What makes a waterfall?

On its way to the sea, a river or stream may plunge over a steep cliff.  If it does, there is a waterfalls in mountains than anywhere else.  Many waterfalls were caused when ancient glaciers of earthquakes created a sharp-edged cliff in the path of a stream or river.  

Often, waterfalls are caused as the river carves away at the riverbed as it flows downstream.  Over the years, a softer place in the riverbed wears down and becomes a steep cliff.

Giant waterfalls are called cater acts.  Where the water does not drop straight down, but rushes down steep slopes instead, it is called a cascades.  If a riverbed slopes even less steeply, it is often called a rapids.  

As far as anyone knows, the highest waterfalls in the world is Angel Falls in Venezuela.  It is a silvery ribbon of falling water that plunges over 3,000 feet down the face of a cliff. – Dick Rogers