dinsdag 24 december 2013

Creating a network and find out the name of a rock!

At the end of a week full of science, I had a touristic trip into the woodlands of Muir. Together with a geologist I met in San Francisco, I traveled to the forest with the large trees seen in the very famous bike chase scene in Star Wars on the second moon of Endor. It was a great trip and I can recommend it to anybody visiting the City of Fog.

The Muir Woods are situated in a valley, where the climate is much different than the surrounding mountain lands. So a geologist and a geophysicist could not resist to climb a mountain to the top (I say mountain, but they were large hills, except when I said that the giftshop woman gave me angry eyes). We decided to follow the Hillside trail, followed by the Ben Johnson trail. These trails gave us a good view of the forest and let us examine some really nice rock outcrops of the mountain. And on one of them I found this rock:



It is a greenish rock, which according to the geologist, could be serpentinite or an olivine containing rock (which I know now, serpentinite is as well, sort of :) ). Me, not being a geologist, wanted to know how he could deduce this. So I asked my fellow geologists I had met in Copenhagen (see this post for some details, not a lot). I posted the figure above and the following photo in our Facebook chat session (very modern, right):


This photo is a zoom-in of the crystal structure. My friendly-geologists from around Europe, started asking me questions about, what is the cleavage, the hardness and does it feel oily like? So I did a hardness test. My fingernail could not scratch it, so the rock hardness is >2.5 (on the Mohs scale), but a copper coin could make scratches on it, so its hardness is <3.5. The cleavage looked conchoidal according to some of the geologists (I'm still not sure how they could see this). Furthermore, I told them that the rock felt smooth, almost oily like. Therefore all the geologists in the chat group decided it should be SERPENTINITE!!! (a metamorphic rock originally containing a lot of olivine). 

This tells me that, if you don't know something, ask your network!

zaterdag 14 december 2013

Attending a talk of one of my scientific inspirations

It all started with a delay of four hours. Being on our route for over an hour (above Scotland), the intercom of the airplane (a MD11 type of aircraft) sounded: "This is your captain speaking and I have some bad news." There was a technical problem that could not be fixed in San Francisco, so it was decided to fly back to the airport Schiphol, Amsterdam. I was just finishing my first beverage. One of my colleagues told me that he had several experiences like this with MD11 aircrafts. They are old and should be taken out of service. But for now we got a different MD11 that would take us to San Francisco. Four hours later than originally planned, we arrived in the Fog City (it was a clear day). However, at the gate after the pilot had shut down the engines, the ground personnel tried to connect the power cables such that the doors could be open. Only this was not working, so 350 already a bit weary passengers were stuck inside the aircraft. And no power means no air-conditioning, so temperatures where rising.

Luckily, we could get off after several minutes. For the first time, I entered the United States of America. I did not get any sleep during the trip, so I was very tired, resulting in a black spot up until the day after. Something with jet lag and air-conditioning. The day after, my colleagues and I decided to rent some bikes. This was a good way to see the city of San Francisco and fight the jet lag.


Here you can see me in front of the famous Golden Gate Bridge on a clear day wearing a fashionable helmet. It was a great day that ended in a shabby Jazz bistro, which had a live performance of a Jazz quartet. Nice!

The next day, the purpose of my trip to San Francisco started, the American Geophysical Union. This was a conference for Earth scientists like me. Presentations about any subject concerning research done on geophysical phenomena (there was also some planetary research, which is different than Earth studies according to many of my colleagues. I just sigh and disagree). This meeting attracts more than 25,000 researchers from all over the world. The massiveness of the meeting can best be seen in the poster-hall:


Thousands of people devoted to do science and try to communicate their ideas to the world. I am in a scientific walhalla! Oh yeah, it only rest me to explain the title. One of my scientific heroes is Margaret Kivelson. She worked on the Galileo satellite data that measured the magnetic field of Ganymede. This little moon (the largest in the solar system) of Jupiter is the only moon with a large intrinsic magnetic field. I studied this moon closely during the end of my bachelor studies, reading a lot of clearly written papers by Kivelson. In that period, I became enthusiastic about science. So Kivelson (sort of) represent the start of my scientific career and at the AGU meeting I could finally attend a talk of her.

donderdag 21 november 2013

Delfi-n3Xt baby sounds...

This morning I got up earlier today to attend the Delfi-n3Xt launch event in our faculty. Delfi-n3Xt is a nano-satellite (the size of a milk carton) which is built by students and staff of our faculty. Launch events are always exciting, because you don't know what will happen. But after two stressful hours we got the confirmation, "Nano-sat number 7 successfully deployed." This was followed by some cheerful cheers. However, was it turned on?

This blog started with some post about listening to satellites using the ground station on top of EWI (faculty of electronic engineering, mathematics and computer sciences). This ground station is mostly set up by a student which I assist in teaching him to track satellites. So this gives me the opportunity to get the telemetry data of the Delfi-n3Xt quite fast. It's good to be a teacher :). The next figure will show the satellite's first sounds in space:


Click on the figure to get a larger view. In the bottom left corner of the blue figure, an S-shaped curve can be noticed. This is the radio signal transmitted by the moving satellite in a frequency-time plot. The vertical axis is frequency and the horizontal axis is time. You clearly see the frequency of the satellite shift with time. This is of course the Doppler effect (please read my blog entries). 

These are the first baby sounds of the Delfi-n3Xt, the second Dutch university-constructed satellite in space. Fully operational! This clearly shows the capabilities of engineering students. Well done.



zondag 17 november 2013

The Earth rotates (except in Copenhagen)

Last week, I was visiting the beautiful capital of Denmark, Copenhagen. I was selected to participate in the International PhD Elite Course "Tectonics" at the University of Copenhagen (READY program), organized by Prof. Hans Thybo and Prof. Irina Artemieva. During this five day course, the participants (PhD students from all over the world and me :) ) were being taught by two experts in the field of tectonics, the wonders of geosciences. From Geology (I write Geology, because it was defined by the lecturer as one of the two only real sciences); Prof. Çelal Şengör from Turkey with a beautiful British-sounding way of lecturing. From Geophysics (capital G, because I disagree with Prof. Şengör ;)); Prof. Seth Stein from the USA, who also brought his wive, Carol Stein. She gave a very interesting view on the Mid-Continental Rift. These last five days were fantastic, because I learned a lot and met numerous interesting people. I recommend any PhD student participating in such a course. It will enlighten your brain. 

The course was given in the Geoscience building of the University of Copenhagen. While entering the main hall, I stumbled onto this view:


A large pendulum was swinging in the centre of the hall. The mass of the solid metal ball was 140 kg. This is the so called Pendulum of Foucault. It proves that the Earth is rotating. At first display in Paris 1851, the pendulum of Léon Focault was the first simple proof that the Earth was rotating in an easy-to-see experiment. The pendulum, swinging in inertial space, would rotate without putting any forces on it. This is because, not the pendulum is rotating, but the Earth, on which the observer is standing. Waiting long enough and you will see the pendulum plane of motion rotating. I recommend you to go and see one (see list), but because you are currently sitting behind your computer, I have a movie:



This video shows the slow swinging motion of the pendulum. I did not film long enough to show you the rotation. Also I think those large ventilation shafts in the floor disturbed the free-motion of the pendulum, because in the evening the plane of motion was in the same direction as in the morning. It was a little bit of a drawback, but I think it is still a cool way to show that the Earth is rotating, just turn off the air conditioning.

maandag 4 november 2013

Secrets of the deep ocean (a Vening Meinesz story)

No, this is not a blog about some random Sci-Fi movie, it really is a blog about the secrets of the deep ocean (sorry guys, no shiny sphere that gives you special powers when you touch it). Already as a kid I was fascinated about large structures in the deep depths of our oceans. I will show you some cool geological features and their origin in the deep depths of the South Atlantic Ocean. Fortunately, Vening Meinesz, the geophysicist I am talking about now for some time, sailed over this huge ocean onboard the K18 submarine (yes, yes, I know, again I am spamming you guys about this very interesting and cool scientist). 

After visited several ports along the eastern South American coastlines, the K18 and its occupants started from Mar del Plata the difficult crossing of the South Atlantic Ocean. Vening Meinesz wrote in Volume III of his "Gravity Expeditions at Sea", the following about this crossing:

The crossing of the Atlantic from Mar del Plata to Cape Town was a strenuous undertaking; it took us twenty-six days and during the first half part we three times ran into bad weather. Twice we struck a strong gale lasting a few days and the writer had to interrupt his observations because of the impossibility to dive in these rough seas. He nevertheless could make fifty-two gravity observations during this crossing. About halfway we touched for a few hours at the island of Tristan da Cunha but the time was too short and the landing difficulties too great for allowing Holweck-Lejay (another land-based gravity measurement device) observations on the island. He could, however, make a pendulum observation near the island over a depth of 1415 m and this result, combined with those obtained during the end of our preceding and the beginning of our further trip, gives valuable information about the isostatic equilibrium of the island. We likewise could make a sounding profile of the submarine slope; it will be given in the next volume of this publication.
     During the second half of the passage the route was chosen to cross the Walfish Ridge and a detailed gravity profile combined with soundings could be made. The ridge proved to be double here; the sounding profile will be represented in Volume IV. Near the African continent the route was directed towards a submarine promontory shown by the charts but we could not find it where it was plotted. The new edition of the Monaco Bathymetric Chart for the South Atlantic, which already contains our sounding profiles, has been rectified in this regard. 

So 52 valuable observations of the gravity field of Earth were made during this crossing, despite two strong gales. I made a figure of his and the sonar crew's measurements done during the crossing.


Click on the figure for a larger image. The black dots in the maps are the location of the measurements. You can clearly see the two stormy events, where it was impossible to dive (the lack of black dots). The top map shows the gravity anomalies modeled by current information and the bottom map shows the height and depth of the Earth. The two profiles underneath are the 2D representation of the gravity anomaly and depth, respectively, of the profile of the voyage. Again you can see the great accuracy of both Vening Meinesz's observations as well as the sonar depth soundings of the crew of the K18 submarine. 

Some cool features can be seen in these images. Despite the height of continents (orange to red in height maps), no large positive gravity anomalies are observed. This was, according to Vening Meinesz (and also according to me), proof that continents are in isostatic equilibrium. Furthermore, you can clearly see the spreading ridge in the middle of the ocean. This is one of the important observations that proves plate tectonics is a good representation of what is going on with the surface of the Earth. Vening Meinesz did not like this theory (in 1930 this theory was considerate to be fringe science), due to the second strong gale he failed to observe this crucial piece of evidence. Maybe, if the wind gods were more favorable, he had to change his mind about plate tectonics. However, if you look at the sonar depth measurements, it is noticeable that there is this symmetry in height (don't look at the short wavelength features). The deepest depths are observed close to the continental coasts and traveling towards the middle of the oceans, the height of the ocean floor goes up almost 1.5 km. This can be explained by plate tectonics very well (maybe some other time, otherwise google it!).

He writes about the second half of the crossing that they sail over the Walfish Ridge (Walvis Ridge mister Vening Meinesz, it is a South African name). I have already written a few words about this part of the voyage, its just one of my favorite deep sea structures on Earth. The Walvis Ridge is seen both in the bathymetry as the gravity anomaly maps, revealing a NorthWestern ridge towards the African continent. As discussed in one of my previous posts, these are remnants of the still active hot spot of Tristan da Cunha. Vening Meinesz sailed over a part of the Walvis Ridge that had a double ridge. This extra feature was created in the time (70 Ma) that the spreading ridge began to migrate westward. It is however (for me) unclear what happened 70 Ma ago. As we go back in time the continents Africa and South America move further towards each other, eventually connecting at the spreading ridge. It is concluded that the continents broke up astride, or in close proximity to the upwelling plume (which is now the hotspot) (O'Connor & Duncan, 1990). Large flood basalts are found both in Namibia (African) and Brazil (South America) that can be connected to the same upwelling plume. On the West part of the South Atlantic, another large deep ocean structure is visible, the Rio-Grande Rise. All these observations give more than enough evidence for the hot spot and the movement of oceanic plates over this upwelling plume. 

Vening Meinesz could not have deduced this from his measurements, but he did see the deep ocean structures with his device. This proved that global gravity measurements of Earth were very important and should be included in any geophysical research. Satellite missions like Champ, Grace and GOCE have since revealed more secrets of the deep depths of the oceans than any nerdy kid could dream off. 


-Reference

J.M. O'Connor, R.A. Duncan, 1990, Journal of Geophysical Research, VOL. 95, NO. B11, PAGES 17,475-17,502

dinsdag 22 oktober 2013

Measuring the geoid. What is the geoid?

During my weekly fitness session with one of my friends, we started discussing gravity (yes, also my friends are geeks (in the good way)). We discussed the measurements done by Vening Meinesz in the K18. He used I pendulum device, that directly measures the downward gravity attraction in the location of the device, plus all the motions of the device itself. On land, these motion are negligible, but on sea the device swings a lot due the ocean waves. Therefore, Vening Meinesz used a submarine to reduce the motions of the measurement device (waves are dampened underwater). Furthermore, he used three pendulums instead of one, which he ingeniously used to separate the motions of the device and the gravity attraction. Explaining this all to my friend, he remarked that it sounded very complicated and asked me if this could be done more easy. "Yes, this is possible", I replied, "with a GPS receiver". "How is it possible to measure Earth's gravity field with a GPS receiver?", my friend replied. You do not measure the gravity directly like Vening Meinesz, but with some cool mathematics, you can get a pretty good idea.

In order to explain what the geoid is, I have to first introduce a different concept. The Earth is not flat (you know this, some just don't accept this), but it is also not a sphere (really?!?). It is more like a flattened sphere, or ellipsoid if you use the proper term. As if the poles of the sphere are pressed inward. Actually, pulled inward. This is because of the rotation of the Earth and the Earth's viscoelastic behavior (in less scientific terms, this means that the Earth is slightly mushy). The ellipsoidal shape is even not true, because the Earth has bumps on its surface. However, we can approximate this shape with a mathematical ellipsoid. The differences from this shape, we call undulations.

The geoid, roughly follows an ellipsoid like this, but has the humps and bumps discussed earlier (undulations). Those undulations, or deviations from the ellipsoid are very interesting and can give us information about processes beneath the surface. So it is worth measuring this shape.



The figure represents the 3D view of the geoid, where we exaggerate the radial variations. The blue colors represent areas where the geoid is below the mathematical ellipsoid and the red areas are above the ellipsoid.

The cool thing about the geoid is that the sea level follows this surface, when there would not be any winds or currents, perturbing the ocean surface (Ok, and you neglect tidal forcing, solid Earth movements and hydrology. But who is not doing this!). So in a sense, when you sail the oceans, you actually follow the curved gravity field of the Earth, called the geoid. Lets make use of this.

My friend (introduced in the beginning) is currently on his way to New Zealand, where he will board the sail boat, "Oosterschelde". This large, three mast, sailing ship will set sail to the Falkland islands (the hard way). They will cross the Indian Ocean, around Cape Horn, and across the South Atlantic Ocean, without stopping at a harbor. During this 50 day trip, my friend will place a GPS device (for the electronic geeks: GARMIN GPS 60CSx. In good conditions, this device can have an accuracy of 2m) and track the location and altitude of the ship.

You would think, "The altitude must be zero (plus the offset on the boat), because the boat is at sea level". However, the GPS receiver will measure its 3D position with respect to the mathematical ellipsoid (WGS84). So it should differ, because it will follow the geoid not the ellipsoid :)

By how much? Well, the Indian Ocean has the largest negative geoid anomaly (the big blue dent in the figure), of more than 100 meter !!! This would be visible, with my 2m accurate, so let the observations begin. In three weeks, he will set sail across some off the most dangerous oceans, but he will manage! On christmas eve, he will be back in Holland. I will let you know, what he observed.



maandag 23 september 2013

Writing is editing, rewriting and reviewing

Today I am working at home, because some strong and skillful looking men are renovating my roof vault (in Dutch: "dakkapel"). Luckily I had one thing on my agenda, editing, editing and editing. I have to rewrite my first scientific paper, because I want to send it to my co-authors in the beginning of next month. So today it is about making order in all my chaotic brain waves and scribbles, during the loud noise from above.

The title of this blog post is my way of living for the last few weeks (oh and "be concise and focus", but that is another story). I've started a course in English article writing, because as you would have noticed (and some of my good friends commented), my writing is not perfect or even close to perfect. So, every wednesday, I am sitting in a classroom with 12 of my peers, learning about the wonders of the English writing process. One of the most important lessons is: "Writing is editing, rewriting and reviewing".

But what is the best way to do this? These are my tips and tricks I learned from other blogs, teachers and fellow students:

  • Put the review article in a drawer for a week (fresh start)
  • Switch off your computer, or switch off internet (no distraction)
  • Go sit in front of nothing (brick wall, or something. Again no distraction)
  • Coffee!
  • Get a red pen, black pen and a blue pen (different colors for different edits)
  • Don't edit everything in the first run (grammar, structure, argumentation, figures, etc...)
  • Use a English-English dictionary, grammar book and style guide.

So for now, put on the kettle and get my pens writing. I am ready to edit!

maandag 9 september 2013

Regional Isostasy: supporting a volcano

Since my participation in the Vening Meinesz project (Read about it in some of my earlier posts), I am reading a lot about this interesting person and his scientific findings. One of his greatest achievements to science is the theory of "Vening Meinesz isostasy" or "regional isostasy". This is a model that I use in my research and it is quite powerful but greatly overlooked. Therefore I thought it would be a good thing to write about here on my blog.

The word isostasy, I would think, is not something you would use in a normal conversation. However, you are reading the blog of a scientific geek (Aren't all geeks scientific, hmmmm), so now you will.

It all started with a man taking a bath. This man was given the assignment to solve a problem for his king. The assignment was to find out if the new crown of the king was made of pure gold. The king suspected the goldsmith of using silver. Archimedes (the man) was asked to do this without melting it. A difficult question in those old times.

Thinking long and hard, Archimedes did not solve the problem. So he decided to take a bath (scientific and engineering problem solving are done best in the bathroom). Submerging in the water he noticed that the water level was rising. This observation made him solve the difficult question of the king. Enthusiastic, he ran outside shouting "I found it", or "Eureka", totally naked (every scientist should do this, I think it is liberating).

The Archimedes principle can also be used to calculate when things float. Objects float when the mass of the displaced water by the object is more then the mass of the object itself. When we talk about solid objects, this will mean that they must have a density which is lower than the displaced water. In geoscience we use this principle to study the loading of mountains and ice-sheets.

When a mountain is in isostatic equilibrium, it sort of means that the mountain floats on the fluid mantle material. Ice and mountains have a lower density than the heavy materials in the mantle, which cause them to float. In the late 1800 two scientists devised a theory to explain this phenomenon. Vening Meinesz and Heiskanen wrote a beautiful piece about these two scientists in their book "The Earth and its gravity field":

Quite frequently two scientists working independently discover an important phenomenon or perfect a significant invention simultaneously  It is well known that the English astronomer Adams, in October, 1845, and the French astronomer Leverrier, in the summer of 1846, independently computed the orbital elements of Neptune. Unfortunately for Adams, the new planet was discovered September 23, 1846, on the basis of Leverrier's computations. A similar thing happened in 1868, when the English astronomer Lockyer and the French astronomer Janssen without knowing each other's results invented a method for observing the prominences of the sun, which previously could be studied only during total solar eclipses. In 1892 both the American astronomer Hale and the French astronomer Deslandres invented the spectroheliograph, an important tool in the hands of astronomers. Einstein delivered a paper on his general theory of relativity on November 11, 1915, to the Academy of Sciences in Berlin, and on November 20 of the same year Hilbert gave at the Scientific Association of Göttingen the results of his investigation of a similar theory. (Don't forget the observation of the Jovian moons by Galileo Galilei and Simon Marius, 1610)
   In the same way it happened that on January 25, 1855, the British astronomer G. B. Airy sent to the Royal Society his paper on the same equilibrium problem Pratt discussed before the same society on December 7, 1854.

Both Pratt and Airy had devised a theory that explained, why mountains won't sink under their weight in to the deep depths of the Earth. Pratt's theory states that mountain material have less density than material at coastal areas. This extra light material is more buoyant and is able to support the extra load of a mountain. Airy's theory puts a sub-crustal root beneath the mountain to give it more buoyancy. You can see this a bit like a floating iceberg. I made this following figure to explain Airy isostasy:


The yellow crustal material floats on top of the dens mantle material. Exactly underneath mountains the crust is thicker, having a sub-crustal root. This is called local compensation. Vening Meinesz found out that mountains can also be compensated regionally. This means that not only the area underneath the mountain supports it, but also the region around it. He hypothesized that the crust could endure stresses and distributes the load to other areas around the mountain. This type of compensation is called regional or Vening Meinesz compensation. This is best seen at the islands of Hawaii (which are big mountains):
In this free-air gravity anomaly plot the Hawaiian islands can be seen in the bottom right corner. The gravity high (purple red) is related to the extra mass of the volcanos. The blue area around (less gravity) is due to the bending of the crust. The volcano pushes the oceanic plate downwards. The complete region reacts to compensate the mountain, keeping it up.

In 1926, Vening Meinesz, onboard the Hrs. Ms. submarine K13, observed the gravity field of those islands. With his theory he could describe the observed gravity field almost perfectly. This was not succeeded by others using the Pratt or Airy theory of compensation.

I made the above figures for an ebook describing GOCE satellite gravity results, showing the GOCO03S gravity model (this model was also used to make the first figure) and its Airy isostatic anomaly (thick lines). The thin lines with circles are the observations done by Vening Meinesz 100 years earlier in a cramped metal tube. At 280 km along the profile all anomalies are positive, which can be correlated with the mountain topography (bottom figure, red diamonds are the K13's depth observations done by its sonar crew). Only the green line (Vening Meinesz isostasy) is close to zero. This means that this theory perfectly corrects the gravity field for the mountain and explains the phenomenon. Vening Meinesz's theory is very powerful, however a bit more complex than Pratt and Airy's theory, so it is unfortunately mostly neglected.

In the Netherlands Vening Meinesz is also mostly forgotten, which is a pity, because it was one of our important scientists. Let's get him in our school books ;), start to remember him again...




maandag 26 augustus 2013

Testing the theory of evolution: The story of the Red Dots

"But you are a geophysicist, not I biologist", I hear you thinking. Yes, that is true, but that does not stop me from looking at science in other fields. I think the theory of evolution is a great way to describe all the diversity we see around us. Not only in animals and plants, but also in man-made objects, politics, design, law, ethics and social interaction. Lets say evolution really is correct and is happening around us (I know that on the internet there is a large debate about its correctness, but I think one side just lack in good arguments and evidence), could we test it? To see if it really works.

Let me explain what I think evolution is about, correct me if you think I am wrong (finally some comments :)). Evolution in systems is about finding the optimal solution for the system to be in. Evolution does not know that it is doing this. The optimal solution changes over time, because of internal and external forces. In this sense evolution is very powerful. It allows the system to cope with change.

Lets explain this in classical Darwin Evolution. It is based on the survival of the fittest (fitness function, we are going to use this later on). Say we have a population of birds on an island. This population contains the same kind of birds, yet every individual bird is slightly different than its brothers and sisters. On the island we have red berries (very tasty) and blue berries (poisonous). The birds need to eat the berries in order to survive. In the earlier days of the birds existence there is a massacre. Lots of birds of this population die because they eat the blue berries. A few birds do not eat the berries, because they don't like the color blue and are afraid of it. Those birds eat the red berries, stay alive and grown baby birds (reproduction). These baby birds are also afraid of the blue berries, because they got the 'afraid' genes from their mother and father. Some baby birds are not afraid (point mutation), but die after eating the blue berries. In the end you have a population of birds that only eats red berries and leave the blue berries alone. In this case the fittest individual was afraid of the blue berries and after some time the optimal solution for the complete population (system of birds) was found.

If you think about this it is an elegant theory that can explain adaptation of systems to any environment. The theory needs four things to work:
  • population of individual that slightly differ from each other (randomness and point mutations)
  • a mechanism to pass on information to future individuals (genes, reproduction)
  • an optimal solution (fitness function)
  • time to let the population evolve to the new equilibrium (sometimes a lot of time)
We can test and even use this theory in computer science and it has been used a lot. In space engineering, we use it a few years now. It is called genetic algorithm and it works! I will try to show you how it works with another simple example. However, don't get fooled by the simplicity, the possible applications are endless.

In this little experiment we have an environment of 256 by 256 positions (yes, this can be reproduced by a string with 2x8 bits). This environment has height differences, there are minimum and maximum height locations. I have created such an environment by putting some random equations together (You can also use the DTM of your neighborhood or country). My environment (call it the garden of Red Rots) is illustrated in the figure:



The red areas are positive height areas and the blue are negative areas. The greenish color represent zero height (or coastal areas after the Great Flood, damn spoiler alert!). In this environment I put at random locations a population of red dots (They are called the Red Dots). Every red dot has a gene of 16 bits (ones or zeros), which give it its location. The good thing about the red dot's life is that in the middle of the day (a for loop run), it can reproduce with a fellow red dot and create two children. This doubles the population. To keep the population stable, 50% of the red dots die depending on their location and a defined fitness function. After the selection, another day will start and this goes on for several generations.

Let the story begin! The Red Dots need water to survive. Lets say the probability of survival is better when they have access to water. In our environment, water can be found in the lower areas. This is what happens (top left to bottom right, read it like a book ;) ):
You see that overtime the Red Dots prefer to go to the lower situated areas. Here they can reproduce and be happy! But then on one day it begins to rain and rain. Floods are threatening the Red Dots at low situated areas. Red Dots that are located in higher areas have a much greater chance of survival and reproduction (which is what we are all here for). This is what happens:

Nine generations after the Great Flood, the Red Dots have climbed the High mountain. But life is not good. Water is scarce and it is very cold up there. Unfortunately after nine generations (should it be 40, nah!!!) the Great Rain stops and so does the Flood. The Red Dots can go back to their old lands, however they remember! In their genes they remember the Great Flood and therefore they won't go to the absolute minimum, but stay half way. Due to this knowledge they find that the probability of survival is around the zero height. This is what happens:

Nowadays the Red Dots live at the coastal areas, where there is enough fish and water to survive. And they all reproduced happily and after. 

Evolution in a few seconds (it took 2 minutes to compute this story). I just applied the four elements (I could not fix a fifth element, Mila did not answer her phone) of evolution in a software program and I could create order out of chaos. Also my system of Red Dots where able to adapt to external forces. Evolution really works!!!




donderdag 22 augustus 2013

Holiday project: my RaspberryPi shows that plants move!

After a few weeks of silence on this blog, a new post. Not about cucumbers, but moving plants (Do plants move? Yes, they do. Just very very slowly).

I bought a RaspberryPi before the holiday and wanted to test its capabilities and see how easy it was to program on it. So, I needed a project. After a view days of thinking I came up with making a time lapse movie (Ok, I know, not the most creative idea, but it was an idea). People might think that I would make a time lapse of the night sky, but I didn't. I am living in Delft, which is next to the Westland. This is a region with the largest surface area of the Netherlands (maybe even the world, I don't know, but you can see it from space, unlike the Great Wall of China) covered with greenhouses. At night they all turn on the lights. This makes it quite difficult to get a good view on the stars and Milky Way. So, I decided to capture other slow moving objects. Plants!!!

Another holiday project of mine is to grow my own fresh herbs. So at home little pots of green plants are scattered throughout the house. I used some of these. I had seen a Youtube movie (I think a TED talk, but I am not sure) about motion of plants and I wanted to see for myself, if this was true. Plants don't have eyes, ears, noses or mouths, so how could they interact with the surroundings without these (for humans) critical sensors. Of course they have the chloroplasts (the greenish color), so I assumed the main motion would have something to do with directing the leaves to the sun.

What I did was the following: After one morning of sunshine I would turn the pots 180 degree, such that the leaves where pointing in the opposite direction of the sun. Then I would start my time lapse recording and wait for results. For this purpose I used a RaspberryPi together with a CCD camera that I also ordered from the RaspberryPi website. On my RaspberryPi I had put the LinuxArch operating software, which made interacting with the RaspberryPi a bit like operating the servers at my work. After some searching on the internet, how to get things working (I am not a Linux wizard, but I am now some sort of first apprentice with the WWW as my mentor), I got it to work (don't use crontab, but the more simple SLEEP shell command does the job much easier). This was my setup:


Above the RaspberryPi, I attached the camera board to a camera stand with some sticky tape. This is the engineering way. Furthermore I mounted an extra external USB hard disk, where all the pictures could be stored on. I used my basil and parsley plants in the first run. The second run I added coriander and melissa to the experiment. Every five minutes a photo would be taken by the RaspberryPi and stored on the USB-hard disk. The results are shown in the next (brilliantly crafted) video:




In the side view the sun is to the right and in the front view the sun is to the back (This was just my reference frame). So you see, plants do move and can interact with the surroundings. You just need to take your time to notice it.




zondag 14 juli 2013

Two historical voyages crossing paths

In one of my previous post, I explained that I am currently working in a project to explain the measurements done by Vening Meinesz, a Dutch civil engineer responsible for high-accurate gravity measurements onboard the Hr. Ms. K18 submarine. He, together with the crew, sailed from Den Helder, Holland to Java, Indonesia. Stopping at harbors along the African, South American and West Australian coast.

At the end of december 1934, the Hr. Ms. K18 left port of Saint Vincent, one of the northern islands of Cape Verde. Cape Verde was also visited by the famous biologist Darwin during his voyage on the HMS Beagle. During this 5 year long voyage Darwin collected many observations that enabled him to establish the evolution theory. A theory that describes the diversity of living creatures and their way of adapting different environments, quite well, if I may say so. 

However this was many years before Vening Meinesz sailed from Saint Vincent. They sailed southwest to the center of the Atlantic Ocean, which is a bit strange if you know that their next port will be Dakar, Africa (which is to the East). Why would they do this? I was looking at some geophysical evidence. It could be that Vening Meinesz would want some nice observations of the mid-oceanic ridge. Remember that the plate tectonic theory was only theorized in the 1960's. 

However I found the direction of the voyage a bit strange. To observe the mid-oceanic ridge best you should sail pure west. Reading the navigation logbook of the voyage I saw that before they reached the ridge, they stayed at a location for one complete day. This was strange because the location had not significant geophysical relevance (just another volcanic landscape). So I decided to read the comments made by Vening Meinesz in his summaries of the voyage. This is what I saw:

Leaving St. Vincent, our route brought us far out into the Atlantic. This loop was due to the crossing of a Dutch areoplane (wow, not aircraft, but areoplane. I like the old times) to the Netherlands West Indies; for providing this plane with the necessary radio-bearings for its position and for giving it indications about the weather, Hr. Ms. K18 was ordered to be stationed for twenty-four hours at a point in the middle of the ocean.

Netherlands West Indies being Curacao. As an Aerospace Engineer, this got my attention. What aircraft? It must be an important crossing, for having the Hr. Ms. K18 have to divert his route. So I did some googling on the web and found the following website.

It was the KLM's maiden voyage to the West Indies. A Fokker F18 (look at the number, both the same!!!) made his 8 day voyage from Amsterdam, Holland to Curacao. The following poster (obtained from the website) shows the route of the Fokker F18:


It states "KLM Christmas Mail Flight to Ned. West-Indie, leaving from Schiphol on 15th of december 1934". The Fokker F18 would eventually land in Curacao on the 22th of December. This would mean that it flew over the Hr. Ms. K18 (number, number) around the 20th, which coincides with the track logbook. If you look closely to the poster (click on it), you can see a small (submarine-shape) figure in the middle of the Atlantic. Could this be the Hr. Ms. K18 with Vening Meinesz onboard? 

The KLM Fokker F18 voyage would be the start of the famous inter-continental airline KLM. Two important voyages in Dutch history crossing paths in space and time, aiding each other. Hr. Ms. K18 provided bearings and weather reports and for the sake of the story, maybe the Fokker F18 transported a Christmas letter for Vening Meinesz which he received on his later visits in South America. The paragraph of his comments did not end and neither did his voyage:

The Navy had consented that the ship, once this duty fulfilled, continued its route for reaching the area of the Mid Atlantic rise and then returned by a different route towards the next port, Dakar. By regularly diving once during the day and once during the night a valuable series of observations was obtained over the whole trip. The soundings over the Mid Atlantic rise showed an irregular topography, suggesting a volcanic landscape. The approach to Dakar provided the writer with a further coastal gravity profile.

The mentioned irregular topography is the old volcanic landscape created by plate motion (not known in Vening Meinesz time), where the age of the landscape decreases towards the center of the rise. I complete this post with the observations of Vening Meinesz (gravity and soundings), such that you can see the scientific value of this voyage. 


In the end I think this crossing of voyages is remarkable and should be remembered.

woensdag 10 juli 2013

Melting of the ice, backwards

A few days ago, two workmen were fixing my sewer and plumbing system underneath my house (It was kinda smelly). During the coffee break (which is the theme in my blog, all good things come from a coffee break), I had to explain what I did at the university. So I explained that I was looking at the motion of the Earth's crust due to ice loading during the late-Pleistocene ice age (well not in those words, and I did not mention, that I was doing this with satellite data, because my experience tells me to leave this part out. If you use the word satellites, people just stop listening and laugh). They found it very interesting ;).

I know, it is an abstract subject and difficult to grasp (it took me several months to fully understand the complexity of the problem, I am still working on how to solve it). Last week I needed to look at the ice sheet, that caused the motion of the crust that we observe today. People have made models on the growing and melting of this ice sheet, using all kinds of observations, from markings on rocks, bird droppings and pre-historic campfires. One of these models is called ICE-5G, constructed by W.R. Peltier from the Department of Physics in the University of Toronto, Canada.

To get a feeling that an ice sheet can deflect the Earth's crust, you should first get a sense of magnitude of this ice sheet. Therefore I made an animation that shows the growing of the ice sheet until its largest magnitude 21,000 years ago (21 ka). The animation starts with the present and goes back in time with steps of 500 years. The color scale illustrates the thickness of the ice sheet, going up to 3 km (that is a lot of ice).


I have not plotted topographic height variations, because I want to emphasize the ice sheet thickness (oh, and really watch the movie at 720p HD).

The movie starts with the view of Northern Europe. The current ice sheet of Greenland is visible and a little bit of ice on the Russian island, called Nova Zemlya (a very important island in Dutch history). The first 8500 years back in time does not show any ice in North Europe. So it gives you some time to orientate yourself. The viewpoint rotates around Scandinavia from Canada and ends in Russia. you see Scandinavia in the middle. 

When going further back in time, some ice is visible in Sweden. Also the ice on the island Spitzbergen grows a little bit. This growing (or melting, because we go back in time, get it?!?) continues and even ice in Scotland is accumulating. The Last-Scottish ice sheet peaks at 13,000 years ago, but vanishes again, when we continue to go back in time. The ice on North Europe, Iceland, Spitzbergen and in the Barentz Sea, however, keeps on growing. 

The Scottish ice sheet reappears 15,500 years ago (or melts away, keep focused, its so confusing.) and continues to grow. Eventually it will be connected to the big ice sheet on top of Scandinavia. This ice bridge is resting on the continental plate underneath the North Sea. Oh yeah, there is a large spike at 18,000 years, but I think this is a glitch in the model/processing (I don't believe in extreme local snowfall), ignore it. 

21,000 years ago the North Europe ice sheet is at its largest. In all its glory pressing down on dirt, rock and crust. This impression, this footprint is still observed today as very small land uplift rates and gravity field changes.


maandag 1 juli 2013

Do it yourself physics: Determining the curvature of the Earth, if you have better equipment

Working on this new project, see previous post, made me enthusiastic to do some gravity experimentation myself. I wanted to see if I can measure the curvature of the gravity field of Earth myself. I only needed a gravimeter (fancy word for very precise accelerometer).

Me, being a 'not-paid-much-just-enough' PhD researcher, I can not buy a very precise gravimeter, but I do have a laptop which contains three accelerometers to protect my harddisk in case of a joint meeting of the laptop and the ground. I wanted to see if I could use these for my little experiment (instead of going on an 8 month dedicated submarine voyage with state-of-the-art instruments, hmmmm, what was I thinking).

My laptop is a Macbook Pro (ok, don't start the discussion about which operating system is better. In the end it is all about the person using it) and I found the following code to (pretty easy) access the accelerometer data. The website for reading the accelerometer data gives a nice and clean syntax description on how to use it. You should download the SMSLib package and unzip it somewhere you want it to be on your computer. Then go, using terminal (unix commands), to the directory where you unzipped the package and give your computer the following command:

./smsutil -i0.1 -c100 -atxyz > testcapture.txt

And try to move your computer in some noticeable way (this gives better data and it gives you a sense that it is working). This commands tells your computer to capture every 0.1 seconds (-i) for 100 samples long (-c, this means ten seconds) measurements from the accelerometer and print it (-a) in the following order:

time x-axis y-axis z-axis

This can be varied in all different ways (-atzyx -atz -axyz, and so on). After the computer is finished, you can check your data, by typing:

less testcapture.txt

First column is time after enter, followed by the three read-outs of the accelerometers. If you did move your computer, the read out will have quite some variations. If you did not touch your computer (what I did), you will see that the z-axis will be close to 1 and the other two close to zero (if your screen made a 90 degree angle with the table top, and the table top was level). The numbers will vary a little bit in time, which is the noise of the accelerometers.

Finding out what the noise of the measurement equipment is always the first thing you should do. So I did not touch my computer and turned on the recording of accelerometer data. Then I calculated the magnitude of of the acceleration vector (math!) and plotted it against the variation of the normal Earth.

This was a little bit of a set back. The accelerometers in my computer are noisier (blue curve) than the variation in the normal Earth signal (red curve). Also the acceleration resolution was almost as big as the normal Earth signal variation itself. These sensors just can not do the trick for my experiment. Maybe it is time to buy pendulum equipment like Vening Meinesz and ask the navy if they have a spare submarine...

zaterdag 22 juni 2013

A submarine voyage into the gravity field of Earth

Plate tectonics is a theory that is only 60 years old. Before this time, people were seeing Earth as a solid un-deformable piece of rock. Imaging you being a geophysicist in those days (ok, if you are currently not a geophysicist this is even more difficult, but in comparison try to explain the wonders of the internet to your grandparents.), having trouble to explain most of the things that where observed.

In those times a civil engineer, educated in Delft (my university :) ), went on a submarine voyage, measuring the gravity field of Earth. Wow, they should make a movie about this (I think they even did)! With his own designed pendulum equipment, the Dutch engineer could measure the gravity field with an accuracy up to a few mGal (which is very impressive, just trust me). Who is this brave, 2 meter tall (which I like because I am the same height), submarine-sailing hero? Born on 30 July 1887 in The Hague, he was named Felix Andries Vening Meinesz.

I am currently working in a project to describe and explain the measurements of Vening Meinesz during one of his famous voyages. The project is making me feel like the Indiana Jones of the Geophysicists, going through old notebooks, carefully reading all the details and trying to get a sense of what he did and when he did it (ok without the whip and the cowboy hat, but still). 

Today, I give you a small sneak preview of my work. It is not finished, but still I think it is cool. The part of his voyage we look at is when he sailed over the Walvis Ridge (yes, it is not Whale Ridge, but the Dutch or South African Walvis), where he did several measurements.


The Walvis Ridge is a large sea mount chain, west of South Africa. It has a great effect on escaped eddies from the Indian Ocean (maybe I will explain this in later posts). The Ridge is formed by hotspot vulcanism (see my post about Hawaii), still today forming the island Tristan da Cunha. After visiting South America, Vening Meinesz, onboard the submarine Hr. Ms. K18, sailed to Cape Town, visiting Tristan da Cunha and crossing the Walvis Ridge. On his way he did 2-4 measurements a day, observing the variations in the gravity field due to masses like Walvis Ridge. This is what he saw:

I made a plot of his measurements and subtracted the ellipsoidal shape of the Earth, this results in the free-air anomaly (deviations from the main signal, you can see so much more!!). In the top figure are the measurements of Vening Meinesz (interpolated), with the black error bars. In red is a state-of-the-art satellite gravity field, having a much smaller resolution and thus dampening the signal, removing high-wavelength features. Features that Vening Meinesz could observe in the submarine, because he was much closer to the source. The bottom plot shows the bathymetry of that part of the Atlantic ocean, clearly showing the elevation difference of the Walvis Ridge. The red diamonds are the locations of the submarine during the measurements. The captain really tried to sail close to the ocean floor. I say,  "Kuddos for him and his sonar-crew, not hitting anything!" (ok, at some points they are below the ocean floor, but blame this on the uncertainty of the bathymetry model, not on the skills of the crew of Hr. Ms. K 18). 

Still today, Vening Meinesz's measurements are very impressive, obtained only by watching the swinging of three pendulums. 






woensdag 12 juni 2013

Destroying one of my childhood's fascinations

This week I received a package from the USA, containing my own Crookes radiometer (only a few bucks at ThinkGeek.com (Yes, I am a geek, but the good well developed kind ;) )). This device is a small mill with black and white vanes in a vacuum pumped light bulb which turns around when you put it in sunlight (any light works!). It looks like this (pictures speak a thousand words, well in my case a few dozen)



My physics teacher used this device to explain that light particles have momentum (he should have known better), and due to the different reaction with the white and black colored vanes, the mill would turn. During my whole life, I was really sure about that this explanation was the effect causing the light-mill in vacuum to turn. Until this week.

My old master supervisor (not that he is old, but I am no longer a master student, he is my colleague now) entered my office room with a cup of coffee (this is of course essential for the story) and saw the Crookes radiometer. After making a comment about me doing Disneyland physics, he pointed at the radiometer and asked: “Do you know why the vanes of the radiometer turn?”. During my master we always had good discussions about physics, which I always lost, but now I could tell him that I knew. “Wrong”, was his response, “Just calculated the acceleration of the vanes due to the light particles” and he stepped out of my office, leaving me behind in total confusion. He always did this during my master research, instead of explaining the principle, he encouraged myself to come up with the answer (I know, this is more pedagogic correct). 

As a good scientist does, I consulted the encyclopedia, or in this era of technology, Wikipedia. The Crookes radiometer page has an excellent documentation about this device. It is NOT radiation pressure due to electromagnetic radiation (fancy words for light, heat and other things you can not see), which is far to small to cause the huge (well, I think they are tiny) vanes to rotate. They give four historical explanations of which two are to small to explain the movement. The other two have to be combined to fully explain the motion. This is real science!!! Initial theories are disputed by better ones, and even in the end there is not one explanation but multiple.

Ok, but what are the effects that cause the radiometer to turn. Even Einstein thought this was a great exercise and did some calculations (well if Einstein worked on it, the problem should be very complex). It sort of is. Air molecules in the near-vacuum (vacuum conditions can not be obtained, this will even stop the radiometer from turning) environment exchanging different amounts of momentum with the vanes due to different temperatures. Just read it here. In the end light has something to do with the motion, it is however not the pressure of the photons.

woensdag 5 juni 2013

Trying to figure out spacetime bending

A few years ago I was obsessed about Einstein's theory of gravity. I wanted to know everything about it, so I browsed a lot on the internet, trying to find information about the topic (I could have gone to the library, however I was still in the frame of mind that everything on the internet is correct). So one day I came across the following website: Bending Spacetime in the Basement. Wow, can one do this at home?!?

First take a good look at the website. He's got a point by stating that he is bending spacetime. It unfortunately has nothing to do with warp-drives and wormholes (Which was what I was looking for), but his experiment is quite cool nonetheless. It somehow proves (I will discuss this later on) that the theory of gravitation found by Newton, not only works for planet and stars, but also for smaller everyday objects. Everything attracts each other.

Impressed by the simplicity of the experiment and the fact that it is about gravitation (I think this is one of the most interesting forces in physics), I showed it to my fellow classmates (I was still studying to become an Aerospace Engineer) and it resulted in heated discussion. Was it really a gravitational pull of the masses that caused the motion in the experiment, or were different forces in play? Maybe it was just tension in the string or a possible magnetic torque. It could even have been a draft (wind) in the basement of the experiment. I always believed (believed in the sense of a good educated guess) it was gravitation at work, but how could I prove this?

My current job is to model the effect of gravitation on the surface of the Earth. The above problem should therefore be a walk in the park for me. I start by assuming that the video coverage is genuine and reports exactly what was going on during the experiment. I also trust our basement spacetime bender and all its statements on his website (again, everything on the internet is true). This enables me to obtain the timing records of the motion, which I can use in my proof.


From the above two stills of the video we can deduce that the full motion - from rest to first contact with the cubic stones - takes about 4:30 min (±15s, he made a time lapse out of it, so the time-resolution of the movie is quite coarse). This gives us an observation with which we can test our models.

So let's make a model that describes this motion. Starting with the law of gravitation of two particles (let's assume that the stones and round-metal objects are point masses. This is what we call modeling, start simple) invented by Newton (He did not know that mass actually bends space and time, but who cares (Einstein did!)):


(Actually this depicts Newton's law of gravitation and his third law of motion) Here, F is the force experienced by the numbered particle, G is the universal gravitational constant, m is the mass of the numbered particle and d is the distance between the two particles. I know equations in a blog will lower its popularity, but hey, it's a physics blog. To clarify, I made a sketch of the situation, and because of symmetry, I only sketched the right part of the rotation device.

Here, M1 is the fixed stone and M2 the round metal object. M2 can only move along the dashed line, s. Half the length of the rotation device is denoted by r and the angle between the initial and current state is depicted by phi (yes, the strange wriggly shape in the bottom corner. It's Greek!). The whole problem can be modeled as a 1D-motion. To find out whether it's only gravitation that moves the rotation device, we calculate to what extend the gravitational pull between the two bodies will affect their movement. The gravitational pull between the two bodies works along the line, d (illustrated in red).

The motion of M2 from its initial resting state can be modeled using a mathematical trick I learned at Aerospace Engineering, namely the state equation and the Euler integrator (I know, this is not the best one, but if you just reduce the timesteps, it will work (hopefully)).
If we can find a relation for double dotted s (as this is the only unknown in this scheme, it really is!), the motion of M2 can be calculated. Double dotted s only depends on the gravitational pull between the masses in the experiment (let's ignore the giant ant, and assume symmetry (which is not entirely correct, but let's start with that and ignore the attraction of the other M1 mass)). So after some proper geometric brain-crunching we obtain a solution for the acceleration felt by M2 (I leave this open for you to do. Hint, it is a tiny-tiny acceleration).

So now it only remains to find values for the geometry of the problem and the masses used: M2 is a lead sinker weight of 169 grams, the rotation bar is 30 cm long, so r = 15 cm, and M1 (the pavement stone, or in Dutch "kinderkopje", which is a bit of an odd name) is 2 kilogram. The difficult bit is to determine the difference between the initial position of the rotation device and the time of impact (in other words what is the angle between the two positions). Or just look at the following figure:


Let's say (wet finger approach (WFA)) this angle is 15 degree ±5 degrees (with this added uncertainty it becomes science ;)). This scientifically approved estimation of the geometry enables us to test the model and find out the duration of the movement. I used the following Matlab script:

clear all;close all;clc;
% The spacetime bending experiment
m1 = 2;
m2 = 0.169;
G = 6.673e-11;
r = 0.15;
% start Euler integration
dt = 1;
tnew = 0;
phinew = pi/2-pi*(15/180);
snew = r*phinew;
sdotnew = 0;
while r*cos(phinew)>0   % M2 hits M1
    % use new values for the calulation
    t = tnew;
    phi = phinew;
    sn_1 = snew;
    sdot_n = sdotnew;
    % Force (gravitation)
    d = sqrt(2.*r^2.*(1-cos(pi/2-phi)));
    alpha = pi/4 + phi/2;
    Fz = G*(m1*m2)./d.^2;
    Falong = Fz.*sin(alpha);
    sddot = Falong./m2;
    % State equation integration
    snew = sn_1 + sdot_n*dt;
    sdotnew = sdot_n + sddot*dt;
    tnew = t + dt;
    phinew = snew/r;
    % plot the results in a figure
    hold on
    scatter(r*cos(phinew),r*sin(phinew),'r')
end
hold off
axis([0 0.4 0 0.4])

The duration of the motion calculated in the simulation is 12.5 ± 5.7 minutes. Looking back at the 4.5 minutes it took in the video, this suggests that the initial angle was 10 degrees (if it is only gravitational attraction that is playing a role). But the overal exercise tells us, that it could be that gravitational attraction between the two masses is the main contender for the motion. Isn't that cool!



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...