A Moving Mud Pot Threatening Railroad Tracks and a Highway, Imperial County, California

David K. Lynch, Travis Deane, Carolina Zamora, Dean G. Francuch, James S. Bailey, Christopher W. Allen, Justin D. Rogers, & Cassandra Gouger

Published August 14, 2018, SCEC Contribution #8562, 2018 SCEC Annual Meeting Poster #277

INTRODUCTION The Salton Trough is a sag in stepover regions between the San Andreas, Imperial and Cerro Prieto Faults in southern California and northern Baja, Mexico. Due to a high geothermal gradient in the Colorado River sediments, the trough contains many CO2-driven geothermal features like gryphons and mud pots, and is home to several geothermal generating plants.
DEVELOPMENTS In 2016 an ambient temperature CO2-driven “mud spring” appeared near a long lived mound spring and began moving southwest toward the Union Pacific railroad tracks and SR111 at about 20 ft per year. It is less than a mile NE of the Wister Fault (SE extension of the San Andreas Fault) and moved as though along a cross fault. As it advanced, the mud spring carved a ~24,000 sq ft basin about 18 ft deep and 75 ft wide (400,000 cf). The spring moved in a fairly straight line and remained a small, discrete, roughly circular structure and did not develop into a linear source, as might be expected if moving along a fault. To our knowledge, such movement and behavior of a mud spring (mudpot, etc.) has not been seen before. Since pumping began in June 2018, the water discharge rate was roughly constant (45,000 gallons per day).
MITIGATION In early 2018 the Union Pacific Railroad (UPR) began taking steps to prevent the spring from undermining their tracks. A number of acoustic imaging studies were carried out, rip-rap was dumped into the mud spring, a 75 ft deep sheet pile wall 120 ft long was built between the spring and tracks and the basin was drained. A well was dug and pumped with the hope of depressurizing the aquifer that is driving the spring. The well encountered highly pressurized artesian conditions at the upper most part of the aquifer at a depth of about 300 ft but did not appear to affect the mud spring. The spring continued its SW movement and eventually met the sheet piles (40 ft from the tracks) where it began to expose them.
CURRENT STATUS In August, as a contingency, UPR began construction of a shoofly (track detour). Two more depressurization wells are being drilled and additional subsurface imaging is being completed. At the time of this writing (mid Aug 2018), the mud spring is stationary because it is being confined by the sheet piles, though it seems likely that the underground source is still moving southwest and will eventually surface in the next few years, possibly undermining the existing railroad tracks or possibly further west under State Route 111.

Key Words
Mud pot spring railroad threat

Citation
Lynch, D. K., Deane, T., Zamora, C., Francuch, D. G., Bailey, J. S., Allen, C. W., Rogers, J. D., & Gouger, C. (2018, 08). A Moving Mud Pot Threatening Railroad Tracks and a Highway, Imperial County, California. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
San Andreas Fault System (SAFS)