There are no words...

Showing my ignorance here, but why is this wrong?

I'm lost too. Is it "area the size of"?

Why not just say "the mud covered a square mile".

The thick mud covered an area of one square mile.

Throwing any more words in there is just daft

I'm surprised they haven't managed to slip in something like "The landslide event left a thick layer of mud..... etc".

'Event' is one of those words that the user slips in sometime before they start a sentence with 'so'.

Why say "covered"

A square mile of thick mud.

But how many football pitches and, as it's thick mud, Olympic swimming pools is that?

I'll allow them 'covered an area of a square mile' since it was a caption to an illustration of the event. But the size of a square mile is a square mile; 'the size' is redundant.

Maybe to the depth of, say, the height of a double decker bus?

weighing as much as 100 blue whales....

The correct unit is obviously 0.12mWA
Wales being the ipso facto unit of area most favoured when describing area, even in countries that have never heard of Wales!

If Wales were suddenly engulfed a in a tidal wave of double-decker buses then how would they report it?

An area in Wales, roughly the size of Wales, has been engulfed by a tidal wave of double-decker sized double-decker buses.

...in other news, social media sites have reported millions of users infected with a virus that randomly sends thinly veiled racial epithets to major news stations. Here's some of your comments on this problem...

Are any of them promising young footballers?

Indeed. How many Ryan Gigg's (RGs) would you need to cover a square mile? Are we talking covered in terms of his body "unravelled" into a uniformed square or are we talking of a radius of impact from his longest kick?

What if RG missed th double decker bus? What then? Would the football move in all that mud? How long would his studs have to be? Surely, the ref would call the game off.