During the ice ages, glaciers, which were prevalent at higher latitudes and elevations, became so large that gravity drove them to lower elevations, eventually all the way to the sea. On their way, glaciers would carve deep canyons in the surface of the Earth. At the end of the ice age, as the ice melted and the ocean level rose, these glacial troughs filled with seawater. These very dramatic-looking canyons with high cliffs hanging over a thin bay of water are known as fjords. Fjords are very common in Norway and Alaska.