Brief by Central Staff
Geology – November 2005 – Colorado Central Magazine
The world is breaking apart here. The question is “How fast?” and a team of geologists and students from the University of Colorado at Boulder and the University of New Mexico has launched a three-year project to find out.
Central Colorado and the San Luis Valley are home to what geologists call the Rio Grande Rift. It begins in New Mexico and extends north to Leadville and beyond — the San Luis Valley and the Upper Arkansas Valleys are a result of the rift.
The crust of the earth is spreading apart in this zone — the Mosquito Range gets a little farther from the Sawatch Range every year. The Sangre de Cristo and San Juan mountains rise a little, while the bedrock floor of the San Luis Valley drops by a minuscule amount.
On the surface, we see mountains on each side of the spreading zone, with a valley between the mountains. Over time, the mountains rise, the valley floor drops, and eventually, the sea sweeps over the floor. To put it another way, the Atlantic Ocean probably looked something like Central Colorado about 70 million years ago.
That’s a long time, but it’s a slow process. Geologists don’t know the exact rate of spreading and related uplift, but they’re trying to determine it. Two dozen state-of-the-art Global Positioning systems will be placed along the rift this winter, with measurements starting next summer.
Most will be in New Mexico, but there will be two in the San Luis Valley near Alamosa and Del Norte, one near Fairplay, and several along the Interstate 70 corridor.
Currently, rift motion is estimated at 0.2 inch a year or less. The more precise surface measurements from the three-year study should provide a better understanding of what’s going on underground.
That, in turn, could predict whether earthquakes and volcanism are likely hereabouts.
The Rio Grande Rift does appear to be growing northward, even into Wyoming, but it’s deep beneath the surface there and doesn’t manifest itself the way it does down here.
But there might be a connection between its extension and minor earthquakes reported in Steamboat Springs; most recent was a 4.1 tremor that hit on Sept. 30. One resident said it felt like a car hitting a house.
The research team wants to work with area schools and governmental agencies. Teachers interested in preparing lesson plans based on the study should contact Anne Sheehan, associate professor of geological sciences at CU, 303-492-4597.
More information about the study is available at www.cires.colorado.edu, and the web offers lots of information about the Rio Grande Rift, some of it even comprehensible to non-geologists.
