California's Catalina Island Will Sink Into Sea; May Cause LA Tsunami

Santa Catalina Island, off Los Angeles. D Ramey Logan via Wikimedia Commons CC4.0

Catalina Island, just south of Los Angeles, is sinking into the ocean, and in a geologically short amount of time it will dip beneath the waves.

Researchers have determined that the isle is descending at a rate of eight inches every thousand years, and tilting while it falls. They found that Santa Catalina Island, as it's formally known, also presents a tsunami risk for Los Angeles, says Chris Castillo, a geophysics researcher at Stanford University. It already has once before: About 500,000 years ago, a major landslide occurred on the island's north face, running into the ocean, and researchers believe it would have created a huge wave heading toward what is now Los Angeles.

The scientists made these calculations by examining submerged terraces on the islands, which show where the shoreline was—where the ocean intersected the land—at various points in its recent past, Castillo says. That allowed them to determine how quickly it is falling into the ocean, says the researcher, who is presenting his results today at the annual meeting of the Seismological Society of America, in Pasadena, California.

The good news: What's "soon" in geological terms is, for humans, a very long time. The island won't fall below sea level for 3 million years, if the current sinking rate continues, Castillo says. "So don't change your vacation plans just yet," he adds. (That means there's also no need, for now, to call off the Catalina wine mixer, nor to evacuate the island's herd of buffalo.)

The island is sinking because two small plates surrounding it are moving past each other. Until recently, the plates where moving toward each other along a curve in a small fault, causing the land to compress and uplift, Castillo explains. This is what formed the island in the first place.

But now the plates are moving apart and the land is falling, a process that is referred to in geology as "elastic relaxation." This same type basic type of geologic process (where the land falls as two plates move past each other) has formed "pull-apart basins" around the world, Castillo says, like the Dead Sea.