New Zealand separated from Australia and Antarctica 80 million years ago, and is now positioned at the boundary between the Pacific and Australian plates. The largely transverse Alpine Fault runs 435 miles (700 km) across the South Island. Crustal compression and distortion across a 155-mile- (250-km-) wide zone has raised the Southern Alps over 13,000 ft (4,000 m) above sea level. The plate boundary continues north as the Hikurangi Trench, a classic subduction zone producing volcanism on North Island, and south as the Macquarie Ridge, where shallow subduction has uplifted the Australian Plate. The main islands of New Zealand are the highest points of an extensive area of continental crust that includes the Challenger Plateau, Chatham Rise, and Campbell Plateau. To the southeast, Campbell Plateau is the largest area of submerged continental crust in the world. Lord Howe Rise was left isolated between Australia and New Zealand by seafloor spreading in the Tasman Sea and by rifting in the New Caledonia Basin and Bellona Valley.