This is a well known issue with the so called Digg effect. I warned people years ago not to aim for Digg traffic because Adsense tracks page impressions and click throughs and Digg users behave like robots, flooding a site with requests and bouncing off right away.
[edit:] Reddit is even worse, higher bouncer rate (95%+), and even lower engagement than Digg.
[edit:] Reddit is even worse, higher bouncer rate (95%+), and even lower engagement than Digg.