California’s coastal communities are increasingly at risk from a potentially dangerous type of ocean surge known as near-shore tsunamis, which are triggered by earthquakes occurring just offshore.
Experts, backed by disaster modeling and local hazard plans, indicate that these tsunamis could pose considerable threats to populated areas along California’s vast 840-mile coastline, from the densely populated southern regions to more remote northern locales.
A critical concern is that depending on the strength and epicenter of an earthquake, threatening waves could reach the shoreline in as little as 10 minutes.
This extremely short response window leaves little to no time for emergency alerts to be disseminated, which raises substantial safety concerns for residents.
Recent hazard mitigation plans published by both the city and county of Los Angeles underscore the urgency of the situation, revealing that locally generated tsunamis could potentially reach alarming heights.
For instance, areas such as Marina del Rey could see waves up to 5 feet above mean sea level, while Manhattan Beach and San Pedro could face 7-foot surges.
Long Beach and Santa Monica Pier may experience waves of 8 feet, and in Malibu, the potential height could surge to 9 feet.
Perhaps most alarming of all is the possibility of waves reaching heights of 30 feet on Catalina Island, depending on seismic activity or underwater landslides.
In Orange County, the hazards are equally concerning. A magnitude 6.8 earthquake occurring offshore could lead to a near-shore tsunami arriving in as little as 15 minutes.
This local-source tsunami could inundate coastal regions in Newport Beach, affecting places like Balboa Island and Balboa Peninsula, with projections indicating that the surge might travel inland up San Diego Creek approaching the 405 Freeway in Irvine.
The San Francisco Bay Area is not exempt from these risks either. Near-shore tsunamis could generate waves as high as 4 feet at locations such as San Francisco’s Aquatic Park and Alcatraz Island, increasing to 9 feet in Bolinas, Marin County, amid other vulnerable locations.
Reginald Harrison, who directs disaster preparedness and emergency communications in Long Beach, acknowledged that while tsunamis are a rare occurrence, they are a legitimate threat for coastal communities.
He emphasized that unlike earthquakes, tsunamis offer some natural warning before they hit, advising anyone near the beach to evacuate to higher ground immediately.
Evacuation from densely populated communities is a challenge that local officials recognize.
A study released in 2020 identified nine densely populated areas that pose particular evacuation challenges, including Naples Island in Long Beach, Oxnard Shores, Balboa Island, and various segments of San Diego’s coastline.
Alameda stands out as exceptionally vulnerable since more than half of its 75,000 residents live within designated hazard zones, and evacuation routes are limited due to the geography of the area divided by a peninsula and the main island.
Despite these risks, local officials argue that significant tsunamis from local faults are infrequent, believing the more substantial threat arises from distant sources, which could still produce wave heights up to 18 feet in Alameda.
Conversely, in places like Redondo Beach, near-shore tsunamis could generate waves as high as 11 feet, surpassing the projected 9-foot waves from distant earthquakes.
Katie Eing, Newport Beach’s emergency services coordinator, pointed out that around 45,000 residents live within the local inundation zone, not accounting for the considerable influx of tourists and workers during peak seasons.
She reiterated the potential devastation that near-shore tsunamis could cause, citing a study from USC indicating that submarine landslides along Southern California’s steep offshore escarpment could unleash 30 to 33-foot tsunamis.
This scenario emphasizes the urgency of timely warnings; given that local-source earthquakes might generate waves arriving within 10 to 20 minutes, citizens may lack adequate time to respond.
The potential for confusion and chaos during evacuations was underscored by an event last December, when a magnitude 7 earthquake struck roughly 30 miles off Humboldt County’s coast.
An expansive tsunami warning was issued, causing alarms to blare across California, from the North Coast to the San Francisco Bay Area.
Fortunately, the generated tsunami only reached a mere 2 inches in height in Mendocino County.
However, the incident highlighted systemic flaws in the evacuation response, as many residents hesitated or were confused about the necessity of evacuation.
One survey respondent from Berkeley conveyed that widespread confusion was rampant, with some questioning why anyone outside the immediate coast should evacuate.
Another echoed a concern regarding the lack of detailed information available to them during the alert, attributing their unawareness to not being enrolled in localized alert systems.
An advantage California had in past tsunami events was clear, timely information; however, confusion can lead to devastating outcomes.
The 2011 magnitude 9.1 Japan earthquake and its aftereffects exemplified this, with a subsequent tsunami that rose as high as 45 feet, resulting in over 18,000 fatalities and severe communication failures exacerbating the disaster.
Many survivors suffered from reluctance to evacuate, a sentiment echoed in the Berkeley survey, where the lack of clear, timely communication was a prominent concern.
Acknowledging these challenges, San Mateo County has developed a tsunami dashboard, allowing residents to check their safety status in real-time by inputting their location, in addition to identifying nearby safe spots.
Last December, road congestion on Highway 1 exemplified potential evacuation challenges when residents attempted to flee from Pacifica; many were unaware that just a few blocks inland from the coast could offer adequate safety.
Some evacuees sought higher ground but drove directly into lower-lying areas, signaling a critical misunderstanding of evacuation protocols.
Emergency management experts have stressed the importance of understanding the geography of tsunamis, stating that evacuation routes should prioritize making way to nearby high ground over lengthy evacuations.
For instance, residents near the Santa Monica Pier can find safety by quickly moving to the bluffs, which hover around 100 feet above sea level, without needing to trek all the way to distant mountaintops.
In numerous San Francisco communities, simply moving a few blocks inland can suffice for safety.
The general recommendation is to prioritize evacuating on foot, cycling, or other non-vehicular methods to avoid traffic congestion, though officials recognize this may prove difficult in car-centric California.
For distant tsunami warnings that allow for more extended evacuation times, the procedures differ significantly.
In Los Angeles, evacuation zones largely include the beach and a few blocks inland; however, there are areas that necessitate vehicular evacuation.
In such scenarios, first responders would assist in directing civilians towards safe zones.
Further planning to enhance preparedness remains a priority, particularly in San Francisco, where there is a need to establish strategies specifically for individuals with disabilities—planned to be completed by 2027.
In cases where high ground isn’t immediately accessible, emergency services may recommend vertical evacuation into taller structures, essential for ensuring the safety of those with specialized needs.
The city’s hazard plans also highlight the necessity of clear signage on sidewalks and roads in vulnerable coastal areas to guide residents during tsunami alerts and other coastal flood threats.
While some coastal regions have started to place tsunami warning signs, the signs are not widespread, creating a gap in public awareness.
Marin County officials echoed similar sentiments, acknowledging the limited availability of signage indicating tsunami inundation zones throughout the area.
Steven Torrence, Marin County’s director of emergency management, highlighted that despite jurisdictional limitations across various districts, it remains crucial to clearly identify inundation zones to ensure community safety.
image source from：https://www.latimes.com/california/story/2025-06-08/how-this-type-of-tsunami-could-spell-disaster-for-california
