Kilauea in 1959
Volcanic Effects On the Human Experience
There's no way around it, volcanoes fascinate, intrigue, terrify and mystify us. From the terrifying explosion of Krakatoa back in 1883 to the almost continuous eruptions of Kilauea and Mauna Poa on the Big Island of Hawaii, these magnificent natural events always seem to give us reason to stop and observe their awesome display of firepower.
And at the same time, there is that basic sense of primordial fear and survival that always seems to come with the news that someplace in the world a volcano is erupting, threatening lives and destroying property.
The Earth's Core
The Earth is Not Solid
Contrary to the popular proverbial expression, it is not feasible or even possible to dig straight down to China. The distance is staggering, 8,000 miles approximately, but the hot, solid iron core of the planet stays at a constant 10,800 degrees Fahrenheit, ( the same temperature as the surface of the sun) a condition which makes the task more than impossible.
Though the inner core is believed to be solid, it is surrounded by a semi-solid, outer core and then a larger, rocky, plastic layer of mantle that sometimes produces magma, the red, fiery liquid that comes poring out of volcanoes as hot lava.
And just in case you are you are interested in the numbers, going from the center outward, they are 760 miles, 1,400 miles, 1,800 and five to 25 miles. That's 760 miles for the radius of the inner core, 1,400 miles for the thickness of the outer core, 1,800 miles for the thickness of the mantle and finally five to 25 miles for the thickness of the crust, depending on whether or not there is an ocean on top.
We Live On The Crust
The outer most layer of the planet earth is called the crust. That's the part that we live on. The crust is shaped into mountains, valleys, plains and plateaus. It varies in thickness and is covered by vast amounts of water, known as an ocean. The ocean (several oceans actually) is not actually considered to be part of the crust.
If the crust was one solid unit with no weak spots, there would be no volcanoes. But since the crust consists of many movable plates of land, cracks can form where the tectonic plates meet and magma can emerge through these cracks and form a volcano. It should come as no big surprise that a majority of the world's volcanoes can be found it concentrated areas, where these sub-continental plates meet.
The Nature of Magma
The earth's mantle is a huge, rock layer that lies underneath the earth's crust. Under most conditions, the material exists in a solid form, but when placed under heavy pressure and heat, the rock strata can form liquid pools that are red hot in temperature. This liquid material is called magma and it is this magma that comes gushing out of volcanoes as lava and then flows down the side of the cone.
Vulcan, The Roman God of Fire
Vulcan Symboloizes the Fire of Creation (and Destruction)
Ancient legend has it that Vulcan, the son of Zeus, was tossed into the sea from Mt. Olympus by his father because he was physically deformed. Here he was raised by the sea nymph, Thetis. Eventually, Vulcan left the underwater world of Thetis and discovered a small Greek island. Here, he built a forge that was used to make nearly invincible shields and armaments for Roman deities.
After his fall from the heavens, Vulcan became the craftsman, who could create marvelous objects from many kinds of different metals. His spirit is also manifest in the numerous volcanoes that have risen from time to time along the northern rim of the Mediterranean Sea. Taking all of this mythology into account, it is no surprise that volcanic activity around the world bears his name, as does the the science of studying volcanoes, which is called volcanology.
Paricutin, a Textbook Cinder Cone Volcano
A Typical Volcano
When we think of a volcano, quite often we are visualizing a cinder cone volcano. This is the most basic type of volcano, where hot magma rises from deep within the earth, forcing the land to rise around the relatively small, column of molten rock. In this type of volcano, one simple cone shaped mountain is formed and when the volcano actually erupts, the magma emerges from the top as lava.
More often than not the liquid lave runs down the side of the cone, but it some situations the lava explosion can be quite spectacular and shoot high into the air.
Stratovolcanoes are complicated versions of a cinder cone volcano.They form tall cylindrical shaped mountains like a cinder cone volcano, but instead of having just one central column of magma, there are many routes for the molten material to travel through. These paths branch out like a tree root, creating a network of molten lava flows that can emerge from various points on exterior side of the volcano. Some of the more notorious stratovolcanoes, include Mount Saint Helens, Vesuvius, Pinatubo and Popocatepetl.
Types of Volcanoes
The Shield Volcano
The other type of volcano is called a shield volcano. These volcanoes are less common, but by coincidence, Hawaii houses many of the shield volcanoes, including Kilauea, which during the month of May (2018) has constantly been in the news because of its many small eruptions and hot lava flows.
Basically, these type of volcanoes get their names because they resemble a warrior's shield, lying on the ground. This rocky mound is characterized by having a very large base, shallow-sloping sides and numerous underground magma plumes, which can produce red hot lava flows at the surface.
Some Scientific Terms About Volcanoes
With volcanoes in the news lately, here is a list of terms that you might want to know.
Active Volcano - any volcano that has erupted in the past 10,000 years and is expected to erupt again
Caldera - a large bowl shaped depression formed at a top of a volcano, when the ground collapses
Lahar - a fast-moving mudflow made of ash and water
Lava - magma that reaches the earth's surface
Laze - mist containing Hydrochloric acid that forms when molten lava flows into sea water
Magma - molten rock below the earth's surface
Pahoehoe - a type of lava that forms a thin wispy crust, when it hardens
Pyroclastic Flow - a high temperature mixture of hot ash and lava fragments that moves out of avolcanic eruption at a high speed
Tephra - any sized material that is ejected during a pyroclastic explosion
Vog - a fog, containg sulfur dioxide that forms near lava vents
Volcanic Ash - lava particles that are less than a tenth of an inch in size
Volcanic Bomb - a mass of molten lava that hardens after it has been ejected into the air by an eruption
Volcanology - the scientific study of volcanoes
Questions & Answers
© 2018 Harry Nielsen