Sunday, 1 March 2009
Scientists Know A Lot About Lava
Magma is molten rock and metal found beneath the surface of the Earth. It is thought that it may exist on other terrestial planets. People commonly think of lava and magma as a liquid, but geologists find that magma is usually a mush - a liquid carrying a load of mineral crystals. We've seen in previous posts how comets, whom also carry mineral crystals, may use electrolysis to generate those huge ionic plasma tails. A comet's tail can be tens of millions of kilometers in length when seen in the reflected sunlight. Comets are very small in size relative to planets. Their average diameters usually range from 750 meters or less to about 20 km. The Earth has a diameter of 12, 800km at its equator. If we were able to look under the bonnet of the planet, so to speak, would we find the same ionic reaction taking place beneath the mantle on a far grander scale?
Scientists know a lot about lava. Lava is the stuff which erupts onto the surface. Magma remains a bit of a mystery to scientists because it is always found beneath the crust, making it difficult to observe. Drillers accidentally hit a pocket of molten rock underneath a working geothermal energy field in Kilauea, on the Big Island of Hawaii. A lucky break for geologists that could allow them to map the geological plumbing that created everything we know as land. Geologists had expected to hit dark molten basalt, because basalt is abundant on the island. Tests of the glass samples found that the material was dacite, an unusual type of magma that is granitic in nature and contains 67 percent of silica. The samples of the magma were found to be "clear and glassy".
Basalt flows cover nearly 70 percent of the earth's surface. Basalt contains around 50 percent silica. Silica is a chemical compound also known as silicon dioxide (SiO2). Silica is most commonly found in nature as sand or quartz, as well as in the cell walls of diatoms. Soda-lime glass accounts for 90 percent of manufactured glass. Soda-lime glass contains about 70 to 74 percent silica. Many glasses contain silica as their main component and glass former. A good quality prism is made with quartz - pure silica. Glass optical fibers are almost always made from silica.
Silica is also the most abundant mineral in the Earth's crust. Although there are few exceptions, the primary constituent of magma is silica. The guy on this site relishes the similarities of glass and magma, and has fun recreating lava flows in the microwave - known affectionately as "the ol' nuker". The reactions are possible due to 'ions' being trapped in the glass. Have you ever noticed that odd air bubble which sometimes get trapped in a glass?
The material that forms magma contains a lot of dissolved gases - gases that have been suspended in the magma solution. As magma decompresses on its journey to the surface, the bubbles grow and approach one another more closely until, eventually, they connect. Volcanic eruptions are thought to be driven by the nucleation and growth of many bubbles within magma. It is known that within gas-charged magmas bubbles grow and shrink by the movement of water in and out of the melt. Researchers have found that the more water there is in the magma, the more likely the volcano is to erupt violently. At depth in the Earth nearly all magmas contain gas dissolved in the liquid, but remember, the samples from Kilauea were found to be "clear and glassy". The gases had remained dissolved, without forming bubbles.
Degassing is the process of removing small suspended gas bubbles and dissolved gas from a liquid. Before applying epoxy and polyurethane compounds, efforts are made to remove any trapped gases. One popular method is by vibration - the mixture is placed on a vibrating table that assists the bubbles in travelling to the surface. Deep inside the planet there is no surface for the bubbles to arise into. Is it possible that the magma is being vibrated at such high frequencies that gases are forced to dissolve? As magma rises to the surface as lava, the vibration could change, allowing gas bubbles to form. At lower vibrations, it would appear that it becomes possible for hydrogen and oxygen to emerge from the magma as water vapor. Lower vibrations are synonymous with lower heat, are they not?
Oil and water do not mix, or rather, they will not mix without the addition of an emulsifier. Emulsifiers help mix ingredients that would normally seperate - oil and water for example. Examples of food emulsifiers are egg yolk (where the main emulsifying chemical is lecithin), honey and funny enough, mustard, where a variety of chemicals in the mucilage surrounding the seed will act as emulsifiers. Of interest, a mustard seed is the most tightly packed seed of all with no room for air inside.
Ultrasonic waves can also be used to mix oil and water, in a procedure known as ultrasonic emulsification. Ultrasonic waves are similar in nature to sound waves, but occuring at frequencies above 20,000Hz (the approximate upper limit of human hearing). The general principle involved in generating ultrasonic waves is to create some dense material to vibrate very rapidly. Because they can vibrate the particles through which they pass, ultrasonic waves are often used to shake, or even destroy, certain materials. Using this technique, two liquids that normally do not mix with each other (such as oil and water) are made to vibrate until they are blended. http://www.youtube.com/watch?v=v8qHKwiBvhI This technique is also often used to remove air bubbles from molten metals before casting so that the finished piece is free of gas bubbles. Are ultrasonic waves responsible for vibrations inside the planet?
In most applications, ultrasonic waves are generated by applying an electric current to a special kind of crystal known as a piezoelectric crystal. The crystal converts electrical energy into mechanical energy, which in turn causes the crystal to vibrate at a high frequency. In a crystal microphone, air pressure deforms the crystal enough to cause very small voltage changes in the crystal. These voltage changes are amplified and used to record or transmit sounds. One of the most effective piezoelectric crystals is quartz. Quartz is of course pure silica.
Ernst Florens Friedrich Chladni (November 30,1756–April 3, 1827) a German physicist and musician. Chladni was born in Wittenberg. His important works include research on vibrating plates and the calculation of the speed of sound for different gases. For this some call him the "Father of Acoustics". He also did pioneering work in the study of meteorites, and therefore is regarded by some as the "Father of Meteoritics" as well.
The technique of showing the lines of nodes on vibrating metal plates by strewing sand on them was developed by Chladni. The first mention of the technique is in his book Entdeckungen ueber die Theorie des Klanges, published in 1787. Until the twentieth century the standard method of setting the plates into oscillation was drawing the rosined hairs of a violin bow over the edge of the plate, which was normally clamped at its geometrical center. Today we place a loudspeaker above or below the plate, and adjust the driving frequency until the plate goes into resonance, and the sand on the surface moves toward the nodes.
Anything that vibrates has a natural resonant frequency and will spontaneously begin to vibrate in response to external vibrations that share the same or a similar resonant frequency. This sympathetic vibration is called resonance, which literally means to re-sound, to echo. A common illustration of sympathetic vibration is to sound a tuning fork and bring it close to, but not touching, another fork of the same frequency, which will then begin to vibrate sympathetically.
The frequencies used by Chladni plates begin around 100 Hz, and can range anywhere upto 20,000 Hz (within the frequencies of human hearing). The plates are vibrating in sympathy to something which surrounds us. What exactly? If you sing near the strings of an undamped piano it will respond with sympathetic vibration. Are the vibrations around us damped until we excite them? I suspect that there are ultrasonic waves in the core of the Earth generating a seething mass of vibrations. By vibrating the plates, maybe we are able to resonate with some of those frequencies. This might start to explain those amazing patterns that we see emerging on Chladni plates.
What has all this got to do with bubbles?