- What is a Volcano?
A volcano can be described as a mountain that leads to a pool of molten rock present below the surface of the earth. Upon building up of enough pressure, an eruption of the molten lava occurs. Eruptions can cause lava flows, hot ash flows, lateral blasts, avalanches, mudslides, falling ash, and floods. Tsunamis and earthquakes are also possible consequences of such volcanoes (Wicker).
- Formation of Volcanoes
When the magma from the Earth’s interiors erupts to form lava deposits and ash flows on the surface due to pressure, a volcano is said to have been formed. As eruption continues, the magnitude of the volcano also grows.
- Categories of volcanoes
There are three categories of volcanoes: active, dormant, and extinct.
- An active volcano has erupted just recently and would do so again in future too.
- A dormant volcano is one that has not erupted in a while, but it could do so in the future.
- An extinct volcano is one that erupted hundreds of years back and will not erupt in future.
- Causes for Eruption of a Volcano
The Earth’s crust comprises a number of plates. When these plates move, friction is caused leading to volcanoes and earthquakes. The theory that explains such plate movement is called plate tectonics.
Figure 1: Volcanic Eruption
- Types of Volcanoes
Volcanoes are classified as four: cinder cones, shield volcanoes, composite volcanoes, and lava volcanoes.
Cinder Cones: These are formed when lava in the form of oval cones deposits around the vent after having been blown our through the vent.
Shield Volcanoes: They contain a shield in the middle surrounded by gentle slopes of basalt lava.
Composite Volcanoes: The volcanoes contain a number of layers f rocks that have erupted and deposited as steep-sided mountains.
Lava Volcanoes: When the lava erupting is too hick that it cannot flow, it gets accumulated near the vent leading to formation of mounds with steep sides.
- What Are Lava and Magma?
The liquid rock present within a volcano is called magma and when the magma flows out of the volcano, it is called lava.
According to Rampino et al., an association has been found between cooling trends that exist for decades together and volcanic eruptions. For example, when there are variations in climate, there is shifting of water and ice masses. This, in turn, may cause the axial and spin rate changes that result in a situation that favors volcanic eruptions.
- Volcanoes and Health Hazards
- Tephra and Ash Falls
Ash is the term used to denote particles that are larger than 2 mm, while tephra is the term used to denote volcanic particles that are fragmentary in nature. Tephra contribute to a number of health issues in people especially due to inhalation, abrasion of skin, and building collapse when accumulated on roofs. It also contributes to detrimental aquatic and terrestrial environments (Oppenheimer).
Tephra might contain fluorine also emitted from volcanoes. When this tephra containing fluorine falls on the ground, it causes health hazards when consumed by grazing animals.
Volcanic ash also contains silica thus, posing dangers in the form of silicosis and chronic obstructive pulmonary disease to humans.
- Pyroclastic Density Currents
Pyroclastic density currents (PDCs) also known as pyroclastic flows constitute a mixture of hot gas and tephra (Sigurdsson). These PDCs have also been monitored to cause deaths in human populations. The deaths may be a result of asphyxia when the ash plugs the airways, thermal lung injuries, and due to thickness burns.
The only way to avert the risks due to PDCs would be prior evacuation as from the sites during the 1980s eruption of Mount St Helens and the volcano eruptions of the Soufrière Hills.
- Volcanic Landslides
Volcanoes tend to collapse as they are built of loose ash and lava that are not consolidated together. Thus, heavy rainfalls or seismic occurrences cause landslides of volcanoes. These landslides cause vast damage to property and lives. If the displacement on the erupting surface occurs on sea beds, then tsunamis are triggered.
- Lahars (Volcanic Mudflows)
The Indonesian term to denote a volcanic mixture of rock debris and water is Lahar. Debris avalanches, rainfall on volcanic eruptions, material that is loosely consolidated, and the melting of snow by pyroclastic mass that is very hot are reasons for the formation of Lahars. Lahars can travel at high speeds. For example, the Lahars formed at the eruption of Nevado del Ruíz in 1985 resulted in a probable number of 22,800 deaths. Lahars travelled at very high speeds of 60 km per hour causing penetrating wound and fractures in populations also apart from deaths.
- Air Pollutants from Volcanoes
A number of air pollutants are emitted from volcanoes such as CO and CO2, SO, HCl, H2S, and radon. Sulfate aerosols emitted from volcanoes cause a number of ailments when humans are exposed to them. Carbon dioxide that accumulates in wells and trenches results in death due to asphyxiation. The respiratory, nervous, and cardiovascular systems are impacted negatively by accumulation of volcanic H2S.
- What Are Hotspot Volcanoes?
While the origin of most volcanoes is at the collision zones of tectonic plates, hotspot volcanoes have their origins at the center of the plates. There are various complicated interactions between hot plumes that arise from deep within the earth and the upper mantle that result in such hotspot volcanoes.
A group of researchers (Scott et al.) have recently found out that finger-like structure actually influence the rising plumes. These finger-like structures are found deep below the Earth’s oceanic plates and carry much more heat energy than the surrounding areas. The new research has exposed the depth and shapes of these channels that give rise to plumes eventually leading to the eruption of hotspot volcanoes. "The exact nature of those interactions will need further study," said French (UC Berkeley graduate student leading the research), "but we now have a clearer picture that can help us understand the 'plumbing' of Earth's mantle responsible for hotspot volcano islands like Tahiti, Reunion and Samoa."
- Conclusion
Thus, volcanoes erupt due to changes in tectonic plates. Research has recently indicated climate changes to be influencing the volcanic eruption, but these climate changes must exist for decades together to cast an effect. Recent research has investigated seismic waves that led to the discovery of long finger-like structures that have higher temperatures than surrounding areas. These finger-like structures are seen to give rise to hotspot volcanoes.
Works Cited
French, Scott, Lekic, Vedran, and Romanowicz, Barbara. “Waveform Tomography Reveals Channeled Flow at the Base of the Oceanic Asthenosphere.” Science, 2013
Oppenheimer, Francis, Volcanoes.. Oxford: Oxford University Press, 2004.
Rampino, Michael R., Self, Stephen and Fairbridge, Rhodes W. “Can Rapid Climatic Change Cause Volcanic Eruptions?” Science, 206.4420 (1979), 826-829. Print.
Sigurdsson H. ed. Encyclopedia of Volcanoes. San Diego, CA: Academic Press, 2000.
Wicker, Crystal, Weatherwizkids, 2013, Web. 20 Oct. 2013.
