Cerro Prieto Volcano

February 20, 2009


Photographer: Dave Lynch
Summary Author: Dave Lynch

Cerro Prieto is a 223 m (732 ft) isolated, inactive volcano found near Mexicali, Mexico (Baja) that rises prominently from the surrounding agricultural fields. It lies on the northwest-striking Cerro Prieto fault. Along with the San Andreas and Imperial faults to the north, Baja represents a transition region between the sliding San Andreas Fault and the crustal opening along the East Pacific Rise, extending stepwise down the length of the Sea of Cortex.

Paleomagnetic data suggests that Cerro Prieto (dark hill) was active between 100,000 and 10,000 years ago. Tales of its most recent activity has been preserved in Cucupas Indian lore. Though this dacitic volcano has been inactive for thousands of years, the region experiences high geothermal heat flow from a shallow magma body, estimated to be only 5 to 6 km (3 to 4 mi) below the surface. Hot subsurface brines are brought to the surface where they evaporate and drive electric generators. An earthquake swarm occurred under Cerro Prieto in February 2008.

The small but conspicuous volcano is topped by a number of microwave communication towers. Nowadays, local kids entertain themselves by writing their names and making drawings on the caldera floor by arranging pieces of volcanic rock. Comparison of this picture with that on Google Earth shows that there is considerable human activity in the caldera.