[2] A number of volcanic cones grew on Ioah and form morphostructures, with a density of about 11.1 vents per 1,000 square kilometres (390 sq mi).

[18][19][20] Volcanic rocks found on Ioah Guyot include alkali basalt, tholeiite and hawaiite, plus ankaramite, phonolite and trachybasalt;[21][22][23] as well as zeolites formed by hydrothermal processes.

[26] Ferromanganese crusts on the seamount contain apatite, asbolane, buserite, calcite, clay, feldspar, ferrihydrite, feroxyhyte, goethite, hematite, quartz and todorokite[27] and reach thicknesses of 10 centimetres (3.9 in),[5] although they only cover small sectors of Ioah Guyot.

[35] During the Aptian-Cenomanian, limestones and volcanic rocks formed sediments on Ioah Guyot which developed a reef system.

[37] Ioah developed the largest reefs of the Magellan Seamounts,[3] with coral material accumulating to thicknesses of 200–300 metres (660–980 ft).

[38] Ferromanganese crusts developed later during the Paleogene[39] and Miocene-Pleistocene,[40] and up to 150 metres (490 ft) sediments accumulated on the summit plateau.

[23] Presently, a rich fauna has been identified on Ioah Guyot, including scleractinian corals without zooxanthelles such as Fungiacyathus pliciseptus and Peponocyathus australiensis which is usually found in much shallower waters.