Answers to Go with Susan Smith

Q. Do you have information on Deep Hole? I’ve been told it is an impressive underwater feature in Spring Lake.

A. Let’s turn to Ron Coley’s recent book, “The Fountains of Saint Mark: The Amazing San Marcos Springs.” This is a big, beautiful book of photographs, maps, drawings and essays.

In the preface Coley writes, “Alonso de Leon described abundant springs that popped up from the ground at the base of a dry and barren hilltop. He called them ‘fountains.’

“His discovery is reported to have happened on Saint Mark’s Day in 1689. Which Hill Country artesian springs he discovered that day is still hotly debated.” Coley likes to think that de Leon had discovered our springs.

Here are excerpts of what Coley wrote about Deep Hole: “Deep Hole, located entirely underwater, is at the end of what is currently referred to as ‘the peninsula’ at Spring Lake. Before General Burleson impounded the headwaters of the San Marcos Springs in 1849, the peninsula would have been a curving palmettocovered savannah.

“Deep Hole is the bottommost bathymetric site in Spring Lake. It is also the lowest naturally occurring discharge point of the Edwards Aquifer. These two elements alone would qualify it as a world-class artesian site. However, even such a designation does not do justice to this complex and amazing phenomenon that occurs at an altitude of 549 feet above sea level on the cusp of the Balcones Escarpment.

“At the very deepest spot in Deep Hole is a large vent very similar in size and shape to my fireplace. This small vent, three feet high and three feet wide, is perhaps the most studied spring opening in the world.

“All of the probes, sampling routines, and data collected to account for what is happening with the San Marcos Springs start and end here. To the best of my knowledge, this single vent is the most reliable source of fresh water anywhere in the American Southwest. Very likely, it is the most reliable source of fresh water in all of North America.

“It is unfortunate that many of the biologists, hydrologists, and geographers that study the San Marcos Springs think that this single orifice alone is Deep Hole. Deep Hole is so much more than one vent, and the spring system has thousands of other openings.

“Leaving the large vent, and traveling along a baseboard of intermittent springs still inside of Deep Hole, you only have to go three fin strokes to come to a large triangularshaped rock that is about the size of a Volkswagen Beetle buried up to its hood in soft, white, constantly shifting crushed limestone and dolomite.

“I have spent hundreds of hours at an approximate depth of thirty feet enraptured by being in a mixing bowl of hydrological cracks, faults, and intricate capillaries. This is the crown jewel of all groundwater resources that have blessed Texas since the earliest of times.”

One question often leads to another; in this case, what is bathymetry?

The National Oceanic and Atmospheric Administration offers this definition: “The term ‘bathymetry’ originally referred to the ocean’s depth relative to sea level, although it has come to mean ‘submarine topography,’ or the depths and shapes of underwater terrain. In the same way that topographic maps represent the three-dimensional features (or relief) of overland terrain, bathymetric maps illustrate the land that lies underwater.

Source: https://oceanservice.noaa.gov/facts/bathymetry.html

San Marcos Daily Record

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P.O. Box 1109, San Marcos, TX 78666