The crater at Kilauea Iki is framed by hapu'u, a Hawaiian tree fern. Craters and calderas are formed when lava recedes and existing cooled material collapses, forming a circular, or oval, indentation in the mountain's surface. The walls of the crater or caldera are usually very steep, as is shown here. Photo by Priscilla Millen..

Calderas and craters are similar in appearance and differ only in size. When lava drains out of the center and the summit collapses, the result is called a crater if it is less than a mile across. If it is more than a mile across, it is called a caldera. The summit area of Mauna Loa is a caldera, called Mokuaweoweo. While Mokuaweoweo is large--three miles across in places--it is not the largest of the known calderas in the Islands. The caldera on Kauai is thought to be the largest; its diameter is twelve miles. The steep sides of this caldera have eroded away. Photo by Glenn Bauer.

This view of Enchanted Lakes from Ka Iwa Ridge reveals this area is part of the Koolau caldera. The surrounding areas are far more eroded than Mokuaweoweo, however. Photo by Glenn Bauer.

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