If you were going for a refreshing swim,
the last thing you'd expect
is to suffocate from toxic gases.
But when it comes to Lake Kivu,
this is one dangerous body of water
you wouldn't want to dive into.
Lake Kivu is on the border
of the Democratic Republic of Congo
and Rwanda.
It covers 2,700 sq km (1,042 sq mi)
and is one of the African Great Lakes.
But it has a dangerous twist.
It contains about 55 billion cubic m (1.9 trillion cubic ft) of methane
and carbon dioxide.
The lake sits on top of active
volcanic hot springs.
So these gases accumulate
in the deepest layers of the lake
at a depth of around 300 m (984 ft).
Usually these gases would bubble out.
But because they're so deep
under the lake waters,
they're under high pressure.
That makes them denser
than the layers of water above.
And the gases can't rise to the surface.
But what if this fragile system shattered,
and the toxic gas
suddenly went to the surface?
And what if you happened
to fall into Lake Kivu at that moment?
If you fell into Lake Kivu,
the first thing you'd notice
is how warm it is.
At the surface,
the water temperature is around 24 °C (75.2 °F).
If you were to dive deeper,
you'd be in for a surprise.
Typically, water in a lake gets colder
the deeper you go.
This process is known as convection.
Cold, dense surface water sinks,
while warm less dense water rises.
But in Lake Kivu, it's the opposite.
You'd feel the temperature
rising as you went down.
You'd also notice
that the water divides into two sections.
There's the low-density
water above 60 m (200 ft)
and the dense saline-heavy lower level.
These two layers hardly mix.
The lower levels have been sitting near
the bottom, untouched,
for thousands of years.
It's this bottom layer of the lake
that might kill you.
The gases stored in the deep lake water
could suddenly release,
creating a toxic gas cloud.
This is a limnic eruption.
Eruptions like this
have devastating effects.
But they are rare,
with only two in recorded history.
The most disastrous one was
at Lake Naos in Cameroon in 1986.
A large, toxic cloud of carbon dioxide
suddenly spread to nearby villages
and asphyxiated 1,800 people.
Now, if this happened at Lake Kivu,
it would be even worse.
Lake Kivu is larger than Nyos.
The death rate of an eruption
here would be extremely high.
And, of course, you'd be at the center of it.
Well, the water would be saturated
with gases.
Additional gas would bubble out
and mix with the atmosphere.
The soil would be dry.
A drought would indicate
that something terrifying
was brewing inside Lake Kivu.
The water would start to evaporate.
The pressure at the bottom
would decrease, and the lake
would release more gases.
Things would get even worse
if there was an earthquake.
It would happen with little warning
and wreak havoc in numerous ways.
It would shake the layers of water
like a can of soda.
And when that can opens,
it would release carbon dioxide.
And the bad news wouldn't end there.
There would also be methane
bubbling out of the lake.
As the methane mixed
with the surrounding air,
it could ignite, setting the lake on fire.
But you'd likely already be unconscious
from all that carbon dioxide.
Your heart rate would increase.
And if by some slim chance
you were conscious,
you'd experience extreme
headaches and dizziness.
Finding yourself
swimming in an exploding Lake Kivu
wouldn't end well.
You'd be looking at anything
from carbon dioxide poisoning
to getting burned by methane-infused fire.
So get out of that
lake as soon as you can.
And if you brought
some portable oxygen with you,
start breathing it.
And maybe drink a glass of water.
But don't dare
try a sip from Lake Natron.
That's a story for another WHAT IF.