A fissure or crack in a planet’s surface that gives way for the molten lava, gases, and ash to erupt from below is known as a volcano. The very word 'volcano' has been derived from the name of the Roman God of Fire ‘Vulcan’. Volcanoes are divided into three major categories, namely, active, dormant, and extinct. An active volcano is one that erupts frequently, though the lifespan may vary from months to several billion years. Mount St. Helens in United States, Mount Damavand in Iran, and Colima Volcano in Mexico are some active volcanoes. A volcano is said to be dormant when it has not erupted for many years but still has the potential to erupt anytime. Mount Kea in Hawaii was last seen erupting in 2460 BC and since then, it has been sleeping. The last category is the extinct volcano type that is unlikely to erupt again because of lack of lava supply. The Hawaiian – Emperor seamount chain in the Pacific Ocean, Hohentwiel, Shiprock and the Zuidwal volcano in the Netherlands are some examples of extinct volcanoes. However, knowing the categories and differentiating the volcanoes still does not solve a major question - how does a volcano erupt? Glance through the lines below to know how is a volcano formed and how does it erupt.
How Does A Volcano Erupt
The earth’s crust is just a small part of the total volume of earth. Beneath the continents that we live on, there lies a 30 km thick crust. This thickness reduces to 10 km below the ocean floor. Below the crust lies the earth’s mantle. Although this mantle is solid rock, it is under extreme high pressures and temperatures, that can reach to even more than 1000°C due to which the mantle can sometimes melt and start squeezing out of the cracks in the rock. This molten rock is called magma. This, then, collects into the vast chambers below the earth’s crust. Compared to the surrounding rock, the melted magma is less in density and hence, floats up to the surface peeping through cracks and fissures in the rock.
Gradually, this magma pushes upwards with intense force. As such, the intense heat melts more rock, thereby adding to the magma mixture. This magma, in turn, starts moving through the crust until the upward pressure exceeds the downward pressure of the surrounding solid rock. As a result, the magma starts collecting in the magma chambers just below the surface of the earth. When the magma pressure reaches to a sufficient high level, the crack opens up in the crust, thereby forcing the molten rock to explode through the earth’s surface. At this point, the magma flows out, which is known as lava, thus, forming a volcano. As a result, what we see spewing through the cracks is a volcanic eruption. The erupting lava is accompanied by ash and volcanic rocks.
The nature of volcanic eruption largely depends on the gas content and the viscosity of the magma material. In case the magma has a high viscosity, the gas bubbles will have a hard time escaping from the magma, thereby pushing up more material and leading to a bigger explosion. However, if the viscosity of the magma is low, the gas bubbles can escape from the magma easily and hence, the lava would not be able to erupt with intense pressure. To add on, this viscosity is often balanced off with the gas content. Say, for instance, if the magma contains more bubbles, the eruption will be violent. On the other hand, if it contains less gas, the lava will erupt calmly. While viscosity depends upon the proportion of silicon found in the magma due to its reaction with oxygen, gas content varies on what kind of material was melted to form the magma.
When the viscosity and gas levels are high, the eruptions from the magmas are highly explosive and destructive. Contrarily, the most subdued eruptions occur from magmas with low gas levels and low viscosity. However, volcanic eruptions never fall into easy categories. As such, eruptions depend upon several stages with varying amounts of destructions at each stage. When the viscosity and gas pressure is low, lava erupts slowly and gradually flows down the surface, thereby leading to minimum explosion. In such a situation, humans have enough time to move away due to the slow speed of such eruptions. However, if the gas has great amounts of pressure, the volcano results in an explosive launch, causing hot gas, ash, and pyroclastic rocks to spread all over.
This is how a volcano erupts and causes the lava to flow onto the surface of earth. Besides, there are different types of eruptions, namely, plinian eruption, Hawaiian eruption, strombolian eruption, vulcanian eruption, hydrovolcanic eruption, and fissure eruption.