What decides market fluctuation?

Once receiving information, the market fluctuates very intensely at the start. Then the market move will turn to be moderate and move around the true market expected value. When information is just received, people concentrate at the two ends; however, as time progresses, people are moving towards the average, which is the market expected value. There is a recent example, which shows such effect. The London major, Boris, announced his support of letting Britain leave the EU. After his announcement, the UK bond market and foreign currency market experienced huge fluctuations. However, now the markets tend to move much less intense. However, I have some questions: what factors decide how intensely the market fluctuates and how long the intense fluctuation lasts. I can think of several factors but have not done any precise data analysis: macroeconomics information tend to make intense fluctuation longer, more surprising information will make fluctuation more intense. The problems here are what decides whether a piece of information is macroeconomics information or microeconomics information, and what makes information more surprising and is measurable (or at least able to be ranked objectively).