Sandstone can create some of the most impressive geological formations on earth. The image on the right demonstrates a bridge that seems so mechanically perfect that looks to almost have been carved. Other formations include standing pillars of sandstone and piles of balancing rocks which have left geologists in amazement since antiquity. Their constant sculpting by wind and water has taken millions of years of reach the current point, but it’s quite unclear why the current point was the one to be reached. The shapes of these sandstone structures are not obvious results of the erosion process and the mechanics of why such bizarre formations come into existence is what today’s paper is looking into.
As a child I, like many children, was a very big fan of dinosaurs. I would like to think that my obsession was perhaps a bit more technical than the average and so I can distinctly remember memorising (or at least attempting to) large phylogenies (those trees of species) often extending long before and long after the reign of the dinosaurs. Today’s paper is about the relation between species, although it isn’t giant lizards, but bony fish, which are the target of the study.
When two tectonic plates run into each other, the normal results is that one goes up and the other is forced down. The plate that moves under the other, the subducting plate, dissolves as the intense pressure and friction melt it and it is also melts as it comes into contact with the mantle. The types of rock melting are very relevant in this process. Obviously the denser the rock, the more likely it will exist in the subducting plate. A simple way to make a mineral more dense is to enclose water within it’s structure to make it a hydrous mineral. Just to be clear, these aren’t the same rocks but waterlogged, the water molecules are inherently linked into the crystal structure of a hydrous molecule as compared to an anhydrous molecule.
Today’s post is going to be very relevant considering recent events. For anyone too far in the future to remember, this week there has been an eruption or series of eruptions of Mount Agung on the Indonesian island of Bali. Luckily I don’t beleive anyone has been killed or even seriously hurt by the volcano despite it being one of Indonesia’s most dangerous. However, the Pacific Disaster Centre is predicting that 5.6 million people may be affected, not by lava or pyroclastic flows, but by the ash. Explosive volcanic eruptions always end up launching fine ash and various aerosols into a wide area which not only has a direct impact on people’s health but also ends up grounding a whole series of flights and in some extreme cases the ash can actually collapse structures under it’s weight.
China is by far the world’s leading producer of wind power with both the largest installed capacity for wind power as well as one of the fastest growing rates of wind power. As of 2016, China has a maximum wind output of 149 gigawatt (double the United States who come second with 74.4 gigawatt and more than the entire European Union) and covers 4% of its national electricity output with it. The Chinese government has pledged to produce 15% of all the nations electricity by 2020 and it is estimated that by 2030 the Chinese Government will have spent a total $500 billion on wind power, theoretically being able to cover China’s entire electricity requirements with wind power at this time (although this is of course unlikely in practice).
In the world around us, and therefore in physics, often the rate of something is proportional to something else. A basic example is that the rate of decay of a radioactive sample is proportional to the amount of the material you have. The more there is, the more chance that any one will decay. In order to model behaviours like this, which are practically omnipresent, we call in the yes men of physics, differential equations. Although it’s a bit cynical to describe them in such a way, differential equations can be used to show almost anything based on the right boundary conditions. As a result mathematical models must be constructed carefully.
If I remember correctly from my days of studying geography in secondary school, there are four main methods of mass transport for a river.
- Traction is where large rocks are rolled along the river bed as the speed of river is not fast enough to move into
- Saltation, where the rocks and pebbles are bounced along the river bed. If the material is of even smaller size such as grains then you get
- Suspension. Relatively obvious, the material is suspended as particles within the water, of course it is also possible for
- Solution to occur. Where the material is dissolved in the water and will only reappear when the concentration gets high enough.
Of course proper potamolagists (people who study rivers) go into a whole lot more technical detail regarding grain size, hydrodynamic properties of the river and the eventual long term trend of particles under transport.