The American Tsunami and the Yellowstone SuperVolcano

Factual Questions
1

So, while laying around my hospital room last week, I watched a lot of the History Channel (how do you verify some of the insane stuff they come up with anyway?–sorry, separate thread).

So they talked about a West Coast Tsunami, bigger and with no adequate warning due on there, and they implied that Yellowstone is also due to blow.

The way things have been lately, I wouldn’t be surprised, but, Great Googaly Moogaly, How accurate are these two in particular and what is their margin for error?

I want the straight dope.

2

USGS on the Volcanic History of the Yellowstone Plateau Volcanic Field

There’ve been 3 big caldera forming eruptions between Idaho and Yellowstone within the last couple million years. The Yellowstone Caldera formed 0.64 years before present (YBP), the Henry’s Fork caldera 1.3 YBP, and the Big Bend Ridge, Snake River, and Red Mountains caldera segments 2.1 YBP. So there’s been an eruption roughly every 650,000 years, but they’re not all at Yellowstone. In other words, Yellowstone itself has not produced a repeating big blast.

As far as the next eruption, USGS says this:

3

My understanding about tsunamis is that they are created by a) landslides under or along the sea and b) earthquakes. Both have so far defied reliable prediction.

Based on what Wikipedia says about earthquake prediction, I wouldn’t get my hopes up. While Time magazine’s 100-year anniversary report on the 1906 San Francisco quake suggests a 60% probability of “a major quake” occuring “in the Bay Area” sometime before 2032, you’ll notice a certain reluctance to specify how big, what faultlline, what neighborhood, etc.

You might as well try to predict earthquakes based on the number of missing dogs and cats. An unnamed man in the Wikipedia article is said to accomplish this with 75% accuracy (although, of course, it does not explain how this accuracy is calculated).

Is there going to be a giant tsunami somewhere on the West Coast? Yeah — and I’ll lay you good odds that it’ll happen for sure in the next 10,000 years.

4

No adequate warning?

As mentioned predicting the earthquakes that tend to cause these is pretty dicey but I thought the pacific area was pretty well monitored for precisely such an event to warn people a tsunami is on the way.

Granted tsunami move very fast so depending how far off the coast the earthquake occurred a warning may not come in time but once given a lot of lives could be saved.

Frankly the New Madrid fault in Missouri is of more immediate worry to me than either Yellowstone or a tsuanmi on the west coast. “Immediate” being a relative term in this case.

5

Depends on what you mean by adequate warning. Any tsunami in Southern California would undoubtedly cause massive property damage. The December 2004 tsunami was warning enough to people: don’t build million-dollar houses along the beach in earthquake country. So far, I haven’t seen any exodus from that real estate.

Can there be enough warning to save some lives? Probably — the Pacific Tsunami Warning System, developed in 1949 in Hawaii after the islands were wracked with various tsunamis, can communicate most predicted tsunamis in time to evacuate some people from endangered areas. It doesn’t predict them all, of course; and there may be very little time for an evacuation to be mounted, as tsunami-force waves travel very, very fast. Even so, there may be false alarms. The system isn’t perfect.

Minutes or hours is still better than the warning we get for earthquakes, though, which is to say, better than no warning at all.

6

The BBC science programme Horizon did a show about the possible Tsunami

http://www.bbc.co.uk/science/horizon/2000/mega_tsunami.shtml

Q&A and full show transcript avalable at the link.

7

As to the SoCal tsunami, there are faults & unstable underwater cliffs not that far north of LA. If those fail, the wave will hit the LA beaches & beach cities within a few minutes of when the earthquake happens. Even with an instant warning & instant response by the public, you’re not going to move very many people very far inland/uphill.

IIRC there is a similar fault/cliff structure not far from Seattle that would / could have a similar effect in that area, possibly massively amplified by the geometry of the Puget Sound & islands.

When any of these US mega-disasters occur, it’s gonna be a large-scale wipeout for the area affected, with national, if not global repercussions on business, food supply, government, etc.

The good news is the likelihood of any given diaster in any given year is low, even whle the likelihood of some disaster in some year between now and, say, 12006 AD is essentailly 100%.

8

In The American Tsunami program that ddgryphon is talking about, they mention that a subduction zone earthquake like the 26 Dec 2004 quake off Indonesia would give Pacific Northwest residents roughly 15 minutes warning before a tsunami hit. In an evacuation drill of one area, most people went for their cars to try to drive to safety, and so would have been sitting in traffic when the wave hit. Some of the evacuation “centers” were nowhere near high enough in elevation. So for a large enough quake that produced a Banda Aceh-type wave, there is still potential for many lives to be lost rather than saved.

yojimbo’s link refers to the possibility of a tsunami striking the east coast of the U.S., and there was a previous discussion about that here.

There seems to be some sort of rule that when producing a show about natural disasters, one must make ominous noises about how the next one is going to impact mankind. So at the end of the program, you’ll almost always see several scientists being asked to give their predictions, but what you don’t see is any waffling or qualifications to the predictions they might have made. Being “wishy-washy” doesn’t make good TV, dontcha know.

The truth is that both are potentially enormous disasters that probably will happen in the geologically near future, which is not the same thing as human-scale near future. The large quake and tsunami one-two punch off the Pacific Northwest coast is of more immediate concern, largely because there is evidence of large earthquakes and tsunamis occurring every 400 to 600 years over the last 3500 years, and the last one was about 300 years ago (IIRC there are actually stories preserved among the local Native American tribes about past events).

There is unfortunately a lot of crappy stuff that winds up on the History Channel, and Discovery Channel, and A&E, and National Geographic, etc., and no easy way for the average person to figure out if what they’re seeing is bullpucky or not. The best suggestions I can make are:

  • Pay attention to the “authorities” being interviewed, and whether or not they have academic affiliations. You might still hear some fringe viewpoints, but at least they have probably been debated already and you might be able to google up some discussions and counterpoints.

If Graham Hancock appears billed as a journalist, all hope is lost.

  • Programs that have educational materials associated with them are good bets to be balanced and accurate (if brief) discussions of topics. Check out the relevant cable channel web site and see of anything’s been made available for use in the classroom (e.g., the History Channel Classroom study guides).

I’ve seen both the Yellowstone and tsunami programs mentioned in the OP, and both are on the level (with of course a few dramatic overtones). The American Tsunami is in fact part documentary, because you get to follow the group of scientists tasked to assess the Indian Ocean tsunami and build a computer model that could then be applied to the Pacific Northwest. Those folks are the real deal.

9

The style of faulting and sea floor topography along the Pacific-North American plate boundary down around Los Angeles is very different from that of the Juan de Fuca-North American plate boundary off the Pacific Northwest coast, so tsunamis would have different triggers in each location.

The plate boundary from Baja California to San Francisco is a strike-slip boundary, which means that the two sides of the boundary fault (i.e., the San Andreas Fault) move mostly side-by-side past each other with no significant vertical component of movement. The Channel Islands off the coast of SoCal are thought to have been “torn off” the mainland as part of this sideways motion along the boundary. The steep underwater slopes around the edges of the islands, like the steep slopes on the mainland coast, are indeed likely candidates for landslides that could cause “localized” tsunamis. (There is a neat perspective view of the sea floor bathymetry on the mainland side where you can see the scar of a landslide on this page, at the very bottom.)

While the sea floor off the Pacific Northwest is not flat (there are seamounts and a huge pile of sediment related to the subduction zone, called an accretionary wedge), the tsunami risk there is directly related to the potential for massive vertical sea floor displacement on the boundary fault, just like the 26 Dec 2004 event off Indonesia.

10

Funny, I’ve generally been paying attention for the last couple of years, and I don’t remember any of this.
:stuck_out_tongue:

11

That was Mega-funny, aerodave :smack:

12

Most of the Washington coastline is cold, rainy, drizzly, rocky rain forest — the Olympic peninsula is one giant National Forest — and Oregon’s larger cities are also inland. At most risk from the instant tsunamis would be Portland, Seattle, Victoria, and cities along Puget Sound. I don’t know the relative population densities but at a guess I’d say mile for mile the Pacific Northwest Coast has fewer people at risk of instant tsunamis than, say, India and Indonesia et al. had for the Boxing Day tsunami.

It’s small comfort, as they’d also be at risk from the preceding earthquake — which, admittedly, have been mostly deep earthquakes at the epicenter. If you can imagine the Juan de Fuca plate driving under the North American plate like a wedge, you get some idea: shallow quakes offshore and getting deeper and deeper as you get farther inland, as the wedge drives downward.

The recent Nisqually earthquake was pretty good-sized, beneath the water — and deep. No tsunami.

Where the tsunami risk will be is the shallow, powerful quakes offshore. My geology professor estimated off-hand that a powerful subduction earthquake could hit 10.0 or greater magnitude, twanging Washington and Oregon like a diving board. Particularly dire predictions on the topic estimate the Washington coastline would raise in elevation between 5 and 30 feet as a result. It’ll happen — but statistically it’s more likely to be 200 years from now than tomorrow morning.

13

OK; I think it’s a law or something. I have to stick my nose in here to defend (somewhat) America’s Tsunamis. The two primary investigators on the cruise that was looking into the cause of the 2004 Indonesian Tsunamis were Kate Moran and Stephan Grilli. Although I don’t study with either one of them, I am an oceanography student at the same school; I have one friend who had Stephan on his PhD committee, and one friend who is working for Kate. (I should also point out that my specialty is air-sea fluxes; I am only now taking my first real course in wave mechanics. What I know about tsunamis you could probably fit into a matchbox, without first removing the matches.)

My interpretation of America’s Tsunamis:

I loved how Discovery showed the how the scientists went about their jobs to find out what was the process that triggered the Tsunamis. I think Discovery did an excellent job showing the work that (those type of) oceanographers do, and its importance to “every-day life.” I also think that most of the images did an excellent job of showing what was going on. I would have liked to have seen a few different ones, but I’ll take what I can get.

On the “personal” side, I thought that Discovery did a good job showing the scientists as people, too. I first met Kate at the annual Boat-Burning/welcome party for new students. She went out of her way to say hello to any new face she didn’t recognize. She is really just a nice, nice person. I think that Discovery (rightly) choose her to be the “spokesperson” because of her qualifications (she has a dual posting - that is she is a professor in two disciplines) and her personality. Not to say anything against the other scientists present, but Kate was the natural choice.

On the “doom and gloom” side. Yeah, America’s Tsunamis was played up. Not in the sense of “oh, it will never happen” - there certainly will be a Tsunamis that hits the Northwest Coast sometime in the next coupla centuries, but in the “it is imminent and WE’RE ALL GOING TO DIE” feeling that they’re so good at including in their specials. (I don’t know if I’ve seen the supervolcano show, but I imagine that it sufferes from the same phenomenon.) OK, the warning system and evacuation routes need to be revamped. I think that we can do that without the “OMGWAGTD.”
In short, good show, good science, turn down the hype, next time.

(Also, I was highly amused that America’s Tsunamis, which was about 2 hours long (minus commercials) spent about 15 minutes (minus commercials) on the effects of a Tsunamis hitting America. They could have picked a better title, but then again, it wouldn’t have had the doom and gloom impact on american audiences.)

14

I want to thank everyone for their answers here. I’ve enjoyed reading the analysis of the programs and figured it was something of a more geological time-line than a people-oriented timeline.

Thank you all.

15

Not only that, but there are records of the tsunami that hit Japan as a result of this quake, so they’ve been able to pin the time it happened down to the hour (between 9 and 10 pm 26 Jan 1700). Click on the link labeled “January 1700” at the page linked to above to get more details.

As I understand it, the volcanism in the Yellowstone area is due to a hotspot that the North American plate is moving over. So you’d expect a line of calderae trailing off to the west, all caused by this same hotspot, and that’s exactly what you’ve cited. So expect the next superbig erruption to be somewhat to the east of Yellowstone.

This is the same kind of thing as the Hawaiian hotspot which has left a trail of islands going off to the northwest as the Pacific plate moves over it.

16

That’s right, I had forgotten about the Japanese records for the most recent tsunami. Pretty cool stuff.

Not only the Yellowstone calderas, but the entire Snake River Plain is thought to be a product of the hotspot’s movement eastward over time.

17

Snopes on Yellowstone: