In February of 1942, Mexican farmer
Dionisio Pulido thought he heard thunder coming from his cornfield. However,
the sound wasn’t coming from the sky. The source was a large, smoking crack emitting
gas and ejecting rocks. This fissure would come to be known as the volcano
Paricutin, and over the next 9 years, its lava and ash would cover over 200
square km.
Magma:-
But where did this new volcano come
from, and what triggered its unpredictable eruption? The story of any volcano begins
with magma. Often, this molten rock forms in areas where ocean water is
able to slip into the Earth’s mantle and lower the layer’s melting point. The
resulting magma typically remains under the Earth’s surface thanks to the
delicate balance of three geological factors.
Litho-static pressure:-
The first is litho-static pressure. This
is the weight of the Earth’s crust pushing down on the magma below. Magma
pushes back with the second factor, magma static pressure.
The battle between these forces strains
the third factor: the rock strength of the Earth’s crust. Usually, the rock is
strong enough and heavy enough to keep the magma in place. But when this
equilibrium is thrown off, the consequences can be explosive. One of the most
common causes of an eruption is an increase in magma static pressure.
Magma contains various elements and
compounds, many of which are dissolved in the molten rock. At high enough
concentrations, compounds like water or sulfur no longer dissolve, and instead
form high-pressure gas bubbles. When these bubbles reach the surface, they can
burst with the force of a gunshot. And when millions of bubbles explode
simultaneously, the energy can send plumes of ash into the stratosphere. But
before they pop, they act like bubbles of C02 in a shaken soda. Their presence
lowers the magma’s density, and increases the buoyant force pushing upward
through the crust.
Many geologists believe this process was
behind the Paricutin eruption in Mexico. There are two known natural causes for
these buoyant bubbles. Sometimes, new magma from deeper underground brings
additional gassy compounds into the mix. But bubbles can also form when magma
begins to cool. In its molten state, magma is a mixture of dissolved gases and
melted minerals. As the molten rock hardens, some of those minerals solidify
into crystals. This process doesn’t incorporate many of the dissolved gasses, resulting
in a higher concentration of the compounds that form explosive bubbles.
Eruption due to unloading:-
Not all eruptions are due to rising
magma static pressure— sometimes the weight of the rock above can become
dangerously low. Landslides can remove massive quantities of rock from atop a
magma chamber, dropping the litho-static pressure and instantly triggering an
eruption. This process is known as “unloading” and it’s been responsible
for numerous eruptions, including the sudden explosion of Mount St. Helens
in 1980. But unloading can also happen over longer periods of time due to
erosion or melting glaciers. In fact, many geologists are worried that glacier
melt caused by climate change could increase volcanic activity.
Finally, eruptions can occur when the
rock layer is no longer strong enough to hold back the magma below. Acidic
gases and heat escaping from magma can corrode rock through a process called hydrothermal
alteration, gradually turning hard stone into soft clay. The rock layer
could also be weakened by tectonic activity. Earthquakes can create fissures allowing
magma to escape to the surface, and the Earth’s crust can be stretched thin as
continental plates shift away from each other.
Prediction of an eruption.
Unfortunately, knowing what causes
eruptions doesn’t make them easy to predict. While scientists can roughly
determine the strength and weight of the Earth’s crust, the depth and heat of
magma chambers makes measuring changes in magma static pressure very difficult.
But volcanologists are constantly exploring new technology to conquer this
rocky terrain. Advances in thermal imaging have allowed scientists to detect
subterranean hotspots.
Spectrometers can analyze gases escaping magma. And
lasers can precisely track the impact of rising magma on a volcano’s shape. Hopefully,
these tools will help us better understand these volatile vents and their explosive
eruptions.
Comments
Post a Comment
Do comments, on which topic do you want the next blog from us i.e. CBSESolver