The Powers Caldera is a buried summit

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

Kīlauea Kīlauea ( , ) is an active shield volcano in the Hawaiian Islands. Located along the southeastern shore of the Big Island of Hawaii, the volcano is between 210,000 and 280,000 years old and emerged above sea level about 100,000 years ago. Hi ...

on the Big Island of

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

. It is the precursor to the modern but smaller Kīlauea Caldera, having formed about 2,200 years ago as a result of powerful

phreatomagmatic eruption Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They differ from exclusively magmatic eruptions and phreatic eruptions. Unlike phreatic eruptions, the products of phreatomagmatic eruptions conta ...

s. These

explosive eruption In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such ...

s lasted for a period of about 1,200 years, during which time the Uwēkahuna Ash Member was deposited. Sometime between 850 and 950 CE, the most powerful explosive eruption sent rocks weighing at least from the summit. Golf ball-sized rocks fell at the coast, away.

Effusive eruption An effusive eruption is a type of volcanic eruption in which lava steadily flows out of a volcano onto the ground. Overview There are two major groupings of eruptions: effusive and explosive. Effusive eruption differs from explosive eruption, ...

s began to fill the Powers Caldera with

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

about 1,000 years ago, breaking the 1,200-year-long interval dominated by explosive eruptions. Lava completely filled the Powers Caldera and then overtopped its rim, solidifying the structure. This was followed by a period of voluminous tube-fed lava flows from 1000 to 1500 CE (including the

ʻAilāʻau eruption The ʻAilāʻau eruption is a prehistoric eruption of Kīlauea volcano on the island of Hawaiʻi in the Hawaiian Islands. Carbon 14 dated from approximately 1410 to 1470 with an eruptive volume of 5.2 ± 0.8 km3 and fed by lava tubes near Kīl ...

), with the modern smaller Kīlauea Caldera having formed inside the buried Powers Caldera in about 1470 CE. Evidence for the existence of the Powers Caldera is based largely on a

fault scarp A fault scarp is a small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other. It is the topographic expression of faulting attributed to the displacement of the land surface by movement al ...

mantled by the Uwēkahuna Ash Member within Uwēkahuna Bluff and exposure of the Uwēkahuna Ash Member in the modern Kīlauea Caldera wall at an elevation more than lower than its occurrence beneath a surface flow near the Tree Molds. This implies that a large depression existed in the summit area of Kīlauea prior to deposition of the Uwēkahuna Ash Member. The boundaries of the Powers Caldera have been inferred by connecting concentric caldera fractures and faults about outside the modern Kīlauea Caldera rim. It is estimated that the Powers Caldera had a depth of at least . The Powers Caldera is named after Howard A. Powers, who conducted a careful field study of the Uwēkahuna Ash Member in 1948 and inferred the existence of the caldera.

References

Kīlauea Calderas of Hawaii Holocene calderas {{Hawaii-geo-stub