Almost exactly one year ago, a very large double strength tsunami struck the Pacific Coast of Japan and washed a huge amount of stuff out into the sea. The oceanic born debris of terrestrial origin looked in places like this:
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Subsequently attempts were made to model the movement of the debris in the Pacific. Some of the debris would likely end up on the coast of the US, so some of the models asked that question: When can Tsunami Salad start to wash up on the beaches of California, Oregon and Washington? I’m sure that everyone who’s thought about this for even a few seconds realizes that when this happens, it will not look like the picture shown above. It might be just the occasional floating bit of plasticky stuff used to make cars or boats or beach-side furniture, bits and pieces of household debris, and the occasionally recognizable Hello Kitty item. Furthermore, these items will be few and far between and by this time, likely, rather sun baked.

One of the models I saw, shown on a TV news show, had the debris moving straight across the Pacific, ignoring the famous Pacific Gyres and other currents. So, it would seem, Japanese Tsunami Debris would not be following the Rules of Physics, and would pass right by the famous Gyre of Garbage that must remain more or less forever (several years, at least) in the middle of the ocean going around and around and getting smaller and smaller until it finally becomes mere molecules. But I doubt that is what happens.

One recent report seems to indicate that at least some of the models are wrong, and the Tsunami Stuff is either not moving where it was expected to move (which I find vary hard to believe) or is much more dispersed than previously expected so as to be essentially invisible to the observers who are, in this case, people who pay attention to Albatross vomit:

Laysan and Short-Tailed Albatrosses typically fly hundreds of miles in search of squid-rich areas northwest of Midway to feed before returning to regurgitate food for their chicks. Anything that is squid-sized or smaller and floats on the ocean’s surface might be eaten by the albatrosses and then fed to their chicks.

So far, nothing has been noted in the Midway Islands, though the debris is supposed to have gotten there by now.

When I want to know about debris in the ocean, I go to my friend and colleague Miriam Goldstein, who knows all about this stuff. She has not covered Tsunami debris in a while, but some time back she did show the following video, and provided a bunch of links to relevant posts.

NOAA has an entire web site dedicated just to Marine Debris. Also, when debris is found on the shore, it can be regarded as data. Reporting debris spotted onshore or from a boat is useful, and there’s an app for that.

Thinking about debris visibility, I’m reminded of a story. Years ago, my friend Karl and I would ride our bikes out of town to a dammed up pond in the Pine Barrens. We would sit on a hill side by the edge of the pond and smoke cigarettes. We normally smoked filter-less ciggs, but sometimes the only ones we could obtain had filters. We would break the filters off, and recklessly discard them in the grass on the knoll where we sat.

Time passed. We stopped going to the knoll, and Karl died. More time passed, and I got a job in compliance archaeology. After a couple of years a big contract came along; we were to survey the area that would be impacted by the construction of a large shopping mall. The survey area, as it turned out, included the pond and the grassy knoll. The pond was actually gone; the dam had broken, flooding the nearby road a few years earlier, and since it had no current function was never repaired.

The knoll was a good place to find an archaeological site, so we dug several test pits on it. We found the broken off cigarette butts that Karl and I had left there. We also found flakes from the prehistoric manufacture of stone tools. The flakes where characteristic of the debris from the Clovis Culture in the area, though we could not be certain of that. Nonetheless, the most likely age of the flakes was roughly 10,000 years old. So, we had two periods of occupation, both probably short term use of the site, not residential or long term in any way. Some Clovis people had stopped here, on a knoll overlooking a stream, for a while, ten thousand years ago, and a couple of kids had stopped here for a smoke a few times about five or six years ago. Nothing else.

We reported this site and suggested that it deserved a further look. Compliance Archaeology is generally divided into three phases (with variations): Survey (that’s when we found the flakes and cigarette butts) is the first phase. Then, “Phase II” (as it is sometimes called) is where you investigate a subset of the previously discovered sites to determine if they are deserving of protection, further work, etc. Then the third phase is, of course, doing whatever is decided to “mitigate” the effects of the proposed construction, and this usually involves extensive excavation.

If this really was a Clovis site, it would likely to through to Phase III. It mattered that the company building the mall was under all sorts of pressure from environmental and other groups who wanted to protect the Pine Barrens (and the Karner Blue Butterfly … this work was going on in an area that included the tiny town of Karner, the type site of that rare and mysterious insect).

So, when the people building the mall accidentally bulldozed the grassy knoll, there was a problem. What actually happened was this: A hapless geo-technical crew doing their work (measuring groundwater patterns by sinking test wells) had driven a bulldozer through the grassy knoll because it was slightly more convenient to do that in order to place their well digging machine. (I learned something from that … subsequently I made it a point to warn contractors and companies overseeing these sorts of things to assume that archaeological sites were everywhere until we cleared specific areas.)

The company building the mall panicked (appropriately). They told us, “spare no expense … save the archaeological site!”

So we tried.

We went to the backdirt pile left by the bulldozer, we went to the area scraped by the bulldozer, and we went to the areas on either side of the bulldozer’s swath and we excavated and excavated and excavated. We moved many cubic meters of dirt looking for something that might be left of the site.

We found nothing. We did not find cigarette butts, we did not find ten thousand years old flakes. We found nothing.

Here’s why. Imagine a thin scatter of objects, maybe 30 objects over an area of 20 by 20 meters. That would be 30/400 objects per square meter. Since the objects are within centimeters of the surface, trained archaeologists can find them at that level of density (though they could also be missed) and in a second look with intensified effort, pretty much all of the objects can be found.

For the sake of argument, assume that all the objects are in the top 2 cm of dirt. That means that the 30 objects are distributed over 800 cubic centimeter’s of dirt, in a relatively visible location where 3/4rds of the objects must be found by being dug up and seen in a screen, and 1/4 of the objects can be spotted on the surface with the eye.

Now take these objects and mix them into one meter of soil … the meter of soil beneath them … and then mix that soil with the same amount of soil taken from nearby (as the site and the off-site areas are bulldozed into one pile). Now, we have 30 objects distributed within 80,000 cubic centimeters, with almost zero objects visible from the surface. In other words, artifact density has gone from 0.037 objects per cubic centimeter to .000375 objects per cubic centimeter.

I would not have assumed in advance that this is a number that crosses the threshold of archaeological visibility, but having spent many hours over a couple of days with a medium size highly experienced crew looking for stuff at that density, I now know empirically that it did in fact cross it.

Japan is 375,000 square kilometers of land. Imagine scraping off the top centimeter of the entire continent. The Pacific Ocean is 165,200,000 square kilometers. The top meter of ocean is thus 162,200,000 cubic meters. If the top centimeter of Japan was scraped off and turned into one cm size cubes and dispersed among the top 10 cm of the Pacific, it would take up about 1 tenth of a percent of the ocean. If 90 percent of that sunk, and half of what did not sink biodegraded into oblivion over a year, then the material would take up 0.006% of the ocean water. That would amount to about five objects per square meter, if the objects were distributed over the top 10 centimeters, and would be quite visible.

I’ve not seen a credible or useful estimate of the actual volume of floating debris from Japan. I imagine it is a tiny fraction of the numbers used here. It is quite conceivable that the odd object will float up on the beach here and there, and the tsunami generated debris field will otherwise not be noted from the Pacific shores of the US at all. Or there could be a steady beaching of small objects that are seen now and then by beach combers. This is seemingly one of those situations where we will learn how these things work from empirical observations better than we will be able to predict what will happen from theory.

Comments

  1. #1 F
    March 7, 2012

    Not quite homeopathically diluted, but hard to find.