The fifteen volcanoes that make up the eight principal islands of Hawaiʻi are the youngest in a chain of more than 129 volcanoes that stretch 5,800 kilometres (3,600 mi) across the North Pacific Ocean, called the Hawaiian-Emperor seamount chain.Hawaiʻi's volcanoes rise an average of 4,572 metres (15,000 ft) to reach sea level from their base. The largest and most famous, Mauna Loa, has built itself up to a height of 4,169 metres (13,678 ft). As shield volcanoes, they are built by accumulated lava flows, growing no more than 3 metres (10 ft) at a time to form a broad and gently sloping shape.