Geology is almost always a matter of epochs and eons, of immense forces acting across vast time. But there are exceptions.
Large swaths of West Texas are dominated by features called coppice dunes. These dunes reveal that, when human activity and extreme weather intersect, landscapes can be rapidly transformed.
If you driven outside El Paso or Alamogordo, New Mexico, or in the oilfield country between Monahans and Pecos, you’ve seen coppice dunes. Each of these sandy mounds is topped with a tough desert plant, typically a mesquite or creosote. For geologists, they’re known as nabkhas, in honor of where they were first studied – the Arabian Desert.
UTEP geology professor Richard “Rip” Langford is a sand-dune specialist.
“So all the terms for deserts either are Spanish,” Langford said, “from the American Southwest and Spain – so mesa, arroyo, things like that – or else they're Arabic.”
Nabkhas, Langford said, embody “desertification” – the process by which fertile lands become desert.
In our region’s most dramatic dunefields – New Mexico’s White Sands, the Salt Basin Dunes – plants have gradually taken hold atop the sands. But with coppice dunes, Langford said, the plants came first, and helped create the dunes.
“Sand piled up around the plant,” he said, “and the plant rose through it and stabilized it. And then you pile up more sand, and then the plant grows through that, and then you pile up more sand and the plant grows through that.”
Mesquites – those hardiest of desert plants – have adapted especially well. Amidst the sands, they modify their root structures, and grow as low shrubs, rather than trees.
But where did the sand come from?
“That desertification – people have thought about what causes it,” Langford said. “And I think the consensus now is that it was a combination of overgrazing and climate and drought.”
Langford is a fourth-generation El Pasoan, and he said when his forbears arrived, this valley was largely a grassland. But intensive livestock grazing in the first flush of settlement denuded those grasslands. And when drought struck, the sandy soil was swept away.
The USDA has operated the Jornada Experimental Range in southern New Mexico since 1912. Scientists recorded the emergence of coppice dunes there after a 1914 drought. But Langford has found that West Texas coppice dunes date to another historic dry spell.
“You can look at the plants in them,” Langford said, “and they have growth rings, annual growth rings. And so if you count the growth rings, almost all the plants in coppice dunes began to form in the great 1950s Texas drought.”
The El Paso area was particularly promising for dune development. For thousands of years, the Rio Grande ended here in a series of lakes. Sands accumulated in those lakebeds. Without grass to hold it in place, that sand could be blown into dunes.
As Langford analyzes nabkhas here, he finds sands and pebbles that originated far away, at the river’s headwaters.
“You can identify every now and then – oh, yeah, that's Sangre de Cristo formation from up by Santa Fe,” Langford said, “or that's a high-grade metamorphic rock from who knows where, somewhere way north in northern New Mexico.”
Coppice dunes have replaced grasslands across thousands of square miles in our region. It’s a reminder that droughts have profound and lasting impacts. And it’s a reminder that while West Texas may be rugged, its ecosystems are fragile.
