Sea levels along the California coastline are projected to climb by as much as a foot — roughly 30 centimeters — within the coming days, as an unusually large pulse of ocean energy travels north along the U.S. West Coast. Oceanographers call the feature a "coastal trapped wave," or Kelvin wave, and it forms part of El Niño, the long-running Pacific pattern capable of delivering powerful storms and floods to some regions of the world while leaving others in drought.
The alert arrives as communities in Southern California are still contending with surf-driven damage from recent weeks, and as sand berms have been built along area beaches in anticipation of additional storms reaching the region.
Not a Tsunami: How the Kelvin Wave Behaves
Despite the volume of water involved, the Kelvin wave bears little resemblance to a tsunami. It does not rear up and crash onto beaches. Instead, it moves as a sustained bulge of excess water — as much as 30 kilometers, or about 18 miles, across — that clings to the coastline as it travels north, eventually reaching as far as Alaska.
That distinction shapes how the hazard unfolds. Rather than a single violent event, the wave represents a gradual, days-long elevation of the baseline sea surface, which then acts as a multiplier on whatever else the ocean and atmosphere deliver at the same time.
Why a Modest Rise Matters
Dillon Amaya, an oceanographer at North Carolina State University, explained that the wave lifts sea states, and that the danger intensifies when it overlaps with other natural forces — storm surge from passing weather systems, large ocean swells, or astronomically high tides. When those factors converge, the risk of coastal flooding and beach erosion rises sharply.
Amaya offered a rough rule of thumb for gauging the effect: every two to four inches, or five to ten centimeters, of background sea level rise essentially doubles flood risk. That amount may sound small on its own, he noted, but because it is distributed across an enormous volume of water and stacks on top of other conditions, the resulting flood exposure becomes meaningful.
- Storm surge pushed ashore by passing weather systems
- Long-period swells arriving from distant storms
- Astronomically high tides that already stress low-lying areas
- Elevated background sea levels sustained by the Kelvin wave itself
Damage Already Recorded in Southern California
The warning lands against a backdrop of concrete losses. In recent weeks, storm surges have eaten away at Southern California beaches and damaged property. In Dana Point and Laguna Beach, communities south of Los Angeles, several houses have been left uninhabitable, and at least one has collapsed completely.
Farther up the coast in Malibu, pounding waves driven by a nearby hurricane eroded the shoreline and opened an enormous sinkhole in the driveway of a home belonging to Hollywood actor Nicolas Cage. Such episodes illustrate how erosion can undermine foundations and infrastructure well before water reaches a structure directly.
El Niño as Both Cause and Symptom
Amaya describes the Kelvin wave as simultaneously a cause and a symptom of El Niño. Its origins lie in waters near Indonesia, where trade winds typically pile up a large reservoir of very warm surface water in the western equatorial Pacific. When those winds die down, the warm water is no longer held in place and begins to shift, setting off the chain of ocean and atmospheric changes associated with the phenomenon.
Because El Niño plays out over months rather than days, the current wave is best understood as one expression of a broader pattern rather than an isolated incident. The same phenomenon that raises sea levels along the West Coast can, in other parts of the world, contribute to drought conditions — a split outcome that reflects how profoundly the redistribution of Pacific heat reorganizes weather far beyond the ocean basin where it begins.
What to Watch in the Days Ahead
For coastal residents and local officials, the practical takeaways center on timing and accumulation rather than a single dramatic moment.
- Watch for the overlap of high tide, storm surge and swell, which is when flooding risk peaks.
- Expect elevated water levels to persist for days, not hours, as the wave travels north.
- Anticipate continued beach erosion in areas where recent surges have already stripped sand.
- Treat even a few additional centimeters of water as significant, given how steeply flood probability scales.
The wave's long journey means the elevated sea state will not be confined to California. As the bulge traces the coastline northward toward Alaska, communities along the route could see similarly raised water levels, with the same compounding dynamics at play wherever weather, tides and swells converge.
For now, the most immediate concern is the interaction between the Kelvin wave and any storm system that develops over the next several days. The sand berms built along Southern California beaches stand as a provisional line of defense, but oceanographers emphasize that the underlying risk stems from the combination of factors — a reminder that coastal vulnerability is rarely the product of one force acting alone.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
