The twin islands, formed from shield volcanoes, have a combined length of 6 km and an area of 12 square kilometers (5 square miles); their population is about 500 people. They are geographic volcanic remnants separated by the narrow 137-meter-wide (449-foot) Āsaga Strait, a natural bridge of shallow coral reef. Before 1970, one had to wade between the two islands at low tide; now a single-lane road bridge over the strait connects villages on Ofu island with those on Olosega.