Marion Island

Marion Island, the larger of the two islands, is located at 46°54′45″S, 37°44′37″E. It is roughly 19 km long and 12 km wide with a surface of 290 km² and a coastline of some 72 km, most of which are high cliffs. The highest point on Marion Island is Mascarin Peak (Formerly State President Swart Peak), reaching 1242 m above sea level. Boot Rock is about 150 meters off the northern coast.

Prince Edward Island is much smaller (only about 45 km²) and lies some 12 nm (19 km) to the northeast. Prince Edward Island is located at 46°38′39″S, 37°56′36″E. At the Von Zinderen Bakker Peak northwest of the center, it reaches a height of 672 meters. There are a few offshore rocks along the northern coast, like Ship Rock (100 meters north of northernmost point) and Ross Rocks (500 meters from the shore).

The island group is about 955 nm (1770 km) south-east of Port Elizabeth in mainland South Africa.

Both islands are of volcanic origin. Marion Island is one of the peaks of a large underwater shield volcano that rises some 5000 m from the sea floor to the top of State President Swart Peak. The volcano was thought to be extinct, but broke out again in 1980 and is since classed as "active".