Glacier Landforms: Trough. Glacial troughs, or glaciated valleys, are long, U-shaped valleys that were carved out by glaciers that have since receded or disappeared. Troughs tend to have flat valley floors and steep, straight sides. Fjords, such as those in Norway, are coastal troughs carved out by glaciers.
Or: Steep U shaped valleys that connect with the sea and fill with water when the glaciers melt. Now keep scrolling;)