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DID YOU KNOW?
DID YOU KNOW THAT FACLON DAM WAS MADE WITH ANCIENT TECHNOLOGY DEVELOPED 2,200 YEARS AGO IN THE ROMAN EMPIRE?
by the CHAPS Program at UTRGV Pozzolan historical reference provided by Herb Nordmeyer
Over two thousand years ago, Roman engineers at a Greek colony near modern Naples in Italy discovered that using a mixture of lime and volcanic ash from Mount Vesuvius yielded a uniquely strong building material. This mixture of volcanic ash, also known as pozzolan, with lime and water became known as Roman Concrete or hydraulic cement and was particularly useful in building harbors and other underwater structures but also was used to build the Colosseum in Rome as well as many Roman buildings and aqueducts that still stand today.
Though the original recipe was lost in time, modern engineers knew enough that when they came to build Falcon Dam in the 1950s, they used 22 million pounds of volcanic ash from a quarry known as La Puerta in Starr County just east of Rio Grande City and mixed it with Portland cement, sand, gravel, and water to replicate the Roman technique and that went into pouring the dam.
A Climate-Changing Event 27.4-million-years ago in the Rio Grande Valley
Twenty-seven million years ago, twenty meters of volcanic ash from a violent eruption of a distant caldera buried the south Texas coastal forest of the Oligocene Epoch, some 60 miles inland from the present Gulf coast in Starr County. Outcrops of volcanic ash can be traced over 200 miles from northern Mexico, Texas, and Louisiana. This deposit is a unique discovery researched by Dr. Juan González, UTRGV professor of Geology for the School of Earth, Environmental, and Marine Sciences and Co-Director of the CHAPS Program. His work has revealed a unique aspect of the geological story of the Rio Grande Valley since he first came upon this outcrop of volcanic ash in 2011.
The volcanic ash used as pozzolan for Falcon Dam comes from this 20-meter-thick deposit of ash known in the geologic literature as the “Catahoula Volcanic Ash.” The ash can be easily seen along Starr County’s main road, US Highway 83/Interstate 2. Once the violent eruption of a caldera injected a large volume of ash into the atmosphere, the ash was transported eastward by the prevailing winds, and eventually, it rained on the earth’s surface. The thick blanket of ash altered the landscape permanently, burying all the vegetation and geographical features in a short period of time, perhaps only a few days to just a few weeks. The exact location of the caldera that produced the ash remains unknown, but it likely had a western source in one of many active volcanic centers in the Sierra Madre Occidental, about 500 kilometers southwest in Mexico. This speculation is supported by the chemical affinity of the ash and its age of 27.4 million years.
The large volume of ash that the eruption poured into the atmosphere was undoubtedly an event of catastrophic proportions and wreaked devastating consequences for the region’s climate, ecology, and environment. Millions of years later, it is possible to observe evidence of the ancient landscape in the occasional fossil impressions of plants, also called “casts.” Large amounts of petrified wood formed as the result of the burial of the maritime forest by the volcanic ash. Through the process of silicification, the substitution of silica from ash dissolved in groundwater for the trees’ original cellulose over the course of millions of years.
It is possible to observe thick outcrops of the Catahoula volcanic ash, it’s almost pure white color, standing out on US Highway 83 in Rio Grande City and the municipality of Escobares.
This aspect of Rio Grande Valley’s geoheritage is highlighted on the CHAPS Program’s Ancient Landscapes of South Texas trail. For more information, go to www.utrgv.edu/ancient-landscapes-southtexas or scan the QR codes below.
