California’s largest lake is doomed
The Salton Sea with Mount San Jacinto in the background — CC photo
A week ago today a good-sized storm blew into Southern California’s desert off the Sea of Cortez, a.k.a. the Gulf of California. In the Salton Basin (a.k.a. the Salton Trough) north of the Gulf winds averaged 40 mph or so, with gusts above 60. The Salton Sea fills the lowest part of the Salton Basin and the winds churned that water, roiled up its murky, anaerobic depths, and released a cloud of stench, mostly hydrogen sulfide, into the air. People who’ve lived in the Basin are used to that smell, but last weekend the wind off the Sea of Cortez picked up that mixed hydrogen sulfide cocktail and blew it to Los Angeles. On Monday, air quality management districts got complaint calls from residents of Simi Valley, almost 200 miles from the Salton Sea.
It took a day or so before everyone agreed that the Salton Sea was to blame for the stench, and now a few more people are aware of the fact that it’s in trouble. There are plans to “fix” the Sea that would cost several billion dollars, which is getting no traction at all in Sacramento given rabid anti-tax sentiment in California. But “fixing” the Sea in the long term is futile, and the reason involves the Colorado River, plate tectonics, and — possibly — the Grand Canyon.
If it wasn’t for the Colorado River, the Sea of Cortez would extend well into California. Most of the Salton Basin lies below sea level, with only a 30-foot berm near Mexicali between it and the ocean. The Basin is a northern extension of the same rift that holds the Sea of Cortez, created by the north end of the East Pacific Rise as it works to splinter the west side of the North American continent. If it wasn’t for that 30-foot berm you could sail from Mazatlan to Coachella for the Music and Arts Festival, though you might need a snorkel to watch the Tupac hologram.
That berm is there because the Salton Basin/Sea of Cortez rift valley is where the Colorado River happens to reach the sea.
Rivers carry sediment, and desert rivers carry a lot of it, and over the years as the Colorado flowed into the Sea of Cortez rift valley and formed a delta, that delta gradually sealed off the Salton Trough from the open sea. Creating the Colorado Delta took a lot of sediment. As the East Pacific Rise wedges the rift valley wider, the valley floor drops. The Geology 101 term for a valley like this is a “graben,” German for “grave.” California has a few of them, including the valley currently occupied by Lake Tahoe. The floor of the Salton Basin has been sinking almost as fast as the Colorado can fill it up, so the Colorado must have had one hell of a good supply of sediment. More than 10,000 cubic miles of sediment, in fact. At Westmoreland, bedrock lies 18,300 feet below the surface. Even in the extreme north of the Basin the bedrock is usually beneath several thousand feet of sediment. That Tupac hologram stood atop about 13,000 feet of the stuff.
It’s been something like 5 million years since the East Pacific Rise started opening up the Salton Trough area, and if you ask yourself where the Colorado River might have found a lot of sediment in the last 5 million years, there’s an obvious answer that leaps up to suggest itself: 5 million years ago is a common estimate of when the river started cutting the canyons along its length, including that Grand one. That obvious answer is a little too easy: The Grand Canyon itself accounts for only about 1,000 cubic miles of potential sediment, and there’s some thought its carving may have begun significantly before Salton Trough formed. That’s okay. The Colorado’s watershed is about a quarter of a million square miles, so there’s a lot of arid land to provide sediment.
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