So what causes a waterfall? Two things are needed. 1. A water supply. 2. A distinct change in land elevation. In Iceland the water supply comes from the glaciers and the often rainy climate. The distinct change in land elevation comes from the fact that Iceland is a volcano, much like the islands of Hawaii (which also have many waterfalls. Water will flow from a higher elevation to a lower elevation, down to sea level. When water cross a sharp drop in elevation, a waterfall is produced.
Waterfalls are a thing of beauty and there was no shortage of beauty in Iceland!