Earth's Fury
Man has always had curiosity about his surroundings. One question is, "How did my surroundings come about?" This question was posed many times throughout our past, but was not researched and documented seriously until 1654. In that year James Ussher, an Anglican Archbishop decided to answer the question. After intense study of the Bible he concluded that the Earth was formed on the night of October 22, 4004 B.C. This highly scientific theory was accepted until the 1800's. A French Renaissance man of Ussher's time, Rene Descartes, thought the Earth was formed through on-going natural processes, but was scared to voice his opinions or publish his thoughts because of the oppressive Catholic church. Until about 1900 every theory on the subject of the formation of Earth was somehow linked to the cataclysmic floods described in the Bible. But, in 1900, some steps were made in the right direction. Scientists concurred that Africa and South America were at one time linked over land, due to similar fossil finds on both sides of the Atlantic. Then, in 1911, German adventurer Alfred Wegener proposed the continental drift theory - based on the South America/Africa connection of common fossils, and similar-looking coastlines. He thought that Africa and South America weren't merely linked, but were one land mass in the past. The theory he came up with for this separation was that the continents floated around, however slowly, on the surface of the world. This is the accepted theory today and scientific studies have so far failed to disprove this theory. In 1915 Wegener came up with the idea of a supercontinent, Pangaea, that was formed in the past. Pangaea has also been found to have existed by unraveling the geologic puzzle that rocks give us.
Continental drift is the theory that the earth has four main layers. The inner and outer cores are at the center of the Earth. The inner is solid iron and nickel and is 750 miles thick. The outer core is molten iron and nickel 1400 miles thick. On top of the outer core is the 1700-mile thick mantle, made of mostly solid silicate material (magma). On top is the crust, made up of plates, which is composed both continental and oceanic crust. The crust is what's under the oceans and what we stand on and it's anywhere from 4-25 miles thick. The crust is made of 14 plates - the North American, South American, Carribean, Cocos, Juan de Fuca, Pacific, Nazca, Scotia, Antarctic, Indo-Austrailian, Fiji, Phillipine, Eurasian, and African plates. The process of continental drift is caused by convection in the mantle. The magma travels in a circular motion in pockets that push the plates along in the same direction as the mantle is moving. Convection causes different zones to appear on plates - subduction zones, rift zones, hotspots, and faults. Where two pockets in the mantle are moving in opposite directions, the plates move away from each other and some of the magma seeps up to make new land in what is called a rift zone. The middle of the Atlantic Ocean has a rift zone it's entire length because the African and Eurasian plates are moving away from the North and South American plates. The Great Rift Valley in Africa is also a rift and it will one day become an ocean. Subduction is when one plate slides under another. In the collision of the Indian plate and the Eurasian plate, the Himalayas are violently being formed as India slams into Russia and then slides under it to make the world's highest mountains. When a plate slides under, it is eventually turned back into magma and spends it's life circulating to a rift zone and then it becomes new land again. It is thought that every 58 million years rock goes from new crust to old crust to magma to new crust again. Hot spots are rare occurences where magma bubbles up from the mantle to form an area far from plate boundaries where magma is pouring out. The Hawaiian Island chain is the result of a hotspot under the Pacific plate. As the plate moves more islands are formed by volcanoes. Faults are when two plates rub each other in a parallel motion and this is where most earthquakes occur. The Pacific plate is rubbing the North American plate like this, and in 150 million years California (on the Pacific plate) will be so lodged in Alaska that they'll have to name a city Los Anchorage. Two-hundred-fifty million years ago when Pangaea was around, the continents were colliding. Presently they are drifting apart and in another 250 million years, there will be a new Pangaea. But who knows what anything besides the continents and oceans will be like in 250,001,999 A.D.
Now for the meat. A volcano is made up of different parts, including the magma, the magma chamber, the pipe, the vent and side vent(s), the cone and subsidary cone(s), the gas, the ash, the lava, and fissures. The magma is the lava while it's still not exposed to the air. The mantle is made of magma. The more viscous the magma, the more violent the eruption. All magma has small amounts of dissolved gases, mainly carbon dioxide and water vapor, which help reduce their viscosity. The amount of explosiveness depends on the escape of dissolved gases, as confined pressures are released during ascent to the surface - like when you open a shaken-up can of pop. The quicker the release of gas, the more violent the explosion. Granitic magma has more sodium dioxide than basaltic magma and is more explosive. Basaltic magma has more calcium oxide and is less explosive. Basaltic magma is 900-1200 degrees C and granitic is only 600-800 degrees C. The magma chamber is a few miles underground and it's a large cavern where a pressured bubble of magma has risen from the mantle to just under the surface and it's the supply of the volcano's magma. The pipe is the release point for the bubble and it extends in a tube to the surface. The vent is where the pipe comes out and the magma explodes from. Side vents are where magma that branches off the main pipe comes out, usually on the side of the cone. The cone is the result of the build-up of dried lava and settled ejecta. It can become mountain-sized and usually does. Subsidary cones are formed by the explosions from side vents. Gas is what is dissolved in the magma and then released when the magma is forced up and to a lower pressure area. This expanding of the gas makes the explosion happen. Ash is very fine material that is spewed from the volcano. It can coat cities inches deep, clog waterways, and float in the upper atmosphere. Lava is just magma after it hits the surface. When it hardens it can take the form of Aa (ah-ah), Pahoehoe (pa-hoy-hoy), pillow lava, ejecta, and pumice. Aa is clinkery blocks that have a rough texture. It was called Aa because natives would say, "Ah-ah" when they walked on it. Pahoehoe is a ropy lava that is like concentric arcs. It's soft and smooth on the top. Pillow lava is formed underwater when fast-cooling lava breaks through rock and hits the ocean. Ejecta is big rocks, dust, and ash is emitted in the eruption. Pumice is very light rock that can float on water because it has so many bubbles in it. After Krakatoa erupted, rafts of pumice were found floating in the surrounding ocean. Fissures occur where two plates are moving apart. They are breaks in the crust and are very close to the mantle. The lava pours out of here and new land is almost constantly being formed. If the eruptions continue stacking up they may form a plateau thousands of feet high, as is the case of the Columbia Plateau in Washington. A fissure is best described as a linear volcanic vent.
There are three types of volcanoes: cinder cone, shield, and composite. A cinder cone is a violent volcano that erupts chunks of rock and dust. A shield volcano is made of layered lava flows that seep from the crater. Composite volcanoes are made of lava flows mixed or layered with rocks and debris. Cinder cones are seldom taller than 1000 ft. and are very explosive. The explosiveness is due to the rapid escape of dissolved gases.
Cinder cones are found mostly in subduction zones, where there is lots of volcanic activity. They erupt amazing pyroclastic flows which can break speeds of 600 mph. Pyroclastic flows are just dust and rocks that are pushed along by a shock wave from the volcano's eruption. They can flatten forests, vaporize lakes, and level towns. When they settle, mud chokes the water and rivers are turned into giant, watery mudslides that kill fish and flood surrounding areas. The very big explosions turn night into day with dust and volcanic ash (tiny lava particles) that are launched into the higher atmosphere. The dust can cool the climate on a global scale and it adds layers to deep-ocean sediments. Volcanic bombs hurled into the air range from hair-thin strings of cooled lava, called Pele's Hair, to football-shaped Spindle Bombs, to boulders that can smash cars.
In shield volcanoes the ejecta is mostly just lava that flows out, reaching top speeds of about 60 mph. There's little danger in these flows because they mostly just travel over previously deposited flows. Only things in the way of the flow get damaged, but there is usually no way to stop it. These flows range from streams of fast-moving lava, to miles-wide, creeping masses of lava, to hot rocks that slowly push down mountain faces and burn whatever gets in their path. The only fear you need to have of shield volcano eruptions is if you're on the slope, or if your house is in the way of the flow and will get burned down. Shield volcanoes are formed slowly and they are flat because the runny lava flows far before it hardens. Their flatness depends on the viscosity of the lava - more viscous making a steeper volcano, and less viscous a flatter volcano. Mauna Loa in Hawaii rises gradually 32,000 feet from it's seabed base 500 miles across to the summit on land - making it larger than Mt. Everest. These volcanoes are found a lot on hotspots and rifts.Composite volcanoes erupt both debris and lava.
After the eruption there are a couple of things that can happen. They can keep erupting, form a caldera or a volcanic plug. A caldera is when the explosion blows the mountain apart and all that's left is a shallow crater that sometimes turns into a lake. A volcanic plug occurs when magma that was left in the main vent hardens and is then exposed when the surrounding cone erodes. These plugs are in the shape of tall, straight spires. Devil's Monument from Close Encounters of the Third Kind is a volcanic plug.
When volcanoes erupt it is a very big event. New land forms and old land is reshaped beyond recognition. Here are some of the biggest volcanoes ever witnessed and recorded.
Krakatoa was an island between Java and Sumatra. In 1883 it erupted. The volcano was built from the ocean bottom over the last 1 million years. It's a cone-shaped mountain composed of flows of volcanic rock alternating with layers of cinder and ash. It was 7,000 feet high before the 1883 eruption. After the eruption the top was submerged to form a caldera 4 miles across. On May 20, 1883 one cone (island) became active. Explosions were heard 100 miles away in Djakarta, and ash-laden clouds reached 6 miles up. By May the activity had died down. Then, on June 11th, the eruptions began again, and by August 26th they were paroxysmal. The lava was so hot it warmed the oceans 10 miles away. The explosions were increasingly violent starting at 1:00 p.m. and at 2:00 p.m. a black ash cloud rose 17 miles over Krakatoa. The climax occured at 10:00 a.m. on August 27th (my birthday), with explosions heard as far as 2,891 miles away in Austrailia and Madagascar. They were the loudest noises ever, and they were heard over 1/13th of Earth's surface. With the force of 67,000 atomic bombs, they shot ash 50 miles in the air. Pressure waves in the atmosphere were recorded around Earth. Then the explosions diminished, and by August 28th the volcano was quiet. It was nighttime for 2 1/2 days afterwards. Small eruptions continued in the following months and in February of 1884, a discharge threw rock over nearly 5 cubic miles and lots of ash fell over 300,000 square miles.
Fine dust from the big one circled the Earth several times and made for spectacular red, blue, and green sunsets the rest of the year. Only 2,667 feet were left of Krakatoa. Two hundred feet of ash and pumice piled on Verlaten and Lang islands and the remains of Rakata. The ash from the explosion was 90% new magma, which means the island wasn't blown up, it just sank into where the new stuff came from. It triggered a series of tsunamis that were recorded in Hawaii and South America. The 120-ft. waves hurled 600-ton coral blocks, wrecked 165 costal villages, and travelled 4370 miles in 12 hours, whereas it would take a good steamer 12 days. (Keep in mind it's a 19th century steamer). The tsunamis killed 36,000 in Java and Sumatra, and all life on Krakatoa was under ash. Plants returned there in five years. Kilauea is Earth's most active volcano. It has been erupting constantly since 1976.
Mt. St. Helens erupted on May 18, 1980. It's horizontal blast shot ash-filled steam and gas up to 670 mph, uprooting six million trees and instantly scattering them over a 130,000-acre area. The weird thing about this eruption was that the blowdown happened in near silence because the ash, dust and fir needles muted the noise. The noise carried just 30 feet when it could have carried a dozen miles.
Mauna Loa is the biggest volcano right now. It rises to 4 km above sea level and its flanks descend 5 km to the sea floor, and the sea floor is then depressed by Mauna Loa's weight another 8 km. This makes it 17 km (56,000 ft) tall. It's mass is 85% of all the Hawaiin islands. It is 120 km long from underwater edge to underwater edge and it is only 100,000-200,000 years old.
Bardardunga in Iceland erupted in October and November of 1996. It was the first glacial eruption scientists had ever monitered start to finish and it was huge. The heat caused biblical floods to erupt. A river in Iceland was crossed with a bridge meant to withstand floods of 317,000 cubic feet per second (cfs), but it was smashed by the 1,600,000 cfs flood that ensued. For a few hours the volume of the water rivaled the flow of the world's second largest river, the Congo. A lake below the volcano which was said to rise 60 feet a year normally, rose 60 feet the first day. The melted water rushed downslope under a glacier and when it emerged it blew off chunks of ice three stories tall a hundred feet from the glacier.
Vesuvius in Italy was an ancient explosion that happened when the Romans were in power. The volcano was situated above the Roman town of Pompeii. One day in A.D. 79 it exploded in a huge ash cloud that rose up in Plinian form, or in the shape of a "T". The gas and dust that fell killed everyone who failed to flee and preserved them to be uncovered in the future. In the town of Herculaneum, a river of hot mud flowed into town and instantly mumified the entire town. Thousand of inhabitants and buildings were stuck just as they were moving when the mud hit them. In 472 A.D. and 1538 A.D. it erupted again, even hitting Constantinople in Turkey with rocks "larger than an ox." Now 2 million people have moved into the dangerous area lured by the beauty of the mountain and by rich soil. Vesuvius has erupted fifty times in the last twenty centuries and killed tens of thousands people.
Paricutin was born in a strange way. On February 20, 1943 a farmer was plowing his field in Mexico when he noticed his field was steaming. He wondered what it was and then it started spewing out rocks and an 80-ft. long fissure opened. In one day it grew to 35 feet tall. In one week it was 150 feet tall, and in one year it was 500 feet tall. By 1952 it stopped growing at 1,353 feet and it buried two towns as it spread.
In conclusion I found that we are obsessed with volcanoes, as with all natural disasters. We don't pay $10 go to see Dante's Peak because it's got Linda Hamilton of Terminator fame. We go because we want to see some ripping special effects explosions. They satisfy our fascination with power and fire. The volcano is the most explosive single event we can ever witness. Bombs don't come close, tornadoes and hurricanes last too long, floods don't have the power, but are merely a side effect of an eruption. Avalanches are great, but a pyroclastic flow has a much greater scope. Wildfires can be intruiging but they are also but a sideshow in the great volcanic circus. The only thing that could beat a volcano is a giant meteor strike, but that's not realistic and we wouldn't be able to witness it at regular intervals - volcanoes erupt every year. Volcanoes are an unstoppable force at their strongest. Man can devise nothing to turn back the force of the plates as they move and send lava up to the surface. We can barely turn back the flows of a slow-moving Aa or pahoehoe to save our measely little settlements. Lasers that show miniscule mountain movements, seismographs that sense the slightest tremors, and robots that can travel into the toxic and hot craters to gather data have all made predicting volcanic activity a more refined and dependable science, but nobody can say for certain when a mountain will blow its top until it's too late to do much anyway. The most we can hope for in the way of efficiency is evacuating areas at the first signs of activity and then just wait. Volcanoes are going to be an everpresent phenomenom and they'll be around till the sun swallows Earth in five billion years.
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