By Raunak Haldipur
Volcanoes are one of the most powerful forces of nature, but the source of its immense power is unseen. This force comes from the heat of the rocks over 15 miles beneath the earth’s surface. Volcanoes are a natural way that the Earth and other planets have of cooling off and releasing internal heat and pressure. A recent study recognising the presence of solid volcanic lava has increased scope for us to understand how and what causes volcanoes to erupt.
Rocks, cracks and magma
Rising magma pushes Earth’s plates apart in the middle of the oceans. Here, and along other weak spots in the plates, hot spots occur. An example of such a hot spot is the Hawaiian Islands. Volcanoes mainly occur along destructive and constructive plate boundaries where plates are pushed together or dragged apart. This tremendous heat melts solid rocks into a white-hot mixture of gas and liquid called magma.
Cracks or weaknesses allow magma to rise up below the Earth’s crust. The gas filled magma is lighter than the unmelted rock, so it rises towards the surface melting gaps in the rock as it rises. It enters a magma chamber, a region of magma that hardened after a past eruption. The magma continues to push and met its way upwards. It pushes through channels of weak, fractured rock, consisting of hardened magma. Eventually, the magma and gas push up to the top of the volcano and blast out through an opening called the central vent.
Lava and tephra
The magma erupts as a fluid called lava or as rock fragments called tephra. Lava can be highly fluid and fast moving, or sticky and slow-moving. Tephra, on the other hand, can be as small as dust or as large as a boulder. Lava cools down to form new rocks. One type of volcano, the composite volcano is formed during successive eruptions of lava and tephra which build a cone around the central vent. Famous composite volcanoes are found in Japan, Italy and USA.
A blessing and hazard?
Volcanoes also have the ability to spew out clouds of thick ash high into the atmosphere. Other than the obvious destruction volcanoes can cause, volcanic ash near active volcanoes is an aviation safety hazard. Volcanic ash is hard, abrasive and can quickly cause significant wear to propellers and turbo-compressor blades. The ash can contaminate fuel and water systems, can jam gears, and make engines flameout. We could see the effect of the Eyjafjallajökull volcanic eruption in 2010 in Iceland and how it caused a disruption in air travel and left thousands of people stranded.
However, volcanoes are also essential for life on our planets. Scientists believe that volcanoes formed the Earth’s first atmosphere by spewing water vapour, sulphur dioxide, nitrogen and carbon dioxide into the air and volcanic eruptions continue to contribute to carbon cycle crucial to life by releasing carbon dioxide. Volcanoes can go through long periods of being very active but they may also become dormant, not erupting for hundreds and thousands of years and eventually they can become extinct, just leaving a cone-shaped hill, never erupting again.
The volcanic discoveries continue
As recent as March 2016, sailors witnessed the birth of an Island due to an underwater volcanic eruption in the middle of the Pacific Ocean. They noticed that the water in the distance had turned a strange colour. As the crew approached, the sea mysteriously turned to stone as the volcano pushed up new land. Before long, the land mass had, as one of the crew described it, bubbled up out of the ocean “like the Sahara with rolling hills of sand as far as the eye could see.”
It has only recently been discovered that most of the magma under volcanoes is solid and becomes molten only when close to eruption. This has been discovered after analysing zircon crystals spewed from volcanic eruptions in New Zealand. It is practically impossible to study magma reservoirs directly since the heat and pressure would destroy any equipment sent below volcanos. This is why geochemists at the University of California studied the zircon crystals from New Zealands Taupo Volcanic Zone to find that most of the magma is solid until just before it erupts.
Magnum of eruption
A team of scientists from Cardiff University has recently found that magma reservoirs are key to volcanic eruptions. By conducting a number of numerical simulations of this process, the research team showed that these large reservoirs are crucial to generating the largest volcanic eruptions on Earth. The team also showed that these large reservoirs can take millions of years to form and this is why ‘super-eruptions’ happen so rarely.
It is believed that these findings could help us understand why some volcanoes erupt frequently and at certain magnitudes. Who knows, in time, scientists may be able to exactly tell the magnitude of the volcano and may even be able to predict when volcanoes are due to erupt.
Featured Image Source: Visual Hunt