The tsunami wave from an anticipated earthquake off the West Coast could reach 100 feet and permanently flood parts of the coast.
The pressure keeps building below the Earth’s surface off the coast of the Pacific Northwest, and a multi-layered disaster could strike at any time. A huge earthquake is brewing along the
Cascadia Subduction Zone that could destroy bridges, reshape the landscape and trigger a massive tsunami. Scientists have known about the looming danger for years, but ongoing research keeps painting a clearer picture of what could happen. Among the dangers: A huge tsunami that will wash over coastal areas and permanently flood them. The quake is a matter of when, not if, said Tina Dura, a geologist and professor of natural hazards at Virginia Polytechnic Institute in Blacksburg, Virginia. "Geologically speaking, we’re well within the window of possibility," she said. Recent research has focused on how
climate change is increasing the impact of the earthquake
on coastal areas that will suddenly sink . Researchers expect the quake will trigger an as much a 6-foot drop in some inland areas — then a massive tsunami will flood those regions, some permanently. "Imagine if, after Hurricane Katrina, after all the horrible things that happened, if we'd also lost big chunks of New Orleans and it never came back," said Diego Melgar, a professor at the University of Oregon and director of the Cascadia Region Earthquake Science Center. The loss of swaths of land is just one of the surreal series of events that will occur when the earthquake eventually strikes, researchers say.
When will the next big Cascadia Subduction Zone earthquake strike?
This is a mix of bad and good news. The quake is a certainty, but could be hundreds of years off. While it could happen at any time, seismologists have estimated there is
a 15% probability of a magnitude 8 in the next 50 years — a substantial risk for such a devastating scenario. "We can’t predict exactly when the next great Cascadia earthquake will occur. It could be tomorrow or decades from now," said Dura. Part of their confidence comes from the history of huge earthquakes in the region. "The last event was in 1700, and paleoseismic records show these earthquakes recur roughly every 200 to 800 years. By 2100, there is a 30% chance of a large earthquake happening," Dura said.
The Cascadia Subduction Zone earthquake
Scientists have a clear picture of what will happen when the earthquake strikes. “First would come extremely strong shaking – shaking that makes it difficult to stand or walk. This would probably last a minute or longer," said Melgar. Next, land along the coast would drop as much as six-and-a-half feet in places, probably within minutes. "Then there would probably be 30 to 40 minutes of seeming peace. But that's a false impression, because the tsunami is coming," he said. The resulting waves would be on the order of the
2004 Indian Ocean tsunami that killed more than 50,000 people. The tsunami wave from an earthquake of this size could get to 90 or 100 feet tall, Melgar said.
Tsunami trouble
When the tsunami wave arrives at the shore "you get this massive surge that lasts for hours, sometimes days," Melgar said. This is where global warming comes in. Two things play a part in creating the catastrophe their research describes. First, the land would have dropped as much as six feet. At the same time,
sea level rise from climate change means that the water which rushes in will cover more land. "You'd hope the tsunami could come to shore, then flow out again and the land would dry out. But there will be parts where it's now below sea level – the water won't flow back," said Melgar. A great Cascadia earthquake could instantly expand flood zones and double flood exposure for residents, structures, and roads. When combined with rising sea levels, these effects could render some coastal communities permanently uninhabitable, said Dura. Even if some areas along the coastline do dry out, they will be much closer to sea level and become
susceptible to nuisance flooding if there's a particularly big storm or high tide.
Little earthquakes won't prevent a big one
The West Coast is subject to numerous small earthquakes all the time, but they're not big enough to relieve the pressure that's being built up along the Cascadia fault line, Melgar said. So much energy has built up in the zone that even a magnitude 8 earthquake wouldn't relieve it. "Remember, the magnitude scale is logarithmic. So each increase in magnitude is an increase of 30 in terms of energy," he said. The great San Francisco earthquake of 1906 was a magnitude 8 temblor and it was devastating. "If we had one magnitude 8 quake here, we'd still have 29 to go to relieve the pressure," he said.
