Earth Notes - Montezuma Well

Flagstaff, AZ – Earth Notes: Montezuma Well

Out among the dry juniper and mesquite country of Verde Valley sits one of Arizona's great surprises. It's Montezuma Well, a large spring-fed pool fed by more than a million gallons of warm water each day.

An outlier of Montezuma Castle National Monument, the Well has drawn native people for millennia. In more recent times, tourists and scientists have arrived.

They've learned that the Well formed as a collapsed cavern. Its waters probably originate on the southern edge of the Colorado Plateau, but follow a circuitous path before bubbling up from the bottom of the Well. On their way, they filter through the limestone, dolomite, and gypsum of the Verde Valley Formation. More water comes from the underlying Supai Formation, and a small amount from very old rock buried 3,000 feet below the surface.

All those rocks leave traces of their chemistry in Montezuma Well's water, which contains lithium, boron, and arsenic. In fact, Montezuma Well has the highest natural concentrations of arsenic of any water in the region. It also contains high levels of carbon dioxide and little oxygen.

As a result, fish can't live there. But it supports at least five species that exist nowhere else, including a springsnail, a water scorpion, and a leech. They make up parts of an aquatic ecosystem that has probably changed little in the last 12,000 years. But it's not isolated. The many migratory ducks that spend winters on the Well's calm waters connect it to other places just as today's tourists do.

-Rose Hauk