At the southern end of the San Andreas Fault in California, where the North American and Pacific tectonic plates famously touch, sits a stinky, gurgling pool of mud. Scientists have been aware of this “mud pot,” as the geothermal feature is known, since the 1950s. But it has recently become a cause for concern because, as Robin George Andrews reports for National Geographic, the mud pot is on the move.
Called the “Niland Geyser” because it is located near the township of Niland in Imperial County, the mud pot began its sludgy trudge at some point between 2015 and 2016. The bubbling pool has since moved about 20 feet each year, carving a 24,000 square foot basin in the ground. Its pace is not particularly quick, but officials are nevertheless worried about what lies in its path.
According to Alejandra Reyes-Velarde and Rong-Gong Lin II of the Las Angeles Times, the mud is creeping in the direction of Union Pacific freight railroad tracks, a petroleum pipeline, fiber optic telecommunications lines owned by Verizon, and part of Highway 111, which connects the Coachella Valley to California’s border with Mexico. To date, attempts to stop the mud pot’s forward march have not been successful. Union Pacific tried to build a 100-foot wall that extended 75 feet into the ground to stop the mud from reaching its railroads. The mud simply oozed beneath the wall.
“It’s a slow-moving disaster,” Alfredo Estrada, fire chief and emergency services coordinator of Imperial County tells Reyes-Velarde and Lin.
Mud pots are not an uncommon geologic feature in volcanic areas; you can see them, for instance, in Yellowstone National Park. According to Live Science’s Laura Geggel, the one in Imperial County resulted from historic earthquakes that formed deep cracks beneath the Earth’s surface, allowing gases to rise upwards. The mud pot’s bubbles, in fact, are caused not by hot water, but by carbon dioxide welling up from underground.
“The carbon dioxide is probably being formed as a result of the geologic processes deep underneath this part of California,” Reyes-Velarde and Lin explain. “As thousands of years of loose sediment dumped by the Colorado River get pushed deeper underground, where there’s more pressure and heat, the material is getting cooked and transformed into sandstone or greenschist rock, which produces carbon dioxide.”
The mud pot’s funky smell comes from the presence of hydrogen sulfide, which creates a rotten egg-like stench. According to Andrews, it is possible that the mud pot is drawing from a reservoir filled with agricultural runoff water, which fosters algal blooms. When algae die, the bacteria that feed on them produce hydrogen sulfide.
While there is nothing inherently strange about the existence of the mud pot, this one is unusual for several reasons. For one thing, mud pots typically form when there are limited quantities of hot water, but the Niland Geyser is producing large quantities of water—up to 40,000 gallons per day. Also, mud pots do not typically move.
“No one has seen a moving mud pot before,” David Lynch, a physicist who studies geothermal features in the area, tells Andrews.
Scientists do not yet know why the Niland Geyser is creeping across California. They can, however, say with certainty that it is not being driven by surges in seismic activity. Ken Hudnut, a research geophysicist with the U.S. Geological Survey, tells Andrews that the San Andreas Fault is heavily monitored, and there are no signs that a large earthquake is brewing. Californians, in other words, can rest assured that the Niland Geyser’s crawl is not an indication that the “Big One” quake is imminent.
In spite of the potential damages it may cause, the mud pot has been given a much less ominous nickname: the “Slow One.” And as its moniker suggests, the mud pot’s steady pace is giving officials time to prepare for its possible intersection with human infrastructure. Detour plans for Highway 111 are already in place, according to Reyes-Velarde and Lin of the Los Angeles Times, and Union Pacific may also consider building a bridge to circumvent the gurgling geyser.