A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface , and thus is not an isl islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to 1,000–4,000 m in height. They are defined by oceanographers as independent features that rise to at least 1,000 m above the seafloor, characteristically of conical form. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. During their evolution over geologic time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface. After they have subsided and sunk below the sea surface such flat-top seamounts are called "guyots" or "tablemounts".