Imagine the Mediterranean Sea as a completely dry desert basin encircled by continents. This was the situation prior to 5.3 million years ago. The northward movement of the African continental plate had sealed off the flow of water from the Atlantic Ocean eastward through the Strait of Gibraltar, leaving only freshwater replenishment from the watersheds feeding the Mediterranean. The rate of evaporation exceeded that of replenishment, and the inland sea dried up.
According to an article in the 10 December issue of the journal "Nature", rising Atlantic waters eventually found their way past the sill which forms the strait. Erosion created a deeper channel, which hastened erosion, in a self-feeding cycle forming a flood of monumental proportions -- a current of 100 million cubic meters of water per second, traveling at 100 kilometers per hour. Due to the gradual slope of the substrate, the flood appeared more like a very fast (and wide) river, rather than like a waterfall. Imagine being in a kayak or raft, on such a rushing flood.
Here's what's remarkable -- the fact of a dry Mediterranean being refilled isn't news -- I recall reading about it in school, a quarter century ago. What has geologists and others stunned is the rate of replenishment -- less than two years. This is the blink of an eye in geologic time.