18 August 2008 Measuring tsunami run-up with Bre

Today was another day that saw Iskatel (our ship and our home, for a few more days) hiding from a storm on the Pacific Ocean side of Simushir Island. As with our stay up at Matua, we decided to try to do at least some science so that the day wasn't a total waste of time. The wind (and the rain) was coming mostly out of the west today, so the Pacific, or east, side of Simushir was mostly protected. More on the definition of "mostly protected" later.In any case, we sent the archaeology survey team plus Bre MacInnes to shore at Mel'nika Bay to a) look for archaeological sites [they didn't find any today] and b) measure how big the 2006 tsunami was here at Simushir. Last year, Bre determined that highest elevation above sea level that the tsunami covered (called the "run-up") at Dushnaya Bay (the next bay to the north) was about 14 m above sea level, and the water extended inland (called the "inundation") about 150 m from shore. Mel'nika Bay is a little bit further away from the epicenter of the earthquake that started the tsunami, so Bre expected the run-up and inundation to be a little bit lower than at Dushnaya Bay.

So how do we figure out run-up and inundation? Well, it is really pretty simple: we walk in a straight line (called a "transect") from the shore headed inland, and we look for what our Russian colleagues call "sea trash." Others might also call it flotsam and jetsam. Sometimes it is drift wood. Sometimes it is a clearly defined row of plastic bottles and fishing floats. Sometimes it is the ever-elusive glass fishing floats.

When we find stuff, we then have to decide if it is likely to have gotten there from normal storm activity, or if it is likely to have been put there by a tsunami. For medium to small tsunamis, we often cannot tell the difference. But in this part of the Kurils, the 2006 tsunami extended quite a bit higher than any of the storms that have passed through here since then.

So, once we've found all the "sea trash" we expect to find, we pick the bit that is at the highest elevation. Back in 2007, this high point was really obvious as a "wrack line," which is an accumulation of all sorts of stuff: sea weed, terrestrial vegetation, plus all the wood and plastic I mentioned before. Now, in 2008, the wrack line has been mostly dispersed. But the wood and plastic are still easy to find.

Now we get to measure it! There are, of course, lots of different ways we could measure any given point on the landscape and figure out the elevation and the distance to the shore. We could use GPSA Global Positioning System (GPS) is a satellite-based navigation system used to track the location or position of objects on the Earth’s surface. (Global Positioning System). But a) even the best [easily available] GPSA Global Positioning System (GPS) is a satellite-based navigation system used to track the location or position of objects on the Earth’s surface. units are notoriously inaccurate at calculating elevation and b) the best [easily available] GPSA Global Positioning System (GPS) is a satellite-based navigation system used to track the location or position of objects on the Earth’s surface. units are very expensive. We could also lug around very heavy and expensive surveying equipment to measure what we want to. But that equipment is, well, you know, heavy and expensive.

Instead, we opt to use a very simple but effective system that combines a stadia rod and a surveyor's level or transit (also called a "nivilier" in Russian [pronounced "nee-vuh-leer" with the emphasis on the last syllable]). The stadia rod is basically a large telescoping pole 5 m long that has centimeter increments marked on it. The nivilier is a telescope mounted to a tripod. If it is set up right, the nivilier looks out at the world perfectly level. Inside the eyepiece, there are cross-hairs that, when sighted onto the stadia rod, can be used to calculate the elevation differences (called the "vertical distance") between the nivilier and the base of the stadia rod (see photo), as well as the distance between the transit and the stadia rod (called the "horizontal distance").

Bre sets up the tripod and the nivilier somewhere upslope of the maximum run-up (i.e., where we found the highest piece of "sea trash"-(marked by the "X" in the illustration)), and the stadia rod will be placed perfectly vertically at the point of maximum run-up. All of the measurements start from where Bre sets up the tripod. After we measure the distance and elevation difference from the transit to the point of maximum run-up, the stadia rod is moved point-to-point towards shore and we measure for key features on the landscape. In my schematic diagram, we would probably measure the low spot (marked by the "A") inland of the beach ridge, the beach ridge (marked by the "B"), and the water level (marked by the "C"). Then, after we account for the height of the tide at that particular place at that particular time of day, we can back-calculate the elevation of Bre's tripod, and its distance from shore. From that, we can then calculate the elevation (run-up) and distance from shore (inundation) of the tsunami!

As I said, it is a really simple system. But it provides a very efficient way for us to measure things on the landscape. Did you notice that in my schematic diagram, the stadia rod is too short for Points A and C? I mentioned above that the stadia rod we use is 5 m long. But Bre's calculations say that the run-up here at Mel'nika Bay was between 7 and 9 m (with inundation 80-135 m inland). How do you think we deal with that situation?

Another situation we had to deal with today (as we often do, working in the Kurils), was the weather. Yes, we were mostly protected from the brunt of the storm today. But we still got to experience many variations on a theme of windy and wet. Windy with fog. Windy with rain. Windy with some mist. We pretty much don't go anywhere without our rain gear, so we were fine. But in order for Bre to be able to use the nivilier, she has to be able to see through it! If she needs to point the telescope into the wind, she has to try to keep the lens from getting too covered with water droplets. I was impressed with the solution she came up with!

First, she lines up the telescope with the stadia rod and takes a quick peek to make her measurement (see photo):

Then, she will quickly slide her notebook in front of the telescope lens to block the wind and airborne water (fog, rain, or mist) and jot down her measurements in the notebook while it's blocking the water (see photo). I thought it was ingenious!

The wind and the rain also made for a pretty interesting time getting back off]the beach and into our zodiac. The wind was blowing offshore, which made it difficult for our zodiac driver, Kolya Illarianov, to actually land. But that wasn't the worst of his problems. A much more serious issue is that the ocean swell had increased to about 2 m, and the waves were breaking pretty dramatically on the short, steep beach. After several attempts to get near enough to us that we could get in, but not so close that the boat was getting smashed by the waves, we finally got all of our crew and our gear into the zodiac. Then, with the help of the oars and a pull from a second zodiac that was standing by, we were able to get out away from the break zone and safely into deep water, where Kolya could then start the outboard engine.

Even though the archaeology survey team didn't find any archaeological sites today, it was still a good "science" day-especially considering we would have just been sitting at anchor otherwise! Now we've "pulled the hook," as they say (lifted the anchor), and are headed south to Urup Island. We are hoping to work a couple of days at the site that was featured in the photo Fitzhugh with tephra layers from the posting on 17 July 2008. Hopefully the latest series of low pressure systems moving across the Sea of Okhotsk will be kind to us, and we will get in a couple more days of field work before we have to pack it all in and head back to Korsakov!

--Dr. E