Why severe change during London Session?

I've seen several times. During London session, the market got rapid change. Most of the Big spikes happen during that session. Why? Because of the 'Time' when most of the Biggies talk out?

London is the Forex capital of the world. The same way New York is known for equities London is known for foreign exchange.

On top of speculative activities, banks also have to process huge orders for their clients so the bulk of activities will happen from 3AM to around 11AM Easter time.