maandag 27 mei 2013

Did Scrat just trip?

This weekend we watched the fourth part of the Ice Age movies, called Continental Drift. Scrat the squirrel, always finding a spot to bury his beloved acorn, breaks a mountain and falls into the core of Earth. Arrived at a very small and solid core, he accidentally rotates the core, causing old continents to break up and drift appar, forming the current continents (Australia, Antarctica, Africa, Europe, South America and Asia. North America is formed at the end of the movie, where Scrat pulls the plug of Scratlantis (Yes, again Atlantis, it just must exist), forming North America.). A really funny scene and it gave me inspiration for this post. This weekend I was struggling to think about a blog subject. Thanks to Scrat, I found my acorn: Continental Drift.

In my research I work with topography, gravity and seismic observations. I am trying to combine all these observations in a new way, such that I get better insight of the old continental structure under Scandinavia, Finland and northwest Russia. The continental drift in that area is not the most interesting effect observed, so we travel to Hawaii (which is always a good thing to do.).

Hawaii is a very interesting place on Earth (yes, the Hoolahoop girls and cocktails, but also geophysically). The islands are big volcanos erupted from the deep ocean floor. This Google maps figure (since Google maps, geology can be done from your lazy chair at home) clearly show that the islands of Hawaii are situated in the middle of the Pacific Plate. This oceanic plate is one of the largest plates on Earth. The boundaries are visible as subduction zones in the northwest (Japan and Indonesia), where a lot of earthquakes and volcanos are present. In the east (USA) a famous transform fault is visible (just use Google and zoom in at the area between Los Angeles and San Francisco, or look up the San Andreas fault on the internet). However in the middle of the Pacific plate, no boundaries are present. So why is there a large volcano?

What I like about this story is when you inspect the bathymetry (the ocean floor topography, keep up, I told you this already) you can see an underwater mountain range situated to the northwest and then suddenly bending straight north. As a little kid, scrolling through many atlas maps, I was amazed by this feature, wondering about the cause. Many years later I found it out.

Cause: Continental drift and a very special volcano. Hawaii is a special kind of volcano: a hot spot. From the deep interior (most scientist say at the core-mantle boundary) hot mantle material is brought up (because hot things always go to the top) and penetrates (...) the Earth's crust creating large volcanos, like those at Hawaii. This would create a single volcano in the middle of the Pacific plate, if the plate wouldn't move. However thanks to Scrat (or mantle convection, we're still debating on this), we have continental drift. The solid top layer of the Earth moves, very, very slowly. This can be observed with for example GPS stations. 

I got this figure from here. It is a good website to start with, if your interested in the topic. The black arrows represent the direction and magnitude of the absolute motion of the individual plates. You can see that the Pacific plate is quite large, covering almost the whole Pacific Ocean. When you look at Hawaii you can see a black arrow pointed in the same direction as the underwater mountain chain (This is no coincidence). With respect to the fixed (we assume it is fixed, we're not really sure, but we're not really sure of a lot of things) hot mantle plume, the plate moves over this hot area, generating several volcanos on its trajectory. So in some sense the underwater mountain chain is a historic scar of the Earth's surface recording its behavior. 

Looking at the magnitude of the velocity of the Pacific plate (look lower left of the figure), we can say that the plate moves with around 25 cm/yr. Knowing this and the length of the straight mountain chain, we can say that the Pacific plate is moving in the same direction for about 50 million years (if the hotspot is fixed, which it is, we think...). Before that an event happened (maybe a large collision with an other plate) causing the plate to rotate in the current direction. The scar before this event was situated to the north (maybe Scrat tripped).

Just looking at topography (and bathymetry, otherwise you only see ocean waves) and GPS observations can solve my childhood mystery. I think Earth sciences are great, and even more today, with access to all this beautiful satellite data (You must say satellite every day, mustn't you. YES!!!). You can play with volcanos and moving plates. And you can write something after seeing Ice Age 4: Continental Drift, hehe...

maandag 20 mei 2013

Today's Atlantis: the Thai Buddist temple Wat Khun Samut Trawat

My last post was criticized about the doomsday prophecies I made about the Fennoscandian area (I think dear Annie missed the non-seriousness in my text, but heck, he/she got a point). The mentioned process of land uplift takes a lot of time and the dramatic geological change will not affect our way of life in a long time. So I decided to write about a geological change that does affect the way of life already today and dramatically in the future. The research I write about is from a couple of my colleagues working a lot with people from Thailand. They are part of a research project called GEO2TECDI-2, which uses GNSS, InSAR and tide gauges to see the movement of the surface of Thailand with respect to the sea level. 

When you look at the topography of Thailand, you will notice that the country is very flat. The difference in height between coastal areas and 500 km inland is only a few meters. This means that if sea level would rise, or the land would collapse (which is already going on very rapidly), most of Thailand will be under water. This means that a lot of the 66 million population will get wet feet. To get an idea of what will happen, the GEO2TECDI-2 research group is examining every source of land and sea motion.

There is one particular area where the effect of this land collapse can be seen very clearly. This is the area around the Thai Buddhist temple Wat Khun Samut Trawat. In 1950, this was still an inland temple surrounded by Thai settlements. Today we can find the current state on Google Earth

Coordinates: 13º  30' 25.42'' N, 100º 31' 53.47'' E, copy the link and post it in google maps

We can clearly see that the temple is surrounded by water and that people have built protective structures to ensure the temples present state. Comparing the current sea shore lines with that of the 1950's tells us that the sea has already taken 1 km of the Thailand mainland. 

The GEO2TECDI-2 research team has accurately measured the sea level rise in the area (tide gauges) for the past 60 years and they found a 25 cm rise in mean sea level. However, this alone could not represent the large land erosion seen today. With InSAR and GNSS measurements they observed a land collapse of 1 meter!!! over the last 60 years. This explains the dramatic geological and social changes in the coastal areas quite well. However, this land subsidence could not be explained by any natural tectonic motion (1-3 mm/yr tectonic uplift and 10-15 mm/yr subsidence after the Sumatra-Andaman earthquake) of the crust. What could it be?

They had an excursion to the Wat Khun Samut Trawat temple. Traveling mostly by boat and they hiked the last bit. During this travel they encountered a lot of shrimp farms (yes, the kind from "My momma always said..."). To grow shrimps you need fresh water (because fresh water shrimps taste better). This fresh water could have be taken from the Bangkok river, east of that area, but industry and population have polluted the river water, making it unusable for shrimp farming. Still, the shrimp farming business in that area is booming. Despite of the law forbidding it, the fresh water is pumped from the groundwater. This is especially clearly visible in InSar images, which show large subsidence in areas where newly build shrimp farms are located. Due to the groundwater pumping, the ground is settled more firmly causing the ground to subside.

It is impossible to ban shrimp farming, because it is the economic driving factor in that area. But it will cause major flooding in the near future. Thanks to the GEO2TECDI-2 research the issue is made visible and they can inform the people of the possible dangers. It is now up to all of us to find out what to do with this information and hopefully find an answer to this complicated question.

dinsdag 14 mei 2013

Drying the Gulf of Bothnia (or "Looking in my crystal ball" or "The cause of WWIII")

Sorry, but I could not decide on the title of this blog post. So I tried a literature technique I learned from reading my first "real" dutch literature novel, "Tjeempie! of Liesje in luiletterland", by Remco Campert, which is a typical dutch novel, full of sex and without story (I hope I do not offend anybody now, but I was a teenage boy, just finding out about the two (sex and good stories) and I did not pay a lot of attention to the last). Remco Campert also had two titles so he put them both on the cover of the book. Just like him, I am now among the great dutch literature writers (literature is the art of writing, not the scientific kind, which is also great, but that is not what I want to talk about (In the next bit I will, just to make things complicated, hmmm lets continue)), writing in English, hmmm...

Enough about the title bit (I just needed an introduction), I want to talk about this phenomenon we observe in Scandinavia, or even more accurately  Fennoscandia (We need Finland and part of Russia in this story). The ground is moving up in this area, or as Anders Celsius (Europeans know him from the temperature scale) would record, retreating of the Gulf of Bothnia. He was the first scientist to measure the water level retreat using abandoned seal rocks. Nowadays we don't use seal rocks anymore (Well in the Antarctics, the use of bird vomit is made for measuring ice sheet history, but that is another story). We use a satellite based height observation system, (you all know it) GPS (not the tomtom kind, but better ones). Several campaigns have measured the speed of the uplift of land (because that is what is happening, not the retreating of the sea), which has a vertical velocity of 1 cm/yr in some areas. One of these measurement campaigns is Bifrost (I am linked to them with my research), this is what they see:

The colors, with the legend in the bottom, are vertical velocity observations. Orange being more than 1 cm/yr (10 mm is 1 cm, pay attention in high school). The red arrows are horizontal velocities of the surface. So a circular area that is coming up, and land is moving away from the centre of this area. It is a bit like pressing your thumb on a piece of pencil gum and removing your finger. It takes some time for the pencil gum to reshape in its old form. This is what we call the viscous behavior of the Earth. Because the Earth is not fully elastic it takes some time to react on loads put on it (or in this case, loads taken off it). What load? I will write about that some other day. 

First I told you about new land in my previous post. So, I made a fancy (beautiful colors) figure of the topography and bathymetry (what the Earth would look like if you remove all the water) of the area.  

This is how the area looks like today (well, the color scale is the height of the area). Red area is the Scandes, the mountains on the border of Norway and Sweden. I used blue for areas where there is water. The data I used to construct this map is to be found on the internet (ETOPO2). The Netherlands are clearly visible (It looks like the whole country is flooded, which it would have been without our waterworks) and the British Isles in the bottom left (You will see why I put those areas in the figure). 

Now lets use my crystal ball (matlab program + a good computer. (title, title!!!)) and see what the area looks like after fully relaxation of the Earth (discussions are still ongoing, but this will happen between the next 1000 years or infinity, lets just say 1000 years, because otherwise it takes a lot of time).

I left the black coastlines of today in the figure, to have a reference. But the whole Gulf of Bothnia is disappeared and dried up (title, title!!!). Remarkable is that a bedding of a river can be seen. I did some research and this is called the Eridanos river, an ancient and forgotten river. Another striking observation is that Sweden and Denmark are connected  causing major conflicts between them starting off WWIII (title, title!!!). Not to mention the economical changes in the area, as old shipping routes are cut off (well maybe, by that time we have airborne shipping routes.). And Northern Europe will have its own Great Lake. 

On the other hand, the Netherlands and London, will have sunken even further beneath the sea level. The region, we call North Holland (depicted now in dark blue), will be several meters below sea level. We need even bigger dikes and waterworks (not even mentioning the global sea level rise of 3 mm/yr). This sinking of land is a by-product of the uplift of land in Fennoscandia. Mantle material is needed to fill the void that is created due to the uplift. This material is gathered from the areas around the uplift. The Netherlands is just on the wrong place in the wrong (well not really, this will take some) time.

vrijdag 10 mei 2013

Why Deep Earth Science?

As a child, you think the Earth is solid. Heck, many adults still think the Earth you walk on is solid, motionless and has infinite strength(...and is flat, well some think this). But it is not. The Earth can behave like a liquid, it moves a lot (in all directions) and it can break. This only takes a lot of time and we humble humans don't have the time to stick around long enough.

We know this only decades now (Ok, the not being flat part, maybe a bit longer). There are many scientists that are trying to figure out the dynamics, mechanics and materials of the Earth. And I am one of them. Well, I am learning to become one of them.

My job at the TU is to find a structural density and viscosity model of the crust and upper mantle below Scandinavia using mainly satellite based gravity data and observations of post-glacial rebound. A lot of deep Earth words, but I will try to discuss them in this blog of mine. The idea for this blog was for me to put my ideas on paper, some of those ideas would be about deep Earth science. Looking back at my previous posts, I found myself lacking in writing about DeepEarth science, so I will try to start now.

Why do we want to know about the processes and structures in the deep Earth? It is a curiosity based research and sometimes I have difficulty to defend this. It sounds much less interesting than orbiting satellites traveling to other planets and artificially programmed robots exploring ancient tombstones. However it is a fascinating research area, where not a lot is known. We like to say we know a lot, but the surface of the Moon and the planet Mars is better known than the deep layers of our home planet, Earth.

I will try in this blog to show you that (deep) Earth sciences is a fascinating research area with all its complexities and incredibly cool observation equipments. Really cool!!! I have to modify ESA and NASA satellite data, with super cool mathematics, using several super computers, producing nice colorful images (all my colleagues have stopped at my door, making comments about them.). All this to explain the movement of the "solid" Earth due to a large ice sheet (3-4 km thick) present 10,000 years ago giving me hints about the structure and rheology of its interior.

What would you say, if I told you that Sweden and Finland are rising (or in their perspective, the sea is retreating) as fast as 1 cm a year. So in my lifetime, the ground is gone up 27.5 cm, creating a lot of neighborhood problems, arguing who gets the 'new' land (Scandinavian countries have the best law system, as it comes to dividing land). This process will continue for a few decades, lifting the current ground to a height of 200 meters, removing the current Gulf of Bothnia.

Asking around, I found out that not a lot of people know this. Well, if I am honest, I did not know this until I began my studies. So as a good scientist would do, I will try to share this knowledge to you, I hope I can keep you interested.