Waves Of Destruction
Storms, tsunamis, watery death; Could it happen here?
Thursday, September 8, 2005
Total devastation. The apocalyptic reports and images from New Orleans pour in through our televisions and computers. Disease, death, and destitution stand in relief against miles and miles of muddy water. As far as the eye can see there is chaos, despair, and gradually increasing outbursts of feverish violence. Roving bands of armed looters stalk the surreal urban bayou like toothy gators, the Superdome overflows with American refugees, corpses float through the Big Easy like some hideous voodoo dream.
A stunned nation drowns in the gruesome, unbelievable images. The response is similar to 9/11. How could this happen here? Why weren’t we prepared for this? Especially after 2004, the worst hurricane season on record?
“It is like our tsunami,” a survivor says, referring to the devastating Indian Ocean event of Dec. 26, 2004, that killed 200,000. And this isn’t an exaggeration. According to reports, when Hurricane Katrina roared ashore on the US Gulf Coast on Aug. 29, it created a 30-foot storm surge.
It’s a haunting analogy. The scope and severity of Katrina rendered one of the most beloved cities in America uninhabitable. Like 9/11, the stark reality of the images has opened a Pandora’s Box of new, disturbing possibilities. Suddenly every coastal community in America is asking, could a similar disaster happen here?
In the case of the Monterey Bay area, the answer is yes, according to Gary Greene of Moss Landing Marine Laboratories.
“Absolutely,” Greene says when asked about the likelihood of a large scale tsunami hitting our shores. “People should be prepared. Not that it will happen tomorrow, but people should be prepared for it.”
Greene is one of a group of local researchers who have spent the last 15 to 20 years studying the cause and effect of tsunamis in the Monterey Bay area. What they’re in the process of discovering is that we are highly susceptible to tsunamis generated by both distant and local seismic activity and by non-seismogenic events—especially the massive landslides which periodically occur on the steep slopes of the deep submarine Monterey Canyon directly off our shores.
Yet according to Steve Ward, a Research Geophysicist in the Earth Sciences Theoretical Seismology and Geophysics Department at UC Santa Cruz, the most likely scenario involving a dangerous tsunami would be a seismic event similar to the Indian Ocean tragedy, a distant earthquake generated far offshore.
“They happen every 40 or 50 years in the Aleutian Islands,” Ward says.
The last such event occurred 41 years ago.
On March 28, 1964, waves generated by a magnitude 8.4 earthquake affected the entire California coastline. From Crescent City to Monterey, they ranged from seven to 21 feet. Hardest hit was Crescent City, where waves reaching over 20 feet destroyed half of the waterfront business district and killed 11 people.
Almost 20 years earlier, on April 1, 1947, a Pacific-wide tsunami was generated by a magnitude 7.8 earthquake near Unimak Island in the Aleutians. A huge wave of 115 feet completely destroyed the US Coast Guard’s Scotch Cap lighthouse on Unimak and killed all five of its occupants. Five hours later, destructive waves reached the Hawaiian Islands without warning, causing considerable damage and loss of life. Locally, 15-foot waves reached the Central Coast of California, killing a man in Santa Cruz. Damage was estimated at $26 million (in 1946 dollars).
The good news is that we have the potential to see distant tsunamis coming. As a result of the 1947 tsunami, the US established a Pacific Tsunami Warning Center in Hawaii. Today, there are six tsunami warning buoys in the Pacific. The buoys transmit data received from sensors placed on the sea floor which measure ocean pressure.
The more tsunamis researchers see, the more accurately they can predict them. By sensing, measuring and identifying tsunamis specific to distant seismic events, they are able to infer, with increasing frequency, where they’re going and what their possible effects will be once they get there.
Yet when a magnitude 7.2 earthquake occurred in Mendocino last June 14, the efficiency of Monterey County’s tsunami warning system was brought into question.
Six minutes after the quake struck at 7:50pm about 90 miles southwest of Crescent City, the West Coast and Alaska Tsunami Warning Center issued a warning for the West Coast from the US Mexico Border to Vancouver Island. While thousands of coastal dwellers in Crescent City and southern Oregon heard tsunami sirens and were safely evacuated within minutes of the warning, most Monterey County residents didn’t even learn about the warning until after the danger had passed.
“It caused a lot of commotion,” Ward says. “Fortunately, it was too small an earthquake to create much of a tsunami. You need at least a magnitude-eight to make a trans-oceanic wave and at least a magnitude-seven to make a local wave.”
Kyle Oden is the Emergency Services Planner in charge of tsunami preparedness at the Monterey County Office of Emergency Services. He feels the potential for large-scale damage from a tsunami in Monterey County is “pretty low,” but admits the possibility of “a high consequence” exists.
“Luckily, the topography of Monterey County doesn’t have large stretches of flat land, so we wouldn’t have large areas inundated with water like we’re seeing in New Orleans,” he says. “But places like Elkhorn Slough might see some damage [and] Monterey harbor might get some street flooding.”
Despite the confusion last June, Oden contends that the tsunami warning system in place is effective.
“We’ve had issues in the past but they’re smoothed out,” Oden says. “If there was to be a warning I would get an e-mail, a page, a call on my cell, a message on my teletype machine, as well as warnings on my radio and television. We want to make sure [the warnings are] redundant so you see them.”
Yet Oden admits that many Monterey County residents “don’t have all these things. Right now the EAS and the radio are the best things we have for the general public.”
The EAS, or Emergency Alert System, replaced the Emergency Broadcast System (EBS) 11 years ago. It interrupts radio and television programs to advise the public of an impending emergency.
The problem is, of course, that most people are not listening to a radio or watching television when a warning is broadcast. To improve emergency awareness, Oden suggests that Monterey County residents log on to the Emergency Digital Information System (EDIS) Web site at www.incident.com/edismail.shtml and ask to be notified by e-mail, cell phone or pager of any type of an emergency warning.
“From there you can set it to pick up anything from the state or just the Monterey Bay region,” Oden says. “It’s pretty useful and free.”
Regardless, Oden admits that in the event of a large-scale tsunami, very little specific preparation has been made.
“We’re working on a more specific response to tsunamis,” Oden says. “For example, tsunami evacuation. At this time, I can’t speak to anything specific as to what shelters or facilities may or may not be flooded. There’s been no study and a lot of that is because we have nothing to base this on. We have to take a worst case scenario—a 20-30 foot rise in sea level—and see what has been affected. But no modeling has been done to date.”
Of course, in the case of a locally-generated tsunami—one generated by a landslide in the Monterey Canyon—any discussion of early warning is probably superfluous, according to University of California at Santa Cruz’s Steve Ward.
“We’re talking about maybe six to 10 minutes of travel time,” Ward says. “Not much time for a warning.”
To make matters worse, a locally-generated tsunami only needs to be a fraction of the size to be equally dangerous as its far-flung cousin.
“The size of a tsunami is the result of the intrinsic size of the earthquake and its proximity,” Ward says. “For example, a 100-watt bulb far away gives off the same light as a five-watt bulb that’s closer.”
Dr. Greene of Moss Landing Marine Laboratories says that Monterey Bay communities have a higher risk of tsunami damage because of the deep submarine Monterey Canyon off our shores.
“The canyon is as deep and big as the Grand Canyon,” Greene says. “Like the Grand Canyon, you see landslides off the steep slopes. These big slabs, varying from tens of meters to a hundred meters thick, slide off into the canyon and have the potential to kick off a tsunami which could affect 20-30 kilometers of coast. This thing could be from a few meters to as many as six meters (20 feet) high. It’s going to be pretty dramatic.”
To better understand this submarine geologic activity, Greene has been working with Steve Ward to map the landslides and look at the most unstable areas of the canyon.
“We want to find the ones that may be most prone to failure in the future,” Greene says. “Ward is modeling these potential failures and what the ensuing wave scenario might look like. We’ve created a range of scenarios. What if [the unstable areas] fail all at once? What if they fail in parts? He’s created a range of potential tsunamis and their potential effect on the shoreline.”
(Go to www.es.ucsc.edu/~ward/ to view a link to QuickTime movies of Dr. Ward’s models.)
To locate these areas of potential failure, Greene has been using manned and remote-operated submersible vehicles (ROVs) to visually survey the canyon’s steep walls, a research technique he employed just four days after the Loma Prieta earthquake in 1989.
“We heard a report of a one-foot tsunami that came into Moss Landing,” Greene says. “We calculated where we thought this wave was generated, then we went out with the ROV [Ventana] and found a small scarp, [(a fracture in the canyon wall)] that we felt was the right size to have produced the wave. And obviously it displayed evidence that this was a recent occurrence.”
Along the freshly scarred wall Greene and his team found a frenzy of fish taking advantage of the exposed benthic fauna. Schools of rock fish were gorging on the giant worm tubes which stuck out of the eroded walls, like giant conduits poking out of a ruined building.
According to Frank Schwing, an oceanographer at the Pacific Fisheries Environmental Laboratory who became interested in the study of tsunamis after noticing a three-foot disturbance in the Monterey Bay tide gauges for a few hours after the earthquake, the small wave generated by this event was fortuitously caught on video.
“It was a cool coincidence,” he says. “Someone was doing some videography at sunset at Moss Landing when the earthquake hit. The video continued to run. You see the dust of the sand come up. Then he caught this three-foot wave running right up the channel to Moss Landing. It looks just like a tidal bore.”
According to Schwing, who has done some tsunami modeling of the Monterey Bay himself, the island at Moss Landing dropped about a foot during the 1989 earthquake.
“When the Moss Landing Marine lab collapsed, it was a large enough displacement of earth and sediment to send out a tsunami of its own,” Schwing says. “So the place that studies tsunamis created a tsunami itself.”
In their recent studies, Greene and Ward have identified some areas of concern.
“We see offshore areas that have some big cracks in them,” Greene says. “There’s an area offshore called the Monterey Meander Mass Wasting Field—it’s located about 15 miles directly offshore of Moss Landing—we’ve been looking at that in detail for the last couple of months and found fresh scarps and fissures and recent expressions of faults. The Monterey fault comes right through there.”
According to Greene, Ward’s models have shown that most of the energy of the landslide, or failure, is directed in the line of the failure.
“If we have a failure on the northern side of the Canyon like where the Monterey Meander is, the resulting movement and energy of the primary wave is applied to the south, in this case directly towards Monterey,” Greene says, “While a secondary, less powerful wave is transmitted in the opposite direction, in this case, Santa Cruz.”
Greene and Ward are in the process of mapping the area around the Monterey Meander Mass Wasting Field “because it looks like the most probable area of failure” and creating a multi-scenario model of possible consequences of various landslides in the area.
According to Greene and Ward, it’s not a question of if, it’s a question of when.
“The thing is, no one knows when the next one will come,” Ward says. “You can assess probability by statistically looking at averages and when a big earthquake happens, but you can never know for sure.”
“The problem is,” Greene says. “We don’t have a good handle on the history of these things.”
Ward says that “paleoseismologists” such as the University of Washington’s Brian Atwater have managed to date five Pacific “mega-tsunamis” in the last 2,000 years by taking core samples along the coast and identifying unusual deposits and by dating tree rings.
“When tsunamis happen they bring all kinds of things from the beach, Greene says. “For example, if you find a layer of beach sand far inland or peat moss or a grassy layer or some other terrestrial material deposited below a layer of sand, you have evidence of a tsunami. We date the material above and below the layer and that’s how we try to get the frequency of tsunamis.”
Native American oral history from the Northwest indicates a time hundreds of years ago when whole villages were wiped out by a wave.
Using core-sample evidence and the study of tree rings, and a written account of the event in the Japanese historical record, Atwater and his team of paleoseismologists provided three lines of reasoning to confirm this event in the year 1700. According to Ward, this historical disaster was roughly equivalent in size to the Dec. 26 Indian Ocean tsunami.
“We’re seeing that an event of this size happens in the Pacific roughly every 300 to 400 years,” Ward says.
So, in other words, we’re due.
“What’s the next big event?” Ward asks. “Probably up in Cascadia [the Pacific Northwest], where you saw the 1700 tsunami. That’s my guess.”
Nonetheless, Greene and Ward both emphasize that the study of tsunamis is “a study in progress.”
“We’re just getting started,” Greene says. “It takes an Indian Ocean tsunami of great magnitude to generate interest. We’ve been doing this for years with little resources. We still don’t have a hell of a lot of support.”
Yet more than eight months after the Dec. 26 Indian Ocean tsunami, there are some signs of increased support. Greene and Ward recently submitted a proposal to the National Science Foundation for a grant to look at the stability of the canyon walls off our shores and Greene feels cautiously optimistic about their chances. Plus, Congress recently passed a bill to increase the number of tsunami warning buoys from six to 20. Yet the small cadre of tsunami researchers feel this is only a good beginning.
New Orleans’ vulnerability to levee failure was no secret, and there have been repeated warnings from the scientific community that global warming and a corresponding rise in sea temperature have the potential to create more “killer hurricanes.” If Hurricane Katrina has taught us anything, it’s that preparing for these worst-case scenarios is a good idea.
VISIT www.incident.com/edismail.shtml to activate emergency warnings; see this website for links to more reports about Hurricane Katrina.