Photo: Lava and gases escaping from vent at night

Hawai'i Volcanoes National Park is home to two of the world's most active volcanoes, Kilauea and Mauna Loa. Here, lava-lit gases pour from Kilauea's unstable Pu'u 'O'o vent.

Photograph by Frans Lanting

Location: Hawai'i

Established: August 1, 1916

Size: 333,000 acres

Hawai'i Volcanoes National Park, on the "Big Island" of Hawai'i, offers the visitor a look at two of the world's most active volcanoes: Kīlauea and Mauna Loa.

More than 4,000 feet high and still growing, Kīlauea abuts the southeastern slope of the older and much larger Mauna Loa, or "long mountain." Mauna Loa towers some 13,677 feet above the sea: Measured from its base 18,000 feet below sea level, it exceeds Mount Everest in height. Mauna Loa's gently sloping bulk—some 19,000 cubic miles in volume—makes it the planet's most massive single mountain.

The park stretches from sea level to Mauna Loa's summit. Beyond the end of the road lies Mauna Loa's wilderness area, where backpackers encounter freezing nights and rough lava trails amid volcanic wonders: barren lava twisted into nightmarish shapes, cinder cones, gaping pits. Kīlauea, however, provides easy access to a greater variety of scenery and cultural sites.

On the slopes of Kīlauea, whose name means "spreading, much spewing," lush green rain forest borders stark, recent lava flows. This natural laboratory of ecological change displays all stages of forest regeneration—from early regrowth of lichens and ferns to dense forest. The rain forest on the windward side of Kīlauea's summit gives way to the stark, windswept Ka'ī Desert on the hot, dry southwestern slope. At the shore, waves create lines of jagged cliffs; periodic eruptions send fresh lava flows to meet the sea amid colossal clouds of steam.

Geological dynamism forms the park's primary natural theme, followed closely by evolutionary biology. Thousands of unique species have evolved on the isolated Hawaiian islands. Cultural sites abound as well, reminders of the Polynesian pioneers who steered their great double-hulled canoes to Hawai'i beginning some 1,500 years ago.

The United Nations has named the park both an international biosphere reserve and a World Heritage site. Many of the park's intriguing native plants and animals, however, are in peril, defenseless against alien species including weedy invasive plants and feral pigs. The native species are carefully protected by the park, which has fenced the park's borders off from feral pigs and taken efforts to eradicate invasive weeds.

Did You Know?

With lava flowing at an average rate of 800-1,300 gallons per second from vents on the east rift zone of Kilauea, more than 500 acres of new land have been added to the island of Hawaii since Kilauea's eruption began on January 3, 1983.

Copy for this series includes excerpts from the National Geographic Guide to the National Parks of the United States, Seventh Edition, 2012, and our National Parks series featured in National Geographic Traveler.

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