Volcanoes and Society

INTRODUCTION

Volcanoes are explosive things of beauty that can tell us much about our past, and that have an impact on our futures. Like humans, sometimes they are passive and unnoticeable, appreciated for their history and geological importance, sometimes aggressive, angry, and very active. By exploring the science behind the formation and activity of volcanoes, and discussing the impact volcanoes have on today's society, we can value their importance at a higher level.

A volcanic event occurs when there is a sudden or continuing release of energy caused by near surface, or surface magma movement. The energy release can occur in the form of earthquakes, gas-emission at the surface, release of heat, explosive release of gases, and the non-explosive extrusion of magma. An event could be destructive without the release of solids or magmatic fluid, or be destructive with voluminous lava flows or explosive activity.

WHY?

As one goes deeper and deeper into the earth, there is increasing temperature with increasing depth. This is because radioactive elements deep within the earth are slowly disintegrating and producing heat. The rock in the earth insulates the heat, so that it accumulates and eventually liquefies the rock insulating it. Only slowly does this heat escape, which leads to the drastic differences of temperature with depth. This difference is referred to as the geothermal gradient. The average geothermal gradient is 2° to 3°C per 100 meters of depth, indicating that heat is flowing outward from inside the earth. Volcanoes are vents for the explosive escape of some of this heat. Magma is a general term referring to a mass of completely or partly molten rock containing the volatile that it acquired at its origin in the upper mantle of the earth. These volatile elements are gases either dissolved in the melt or as bubbles of gas that escape when the rock reaches the surface and solidifies. Volcanoes erupt because magma is less dense than the solid rocks surrounding it in the mantle of the earth. As it nears the surface, the volatile gases expand and boil out of the rock, and this force of explosion propels lava from the vent.

WHAT?

Magma is composed of silicates, or combinations of other chemical elements with silicon and oxygen. The amount of silica (SiO2) controls the viscosity, or the resistance of a substance to flow. The higher the silica level, the more viscous the magma is. In a magma melt, molecules are polymerized. This means they cluster and form larger complexes by repeated linking of the same molecular groups. The silicon and oxygen atoms in magma are bonded strongly together molecularly. The more bonds there are, the more viscous the magma is. Therefore, the more silica there is in a magma, the more viscous it is. Temperature is also related to viscosity. The hotter a substance is, the less viscous it is, just like those big vats of syrup in dorm cafeterias. Viscosity is important because it determines the type of eruption that will occur, and thus what shape or type of volcano will be formed by the eruptions. Gases are easily released from low viscosity substances. In more viscous magmas, gases are not released easily, and build up. When the pressure builds, a violent eruption can occur. Differences in eruptions based on the composition of the magma produce different type of volcanoes (figure 1).

Low viscosity lavas produce shield volcanoes, named after their appearance, which is much like a Roman shield. They have relatively little explosive activity, and are characterized by lava flows, which create their slowly sloping sides of 15° or less. Lava flows are distinguished by the Hawaiian terms pahoehoe, referring to the smooth and curving pattern appearance, created when the top crust of the lava is pulled and twisted by the flow beneath it, and aa, an exceedingly rough rubbly surface with angular and jagged fragments (figure 2).

figure 2

Shield volcanoes have broad summit areas because of these flows, and are some of the largest volcanoes.

High viscosity magmas tend to produce taller, steeper, more explosive volcanoes. Cinder cones are relatively small volcanoes, with steep slopes of 30° to 40°. The eruptions consist of steaming gases that carry with them pyroclastic rocks, or material ejected from volcanoes as solid fragments. Stratovolcanoes are also produced by high viscosity magmas. The viscosity level makes the lava more brittle, and while some pyroclastic material is emitted, molten rock also escapes. This combination produces a higher structure. Stratovolcanoes are constructed from multiple eruptions of this nature, creating a layered and very high structure. Lava domes are formed by the slow extrusion of highly viscous magma. They are usually formed by a large explosion caused by the built-up pressure of the gases trapped in the thick molten rock, but after that, when the gas pressure is decreased, the magma oozes out slowly. Before 1980, Mount Saint Helens was an example of a stratovolcanoe. Since its massive explosion in that year, a lava dome has grown up inside the crater that that event left.

WHERE?

Volcanoes can occur solitarily or in belts and chains. The location of these volcanoes splits them into three groups. Rift volcanoes, subduction volcanoes, and hot spot volcanoes. This has a lot to do with plate tectonics, or moving of the segments of the earth's lithosphere.

· Rift volcanoes occur where the plates are moving away from each other. They fill the separations with lava flows, creating new sea floor and mountain ridges beneath the waves.

· Subduction volcanoes form where the plates collide and slide over each other. They create ridges and peaks. The Ring of Fire is a famous chain of volcanoes that rim the Pacific Ocean. About 1,000 live subduction volcanoes occur in this ring, and in any one-year, approximately 40 will be in some state of eruption. The Ring of Fire is composed of stratovolcanoes, which normally occur in chains, and account for over 95% of the world's active volcanoes (figure 3).

· Hot spot volcanoes are the exception to the rule of volcanoes occurring along plate margins. There are constant zones of magma within the earth in some places beneath the plates. The magma pierces through the plate. As time passes and the plates move, new volcanoes appear, and the extinct volcanoes are carried away with the drift of the plates. The common forms of hot spot volcanoes are shield volcanoes, like Mauna Loa of the Hawaiian Islands.

Many factors determine the location, appearance, and amount of activity of each volcano. The location and consistency of magma determine the type of explosion, which determine the type of volcano that is formed.

The Societal Effects of Volcanoes

Volcanoes are known for their violent eruptions and lava flows, but there are many benefits that volcanoes provide for society. Volcanoes help enrich soil for farming and in some cases provide reservoirs for the storage of ground water (Chester 186). Moreover the earth's valuable resources are formed in volcanoes. These elements include fluorine, sulfur, zinc, copper, lead, arsenic, tin, molybdenum, uranium, tungsten, silver, mercury, and gold (Chester 186). Society makes use of all of these elements that volcanoes help to provide. Geothermal power is an alternate energy source that is better for the environment and volcanoes provide this to society also. Volcanoes even help us understand past civilizations and cultures. The lava preserves fossils and artifacts that scientists can learn from (Chester 186). The picture below is a fossilized fish that was preserved by volcanoes.

There are five gases that are produced by volcanic activity. All of these gases are harmful except for water vapor. These five gases are water vapor, carbon dioxide, sulfur dioxide, fluorine, and chlorine. Carbon dioxide is one of the main causes of the Greenhouse effect, but there are not significant amounts for the carbon dioxide emitted from volcanic eruptions to contribute to the Greenhouse effect. Humanity is responsible for emitting 110 billion tons of carbon dioxide each year, while volcanoes only contribute 10 billion tons (Fisher). Sulfur dioxide can have a short-term effect on the weather. A sulfuric acid aerosol can remain in the atmosphere for years after an eruption (Fisher). This aerosol blocks the sun and causes cooler temperatures globally. The sulfur dioxide eventually depletes, but is replenished by each eruption rich in sulfur dioxide. Fluorine can be a deadly to animals after an eruption. It tends to condense in rain and coat grasses and plants (Fisher). The fluorine is poisonous to animals that eat the fluorine-coated grass and plants. Chlorine is emitted as hydrochloric acid into the atmosphere. Chlorine destroys the ozone layer that protects the DNA of plants and animals (Fisher). Water vapor is the only one of these gases that helps society by replenishing the water supply.

There are many hazards from volcanic eruptions. The different kinds of hazards can be lava flows, pyroclastic fall deposits, volcanic gases, tsunamis, and many more (Chester 193). Lava flows have killed a relatively small number of people. The majority of the damage to society from volcanoes is economic, agricultural, and settlements can be ruined (Chester 186). The damages can be increased with the change of human population is certain areas. The more people that live in hazardous areas, the higher the risk is.

A way to limit the hazards is the prediction of eruptions. There are two options for predicting volcanic activity: general prediction and specific prediction. General prediction is the study of past volcanic activity that can predict the frequency, magnitude, and style of eruptions (Chester 196). Specific prediction focuses on predicting the actual time of eruptions. This time is found based on surveillance of the volcano and monitoring its changes (Chester 194). The success of prediction depends on a lot of time and money that puts more advanced nations ahead of the poorer countries.

Many people believe that there is action that should be taken on an international level to improve the monitoring of volcanoes. They propose that we use satellites to keep an eye on the shape of volcanoes. Mass production of seismographs, tiltmeters, and gas detectors would observe seismic activity, ground deformation, and gas emission (Chester 192). These advancements would possibly help to figure out how volcanic plumbing works. Scientists also suggest that we test climatic change and study ice cores to find emissions from past eruptions (Chester 192). All of these options would help us maintain a low risk factor for future eruptions.

Discussion

Volcanoes provide a multitude of benefits that unfortunately bring high risks with them. Do volcanoes have a positive or negative effect on society? The answer to this question does not have a black and white answer. There are the positive effects of enriched soil and their help in creating earth's early atmospheres and minerals. The negative effects seem to over power the positive ones on the short term. The risk of possible death and serious injury is frightening, but not that common of an effect. The real negative effects come from the gases emitted during volcanic eruptions. Chlorine and sulfur dioxide are extremely harmful to the Earth and its environment, but man needs to stop polluting to help limit the effects of volcanoes.

The eruptions of Mount St. Helens in 1980 are a good example of the effects on society of volcanic activity. On March 27, 1980 Mount St. Helens erupted, creating an ash plume about two kilometers above the volcano and an eighty-meter wide crater (Tilling 99). In the next few weeks there were more violent eruptions that emitted and ash column 24 kilometers into the atmosphere and approximately 1.1 kilometers of ash was ejected (Tilling 99). The human casualties of these eruptions are 57 lives lost, and numerous injuries. There was over $1 billion dollars in damages to the communities surrounding Mount St. Helens. Many communication and transportation systems were disrupted due to the eruptions. The tourist industry was greatly effected immediately following the eruptions, but now the volcano has become a tourist attraction.

Volcanoes are natural wonders that should be appreciated and studied. As a society we need to make the best use of the resources that volcanoes provide for us. There are many negative effects, but there are a few positive ones too. We also need to be careful to limit the hazards of volcanoes as much as possible.

VOCABULARY

Magma - a mass of completely or partly molten rock containing volatile materials either dissolved in the melt, or as bubbles of gas.

Lava - molten rock at the surface of the earth.

Viscosity - the "stickiness" or resistance of a substance to flow. The inverse of fluidity. The viscosity of magma depends on the chemical composition, silica content, amount and condition of gas in it, the amount of solid being carried by it, and the temperature

Pyroclastic material - material ejected from volcanoes as solid fragments

BIBLIOGRAPHY

Decker, Robert W. and Barbara B. Mountains of Fire. Cambridge University Press. Cambridge: 1991.

Francis, Peter. Volcanoes - A Planetary Perspective. Oxford University Press. Oxford: 1993.

MacDonald, Gordon A. Volcanoes. Prentice Hall, Inc. Eglewood Cliffs: 1972.

http://www.dc.peachnet.edu/~pgore/geology/goe101/volcb.html

http://www.volcav.si.edu/gvp/

http://magic.geol.ucsb.edu/~fisher/volcano.html