SAN DIEGO ASSOCIATION OF GEOLOGISTS

1998 Field Trip to Imperial and Mexicali Valleys
Cerro Prieto geothermal area

Our guide tried to keep us out of trouble beyond this warning sign at the entrance to the surface geothermal activity area. Cerro Prieto geothermal zone is located in the alluvial plain of the Mexicali valley, above a spreading center bounded by the south end of the Imperial Fault on the northeast and the north end of the Cerro Prieto Fault on the southwest. Both faults are right lateral strike slip, part of the San Andreas Fault system.		Photo by Glen Foss
Photo by Lowell Lindsay			We observed bubbling mudpots, fumaroles, and a recently erupted geyser.
Mudpots in foreground. Cerro Prieto Volcano in background. Early explorers Hernan Cortes and Melchor Dias (mid 1500's) saw steam and sulfurous gases rising from the Cerro Prieto area. Intermittent steam geysers associated with seismic activiy have been documented back to 1852.			Photo by Phil Farquarson
Photo by Glen Foss			Fumaroles Groundwater in sandstones and gray shales from the Colorado River delta are heated at depth. Formation temperatures at 2500 meters are estimated at 350°C.
Photo by Glen Foss			"Mud volcano" fumarole
Mud volcano (right) Note on geysers from Lowell Lindsay: There definitely was a geyser at Cerro Prieto which erupted for several months, reaching heights of approx 10 meters, circa 1991. Photos are posted in the Comision Federal Electricidad (CFE) Visitor Center at Cerro Prieto and I'm sure there's plenty of documentation there on it. I will dig for the e-mail addresses of the geologist who showed me the site as well as the field engineer who toured our group through the area. They also tell of major geyser activity in the 1890's, all of which is to be expected from such a major geothermal field (2nd largest in the world) over a near-surface spreading center.			Photo by Barbara B. Birnbaum
Photo by Lowell Lindsay		Yes, it's very warm.    Yellow mineral of this fumarole is sulfur.
		Photo by Barbara Birnbaum
Our tour concluded back at the Visitor Center with a video on geothermal development in Mexico and a tour of the exhibits and displays.			Photo by Lowell Lindsay