[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.88,0:00:12.13,Default,,0000,0000,0000,,In February of 1942, \NMexican farmer Dionisio Pulido
Dialogue: 0,0:00:12.13,0:00:15.96,Default,,0000,0000,0000,,thought he heard thunder \Ncoming from his cornfield.
Dialogue: 0,0:00:15.96,0:00:19.74,Default,,0000,0000,0000,,However, the sound wasn’t coming \Nfrom the sky.
Dialogue: 0,0:00:19.74,0:00:25.44,Default,,0000,0000,0000,,The source was a large, smoking crack \Nemitting gas and ejecting rocks.
Dialogue: 0,0:00:25.44,0:00:29.56,Default,,0000,0000,0000,,This fissure would come to be known as \Nthe volcano Paricutin,
Dialogue: 0,0:00:29.56,0:00:36.71,Default,,0000,0000,0000,,and over the next 9 years, its lava \Nand ash would cover over 200 square km.
Dialogue: 0,0:00:36.71,0:00:39.06,Default,,0000,0000,0000,,But where did this new volcano come from,
Dialogue: 0,0:00:39.06,0:00:43.16,Default,,0000,0000,0000,,and what triggered \Nits unpredictable eruption?
Dialogue: 0,0:00:43.16,0:00:46.69,Default,,0000,0000,0000,,The story of any volcano \Nbegins with magma.
Dialogue: 0,0:00:46.69,0:00:50.82,Default,,0000,0000,0000,,Often, this molten rock forms \Nin areas where ocean water
Dialogue: 0,0:00:50.82,0:00:56.09,Default,,0000,0000,0000,,is able to slip into the Earth’s mantle \Nand lower the layer’s melting point.
Dialogue: 0,0:00:56.09,0:01:00.11,Default,,0000,0000,0000,,The resulting magma typically remains \Nunder the Earth’s surface
Dialogue: 0,0:01:00.11,0:01:04.23,Default,,0000,0000,0000,,thanks to the delicate balance \Nof three geological factors.
Dialogue: 0,0:01:04.23,0:01:06.86,Default,,0000,0000,0000,,The first is lithostatic pressure.
Dialogue: 0,0:01:06.86,0:01:11.78,Default,,0000,0000,0000,,This is the weight of the Earth’s crust \Npushing down on the magma below.
Dialogue: 0,0:01:11.78,0:01:16.57,Default,,0000,0000,0000,,Magma pushes back with the second factor, \Nmagmastatic pressure.
Dialogue: 0,0:01:16.57,0:01:20.50,Default,,0000,0000,0000,,The battle between these forces \Nstrains the third factor:
Dialogue: 0,0:01:20.50,0:01:23.70,Default,,0000,0000,0000,,the rock strength of the Earth’s crust.
Dialogue: 0,0:01:23.70,0:01:26.85,Default,,0000,0000,0000,,Usually, the rock is strong enough \Nand heavy enough
Dialogue: 0,0:01:26.85,0:01:28.92,Default,,0000,0000,0000,,to keep the magma in place.
Dialogue: 0,0:01:28.92,0:01:34.70,Default,,0000,0000,0000,,But when this equilibrium is thrown off, \Nthe consequences can be explosive.
Dialogue: 0,0:01:34.70,0:01:37.42,Default,,0000,0000,0000,,One of the most common causes \Nof an eruption
Dialogue: 0,0:01:37.42,0:01:40.32,Default,,0000,0000,0000,,is an increase \Nin magmastatic pressure.
Dialogue: 0,0:01:40.32,0:01:43.59,Default,,0000,0000,0000,,Magma contains various elements \Nand compounds,
Dialogue: 0,0:01:43.59,0:01:46.74,Default,,0000,0000,0000,,many of which are dissolved \Nin the molten rock.
Dialogue: 0,0:01:46.74,0:01:53.07,Default,,0000,0000,0000,,At high enough concentrations, compounds \Nlike water or sulfur no longer dissolve,
Dialogue: 0,0:01:53.07,0:01:56.89,Default,,0000,0000,0000,,and instead form \Nhigh-pressure gas bubbles.
Dialogue: 0,0:01:56.89,0:01:59.12,Default,,0000,0000,0000,,When these bubbles reach the surface,
Dialogue: 0,0:01:59.12,0:02:02.32,Default,,0000,0000,0000,,they can burst with the force \Nof a gunshot.
Dialogue: 0,0:02:02.32,0:02:05.95,Default,,0000,0000,0000,,And when millions of bubbles \Nexplode simultaneously,
Dialogue: 0,0:02:05.95,0:02:10.20,Default,,0000,0000,0000,,the energy can send plumes of ash \Ninto the stratosphere.
Dialogue: 0,0:02:10.20,0:02:15.50,Default,,0000,0000,0000,,But before they pop, they act \Nlike bubbles of C02 in a shaken soda.
Dialogue: 0,0:02:15.50,0:02:18.36,Default,,0000,0000,0000,,Their presence lowers \Nthe magma’s density,
Dialogue: 0,0:02:18.36,0:02:23.10,Default,,0000,0000,0000,,and increases the buoyant force \Npushing upward through the crust.
Dialogue: 0,0:02:23.10,0:02:28.19,Default,,0000,0000,0000,,Many geologists believe this process \Nwas behind the Paricutin eruption
Dialogue: 0,0:02:28.19,0:02:30.01,Default,,0000,0000,0000,,in Mexico.
Dialogue: 0,0:02:30.01,0:02:33.52,Default,,0000,0000,0000,,There are two known natural causes \Nfor these buoyant bubbles.
Dialogue: 0,0:02:33.52,0:02:36.69,Default,,0000,0000,0000,,Sometimes, new magma \Nfrom deeper underground
Dialogue: 0,0:02:36.69,0:02:40.66,Default,,0000,0000,0000,,brings additional gassy compounds \Ninto the mix.
Dialogue: 0,0:02:40.66,0:02:44.81,Default,,0000,0000,0000,,But bubbles can also form \Nwhen magma begins to cool.
Dialogue: 0,0:02:44.81,0:02:50.15,Default,,0000,0000,0000,,In its molten state, magma is a mixture\Nof dissolved gases and melted minerals.
Dialogue: 0,0:02:50.15,0:02:55.62,Default,,0000,0000,0000,,As the molten rock hardens, some of those \Nminerals solidify into crystals.
Dialogue: 0,0:02:55.62,0:02:59.62,Default,,0000,0000,0000,,This process doesn’t incorporate \Nmany of the dissolved gasses,
Dialogue: 0,0:02:59.62,0:03:02.91,Default,,0000,0000,0000,,resulting in a higher concentration \Nof the compounds
Dialogue: 0,0:03:02.91,0:03:06.36,Default,,0000,0000,0000,,that form explosive bubbles.
Dialogue: 0,0:03:06.36,0:03:10.33,Default,,0000,0000,0000,,Not all eruptions are due \Nto rising magmastatic pressure—
Dialogue: 0,0:03:10.33,0:03:15.06,Default,,0000,0000,0000,,sometimes the weight of the rock \Nabove can become dangerously low.
Dialogue: 0,0:03:15.06,0:03:20.23,Default,,0000,0000,0000,,Landslides can remove massive quantities \Nof rock from atop a magma chamber,
Dialogue: 0,0:03:20.23,0:03:25.20,Default,,0000,0000,0000,,dropping the lithostatic pressure \Nand instantly triggering an eruption.
Dialogue: 0,0:03:25.20,0:03:27.92,Default,,0000,0000,0000,,This process is known as “unloading”
Dialogue: 0,0:03:27.92,0:03:30.82,Default,,0000,0000,0000,,and it’s been responsible \Nfor numerous eruptions,
Dialogue: 0,0:03:30.82,0:03:35.54,Default,,0000,0000,0000,,including the sudden explosion \Nof Mount St. Helens in 1980.
Dialogue: 0,0:03:35.54,0:03:39.11,Default,,0000,0000,0000,,But unloading can also happen \Nover longer periods of time
Dialogue: 0,0:03:39.11,0:03:41.76,Default,,0000,0000,0000,,due to erosion or melting glaciers.
Dialogue: 0,0:03:41.76,0:03:45.23,Default,,0000,0000,0000,,In fact, many geologists \Nare worried that glacial melt
Dialogue: 0,0:03:45.23,0:03:49.72,Default,,0000,0000,0000,,caused by climate change \Ncould increase volcanic activity.
Dialogue: 0,0:03:49.72,0:03:54.30,Default,,0000,0000,0000,,Finally, eruptions can occur when \Nthe rock layer is no longer strong enough
Dialogue: 0,0:03:54.30,0:03:56.74,Default,,0000,0000,0000,,to hold back the magma below.
Dialogue: 0,0:03:56.74,0:03:59.94,Default,,0000,0000,0000,,Acidic gases and heat escaping from magma
Dialogue: 0,0:03:59.94,0:04:04.57,Default,,0000,0000,0000,,can corrode rock through a process \Ncalled hydrothermal alteration,
Dialogue: 0,0:04:04.57,0:04:08.45,Default,,0000,0000,0000,,gradually turning hard stone \Ninto soft clay.
Dialogue: 0,0:04:08.45,0:04:12.09,Default,,0000,0000,0000,,The rock layer could also be weakened \Nby tectonic activity.
Dialogue: 0,0:04:12.09,0:04:16.78,Default,,0000,0000,0000,,Earthquakes can create fissures \Nallowing magma to escape to the surface,
Dialogue: 0,0:04:16.78,0:04:19.79,Default,,0000,0000,0000,,and the Earth’s crust \Ncan be stretched thin
Dialogue: 0,0:04:19.79,0:04:23.27,Default,,0000,0000,0000,,as continental plates \Nshift away from each other.
Dialogue: 0,0:04:23.27,0:04:26.22,Default,,0000,0000,0000,,Unfortunately, knowing \Nwhat causes eruptions
Dialogue: 0,0:04:26.22,0:04:28.62,Default,,0000,0000,0000,,doesn’t make them easy to predict.
Dialogue: 0,0:04:28.62,0:04:31.84,Default,,0000,0000,0000,,While scientists can roughly determine \Nthe strength and weight
Dialogue: 0,0:04:31.84,0:04:33.23,Default,,0000,0000,0000,,of the Earth’s crust,
Dialogue: 0,0:04:33.23,0:04:37.01,Default,,0000,0000,0000,,the depth and heat of magma chambers \Nmakes measuring changes
Dialogue: 0,0:04:37.01,0:04:40.39,Default,,0000,0000,0000,,in magmastatic pressure very difficult.
Dialogue: 0,0:04:40.39,0:04:44.30,Default,,0000,0000,0000,,But volcanologists are constantly \Nexploring new technology
Dialogue: 0,0:04:44.30,0:04:46.84,Default,,0000,0000,0000,,to conquer this rocky terrain.
Dialogue: 0,0:04:46.84,0:04:49.75,Default,,0000,0000,0000,,Advances in thermal imaging \Nhave allowed scientists
Dialogue: 0,0:04:49.75,0:04:52.41,Default,,0000,0000,0000,,to detect subterranean hotspots.
Dialogue: 0,0:04:52.41,0:04:55.84,Default,,0000,0000,0000,,Spectrometers can analyze \Ngases escaping magma.
Dialogue: 0,0:04:55.84,0:05:02.10,Default,,0000,0000,0000,,And lasers can precisely track the impact \Nof rising magma on a volcano’s shape.
Dialogue: 0,0:05:02.10,0:05:06.60,Default,,0000,0000,0000,,Hopefully, these tools will help us better\Nunderstand these volatile vents
Dialogue: 0,0:05:06.60,0:05:08.80,Default,,0000,0000,0000,,and their explosive eruptions.