It is a shallow seamount, reaching a depth of 30 metres (98 ft) below sea level[1] and is a regular single-peaked mountain with a westerly spur and little relief otherwise.
[2] Volcanic rocks taken from Shimada are considered to be icelandites.
[1] These mechanisms cannot really explain the origin of Shimada Seamount, however;[2] it may be part of a hotspot trace.
[4] Evidence from core samples around the seamount, the appearance of the summit area,[5] and the presence of thin manganese crusts imply an age of about 10,000 years for some volcanic rocks at Shimada; the rocks are too young to be dated by potassium-argon dating, and all the evidence indicates that volcanic activity at Shimada is of late Quaternary-Holocene age.
[6] Possibly alive Lithothamnium corals have been dredged at Shimada from a depth of 110 to 130 metres (360 to 430 ft).