After the North Magnetic Pole was located in 1831, explorers and scientists began looking for the South Magnetic Pole. One of the explorers, James Clark Ross, a British naval officer, identified its approximate location, but was unable to reach it on his 4 year-expedition from 1839 to 1843. Commanding the British ships Erebus and Terror, he braved the pack ice and approached what is now known as the Ross Ice Shelf, a massive floating ice shelf over high. His expedition sailed eastward along the southern Antarctic coast discovering mountains which were since named after his ships: Mount Erebus, the most active volcano on Antarctica, and Mount Terror.