and the water is 5 ft. (17m) deep. The Well is still an active spring with a constant flow of 1,100 gallons of water entering at the bottom every minute (4,164 l per min). The water exits through a side cave and empties into an irrigation ditch outside the Well; the water level in the Well rarely changes! Because the water of Montezuma Well comes from an underground stream, it has a constant temperature of 76F (25 C). High concentrations of the oderless gas, carbon dioxide, are dissolved into the water as it passes through the miles of underground limestone deposits before entering the Well. As the water enters the Well, the limestone falls out of solution and the carbon dioxide is released as a dissolved gas into the water. The rich supply of dissolved carbon dioxide has apparently prevented many aquatic animals, especially fish, from living in these waters.
[Cover Page] [Life in the Well]