Hawaii. The South Coast. Both considered to be slices of paradise. But, the Hilina Slump could change all of that …it could wipe out the California Coast as we know it.
The eruption of Kilauea volcano was devastating to many on the southern end of Hawaii’s Big Island.
But the slow-rolling disaster has implications for the California coast because of a geological feature known as the Hilina Slump that some say could turn the next major eruption into a catastrophe unlike anything witnessed in modern times.
What does that mean for Santa Barbara?
Large, locally generated tsunamis in California are estimated to occur once every century; 13 possible tsunamis have been observed or recorded from local earthquakes between 1812 and 1988, according to the city’s Tsunami Response Plan.
Should a tsunami hit Santa Barbara, the areas most affected would be the southern areas near the coast including the airport, and damage would depend on “sea bottom and coastal topographic characteristics” as well as the incoming direction of the tsunami.
The May 2018 Kilauea eruption spewed lava into residential subdivisions in the Puna district, prompting mandatory evacuations of two subdivisions: Leilani Estates and Lanipuna Gardens.
While no one was killed, more than 700 homes were lost when the 4,190-foot-tall shield-type volcano blew its top, several hours after a magnitude-5 quake struck the island.
The U.S. Geological Survey says Kilauea released enough lava to fill 3,400 Olympic-size swimming pools every day – a record for the volcano – enough to cover Manhattan Island to a depth of more than 61/2 feet.
Recovery continues to this day, at a cost that could top $800 million, according to Hawaii County officials.
The Hilina Slump is a 10-by-15-mile feature partially detached from the seaward flank of Kilauea. While movement of the feature is nothing new, some have long viewed it as a candidate for catastrophic collapse. But USGS notes it has “never failed.”
Immediately after the eruption, however, rumors spread online that a collapse was imminent, and that a megatsunami would sweep across the Pacific Ocean, hitting California in a matter of four hours – a doomsday scenario that’s been around for some time.
In reality, the slump – a spot where the flank of the cliff on the southern coast of the island moves farther toward the ocean – has been moving for a long time, according to researchers at the UC Berkeley Seismology Lab.
A magnitude 7.2 earthquake that struck Nov. 29, 1975, caused it to slide by about 11 feet, but there was no giant wave.
It was a different story following the 7.9-magnitude Kau earthquake on April 3, 1868. In that event, the moving slump resulted in a tsunami with maximum waves of 60 feet that drowned more than 40 people.
All the deaths were in the local area.
But in a complete failure of the southern cliff along what’s called the extensional Hilina Fault system, “a huge, sudden disaster” is envisioned, in which 10 percent of the island could be affected by the collapse. An earthquake of magnitude 9 would be possible – comparable to the largest quakes ever measured – generating a tsunami with an estimated wave height of more than 1,000 feet in the islands.
That’s what happened, say UC Berkeley researchers, some 110,000 years ago: “Hawaii was rocked by such a slump and engulfed in the resulting huge tsunami.”
A repeat of such a catastrophe is highly unlikely, researchers say, “and it may take many millennia for it to occur.”
Still, like the tsunami generated by the 2011 Fukushima, Japan, earthquake that destroyed the harbor in California’s Crescent City – 4,700 miles away – one caused by the slump or unrelated major volcanic or seismic activity could pose similar risks to the Southern California coast – 2,400 miles away.
James Reilly, who heads the USGS and recently flew over the area with agency Volcano Hazards Program Coordinator Charlie Mandeville, said the detachment in question consists of two normal faults moving seaward.
According to Mr. Mandeville, there was almost no movement during this last eruption cycle suggesting the fault system is currently “locked.”
“Along the abyssal flanks (10,000 to 20,000 feet down) of all the islands there are impressive debris fields indicating there have been numerous past mass wastage events,” he said. “If they fail rapidly (not by creep) the potential for tsunami development is pretty high with big waves.”
Still, a fact sheet from the USGS days after the eruption states, “Geologic history combined with models of south flank motion suggest that the likelihood of a catastrophic failure event is incredibly remote. There are certainly signs on the ocean floor for landslides from other volcanoes on the Island of Hawaii and from other islands, but none are associated with Kilauea.”
In addition, the agency said at the time, “Kilauea has experienced much larger earthquakes and magmatic intrusions in the recent past.”
A 2006 Rice University study found that movement at Kilauea may have stabilized the slump.
“From previous studies, we know that Kilauea is the site of an active landslide, the Hilina slump, which has moved in historic times,” Julia Morgan, assistant professor of Earth Science at Rice, said at the time. “We now recognize that Kilauea also experienced a catastrophic landslide in the past, possibly within 25,000-50,000 years, which is quite recent in geologic terms.”
New findings presented by Dr. Morgan 12 years ago showed that debris from the last catastrophic landslide on Kilauea “is forming a buffer that stabilizes the Hilina Slump.”
Dr. Morgan and her colleagues, Gregory Moore at the University of Hawaii and David Clague at Monterey Bay Aquarium Research Institute, reached this conclusion “after a comprehensive analysis of two offshore seismic and seafloor mapping surveys conducted in 1998 by the Lamont-Doherty Earth Observatory and MBARI.”
What they found was a detached portion of Kilauea similar in size to the slump, but northeast of it.
“When this section of the volcano slid away, it settled beneath the ocean at the base of Kilauea,” according to Dr. Morgan’s report for Rice University.
As the volcano grew and slid toward the ocean, the debris piled up, “much like snow piles up in front of a snowplow.” The result, researchers found, is a “broad, bench-like, submarine structure” sitting at the foot of the mountain, 15-20 miles offshore.
“The downslope edge of the Hilina slump now impinges on the outer bench.”
For Santa Barbara, the real threat of a tsunami may actually be closer to home.
Several active offshore geological faults subject the region to seismic action at any time, including the Mesa Fault, the Santa Ynez Fault in the mountains and the Santa Rosa and other unnamed faults near the Channel Islands.
Tsunami action from the vicinity of the Aleutian Islands and Kurile Islands is also possible.
Two events have produced what authorities call “substantial tidal action” in Santa Barbara:
• Feb. 27, 2010: Chile suffered a magnitude 8.8 earthquake, which caused a tsunami of .91 meters in Santa Barbara, damaging the dredging equipment in the harbor/waterfront area.
• March 11, 2011: A magnitude 9 earthquake in Japan generated a tsunami that caused $70,000 damage to a crane, bait barge and several boats.
Another Chilean quake, this one in 1960, reportedly caused a drifting oil exploration barge to ram a new dredge, causing at least $10,000 in damage. Another $10,000 in damage was reported when a 40-foot boat was set adrift.
In a report for Southern California Edison pertaining to the building of the San Onofre Nuclear Generating Station, Marine Advisors Inc. of La Jolla indicate that a quake-generated wave of 15 to 20 feet may have hit Santa Barbara in December 1812.
Depending on where a tsunami originated and the strength of the earthquake that caused it, the Channel Islands, about 30 miles offshore from the city, could provide some shelter.
Should an evacuation be ordered because of tsunami, proposed evacuation routes include one-way traffic on Castillo, Garden, Cesar Chavez and Milpas streets (leaving one lane open for first responders) and routing traffic on Cabrillo Boulevard west to La Marina and east to Hot Springs Road.
Authorities have identified the following traffic control points:
• Shoreline Drive at La Marina
• Cabrillo Boulevard at Highway 101
• Castillo Street at Montecito Street
• State Street at Gutierrez Street
• Garden Street at Gutierrez Street
• Salsipuedes Street at Calle Cesar Chavez
• Milpas Street at Quinientos Street
• Cliff Drive at Loma Alta
The Hilina Slump gets no mention in the city’s Tsunami Response Plan.
Matthew Blackett, a senior lecturer in physical geography and natural hazards at Coventry University in England, places the Hilina Slump in the second spot on his list of five “little-known natural disasters that have been predicted.”
“Forget the widely-publicized megatsunami threat that has been attributed to the potential collapse of the Cumbre Vieja volcano on La Palma in the Canary Islands,” he wrote. The Hilina Slump “could drop (about 2,900 cubic miles) of rock into the Pacific Ocean, generating a megatsunami that would propagate around the Pacific Ocean and reach the western seaboard of North America in a matter of hours, inundating coastal communities.
He noted that in 1975 movement of the slump “generated a smaller, yet destructive tsunami that reached California.”
“Given that the slump is continually active and moving, it might only take a jolt from an earthquake in the tectonically active state to set in motion this catastrophic chain of events.”