The talk will present the notion of exploratory search as a means to go beyond "lookup", like learning or investigating (Marchionini 2006), and sketch its usefulness in new applications such as Digital Humanities. In detail, I want topresent a new approach to the analysis of topics and their dynamics over time. Given a large amount of time stamped textual data, we can identify "hotly discussed" concepts by analysing the rate a term changes context. Adopting the notion of volatility from econometrics, context volatility can be used to detect "weak signals" or semantic change independent from pure counts of frequency.