Natural Disasters

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Natural Disasters

Types of Volcanoes

According to geologists, there are several types of volcanoes classified based on “geomorphic form, magma chemistry, and explosiveness of the eruption” (Abbott, 2009). Six types of volcanic eruptions include Hawaiian eruption, strombolian eruption, vulcanian eruption, plinian eruption lava domes and surtseyan eruption. The Hawaiian types of volcanic eruption are characterized by fluid basaltic magma that is low in gas hence can flow for miles before cooling down. They mostly begin as a fountain through a vent or a fissure and since they have few gases, the silicon manages to hold together and it flows without becoming explosive. Strombolian eruptions are bursts of lava that is fluid, mostly basaltic andesite, with a lot of gas and bubbles up from the vent for about a few hundreds of meters. Such eruptions are characterized by small lakes of lava and may erupt in several forms such as hardened rocks, spatter and bubbling lava.

Vulcanian on the other hand is violent and explodes up a few kilometers in the air. It is composed of andesite or rhyolite that results from fragmentation and explosion of viscous lava in a vent. Such eruptions are powerful and send their contents far, producing ashy clouds that contain hot gas and rocks that are fluid-like. They are usually not very large and could come before an even bigger eruption. Plinians are usually large and quite explosive. They are induced by fragmenting of gaseous magma that is usually viscous containing rhyolite and dacite. They can release ashes and gaseous clouds that may go as high as 50 kilometers up in the air. They are known to be most destructive as they can send their magma far since it contains a lot of gas, encouraging the explosions. Lava domes are formed when viscous lava containing dacite or even rhyolite is ejected through a vent without exploding. Such lava does not travel far and forms a dome, which usually rises up to a few meters and then falls back. The domes could be destroyed by other building domes. They usually have long, short or bubbly ejections and take different forms depending on the type of rocks. Lastly, surtseyan eruptions are ones that occur when there is a reaction of magma and water, mostly happening in sea. They occur when magma under the sea grows fully to a point of breaking the water surface. The lava or magma from such eruptions is basaltic and creates steam from the water as well as scoria. This is usually referred to as hydromagmatic explosion because water is involved (Ball, 2011).

Volcanoes in Different Regions

There are different types of volcanic eruptions at different intersections of the tectonic plates, which determine the type of magma or eruption that can occur at the particular place (Abbott, 2009). However, there are exceptions such as Hawaii where hotspots cause volcanic activity hence volcanic eruptions. Most volcanic activities are known to occur at plate boundaries where there are activities that trigger friction, causing heat. Converging plates come together and one may move down below the other raising its heat, which causes melting. Hence, magma is formed and travels upward as it is light. Mt St. Helens is one example of such a volcanic eruption. This magma is quite viscous due to high content of silica. Divergent plates usually move from each other in mid oceans. The oceanic crust will then be formed by the molten rock. This way, there is hot molten rock rising through the vents. Islands such as Iceland were formed this way (usgs.gov, 1999).

Volcanoes that Killed People

In the past five hundred years there have been many volcanic eruptions, although majority are in scarcely populated areas hence posing lesser threat. However, there are types that are likely to be most dangerous in terms of their volatility, especially the very explosive ones. An example is the St HelensMountain that explodes releasing ash and gas, which u contributes to explosions. On the other hand, in Hawaii, the eruptions are not as explosive and do not pose much danger but are only effusive. There are long-term casualties or effects of destructive volcanoes such as causing many cloudy ashes in the atmosphere that block sunlight. In addition, many people could die if the explosions reached residential areas (Abbott, 2009). However, considering that today people live in urban areas, explosive places are likely to be less inhabited hence there would not be many casualties. Through scientific predictions, people can be warned before such an eruption occurs. Volcanic gases such as sulfur dioxide can contribute to global cooling. This gas condenses in the stratosphere to form sulfuric acid forming aerosols that radiate the sun back to space causing cooling (usgs.gov, 2011).

Mass Movement Causes

It is important that people understand and distinguish immediate and underlying causes of mass movement since it leads to loss of many lives. Examples of mass movement are landslides, mudslides, avalanches and slumping. Mass movement is usually the movement of large amounts of soil, rock, and weathered materials due to force of gravity that happens in sloped areas, with the major cause being gravitational forces (Abbott, 2009). Distinguishing the causes of mass movement makes it possible for people to plan ways of preventing the mass movement. Underlying causes of mass movement can be stopped before they hit, and evacuations can be done as quickly as possible before immediate causes strike (Abbott, 2009). Underlying movement such as solar radiation and precipitation that causes water to percolate the surface contributes to mass movement. Mass movements cause erosion that continues to weather away rocks causing more risk. Some can be prevented while others cannot. Mass movement on hills near us can be prevented through stopping the immediate causes from influencing the underlying causes. Some examples of mass movements are volcanic avalanches that occur near mountains such as those that happened in Mount St. Helens before an eruption happened where building up lava forced a weak rock to fall off, resulting in an avalanche. Another example is the landslide in El Salvador that was caused by an earthquake. Other examples are snow avalanches in the HimalayasMountain (physicalgeography.net, 2010).

How Volcanic Activities Cause Mass Movement

Volcanic mountains can trigger mass movement in several ways such as causing avalanches on sloped mountains. For instance, in the avalanche of Mt St. Helens, there was magma activity before eruption, causing a weak rock to fall off and sending down a lot of debris (Abbott, 2009). In another way, volcanic eruptions in the sea can cause water to rise to high levels that cause tsunamis that are known to result in many deaths and destruction. Moreover, in high rising volcanoes, some of the rock may not be well held to the slope hence gravity could cause a landslide. In another way, volcanic activities can cause an earthquake, which can trigger landslides, and in snow-capped mountains, there can be avalanches due to heat that melts the ice causing sudden flow of the ice down the mountain. Volcanic activities are also known to cause mudslides when they cause eruption (U.S. Geological Survey Fact Sheet, 2008).

References

Abbott, P.L. (2009). Natural Disasters, 7th ed. New York: McGraw-Hill

Ball, J. (2011). Types of Volcanic Eruptions. Retrieved from http://geology.com/volcanoes/types-of-volcanic-eruptions/

physicalgeography.net. (2010). Hill slope Processes and Mass Movement. Retrieved from http://www.physicalgeography.net/fundamentals/10x.html

usgs.gov. (2011). Volcanic Gases and Climate Change Overview. Retrieved from http://volcanoes.usgs.gov/hazards/gas/climate.php

U.S. Geological Survey Fact Sheet. (2008). What Are Volcano Hazards? Retrieved from http://pubs.usgs.gov/fs/fs002-97/

usgs.gov. (1999). Hot spots: Mantle thermal plumes. Retrieved from http://pubs.usgs.gov/gip/dynamic/hotspots.html