Sunday, October 20, 2013

Geo 365: Oct. 20, Day 293: Evacuation Route?

This is the "evacuation plan" in the event of a great Cascadia Subduction Zone earthquake (North is to the top, in the map.) on  the south shore of Yaquina Bay. Newport proper is on the north side, and aside from Oldtown and the port, largely built on an elevated marine terrace. People near the shore there- and it is a very congested work and tourism area- can quickly and easily walk up the hill to safety. The south shore, though, is built upon unconsolidated sediments that have accumulated since the Pleistocene-Holocene boundary, when sea levels rose roughly 100 meters as the great continental icecaps melted back. As such, it's low and flat- it's attractive for building and development, but highly at risk in case of a significant tsunami.

Now under normal circumstances, it would be only a few minutes to hop in one's car and zoom off to high ground. But many, if not most, bridges along the coast are not seismically fit and are likely to collapse. Access to the north likely simply won't be there. There are hills to the south, but traffic will almost certainly be in a panicked snarl, and it's too far to walk. So as illustrated above (and on page 31 of this PDF), the thousands of people present in this area, including those at Hatfield Marine Science Center, the Oregon Coast Aquarium, and now the Marine Operations Headquarters for NOAA, along with dozens of small businesses and shops (Rogue Brewers is on the water north of the evac route), are supposed to high-tail it to a small hill- which doesn't look like it tops 50 feet- along the southern ramp of the Bay Bridge. As the sign explains, it's a 14 minute walk to "safe haven hill," and the first wave may arrive as quickly as 15 minutes.

My personal evacuation plan, therefore, is not to be here when the big one hits. Seriously. Since visiting this display last spring, this area has suddenly become one of fear for me. It may be over-reaction, but the entire development looks like a death trap to me. I'm sure I'll visit it again, from time to time, but I'll never feel comfortable there.

Photo unmodified. May 6, 2013. FlashEarth location.

Followup: 2:30 PM- Just looking at the photo more carefully, I realized elevations are noted in various spots. (You'll need to look at the full-size version of the photo to make them out.) They're not noted in any key that I see, nor are they explicitly labeled as elevations, but I see no other possibility for what those numbers mean. "Safe haven hill" is supposed to be 69 feet elevation, and I consider 50 feet (based on the tsunami in Tohoku, Japan) to be a worst-case scenario. Furthermore, the whole area around the south causeway up to the bridge is pretty well up there, and getting to that area looks significantly quicker than "14 minutes to safety" estimate on the sign. From there, it looks like you could go right up the side of the hill. So long and short, I feel significantly better about the situation now than I did this morning when I wrote this post.Still, the sheer number of people that will need to cram into that small area is daunting. Note there's a small residential neighborhood on the west side of the hill, too!


Lyle said...

On this topic have you read Cascadia's Fault? Its an interesting tale of how geologists eventually were convinced that there were indeed big earthquakes on the subduction zone. Originally the zone was supposed to be dead, then ghost trees and marshes were found, surveying found elevation changes and gps surveying reinforced this. Finally the trees killed in the last event were killed around 1700 and then records were found of an orphan tsunami in Japan which provided the dateof Jan 27/26 1700 about 9 pm local time in Oregon.

Lockwood said...

Haven't read the book, but a lot of that work was being done by geologists when I was an undergrad. So I've attended a number of seminars by the people who actually did the work.