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Volcanic Ash in the Rio Grande Valley

Back in 2011, a UTRGV professor, discovered volcanic ash near Rio Grande City. An area of over 200 miles, stretched from south Texas into northern Mexico, covered by tens of feet of ash. But where did it all come from?

“This was huge. This was a really really big event.”

We are walking on top of history. And as we head back in time, the Valley looked a lot different than it does today.

“So this would have been the shoreline. Anything east of where we are would have been deep water in the Gulf of Mexico,” says Dr. Juan Gonzalez.

Dr. Gonzalez is a professor in the School of Earth, Environmental, and Marine Sciences at UTRGV, and one of the few who knows about a unique discovery that helps tell the geologic history of the Rio Grande Valley – volcanic ash.

“What it represents is a major volcanic eruption that was produced somewhere west of here most likely.”

Gonzalez first discovered the ash near Rio Grande City in late 2011. But that find was just the tip of the iceberg.

“We’re seeing the top of it. Anything below our feet here goes uninterrupted for about 20 meters of volcanic ash.”

An area of over 200 miles, stretched from south Texas into northern Mexico, covered by tens of feet of volcanic ash.

“In all likelihood, it is from a caldera in the Sierra Madre Occidental in Mexico. And now we know the exact age of the deposit is 27.2 million years.”

That eruption 27 million years ago blanketed Starr County with close to 60 feet of ash. It’s enough to change the entire landscape of the Rio Grande Valley, and its climate.

“This was a life and climate changing event without any questions. Without a question.”

The evidence is all around us. In Roma, a house surrounded by petrified wood, a process that turns trees into rock over millions of years. In Rio Grande City, gas pockets that have hardened into quartz, with uranium buried deep within.

“It’s a lot of petrified wood. I’ve found plenty on various excursions and expeditions and whatnot, but nothing of this size.”

Now – Dr. Gonzalez’s work focuses on pinpointing exactly which volcano was the source, and determining how much damage it may have done.

“We are working on the source. Clearly it has to have a western source. Good candidates for it are large calderas in the Sierra Madre Occidental that were blowing their tops violently, because this is a very explosive type of magma.”

It just goes to show that sometimes, you never know how much history is around you, even under your feet.

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