The most active volcano on Hawaii's Big Island is Kīlauea.
Kīlauea is a broad shield volcano on the southeastern side of Hawaiʻi Island and forms part of Hawaiʻi Volcanoes National Park. Unlike steep, cone-shaped composite volcanoes, shield volcanoes are built by many flows of relatively fluid basaltic lava, producing wide slopes.
Its summit includes the Halemaʻumaʻu crater within Kīlauea Caldera. The volcano has been especially notable for long-lasting activity: the Puʻu ʻŌʻō eruption began in 1983 and continued for more than three decades before ending in 2018. That year also brought major lava flows and a dramatic collapse of the summit crater.
Kīlauea is often confused with Mauna Loa, which is larger and rises higher above the seafloor. Mauna Loa is also active, but Kīlauea has historically been the Big Island's most persistently eruptive volcano. Its name is commonly translated as “spewing” or “much spreading,” reflecting its lava-producing nature.