From Wikipedia: "The strong winds of the Southern Ocean give rise to correspondingly large waves; these waves can attain great height as they roll around the Southern Ocean, free of any interruption from land. At the Horn, however, these waves encounter an area of shallow water to the south of the Horn, which has the effect of making the waves shorter and steeper, greatly increasing the hazard to ships. If the strong eastward current through the Drake Passage encounters an opposing east wind, this can have the effect of further building up the waves.[22] In addition to these "normal" waves, the area west of the Horn is particularly notorious for rogue waves, which can attain heights of up to 30 metres (98 feet).[23]"