Volcanoes often vary in terms of shape and structure. Some volcanoes can be small, cone-shaped, or some can be characterized as simply cracks in the earth’s crust where lava and other volcanic materials erupt; some volcanoes can be large and shaped like domes, shields; and lastly, there are volcanoes that are shaped like a mountain with a matching crater or a system of craters on its summit. There are numerous mechanisms how volcanoes are formed: the most common type of volcanism (mechanism how volcanoes are formed) is hot spot volcanism.
Most volcanoes are formed when an unusual magma activity forms in the lower mantle. Because magmas are basically hot molten rock beneath the earth’s surface, they are bound to expand. As they expand, they push up into the upper mantle. As the deposition of more magma from the lower mantle continues, a hot spot of magma gets created . The process continues for thousands or even millions of years until a volcano visible on the earth’s surface get created. The volcanoes that can be found in Hawaii can be perfect examples of volcanoes formed via this type of mechanism .
When volcanoes erupt, they release materials such as volcanic gases, lava, and volcanic ash. The destructive power of the earth’s volcanoes greatly varies. There are some volcanoes that are dormant; some are more active. There are active volcanoes that explode more violently than the others just like how there are active volcanoes whose explosions can be hardly felt or unseen. The factor that makes all the difference in the earth’s volcanoes’ explosive and destructive power is the composition of the magma inside it. When volcanoes erupt, the volcanic materials inside it basically get catapulted out into the atmosphere.
The next question now would be what materials are there inside a volcano? The answer is it differs. When volcanoes erupt, they emit volcanic gases. Volcanic gases are mainly composed of water vapor, carbon dioxide, and sulfur dioxide. Some volcanic eruptions may also include other gases like hydrogen chloride, hydrogen sulfide, and hydrogen fluoride. Volcanic ash or highly pulverized volcanic rocks may also be released. This may be seen as a cloud of black smoke surrounding the volcano. The size of the cloud often depends on the explosiveness of the eruption.
The worst possible aftermath of a volcanic eruption is a phenomenon called a volcanic winter. A volcanic winter is an event wherein the climate and temperature regulation cycle in the earth gets extremely disrupted as a result of a major or catastrophic volcanic eruption. This is often caused by the deposition of huge volumes of volcanic ash in the atmosphere that occludes the sun making the average temperature on the lower part of the atmosphere drop.
The heat that often radiates up from the lower atmosphere also gets absorbed by the ash cloud which makes the average temperature on the upper part of the atmosphere higher . The overall result is a volcanic winter. Some of the theorized results of a volcanic winter are famine , the death of livestock animals, and even mass extinction.
Average volcanic eruptions do not produce such violent effects or aftermaths. On average, volcanoes should only emit ash deposits on the atmosphere that would only affect a small to medium area around the vicinity of the explosion. The new deposits of lava as a result of the explosion may also cover existing structures near the foot of the volcano.
Foulger, G. "Are "hot spots" hot spots Abstract." Journal of Geodynamics (2012): 1-28.
Rafferty, J. "Volcanic Winter." Britannica Encyclopaedia (2014): http://www.britannica.com/EBchecked/topic/1559899/volcanic-winter.
SDSU. "Intraplate Volcanism." SDSU (n.d.): http://www.geology.sdsu.edu/how_volcanoes_work/intraplvolc_page.html.
Zhang, D., R. Blender and K. Fraedrich. "Volcanoes and ENSO in millennium simulations: global impacts and regional reconstructions in East Asia Abstract." Theoretical and Applied Climatology (2013): 437.