Hawaii Volcanoes National Park delivers the goods: towering flumes of gases erupting from the gut of the earth, glowing red rivers flowing like taffy, and the enormous bomblast where heat meets cold at the ocean in a conflict that is old as time itself. Pu'u (cone) O'o (pictured above), is part of the major Kilauea Volcano's east rift zone. It blew its cork most recently in 1983 and has been gurgling lava ever since, including 40-plus fiery fountainheads and one major explosion in 1997 that collapsed the height of the cone hundreds of feet within 24 hours. The lava rivers change direction.These days you can see the fresh stuff not in the park, but down the coast from Hilo in Kalapana. For a dramatic aerial view, hop aboard one of the Blue Hawaiian helicopters that leave from two locations on the island.
Halemaumau Crater, the home of Volcano Goddess Pele, is within the larger Kilauea Caldera, the centerpiece of the national park. In the middle of the night (fortunately) in March of 2008, Pele threw a major hissy fit, blowing away what had been the viewing platform at the lip of the crater. The road around the park has been closed ever since, but you can get a good look from the Jaggar Musuem, which is a few miles from the entrance station.
Numerous hikes and drives give you perspective on these outbursts; Hawaii the Big Island Trailblazer (new edtion 2013) has more details.