Sunday, 23 June 2013
Tuesday, 29 January 2013
|Ben, Daria and Isobel investigate the stratigraphy|
Wednesday, 23 January 2013
All in all it's been a successful first field season - we've been to 6 new sites, collected 225 modern marsh samples, and nearly 4 metres of sediment to analyse when we get back. That's going to be a lot of time spent looking down a microscope counting diatoms!!
Tuesday, 22 January 2013
|Taking great care to not leave any trace of|
where we've sampled on the marsh!
We found an excellent marsh to work on, which allowed us to take lots of samples to help us properly understand the present day environment. In our work we need a sound understanding of what is happening today to be able to interpret what happened in the past. We take small samples along a transect across the marsh from the mudflat exposed at low tide, across the low marsh, high marsh, and up to where freshwater vegetation grows. We look at how diatom communities (small microscopic single-celled algae) change across these different zones as the amount of tidal inundation decreases the further you get from the sea. We mainly find marine diatom species in mudflat samples and freshwater diatoms in the high marsh samples. Then when we look at our sediment cores from the past, if we find lots of marine diatoms we interpret the environment at this time was most like the present day mudflat. From this we are able to reconstruct how the land level has changed through time.
|Taking a modern sample from the low marsh|
|Freshwater diatom of the Pinnularia genus (about half the width of a |
human hair - thanks to Melanie Leng for giving this comparison!)
When the shaking happens the land can go up and down. Some places change from being high up before the shaking to being lower down after. Other places change from low down to higher up.
We're describing the vertical component of coseismic deformation resulting from a subduction zone earthquake. This is typically less than a few metres (either uplift or subsidence) for sites on the Chilean mainland. R. Grapenthin, Univ. Alaska, niftily visualises this phenomenon for the 2011 Japan earthquake.
We look for things that can tell us how and when the land has changed in the past and when waves have covered the land. To do this we look at tiny bits of rock and very small living things.
We're particularly interested in working out when past earthquakes and tsunamis have happened and how big they've been. As part 1 mentioned, historical records may be too short to provide a realistic assessment of seismic hazards. Instead, we turn to sediments (tiny bits of rock) from coastal environments. Certain low energy settings, like the tidal marshes north of Valdivia, preserve evidence for both tsunami inundation and coseismic deformation. The very small living things are diatoms, single-celled algae. More on how we use diatoms to look at land-level change in the next blog post.
We have found the biggest shaking and largest waves happened four times in the past 1000 years in the area we are working.
Ed's PhD, based on sites a few hundred kilometres south of this project, found sedimentary and diatom evidence for the 1960 and 1575 earthquakes, as well as two older earthquakes predating written records in Chile.
We thought we'd expand on our last blog post today and use some less common words to explain what we're up to. There were many other great common word distillations of projects, research areas and whole careers in science generated in response to the Up-Goer Five text editor. You can read them in the tumblr curated by Chris and Anne from Highly Allochthonous.
So, here's what we were trying to convey in the thousand word post (or ten hundred as those pesky Americans keep saying). The common words are in italics.
When the ground shakes a lot it can kill many people.
Earthquakes! You got that bit, right?
Ground shaking can also form very big waves of water which cover lots of the land, and kill more people.
Tsunamis. Created in this instance by strain release during an earthquake resulting in deformation of the sea floor. Tsunamis can also be formed by landslides, volcanic eruptions, meteorites and iceberg roll events.
It is important to understand when and where this happens so that we can make people safer in years to come.
The past is the key to future preparedness and hazard mitigation. We want to know how frequently earthquakes and tsunamis occur and their maximum possible sizes. Historical records are valuable, but in many areas do not go back far enough. Even in Japan, home to the most comprehensive records of tsunamis, historical records may underestimate the size of previous seismic events. See this from the Japan Times for more.
Part 2 to follow...
Thursday, 17 January 2013
Here's a summary of our past and present research in Chile using only the 1000 most common words used in the English language:
When the ground shakes a lot it can kill many people. Ground shaking can also form very big waves of water which cover lots of the land, and kill more people. It is important to understand when and where this happens so that we can make people safer in years to come.
When the shaking happens the land can go up and down. Some places change from being high up before the shaking to being lower down after. Other places change from low down to higher up. We look for things that can tell us how and when the land has changed in the past and when waves have covered the land. To do this we look at tiny bits of rock and very small living things. We have found the biggest shaking and largest waves happened four times in the past 1000 years in the area we are working.
Thanks to Chris Rowan and Anne Jefferson of the Highly Allocthonous blog for passing on the idea. Head over to the Up-Goer Five Words Box to try it for yourself.
We collected lots of samples of sediment from intertidal marshes close to the mouths of the rivers that cross the plain. We're particularly interested in tidal marshes as they provide evidence for how the land or sea has changed in level over time. On a positive note, we found some good sites and collected lots of samples. Unfortunately we seemed to spend a lot of our time watching the tide go up and down, sometimes until it got too dark to actually see what we were doing!
|Ed at Queule with sediments that we think|
were deposited before and after the 1960
earthquake and tsunami
We've also been back to Valdivia and sampled a marsh on Isla del Rey, an island in the Valdivia Estuary. We're pretty pleased with the samples from here, not just because we found a good site, but also because we managed to get to the site in the first place! First we needed to find a boat to take us there, then were trapped and had to escape from a very talkative postman on the island (who wanted to tell us everything from the entire history of Chile to the material used to surface the road in response to us asking who owned the land), and finally we needed to get a boat back. The latter proved to be the most tricky, but it seems in Valdivia it's possible to hail a boat like you hail a taxi!
Monday, 14 January 2013
|Ed digging a pit / pogo-sticking!|
|10cm of tsunami sand (light grey)|
separating two different types of sediment
Thursday, 10 January 2013
|Rudolfo at Valdivia's Seismological Museum|
|The local neighbourhood in Valdivia!|
|Trees killed by the 1960 Valdivia earthquake|
|Tsunami deposits south of Valdivia|
|Too many horseflies!|
Just a shame about the 3 hours it took us to get back, after getting stuck behind a lorry full of shells travelling at 10 km/hr and it taking an hour and a half to get a ferry across the estuary!
Monday, 7 January 2013
|Emma, Marco and Ed|
Pleasingly the School of Marine Sciences smelt of the sea; however, lunch looked distinctly like chicken! Marco's office looks straight out over the bay, though you'll have to squint to see it in the photo.
We're now heading south on the overnight bus to Valdivia for the start of the fieldwork. Thanks to Ulises at Camila 109 (where we stayed last night) for helping us navigate Chilean bus ticket booking.