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The Making of a Mountain: the Chinati Volcano

photograph by Christopher Hillen. The Chinati Mountains, pictured above from Pinto Canyon Road, on a snowy day, were the site of a massive volcanic eruption, which shaped large swaths of the West Texas landscape.

How is a mountain made? The story often spans millions of years. But not always.

On one explosive day, some 33 million years ago, the Chinati Volcano erupted. Chinati Peak, the monumental summit 40 miles southwest of Marfa, is one result. But the eruption literally laid the foundation for life in much of the Big Bend.

Eruptions, intrusions, lava flows – volcanic activity roiled what's now West Texas from 45 to 20 million years ago. But the Chinati eruption was the biggest. 

How big was it?

Blaine Hall was a native West Texan and veteran geologist. In this conversation, he pointed to the most destruction volcanic event in U.S. history – the 1980 Mount St. Helens eruption – for comparison.

“We think there was a lot of material erupted then,” Hall said, “and it affected us so strongly. You look at the volume of material that was erupted at St. Helens, and you look at the amount of material that was erupted at the Chinati, and Chinati was a thousand times larger.”

The Chinati Volcano is thought to have produced a “pyroclastic flow” – a chaotic mixture of rock, gas and ash. More than a thousand cubic kilometers of such material shot skyward – and then flowed, at high speed – over a vast area. 

The largest volcanic eruption in recorded human history was Indonesia's Mount Tambora, in 1815. Its pyroclastic flows killed at least 10,000. And the ash it ejected triggered the “Year Without a Summer” – global temperatures dropped, and harvests failed in Europe. The Chinati eruption was five times larger than Mount Tambora.

The Chinati Mountains themselves are a caldera – the collapsed jumble that remained after the eruption.

But that eruption spread molten rock and ash in an area from south of present-day Alpine to near Van Horn – which endures in rocks called the Mitchell Mesa Formation. The formation is up to 255 feet thick. If you live in Marfa, it's the ground on which you stand. The volcanic formation constitutes the Marfa Plateau – the high prairie expanse that's been a boon to pronghorn and grassland birds for millennia, and, more recently, for ranchers. 

The English Romantic poets spoke of the intimate connection between the sublime, and the terrifying, in natural phenomena that strain human comprehension. The shining Marfa grasslands are certainly sublime – as is the jagged rocky maze of Pinto Canyon and the Chinatis. That beauty is tied to the volcanic terror of the most explosive day in West Texas history.

Drew Stuart is the producer for the Marfa Public Radio series Nature Notes.