Kilauea Crater Rim Drive
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Crater Rim Drive, Stop 4 - Kilauea Overlook
Kilauea Overlook, about 2 miles (3 km) east of the Visitor Center, provides an excellent view of Kilauea Caldera. On the horizon is the Ai-laau shield. This vent was active about 350-500 years ago and sent lava all the way to the ocean. The path to the overlook is on ash from the 1790 explosive eruption of Kilauea. The caldera probably formed during this eruption. Collapse to produce the caldera is the result of magma withdraw from the chamber 3-6 miles (2-4 km) below the summit. Kilauea Iki is in the center of the photograph. Puu Puai cinder cone is on the rim (just right) of Kilauea Iki.
In addition to ash, large blocks up to 6 feet (1.8 m) in diameter are on the rim. These blocks were torn from the walls of the vent and thrown to their present location. The tephra deposit from the 1790 eruption is only a few feet thick on this side of the caldera. The scale on the block is about 5 inches (12 cm) long.
Kilauea Caldera has changed dramatically in the last 150 years. This map was made by U.S. Exploring Expedition. Notice the presence of a large ledge within the caldera. The expedition's geologists, James D. Dana, made significant contributions to the understanding of Hawaiian volcanoes and is considered by some as America's first volcanologist. Prior to 1924, a large lava lake covered most of the floor of the caldera. Since the 1924 eruption, lava has been restricted to Halemaumau or fissures in the summit area and, overall, the caldera is being filled gradually by lava.