All language subtitles for [English] How do sinkholes form_ - Elise Cutts [DownSub.com].English

It was a rainy December morning
in San Francisco’s Sea Cliff neighborhood

when the Earth opened up.

The ground suddenly fell away
into a 12-meter-deep sinkhole

that engulfed a garage,
part of a street,

and a luckily unoccupied
multi-million-dollar mansion.

Sinkholes can seem
to strike out of nowhere,

collapsing roads or even
whole city blocks in a flash.

And they’re more common
than people often think.

For example, there are tens of thousands
of sinkholes

in the US state of Florida alone,

which range from less than a meter
to over 100 meters wide.

Sinkholes form when something
carves away space underground.

And in nature, that something
is usually water.

Rainwater is typically slightly acidic,
so it can melt away bedrock,

forming cavities and caves
deep below the surface.

At this point, there might be
no sign of trouble.

But as water keeps flowing down
into the bedrock cavities,

it carries overlying sediment
and soil with it,

forming a hidden hole
in the soft sediments above.

These sinkholes can collapse
without warning,

especially if the uppermost layer
concealing the hole is rigid.

In this case, a passing vehicle
or pedestrian

might be just enough weight
to trigger a collapse.

For example, in West Florida in 2023,

a sinkhole suddenly opened up
under a passing car,

trapping its two passengers
in a growing pool of muddy water

until they were rescued.

While these types of collapses
can be particularly shocking,

many sinkholes are less notable as they
develop over longer periods of time.

They can open up gradually as a column
of sediment washes down

into a cavity below,

or when water accumulates
in a shallow depression of rock

and slowly eats it away.

Some conditions can make
sinkholes more likely.

They often form in karst landscapes,

or regions where the bedrock is
composed of water-eaten limestone.

This is because limestone
is a carbonate rock,

which dissolves easily in acid.

But sinkholes in karst landscapes
aren’t always disasters—

some are geological marvels.

The legendary cenotes of Mexico’s Yucatan
Peninsula are water-filled sinkholes,

which were used by the ancient Mayans
as places of ritual

and were believed to be openings
to the underworld.

And sinkholes can also be deep
wells of biodiversity.

600 meters down at the bottom
of the world’s largest sinkhole,

China’s Xiaozhai Tiankeng,
or “Heavenly Pit,

an untouched forest hosts a distinct
ecosystem of rare plants and animals,

including ginkgo trees
and clouded leopards.

Of course, most sinkholes
aren't considered natural wonders.

In fact, many aren't natural at all.

A broken pipe among the mazes of plumbing
beneath our cities

can pour water into the ground

and open up an escape channel
for sediment-laden water.

A situation like this is what led to the
Sea Cliff neighborhood sinkhole in 1995.

More recently, in 2007 in Guatemala City,

the combination of heavy rainstorms
and a leaking sewage line

caused a 60-meter-deep sinkhole to open up
in the middle of a city street,

taking three victims with it.

And other human activities
like pumping up groundwater

and drilling for fossil fuels
can also trigger sinkholes.

Meanwhile, climate change is intensifying
drought and rainfall around the world,

which together, can carve out
sinkholes more effectively.

Storms are obviously
powerful agents of erosion.

And droughts can encourage sinkholes
to collapse by lowering the water tables,

which help support overlying sediments.

Because many sinkholes are the
result of human meddling,

we can prevent them
by regulating industry,

limiting the amount
of groundwater we pump up,

and by better maintaining
plumbing systems.

It's even possible to spot potential
sinkholes using tools like radar,

or by running electrical currents
through the ground

and measuring its resistance.

But even if we found every sinkhole
lurking below the surface today,

there would soon be more to discover.

The Earth might seem
like it’s standing still,

but there’s a lot going on
just below your feet.