[Roaring, rushing noises]

People: Whoa. Whoa. That's bad.

[Announcer] It's Sunday, and 
the side of a mountain has just collapsed.

It crashes through the river that

runs through the Rhondda Var,
near Tylorstown.

Nobody is injured, but
it's only today

the sheer scale of that collapse
is obvious.

Something else that is clear

is the amount of coal

that was still 
on this mountainside.

Gerald watched it all happen.

[Gerald Durham]
There was a roar,

and you could see the muck

starting to slip
from the top area, there.

Within a couple of hours,
the whole lot had come down there.

[Announcer] Do you feel vulnerable?

[Gerald] Yeah. Yeah.
With this going on, yeah.

These valleys are surrounded by coal.

They were built on coal.

It's a frightening prospect,
you know.

If that could've happened

on this side of the mountain,

it would be a totally different outcome.

[Announcer] His father Cliff
is a former miner.

You look at this landslide now,
what goes through your mind?

[Cliff Durham] Oh, Aberfan,
straight away.

Believe me, we don't want
to see that again.

I wouldn't.

[Announcer] I've been
speaking to people

on this street.

It's Bryn Heulog, and it's
opposite to the landslide.

They described yesterday as eerie.

The sound of slurry
crashing down the mountain.

They are just thankful
that this happened

in front of their homes,

not behind them.

The greenery of the valleys

disguises the amount of coal
that is still hidden here.

In the 1970s, 80s and 90s,

the land was reclaimed.

But now, there are calls
by local people,

to inspect all the areas
where coal was dumped.

[Chris Bryant] We should definitely

be inspecting all the former
coal tips.

Making sure that if
there is excessive water in there,

that that is being drained off,

make sure everything is safe.

Because obviously, people 
have seen the horrific pictures

on television news, of
what's happened in Ponte Guy.

People might not have seen it
for themselves.

It is much bigger than
it looked on television.

So, people are, of course, worried.

It is one thing, having water coming,

coursing through your house.

It is quite another, having, um,

slurry, and the top of the mountain

coming down through your house.

[Announcer] But, who is responsible?

Who owns the land?

The Coal Authority says,
it's not them.

The Councils say,

they're not sure if they do.

Who is responsible for these sites,

and who is maintaining them?

[Andrew Morgan] At present,

we are in discussion with

Natural Resources, Wales.

Clears on the side of the hill.

It is the big one.

Rhondda Var is a concern to us.

We have engineers on site right now,

monitoring it.

[Announcer] Do you think that is
your land,

or Natural Resources Wales' land?

[Mr. Morgan] We are still in discussion
over that.

Um, but at present,
we have engineers on site,

trying to understand
if there is a risk

to the properties, or the public.

Certainly there is some concern

about the moment that happened
yesterday,

and what's caused it.

Is it just water on the surface,

or is there a deeper issue
within the mountain?

That is currently under investigation.

[Rushing noises.]

[Announcer] This is what happened

after a weekend of heavy rain.

These valleys know all too well

of the histories with landslides.

Now, some are questioning

whether this was a one-off,

or an early warning.

Rob Osbourne, ITV News.