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Climate Minute: How we got the Edwards Aquifer

Sarah Spivey explains how climate change and plate tectonics gave San Antonians their most abundant source of drinking water

SAN ANTONIO – Let’s travel back in time to the Cretaceous Period, 100 million years ago. Dinosaurs roam the land, the atmosphere is 10-15 degrees warmer, there are no ice caps at the poles and San Antonio is underwater.

100 million years ago, shallow seas covered a good portion of Texas.
100 million years ago, shallow seas covered a good portion of Texas. (Copyright 2020 by KSAT - All rights reserved.)

Aquifer Formation

Shallow seas covered a good portion of Texas, and prehistoric mollusks, corals and other tiny sea creatures thrived. These organisms, made of carbonate material, eventually died and their remains settled in the mud of the sea bed. Over time, intense heat and pressure from plate tectonics transformed the carbon-rich mud into limestone bedrock.

Rain, which contains weak acid, eventually dissolved the limestone, creating the pourous “karst” and formed caves and conduits. Today, this vast system of “holey” limestone around South Central Texas is called the Edwards Aquifer.

The porous limestone which makes up the Edwards Aquifer
The porous limestone which makes up the Edwards Aquifer (Copyright 2020 by KSAT - All rights reserved.)

How the Edwards Aquifer works

There are three zones of the Edwards Aquifer - the Contributing Zone, the Recharge Zone and the Artesian Zone.

The three zones of the Edwards Aquifer.
The three zones of the Edwards Aquifer. (Copyright 2020 by KSAT - All rights reserved.)
  • Rain falls along the higher elevations of the contributing zone - think the Hill Country - and trickles downhill thanks to gravity
  • Runoff eventually makes it to the recharge zone, which is where it falls into the pourous karst and openings to caves and conduits. Areas along the recharge zone include the Balcones Fault Zone like Government Canyon
  • Water pressure builds underground, and we dig wells to harvest the water along the Artesian Zone
A cross-section of how we access water from the Edwards Aquifer.
A cross-section of how we access water from the Edwards Aquifer. (Copyright 2020 by KSAT - All rights reserved.)

Impact of Climate Change on the Edwards Aquifer

Climate change over millions of years of history is normal. There have been warm periods and cold periods in our Earth’s 4.5 billion-year-old history. In fact, without the 10-15 degree warmer atmosphere of the Cretacious Period, the shallow seas over San Antonio may not have existed, thus the Edwards Aquifer itself may have looked very different than it does now.

However, the general consensus of scientists around the world is that the climate is warming at a pace we’ve never seen before because of greenhouse gas emissions. In San Antonio, that could mean periods of drier and hotter weather, which would result in less water to harvest in the aquifer and more water restrictions for locals.

For more on our changing climate, please visit the KSAT Climate page.


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