喀拉喀托之子在半夜醒了：七百公里外都听得见，八个机场关闭，二十七万人走不了，地面上没有一个人死

Start with a number: two hundred and seventy thousand.

That is how many people were stuck inside Indonesian airports in early September this year.

There was no typhoon in Indonesia those days, and no strike at the airports.

The reason was that a volcano woke up.

The volcano is called Anak Krakatau, and it sits in the Sunda Strait between Java and Sumatra.

"Anak" in the name is simply the Indonesian word for "child".

So its full name, translated directly, is "Child of Krakatoa".

The name has a source.

In 1883, the old Krakatoa volcano erupted, one of the most violent eruptions on record.

The sound of the explosion carried thousands of kilometres, the ash drifted to great heights, and for a year or two afterwards weather around the world was affected.

After that, the old mountain had essentially blown itself away, leaving only a few remnant islands above the sea.

By the 1920s, on the site of the old mountain, the sea floor had slowly built up a new small mountain.

That is the one standing there now, which is why it is called the child.

This child is not a quiet one.

In 2018 a large piece of it collapsed into the sea, setting off a tsunami in which more than four hundred people died.

So Indonesia has watched it closely; back in early July this year the alert level was already raised to the third of four — the second highest.

This September's eruption began late on a Friday night.

The scale was considerable.

The ash column reached six thousand metres on the Java side, and at its highest fifteen thousand metres over Sumatra and Banten.

What does fifteen thousand metres mean?

Airliners cruise at roughly ten to twelve thousand metres — which is to say the ash column stood higher than planes normally fly.

The explosion that night could be heard seven hundred kilometres away.

But what is genuinely notable this time is the casualty figure.

Nobody died.

No village was evacuated.

The authorities drew a three-kilometre exclusion zone and barred boats from approaching. That was it.

This was a large eruption that caused almost no damage on the ground.

All of the damage happened in the air.

The reason is not complicated.

Volcanic ash is not smoke; it is extremely fine rock particles and shards of volcanic glass.

Once it is drawn into an aircraft engine it melts, and then hardens again inside.

The engine loses its power, and in bad cases shuts down outright.

It will also scour the windows at the front of the aircraft opaque.

Not one of these failures can be repaired in the air.

So civil aviation's approach to volcanic ash is blunt: go around it, or do not fly.

On 6 September, Indonesia closed eight airports at once, including the largest in the country.

More than one thousand five hundred and fifty flights were cancelled or delayed in total.

At the largest airport alone, over nine hundred were affected.

More than two hundred and seventy thousand passengers were stranded.

The great majority of those people will never in their lives go near that volcano.

Many of them could not even tell you its name.

But that mountain decided whether they got home those few days.

And that is the point I want to make.

In 1883, the volcano killed directly, with a tsunami and pyroclastic flows.

In 2018, it was a tsunami.

This time, it did not touch a single person.

All it did was put a column of ash into the sky, and the whole region's air network stopped.

Same mountain, same kind of eruption, striking something completely different in a different era.

Because what changed over these hundred-odd years is not the mountain. It is us.

Think about it:

In the life you have now, how many things only work because the road through the sky is open?