Cause
Sites such as Slashdot, Digg, Reddit, StumbleUpon and Fark consist of brief submitted stories and a self-moderated discussion on each story. The typical submission introduces a news item or website of interest by linking to it. In response, large masses of readers tend to simultaneously rush to view the referenced sites. The ensuing flood of page requests from readers can exceed the site's available bandwidth or the ability of its servers to respond, and render the site temporarily unreachable.
Read more about this topic: Slashdot Effect