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  • 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.

  • 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.

  • The first is lithostatic pressure.

  • This is the weight of the Earth's crust pushing down on the magma below.

  • Magma pushes back with the second factor, magmastatic 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 magmastatic 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.

  • Not all eruptions are due to rising magmastatic pressuresometimes the weight of the rock above can become dangerously low.

  • Landslides can remove massive quantities of rock from atop a magma chamber, dropping the lithostatic pressure and instantly triggering an eruption.

  • This process is known asunloadingand 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 glacial 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.

  • 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 magmastatic 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.

In February of 1942, Mexican farmer Dionisio Pulido thought he heard thunder coming from his cornfield.

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    lauren.huang posted on 2020/10/02
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