this is not your everyday little river.... It runs along the tectonic fault between the European continental plate (on the left) and the American tectonic plate (higher cliff on the right). It is estimated that the terrain on the left subsided by about 4 meters over the last 1000 years, which would not be a big deal except that as a result the lake flooded the site where first meetings of Icelandic Parliament were held (Thingvellir)