what is a chain of underwater mountains called
Seamount
Introduction
seamount is a large geologic landform that rises from the ocean floor but that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock.
A seamount Seamount Seamount.
Seamount Seamount Seamount
Introduction Introduction Introduction
A seamount is a large geologic landform that rises from the ocean floor but that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. A seamount is a large geologic landform that rises from the ocean floor but that does not reach to the water's surface (sea level) A seamount is a large geologic landform that rises from the ocean floor but that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to in height. 
wiki:5259395
Seamount [SEP] Introduction
A seamount is a large geologic landform that rises from the ocean floor but that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to in height. They are defined by oceanographers as independent features that rise to at least 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.