The Rio Grande Rift and River

Subduction of the Farallon plate and ocean ridge along western North America converted the boundary between the Pacific plate and North American plate into the San Andreas transform / strike-slip boundary, and North America began to stretch northwest-ward. Underneath North America, the Farallon slab continued to be subducted, likely flatly, coinciding with uplift and compression of the Laramide Orogeny between 75 to 55 million years ago. Sometime after the compression ends, it is likely (but under debate) that the slab broke-off and sank into the mantle opening up mantle upwelling, and beginning extension and opening the of the Rio Grande Rift beginning about 36 million years ago. The rifting (stage 1 of the Wilson Cycle) formed towering cliffs and wide basins through which the Rio Grande River flows (picture below shows the river and Taos bridge in 2007).

The Rio Grande Rift runs north to south (see map below) for 5,000 kilometers from the San Juan Mt.s in Colorado to Chihuahua, Mexico. It varies in width from 30 to 100 km and is between several hundred to several thousand meters. Deep drought has extremely impacted the river, which did not flow last summer in Big Bend National Park last summer. Picture below shows visitors walking on the dry river-bend last summer.

The Rio Grande rift is still opening based on geodetics, and ongoing geologic activity is evident through high heat flow, hot springs, continued earthquake activity, and some of North America's most recent lava flows.

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