destruction at Pompeii.

But volcanoes can be bigger, badder, and have wider-ranging effects than you might expect.

The aftermath of huge volcanic eruptions can cause other natural disasters or widespread

cooling, and they've even altered the DNA of a disease-causing bacterium.

A volcano is a vent that allows molten rock – called magma when it's underground and

lava above ground – to be squeezed out onto Earth's surface.

And when they form, it's literally Earth-changing.

When two sections of the Earth's crust, called tectonic plates, move away from each

other, there's room for magma to flow up and make new crust.

That's how the mid-ocean ridges were formed!

Or, when two tectonic plates move toward each other, the denser plate might sink below the

other one, and melt as the temperature increases.

In both cases, sometimes magma seeps up to the surface through vents or cracks called

fissures – and, hello, volcano!

Volcanoes can also form over hotspots – super hot areas below the Earth's crust, which

can melt tectonic plates.

And as the plates move, the hotspots stay put.

So they can form a chain of volcanoes, like the Hawaiian islands.

The basic signs of volcanic activity are lava flows and heat – but that's only the beginning.

More explosive eruptions can spew lots of particles and gases into the atmosphere…

which, as you might imagine, can mess stuff up.

Now, some of those chemicals are well-known greenhouse gases, like carbon dioxide.

Volcanic eruptions nowadays currently release less than a percent of the carbon dioxide

released by human activities.

But millions of years ago, it's possible that lots of extreme volcanic eruptions contributed

to global warming, and its evil twin: ocean acidification.

See, carbon dioxide in the atmosphere can also dissolve in the oceans, making them highly

acidic and dangerous to all kinds of marine creatures.

More recent eruptions can have big effects, too.

Like, take sulfur dioxide.

When it enters the stratosphere, it can react with water vapor to form a bunch of droplets

of sulfuric acid, which can reflect solar radiation and cause cooling of the lower atmosphere.

Depending on how big the eruption is, these sulfur aerosols can float around in the stratosphere

for a while, along with all the tiny particles of ash.

This cooling can affect huge regions of the globe, causing volcanic winters.

And if that doesn't sound concerning enough, big volcanic eruptions can also prevent raindrops

from forming, and lead to drought.

See, a raindrop forms when water molecules hitch onto a tiny particle of dust, until

the drop gets big enough and can't float in the air anymore.

But when there's all this extra stuff up there, like ash or other particles, the water

in a cloud gets spread out over too many droplets.

Each droplet takes longer to grow, so more water stays up in clouds instead of falling

as rain.

And that's not the only water-related problem… volcanoes can also cause tsunamis.

Big underwater eruptions, volcanic collapses, or the hot debris that explodes from volcanoes

into the ocean can form massive waves.

The Krakatoa eruption in 1883, for example, caused the largest volcanic tsunami on record

– the biggest waves were around 40 meters tall, and affected sea levels all over the

world.

Basically, volcanoes can spawn all kinds of disasters.

And the bigger the eruption, the bigger the consequences.

So let's take a look at the most destructive volcanic eruption since humans have been on

Earth:

In 1815, Mount Tambora in Indonesia erupted and spewed out some 150 cubic kilometers of

ash, plus lots of other junk into the atmosphere.

It was incredibly destructive for the local population, of course – but it also had

global effects.

The particles from that volcano hung around in the atmosphere for two years, cooling global

temperatures as much as 3° Celsius, and giving 1816 the nickname: “the year without a summer.”

Plants need sunlight and heat to grow, and humans depend on crops for food.

So, less sun, extra frost, and cold summers – even as far as North America and Europe

– meant famine that spanned most of the globe.

This eruption also altered the course of a disease.

The sulfur aerosols released by the eruption affected the climate in India: first there

was drought, and then some late flooding.

This weird weather changed the ecology in the Bay of Bengal, giving rise to a new strain

of cholera bacteria – the kind that infects your intestine and causes diarrhea, dehydration,

and sometimes death.

Cholera used to be contained within the Ganges delta, but this mutant strain spread and took

the world by storm.

Today, there are millions of cases of the disease each year.

But among all the disastrous impacts worldwide, the bizarre weather also made for a wet, yucky

vacation at Lake Geneva – where Mary Shelley and her author companions were staying.

The gloom gave her inspiration and time to write the novel Frankenstein.

So, volcanoes: not just the mother of disasters, but also the mother of monsters.

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