Mt. St. Helens, Mt. Vesuvius, Mt. Pinatubo; you know what they are, Volcanoes! They are found everywhere you may go. They come in many shapes and sizes. They even change history! People have mythologised about how they were formed and why they erupted. Now, we know how they erupt. We also know much more about the geology of volcanoes and what causes them.
The Cause of a Volcano
A volcano is a small opening in the crust of the earth. It leads to the magma chamber which is a pocket of earth that is filled with magma. A volcano usually erupts when two of the Earths plates rub together and cause friction. The volcano then fills with gas which can not be held for very long. The perfect example is when you shake up a bottle of soda and the cap pops off. This is very much the same thing only the cork is a small piece of the Earth’s crust. Lava (magma when it has come out of the Earth) and ash come spewing out of the volcano and spread out causing destruction and death. Although the basic cause of eruption is the same, different types of volcanoes erupt in different ways.
Types of Volcanoes
There are various types of volcanoes around the world. They include Shield, Cinder Cone, Composite, Compound, Strato, Dome, Pyroclastic, Fluted Cone, Strombolian, Vulcanian, Hawaiian and Peleean. They can be dormant, extinct and active.
Shield volcanoes are the largest volcanoes on the face of the Earth. Shield volcanoes are made almost totally of Basalt. They are the result of lots of runny lava that came out and ran down the side of the mountain. Some of the major Shield volcanoes are Kilauea, Mauna Loa, Fernandina, Erta Alc, Tolbachik and Masaya. And that’s just a few of them.
Strato volcanoes are 60% of all the volcanoes in the world. They are made up of about half lava and half pyroclasts. Strato volcanoes have caused the most casualties of any volcano. Because they are half tephratic (tephratic material is ash and cinders and blocks) material, they are not kept together very well. They are shaken by earthquakes and rained upon, so they’re not very stable. There were many mudflows at Mt. Pinatubo, a strato volcano, because it was made up mostly of pyroclasts. At Unzen, a strato volcano in Japan, one of its flanks fell off into a small sea. This disaster caused another. There was a huge tsunami that killed 15,000 people.
Rhyolite caldera complexes are what is left of extremely explosive volcanoes that collapsed on top of themselves. We haven’t seen one of these since 83 AD They are in Yellowstone, La Primavera, Rabaul, Taupo, Toba and elsewhere.
Flood basalts are much like mudflows. Flood basalts slowly ooze down the volcanoes and can be 50 ft. thick.
Lava produced by Mid-Ocean Ridges is called Mid-Ocean Ridge Basalt, also known as MORB. MORB is the most commonly found rock type on the Earth’s surface. Mid-Ocean Ridges are the locations of thousands of earthquakes. The eruptions of Mid-Ocean Ridges have never been witnessed, although they can be found all over the world.
Volcanoes can be found on every continent. There are many volcanoes under the ocean! They erupt and form new islands. They are called submarine volcanoes. They erupt and all of the lava and ash goes to the top of the ocean and builds up. The ash and lava will dry and grass will grow and it will become a full fledged island.
The Ring of Fire is the most well known chain of volcanoes. It reaches over Asia and up to Alaska. The Ring of Fire consists mainly of constantly active volcanoes. A constantly active volcano erupts all of the time, allowing a little bit of lava to flow. They are always forming new islands and expanding them.
There are six known volcanoes on the South Pole. They are Mt. Bird, Coulman Island, Mt. Discovery, Mt. Erebus, Mt. Harcourt, and Mt. Terror. Mt. Bird is a Basaltic Shield. Coulman Island is several overlapping shield volcanoes. One of the most impressive sites on Coulman Island is the Coulman Caldera. It is 3 miles wide and 2,300 ft. deep. Coulman Island is 7.2 million years old. Mt. Discovery is a Central volcano. Mt. Erebus is an active volcano on Ross Island. Mt. Harcourt is another strato volcano. Mt. Terror is a very large basaltic Shield. Volcanoes such as these provide interesting opportunities for geological research.
Some volcanoes erupt all the time. These are called constantly active volcanoes. Stromboli, in Italy, is one such example. Another example is Izalco, in El Salvador. It has been constantly active since 1770. There are many constantly active volcanoes in the Ring of Fire.
After long periods of dormancy, volcanoes are usually very violent. This is because the lava has become sticky, and highly saturated with steam and gases, such as, carbon dioxide, hydrogen, carbon monoxide, and sulfur dioxide. These gases spew out and form large clouds. The clouds produce acid rain, and lots of lightning. Large chunks of lava are shot out like shotgun shells. Depending on their weight, and size, they will be called bombs or cinders. If they are very fine they will be called ash. These different pyroclasts will fall on the volcano and, over time build up the volcano. The lava also rises and oozes down the mountain, spreading out as it goes down. This will continue for some time. After that the volcano starts cooling down, releasing hazardous gases. And after all of this, the volcano is dormant again.
Volcanoes also have a damaging effect on the weather. In 1982, El Chichon, in Mexico, erupted. El Chichon was just a small volcano. However, there are still small clouds of ash hanging in the sky because of it. It was a very unlucky year that year because it happened to be an El Nino year. The volcanic eruption just exasperated the bad situation.
Tephra is the discharge that comes out of the volcano. It comes in three different forms, accessory, accidental, and juvenile. Accessory is made up of the volcanic cone that is shot everywhere when the volcano erupts. Accidental is sub-volcanic rock. It is carried up from the mantle or the lower part of the crust. Juvenile is made from pure magma. When the volcano erupts, shards of magma are shot miles high. Tephra gets a different name according to its size and weight and color. There are cinders, which are small glassy rocks. Also there is the ash, which is, at the largest, 2 mm. There are different types of ash. Juvenile and accessory are the origins. Ash can also be vitric, crystal, and lithic. Lapilli are shards of dried magma, which also can have accessory and accidental origins. Blocks are large chunks of solid rock that are at least 256 sq. mm. formed from rocks that were formed in previous eruptions. Bombs are small clots of magma that have a diameter of 64 through 256 millimeters. Their shapes are spherical, spindle-shaped, ribbon, and bread crust. Scoria is rich in iron and magnesium. However, it is very poor in silica. Pumice is the exact opposite. It is poor in iron and magnesium, yet very rich in silica. This results in the color of Pumice being much lighter. Pele’s hair is naturally spun glass. It is usually gold colored. Pele’s tears are very dark droplets of solidified glass. They can be tear-shaped, spherical, or almost cylindrical. Limu O Pele are sheets of natural glass that result when magma is discharged underwater and the water bonds with the magma and cools it which makes glass. Most of the time it doesn’t stay a sheet of glass for long. It is washed ashore, battered by the wind, and sometimes trampled underfoot. Spatter is a terrible mess. It gets all over the trees and the house and even the pets.
Igneous rocks are a large part of volcanoes. There are a huge amount of types! There are also many minerals in them. These are some of them: quartz, feldspar, pyroxene, plagioclose, mica, hornblende, calcite and others.
Lava is just molten rock. While it is sitting idle in the magma chamber, it is magma. But as soon as it is discharged, it becomes lava. There are four basic types of lava. The type of lava depends on the amount of silicate in the lava. The four types are basalt, andesite, dacite, and rhyolite. If the percentage of silica and the amount of gas in the lava is high, the eruption will be very explosive. Carbon dioxide, carbon monoxide, hydrogen, methane, hydrochloric acid, chlorine, fluorine, hydrogen sulfide, and sulfur dioxide are the gases that are ejected in the eruption. These gases have been an early warning system for volcanologists studying some of the worlds most famous volcanoes.
There are many very famous volcanoes. They are not famous for their beauty or height. They are famous for their destructive power. Some of these may sound familiar: Mt. St. Helens, Mt. Fuji, Mauna Loa, Mt. Vesuvius, Krakatau, Tambora, Mt. Etna and of course, Paracutin. A famous volcano in Oregon is Mt. Mazma. It blew its top and became Crater Lake. Paracutin in Mexico was just a piece of the Earth. The story was that a farmer was out plowing his field and a hole in the ground appeared just after the plow went through it. The farmer thought nothing of it at first, but it started to grow bigger and fume. His bull got scared and ran off. The farmer decided that this was a good idea and did the same. Eventually, the small hole in the ground became a full fledged volcano. It destroyed his house and the nearby village. They rebuilt the town (farther away of course) and all was well. Paracutin erupted in 1943 and ended in 1952.
Mt. Vesuvius is probably the most well known volcano in the world. The first time she blew her top, she covered the town of Pompeii in soot and ashes. No one was safe from the downpour of ashes. There were so many ashes that things like freshly baked bread and walnuts were carbonized. One piece of bread was so well preserved that the bakers stamp was still clearly visible. A faithful guard dog was found rolling on its back. Most likely it was standing guard and some burning ash fell on its back. Trying to get the ash off its back the dog was buried. Skeletons were found buried in the ash but the downside was that their bodies had decomposed over time. They solved this by removing the skeletons and pouring plaster in the cavities.
Mt. St. Helens is a Strato volcano. It covered 150 sq. miles with ash. Mt. St. Helens lost approximately 1,300 ft. off it’s height because all of the ash and lava had covered up the area around it. Mt. St. Helens claimed the lives of about 60 people. The rest of the people got smart and started farming the land. It was so fertile from all of the ash and lava that almost anything would grow there. The 1815 eruption of Tambora, in Indonesia, had 10,000 times the explosive energy of an atomic bomb. Tambora is a stratovolcano. It formed a caldera that was 4 miles in diameter. One hundred and fifty cubed kilometers of ash was thrown into the air. It fell as far as 800 miles away! Tambora ended up killing 92,000 people! Not only was it the largest eruption ever, but the most violent and the most deadly.
Mt. Pinatubo is on the island of Luzon (in the Philippines). It erupted in 1991 after being dormant for 6 centuries. There are many myths concerning the worlds most famous volcanoes.
There are many ancient myths concerning volcanoes. The most interesting are Native American legends. The Aztec legend of Popocatepetl is like Shakespeare’s Romeo and Juliet. Popocatepetl was in love with a woman named Iztaccihuati. Iztaccihuati was wrongly informed that Popocatepetl was dead. She mourned over him and killed herself. Popocatepetl returned and saw that she had killed herself. He grieved over her and built a large mound and put Iztaccihuati’s body on top of it, vowing to never leave her again. To this day you can see a woman’s body on top of the volcano, and Popocatepetl keeping his promise to never leave her side for all eternity.
There is a legend that came from the Puyallup tribes that is about an old woman that was turned beautiful by a magical great chief. There once was a natural stone bridge. It was called Tamanawas Bridge or the Bridge of the Gods. It was said that the only fire in the world burned at the middle of the bridge. A very old woman lived on the bridge and tended to the fire. Her name was Loowitlatikla, which meant Lady of Fire. She was so kind and faithful that the Great Chief, Tyee Sahale, decided to give her the gift of eternal life. She wept bitterly about it though because she did not want to live her life as an old woman. So Tyee Sahale decided to give Loowit one wish. She wished that she was beautiful. He granted her wish. The news of her beauty spread all over the world. Tyee Sahale’s two sons, Wyeast and Klickitat both fell madly in love with her. They fought for many days and nights and burned down the forests and villages. Tyee Sahale saw all of this and became very angry. He struck the bridge and it fell into the water below. He also struck down the three lovers. However he decided to raise mountains in their places. Loowitlatkla’s mountain was dazzling white, because she was so beautiful. Wyeast’s mountain lifts its head tall in pride. Klickitat’s mountain bows its head in sorrow.
There is a legend created by the Cowlitz tribes about Mt. Rainier and its wives, Mt. St. Helens and Mt. Adams. Mt. Rainier got into an argument with its wives and Mt. St. Helens got so jealous that she blew her top and knocked Mt. Rainier’s head off.
Volcanoes are a wonder of nature. A skeptic would say that volcanoes only destroy, but I want to know where we would be without them. They are always creating new islands. Volcanoes have had a huge impact not only on world formation, but also mythology, religion, and science. These have been indentions on life here on Earth. Volcanoes are certainly one of God’s more beautiful works.
Kunhardt, Edith Pompeii...Buried Alive Random House, Inc. 1987, 48
Lewis, Thomas P. Hill of Fire HarperCollins Publishers 1971, 64
Cole, Joanna The Magic School Bus Inside the Earth Scholastic Inc. 1987, 40
Steedman, Scott Volcano & Earthquake Alfred A. Knopf, Inc. 1992, 64
U-V The World Book Encyclopedia 1970 Volume 19 370
HTTP//VOLCANO.UND.NODAK.EDU Volcano World
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