This is Malham Cove, a fairly well-known scenic location in the Yorkshire Dales (northern England). This is the first time in about 200 years that water has flowed over the cliff - it's about 70m (230 feet) high.
Some background: a particularly intense storm, named Desmond, passed over northern England and southern Scotland on Saturday and early Sunday. It produced the highest rainfall ever recorded in a 24-hour period in England - just over 340mm (14.4 inches). This is about a month's normal rainfall in one of the wettest parts of the country. Unsurprisingly, it has caused extensive flooding and other damage across a wide area: several thousand houses and other buildings flooded, and tens of thousands without electricity.
Malham, too, got a lot of rain on Saturday. The underlying rock in the area is limestone; this dissolves (very slowly) in rain water, so here, as in other so-called "karst" areas, extensive cave systems have developed. The river in the upper part of the valley flows towards the cliff, but sinks into a hole in the ground a couple of miles before it reaches it. It then emerges again at the base of the cliff, and continues flowing down the valley in the open. At least, that's what it normally does - after Saturday's rain, there is presumably so much water in the river that it can't all go through the cave, and the rest continues flowing on the surface and over the cliff.
