Philipp Lenssen analysis different kinds of events in the post Different types of Google trends. He graphs (using Google Trends) the search popularity of different types of keywords over time, and observes how known events have a steady rise and sharp drop (e.g. Christmas) while unknown events have a sharp rise and steady drop (e.g. tsunami). And so forth.
Different types of Google trends
Analyze Google Trends patterns to distinguish between expected and unexpected events. Known occurrences like Christmas show a steady rise and sharp drop, while sudden events like tsunamis exhibit a sharp spike followed by a gradual decline.