History

Pilot Knob: Largest Extinct Volcano Remaining in Central Texas

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Pilot Knob is a formerly extremely active volcano that existed in Texas, which, although inactive for millions of years, is still a site to see. The remains of its lava flow can still be seen (pictured above) and its effects in the area are still felt today (in the form of soil contributions.) Although it merely resembles a small hill which you would barely look twice at, a driving down McKinney Falls Parkway features the small hill, approximately 100-150 feet in height, resembling a standard Texas Hill Country view. But, the material that lies beneath it is actually volcanic igneous rock, and it’s the largest of 75 which were active in the Lone Star State, with a diameter of more than two miles!

Back during the time that Pilot Knob was an active volcano, the area where the city of Austin now sits was covered with a shallow sea and sea life that was plentiful, in a tropical climate. Dinosaurs were abundant and tall – they could traverse the distance from Fort Worth to San Antonio without fully submerging themselves. There were also earthquakes resulting from volcanic eruptions, but the most volatile in their habitat were the violent explosions from the very same.

Pilot Knob: Largest Extinct Volcano Remaining in Central Texas

Photo: Facebook/Traces of Texas

The hill that remains today is merely a part of the original Pilot Knob volcano, which was once an ominous site at many thousands of feet in height. “There was quite a lot of activity, just here in Central Texas,” Leon Long, professor emeritus of geology at the University of Texas, explained to the Austin American-Stateman. Long believes that the remains of Pilot Knob make it the only exposed submarine volcano in Texas which geologists are aware of.

At the time that it would’ve been partially submerged partially above the water level, steam explosions would have been a regular activity as seaweed and water encountered hot magma. From that, the volcanic material would have been pulverized, blown high up into the air, and would have settled into the surrounding sea floor. “These (explosions) ended up producing an explosion crater, which was several hundred meters deep,” explained Don Parker, professor emeritus of geology at Baylor University. Seen from overhead, at the time, it is presumed that Pilot Knob appeared like a shallow lagoon surrounded by beaches.

Formed during the Cretaceous Age, Pilot Knob developed in a period of volcanic activity approximately 120 million years ago. Today, its remains can be viewed by those that visit McKinney Falls State Park, including the volcanic ash bed which was left exposed beneath the limestone overhands in both the upper and lower falls. The volcanic material also assisted the modern-day Texas farmer to prosper. That which developed through the volcano’s explosions has helped to enrich the soil in the surrounding area. It also spawned Texas legends, including the thought that Spaniards at one time had buried gold on the volcano’s highest peak, or that Native American tribes had buried treasure there. To date, however, there has been no proof of such theories. Its name is believed to have been derived from the need of area settlers to navigate the area – being able to see the “knob” of the hill for miles around.

Pilot Knob: Largest Extinct Volcano Remaining in Central Texas

Photo: Facebook/Hortenstine Ranch Company

Today, Pilot Knob overlooks some area housing and construction but hasn’t been the cause for worry for a considerable amount of time. The volcano has been considered extinct as opposed to dormant, which means that it is no longer active, nor is it likely to ever be again. But, the opportunity to see an area that once held such tumultuous activity in Texas is a unique one not afforded to many. Situated 8 miles south of Austin and close to McKinney Falls State Park and Austin-Bergstrom International Airport, Pilot Knob can be reached by driving out Highway 183 past the airport, where the hill is visible on the right, just past Onion Creek. Directions to circuit what would have been the mouth of the volcano can be found at the link provided here.