If you go back a mere 40 years or so, not a long time really, then you pretty much arrive at the time when the modern study of ancient tsunamis began. Before then there had been some work, but it really kicked off with Brian Atwater and his work on the 1700 CE Cascadia earthquake and tsunami. His seminal work pieced together all the evidence that basically said there was a big earthquake and it generated a huge tsunami. The evidence included the now-famous ghost forests you can find along the Washington State coast if you know where to look. It also included a long thin strip of sediment sandwiched between peat layers like a jam sponge cake that you can easily pick out on river banks as they near the sea. This evidence had been there for nearly 300 years waiting for someone to come along and have a Eureka moment. This is where the glasses come in.
Like anyone who is myopic, you need glasses to see properly. It is the same with a scientist. Scientific discovery isn’t as you see in the movies where handsome actor A says to an even more ridiculously handsome actor B something like “I know what this is, look at that rock, it’s obvious…” OK, so that was a B-movie, but the point is that invariably with the study of ancient tsunamis nothing is obvious. While it is often the case today that a tsunami researcher wanders down to a bit of coast, pokes around a bit, and finds an ancient tsunami, this does not mean that it is easy. A lot of work has gone in before a spade has been put into the ground. Maps, satellite images, historical documents, academic papers, and old traditions have all been studied to try and make every moment you spend “on the ground” actually worth it. After all, research funding does not grow on trees and it needs to go a long way.
In the early days of tsunami research, it wasn’t exactly the Wild West but the world’s coastlines were pretty much your oyster. They were a blank sheet. We knew where a lot of historical tsunamis had happened, but when you dipped into prehistory there were no newspaper accounts, no convenient photos or tweets on the internet. It was down to science. The downside, though, was that unlike today where you can take university courses about tsunamis or even do a thesis about them, in the beginning of the study of ancient tsunamis there was no rule book, no textbook to learn from; we were making the rules up as we went along.
“The more we learn, the more we change our way of seeing the evidence around us.”
In the beginning, our eyes were open but not seeing: what were the signs that indicated that an ancient tsunami had been here? Many times over the years, I have been asked what a tsunami deposit (the geological evidence) looks like. That is a bit like asking “how long is a piece of string?” There is no one-size-fits-all answer. I have come up with what I feel is about the only reasonable answer to that question: it is a deposit that is out of place. A bit like a weed in garden, there is something not quite right about it. In many cases it is obvious; you are standing two miles inland on the edge of a river bank and can see a beautiful yellow sandy layer sandwiched between two dark brown peats. The sandy layer extends as far as the eye can see in both directions, it is chock full of sea shells, and lies on top of a layer of dead trees all pointing inland in the direction they fell.
OK, that might be a bit of a researcher’s dream, but there are deposits like that. A layer of sand that has come from the sea, bowled over a forest, and deposited sand and shells two miles inland. You don’t have to be a genius to figure that out—or rather, you don’t have to be one now, but when we started it was head-scratchingly interesting and needed a lot of laboratory analysis to work out all the details. We have “banked” all of that information now and so do not need to reinvent the wheel for some types of deposit—in a sense, that information represented the first pair of glasses. We could see better and we could find tsunami deposits!
Through the years my “glasses” have been changed regularly. As the years go by, the banked information from a seemingly endless variety of deposits has grown and so what used to be seemingly impossible to figure out is now much easier to recognize. However, all that has really happened is that we have moved on to harder cases or revisited cases that were less obvious the first time around now equipped with new insights. The more we learn, the more we change our way of seeing the evidence around us.
“There is a saying in earth science: ‘the present is the key to the past.’ Well, our work puts a spin on that: ‘the past is the key to the future.'”
There have been several occasions where I have given myself a hearty head smack when I have revisited a site and the veil has been lifted by my new glasses. It is good to know that we do not know everything, but equally it is good to know that we are learning more every year. If nothing else, we are keeping the tsunami optician in business and in doing that we increase our understanding of these devastating events. There is a saying in earth science: “the present is the key to the past.” Well, our work puts a spin on that: “the past is the key to the future.” Bigger tsunamis have occurred in prehistory than we have ever seen in historic time. We need to learn as much about these as possible in order to be prepared for them in the future, and for that there will continue to be a need for new glasses.