When it came to deciding what topic to choose for this research paper, I selected volcanoes because they have always captivated me. After all, I’ve seen them my whole life in books and in movies. Lakes of fire and explosive aerial bombs tend to be fascinating. But the thing was, I didn’t really understand how it all worked. I wanted to find out more. Specifically, I wanted to know how volcanoes are created. What are the processes at work that cause volcanoes to erupt? And how are volcanoes involved with the way the earth has formed? Using the Geosystem’s textbook, as well as publications from the Smithsonian Institution and National Geographic, I discovered that volcanoes offer much more than meets the eye, as they are as crucial to the formation of earth’s structures as anything else on the planet.
It’s no wonder volcanoes have captured my interest. It seems throughout time, people have been captivated by volcanoes. According to the Smithsonian Institution, early Roman cultures believed in a deity known as Vulcan, the god of fire (Simon, 1988). It was thought that Vulcan lived beneath a mountain in what is now Italy, where he forged weapons made of fire for other gods. Whenever a volcano erupted, Romans assumed Vulcan was hard at work, or perhaps angry. Of course, scientists today know that volcanoes are columns of ascending magma that erupt at the surface in the form of lava and other volcanic materials, creating mountains, cones, and hills. But that description doesn’t give the full story. To understand how volcanoes work and their impact on the earth, we must also discuss the basics of plate tectonics.
Earth is made up of many layers of dense rock. The outermost layer is called the lithosphere, which includes the crust. The Earth’s lithosphere is broken up into huge slabs of rock that fit together like pieces of a cracked eggshell. These plates are constantly moving over the upper mantle of the Earth, where it is so hot that rocks can melt to form magma. Most volcanoes (and earthquakes) form near the boundaries where these enormous plates converge, diverge, or slide past one another, allowing magma (molten rock) to break through the plates or ooze from the edges. When magma reaches the surface it becomes lava, extrusive rock material that shapes new volcanic landforms. Volcanic activity occurs throughout the entire world, and under several different conditions.
Areas where tectonic plates collide, forcing one plate to subduct under the other, are known as subduction zones. The portion of the lithosphere that is forced underneath will begin to melt in the upper mantle, becoming magma. Since magma is hotter and lighter than surrounding rock, and filled with gas, it can rise through fissures and cracks to the surface. Eruptions can also occur in mid-oceanic rifts. These are zones in which two plates drift apart, creating a crack in the earth’s crust. Magma fills in these gaps, forming new rock on the ocean floor. Volcanic activity that occurs in the middle of plates, as opposed to their boundaries, is caused by hot spots. When hotspots are located near thin areas of crust, plumes of magma rise to the surface and puncture the plate, forming volcanoes. Many volcanic islands are formed this way, such Iceland and Hawaii.
Properties in the magma itself, such as its chemical makeup, gas content, and temperature, will affect how the magma will erupt, and the types of landforms it will produce as a result. Depending on the composition of the magma, eruptions can occur explosively or effusively, or somewhere in between. Either way, various volcanic materials will exit the volcano, such as ash, cinder, gasses, and lava. Chemical properties will also determine the lava’s viscosity. Lava that reaches the surface with low silica content and high temperatures, for example, is very fluid and can travel vast distances, creating massive shield volcanoes, such as those found in Hawaii. These factors all contribute to the types of landforms volcanic eruptions can produce.
Now that we have explored the ways in which volcanic activity occurs, we can look into the various volcanic landforms that appear as a result. As mentioned, new landforms are created when materials that pass through the central vent of a volcano accumulate on the surface. Perhaps the most well known type of volcanic landform is the composite volcano. Composite volcanoes are the typical volcanoes we see in movies. They are created by a series of explosive eruptions of ash and pyroclastics, which build up in layers, creating a steep-sloped, conical shape. Perhaps the most famous composite volcano is Mount St. Helens in Washington, which erupted in 1980, destroying countless acres of land with surges of hot gas and ash-filled pyroclastics that travelled at speeds of up to 250 miles per hour (Christopherson, 2015).
Volcanic eruptions of this size and magnitude often create other landforms on the earth, such as craters or calderas. Craters, such as the one that formed atop Mount Saint Helens, are circular surface depressions near the summit of a volcanic mountain, which are usually vents for future volcanic activity. Calderas are another type of surface depression that forms when volcanoes collapse in on themselves after an eruption. Calderas may eventually fill with rainwater and become lakes, such as Crater Lake in Oregon (Christopherson, 2015).
The product of effusive eruptions, shield volcanoes are the largest of the landforms created by volcanic activity. Because of outpourings of low viscosity lava, these sticky lava flows pile up over time, like pancakes, rising high above surrounding landscapes to form gently sloped mountains that resemble warrior shields. Major examples of shield volcanoes are the Hawaiian Islands. In fact, the entire chain of Hawaiian Islands are shield volcanoes, created by movement of the Pacific plate over a mantle plume. Millions of years ago, the Hawaiian Islands began to form as volcanic eruptions of basaltic lava hardened on the seafloor. Layer by layer, these enormous underwater mountains began to rise above sea level, and appear as islands. Today, Hawaii’s largest volcano is the Mauna Loa, stretching 70 miles long and rising 30,000 feet above the ocean floor (Luhr, 2003).
One of the smaller landforms, the cinder cone, is another classification of volcano. Cinder cone volcanoes are small cone-shaped hills that are created by moderately explosive eruptions of ash and cinder. Unlike composite volcanoes, cinder cones are not cemented together by layers of lava. Instead, volcanic rock fragments form an eruption cloud, which then falls back down to earth around the central vent, forming oval hills. Cinder cone volcanoes often form on the flanks of other volcanoes. On the Ascension Island, located in the Atlantic, there are over 100 cinder cones scattered throughout the island, which itself is a composite volcano (Christopherson, 2015).
With the unpredictable nature of magma and lava, and the dynamics of moving plate tectonics, it’s fair to say that volcanoes are some of the most dangerous natural phenomena in the world. Composite volcanoes such as Mount St. Helens, or Mount Pinatubo in the Philippines, have accounted for mass destruction and large death tolls. Pyroclastic material, invisible hot gasses, and aerial bombs are all devastating threats to life. But despite being extremely destructive, volcanoes have also helped shape earth into the beautiful, hospitable planet it is today. In fact, life on earth probably wouldn’t exist without them (Fradin, 2007). That’s because, aside from creating islands such as Hawaii and Iceland, volcanic processes have produced gasses that liquefied into the oceans we have today. And although volcanic eruptions can destroy forests and crops, chemicals in the lava give way to nutrient rich soil. Life returns. Valuable minerals and gemstones can rise from the magma as well, allowing people to mine silver, gold, and diamonds. Scientists have even learned to use volcanic activity to generate electricity.
Volcanoes are captivating examples of the dynamic forces at work beneath our feet. Along plate boundaries and hotspots, they have created underwater ridges and landmarks that have lasted millions of years. They have brought destruction, but they have also garnered life. And as tectonic plates continue to slide across the planet, volcanoes will continue to play a crucial role in the formation of new land, and new life.
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