We Nor’westerners are often prone to complacency when looking at tornados, hurricanes, tropical storms and other climate disasters in our old continental U.S.. Our response is usually something like “Tsk tsk. Isn’t that too bad?” Because we live on the continent’s last few feet of real estate, we acknowledge the news without having really deep feelings for local trauma of the moment in other regions.
Our own Northwest neighborhood doesn’t host many such events. Oh, we have windstorms and occasional flooding. Once in awhile, forest fires come uncomfortably close. Really though, most of us here remain unaffected in any direct way.
BUT - geologic history tells us Yellowstone Park used to be about 500 miles west of where it is now - west of downtown Boise in Southwest Idaho. Mt. St. Helens has blown its top and killed some folk in our lifetimes. Rainier, Hood, Baker, Shasta and a few other so far peaceful mountains in our region give off occasional rumbles. Just to keep us on our toes. No, nothing major in the neighborhood. Recently. Yet.
Still, we denizens of Oregon’s coastline are almost always of two minds when the morning alarm goes off. Today’s just another day - or - today may be our last day. It sort of depends on whether you’re a risk taker. After all, that Cascadia Subduction Zone and the Juan de Fuca tectonic plate are our constant neighbors. The tsunami starters.
This geologic “Sword of Damocles” exists not over our heads but off the shoreline. The plate and zone are about 40-80 miles out and affect - or could violently affect - an area from Vancouver Island to San Francisco.
It’s been a long, long time since there’s been a major “shaker” hereabouts. Most quake-watchers count January 27, 1700, as the last “big one.” It is thought to have been larger than the one that swamped Fukishima in 2011. Better than 9.0 on a Richter Scale - had there been a Richter Scale in 1700.
Next largest was more recent - March 27, 1964. Worst of it was in Alaska but four kids were killed in Newport, here on our Central Oregon coast, with houses and infrastructure destroyed down to Crescent City, CA.
There’s been serious exploration on the Oregon coast, some up the Sixes River about where Curry and Coos County meet up. Harvey Kelsey, and Eileen Hemphill-Haley of Humbolt State found evidence of 11 large, tsunami-producing earthquakes off our coastline during the last 6,000 years.
Their work also showed each of the11was accompanied by a tsunami that spread beach sand more than two miles inland. Even way uphill! Lots of sand. Imagine the strength of the ocean push that could do that.
Then there’s this. Last of the big 11 was about 1700. Scientists think there’s an overall average reoccurrence interval of between 300-5,500 years. Given the last big shaker was in 1700 and we’re now at 2015, we’re about 300 years out. So, those who calculate such things figure we’ve got a 10-20% chance of a big one in the next 50-100 years. Plus or minus a year or two.
Now, 10-20% chance of being drowned on any given day might seem statistically pretty unlikely where you sit. But, suppose you sat here! Right next to we folk who daily watch the usually peaceful blue Pacific. If it were your home - your family - YOU - would you be comfortable? Only a 10-20% chance of being wiped out today. Nuthin’ to worry about. Right?
But we’re not done yet. Suddenly, the Cascadia fault has gone silent! No noise. No movement. Nothing. And scientists are concerned. For four years, they’ve been dropping special seismometers to the ocean floor and getting zero readings. Nothing. They fear the Cascadia plates are locked. (more…)