Why do riots spread as they do?

[Global Geezer]

I can understand if they are in areas where people have similar axes to grind; such as in the 'Textile Towns' in 2001 when the Asian youth rose up against feelings of being alienated and ossified from wider society.

I can even understand riots spreading within a certain area, such as Tottenham in 2011, being followed up by Enfield and Tottenham Hale retail park.

But some riots just seem very indiscriminate: Last year, trouble broke out in Amiens, at the top of France; the following night, it was reported in Toulouse, right at the other end of the country.

At certain times, you have the 'usual suspect' areas (Tottenham, Brixton, Hansworth, Toxteth, St. Pauls etc) but other times, they spread like wildfire around areas which are largely unconnected. In 1991, trouble flared in Telford, Cardiff, Oxford, Dudley and Newcastle, and none of those places are either culturally similar, or near to eachother.

So why do they spread as they do?
Is there a kind of 'hundredth monkey syndrome' where a thought or fear moves almost 'telepathically' amongst the criminal underclass of a nation - even if they are hundreds of miles apart.

How does social media affect the spread of civil unrest?