At  (including Svalbard and Jan Mayen) (and  without), much of the country is dominated by mountainous or high terrain, with a great variety of natural features caused by prehistoric glaciers and varied topography. The most noticeable of these are the fjords: deep grooves cut into the land flooded by the sea following the end of the Ice Age. Sognefjorden is the world's second deepest fjord, and the world's longest at . Hornindalsvatnet is the deepest lake in all Europe. Norway has about 400,000 lakes. There are 239,057 registered islands. Permafrost can be found all year in the higher mountain areas and in the interior of Finnmark county. Numerous glaciers are found in Norway.