People have always compared an erupting volcano to a person slowly getting angry. At first, the person is calm and everything seems to be alright. Then, for one reason or another, some sort of bad news hits or somebody else says the wrong thing. The person then begins to flush and his blood begins to boil. Then, when the person could not contain himself any longer, he explodes into a wild burst of anger. Volcanoes are commonly perceived to erupt in much the same way.
Volcano Eruption
Volcanoes are in the news once again recently, as an Icelandic volcano under the Eyjafjallajokull glacier erupted last April 14. This event did not come as a complete surprise to those who were monitoring the volcano, as there had been an increase in volcanic and seismic activity in the area since December 2009. During that time, thousands of small earthquakes were happening in the area. Nearly 3,000 earthquakes were recorded by early March and magma was beginning to pour out to the surface. An eruption occurred in March 20, but this was a somewhat silent eruption compared to what happened a few weeks later, as it came from a fissure vent instead of underneath the glacier.
The second eruption had been widely publicized due to the massive amount of volcanic ash that spewed out of the volcano, causing flights to be cancelled for a number of days all across northwestern Europe. This resulted to countless stranded travelers all over the world for six days since April 15.
Like when people lose their tempers, volcanic eruptions do not happen as abruptly as we think. They are often a result of a build-up of activity under the Earth’s crust. The mantle, which is directly underneath the crust, is made up of solid rock and is subject to immensely high pressures and temperatures. This area can go beyond 1,000 degrees Celsius. Molten rock, also known as magma, is a result of these pressures and temperatures. The magma collects under vast chambers underneath the crust, after it seeps out of the cracks in the mantle.
A Structure of Typical Volcano and its Geologic Hazard
Diagram obtained from USGS
Magma is less dense than rock. When something is less dense, it floats to the surface. This is best described when oil is poured into water. Therefore, once magma collects under the rocky crust, it will seek out the weak parts of this area. Magma is likely to contain dissolved gases and water. The dissolved gases and water will turn into gas and steam when the magma reaches the surface, and this is what causes a violent eruption. To illustrate this further, it is like shaking a can of soda and popping the tab open. Once magma has reached the surface, it is now called lava.
The shape of a volcano and the nature of its eruption come as a direct result of the lava viscosity that flows out of a volcano. A wide shield volcano is a result of lava that flows out easily. A cone-shaped volcano is a result of a thicker type of lava. If lava is extremely thick, however, it creates a bottle neck and will usually result in violent eruptions.
