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In February of 1942, [br]Mexican farmer Dionisio Pulido

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thought he heard thunder [br]coming from his cornfield.

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However, the sound wasn’t coming [br]from the sky.

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The source was a large, smoking crack [br]emitting gas and ejecting rocks.

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This fissure would come to be known as [br]the volcano Paricutin,

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and over the next 9 years, its lava [br]and ash would cover over 200 square km.

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But where did this new volcano come from,

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and what triggered [br]its unpredictable eruption?

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The story of any volcano [br]begins with magma.

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Often, this molten rock forms [br]in areas where ocean water

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is able to slip into the Earth’s mantle [br]and lower the layer’s melting point.

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The resulting magma typically remains [br]under the Earth’s surface

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thanks to the delicate balance [br]of three geological factors.

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The first is lithostatic pressure.

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This is the weight of the Earth’s crust [br]pushing down on the magma below.

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Magma pushes back with the second factor, [br]magmastatic pressure.

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The battle between these forces [br]strains the third factor:

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the rock strength of the Earth’s crust.

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Usually, the rock is strong enough [br]and heavy enough

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to keep the magma in place.

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But when this equilibrium is thrown off, [br]the consequences can be explosive.

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One of the most common causes [br]of an eruption

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is an increase [br]in magmastatic pressure.

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Magma contains various elements [br]and compounds,

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many of which are dissolved [br]in the molten rock.

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At high enough concentrations, compounds [br]like water or sulfur no longer dissolve,

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and instead form [br]high-pressure gas bubbles.

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When these bubbles reach the surface,

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they can burst with the force [br]of a gunshot.

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And when millions of bubbles [br]explode simultaneously,

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the energy can send plumes of ash [br]into the stratosphere.

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But before they pop, they act [br]like bubbles of C02 in a shaken soda.

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Their presence lowers [br]the magma’s density,

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and increases the buoyant force [br]pushing upward through the crust.

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Many geologists believe this process [br]was behind the Paricutin eruption

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in Mexico.

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There are two known natural causes [br]for these buoyant bubbles.

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Sometimes, new magma [br]from deeper underground

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brings additional gassy compounds [br]into the mix.

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But bubbles can also form [br]when magma begins to cool.

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In its molten state, magma is a mixture[br]of dissolved gases and melted minerals.

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As the molten rock hardens, some of those [br]minerals solidify into crystals.

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This process doesn’t incorporate [br]many of the dissolved gasses,

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resulting in a higher concentration [br]of the compounds

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that form explosive bubbles.

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Not all eruptions are due [br]to rising magmastatic pressure—

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sometimes the weight of the rock [br]above can become dangerously low.

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Landslides can remove massive quantities [br]of rock from atop a magma chamber,

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dropping the lithostatic pressure [br]and instantly triggering an eruption.

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This process is known as “unloading”

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and it’s been responsible [br]for numerous eruptions,

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including the sudden explosion [br]of Mount St. Helens in 1980.

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But unloading can also happen [br]over longer periods of time

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due to erosion or melting glaciers.

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In fact, many geologists [br]are worried that glacial melt

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caused by climate change [br]could increase volcanic activity.

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Finally, eruptions can occur when [br]the rock layer is no longer strong enough

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to hold back the magma below.

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Acidic gases and heat escaping from magma

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can corrode rock through a process [br]called hydrothermal alteration,

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gradually turning hard stone [br]into soft clay.

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The rock layer could also be weakened [br]by tectonic activity.

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Earthquakes can create fissures [br]allowing magma to escape to the surface,

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and the Earth’s crust [br]can be stretched thin

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as continental plates [br]shift away from each other.

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Unfortunately, knowing [br]what causes eruptions

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doesn’t make them easy to predict.

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While scientists can roughly determine [br]the strength and weight

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of the Earth’s crust,

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the depth and heat of magma chambers [br]makes measuring changes

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in magmastatic pressure very difficult.

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But volcanologists are constantly [br]exploring new technology

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to conquer this rocky terrain.

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Advances in thermal imaging [br]have allowed scientists

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to detect subterranean hotspots.

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Spectrometers can analyze [br]gases escaping magma.

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And lasers can precisely track the impact [br]of rising magma on a volcano’s shape.

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Hopefully, these tools will help us better[br]understand these volatile vents

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and their explosive eruptions.