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Kulanaokuaiki Tephra (ca. A.D. 400–1000): Newly recognized evidence for highly explosive eruptions at Klauea Volcano, Hawai‘i

¹ Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, Washington, D.C. 20013–7012, USA
² U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, Hawaii 96718, USA
³ U.S. Geological Survey, MS-910, Menlo Park, California 94025, USA
⁴ U.S. Geological Survey, MS-926A, Reston, Virginia 20192-0002, USA

Correspondence: E-mail: fisker{at}si.edu

Klauea may be one of the world's most intensively monitored volcanoes, but its eruptive history over the past several thousand years remains rather poorly known. Our study has revealed the vestiges of thin basaltic tephra deposits, overlooked by previous workers, that originally blanketed wide, near-summit areas and extended more than 17 km to the south coast of Hawai‘i. These deposits, correlative with parts of tephra units at the summit and at sites farther north and northwest, show that Klauea, commonly regarded as a gentle volcano, was the site of energetic pyroclastic eruptions and indicate the volcano is significantly more hazardous than previously realized. Seventeen new calibrated accelerator mass spectrometry (AMS) radiocarbon ages suggest these deposits, here named the Kulanaokuaiki Tephra, were emplaced ca. A.D. 400–1000, a time of no previously known pyroclastic activity at the volcano. Tephra correlations are based chiefly on a marker unit that contains unusually high values of TiO₂ and K₂O and on paleomagnetic signatures of associated lava flows, which show that the Kulanaokuaiki deposits are the time-stratigraphic equivalent of the upper part of a newly exhumed section of the Uwkahuna Ash in the volcano's northwest caldera wall. This section, thought to have been permanently buried by rockfalls in 1983, is thicker and more complete than the previously accepted type Uwkahuna at the base of the caldera wall. Collectively, these findings justify the elevation of the Uwkahuna Ash to formation status; the newly recognized Kulanaokuaiki Tephra to the south, the chief focus of this study, is defined as a member of the Uwkahuna Ash. The Kulanaokuaiki Tephra is the product of energetic pyroclastic falls; no surge- or pyroclastic-flow deposits were identified with certainty, despite recent interpretations that Uwkahuna surges extended 10–20 km from Klauea's summit.

Key Words: Klauea volcano • pyroclastic eruptions • high TiO₂ and K₂O marker unit • pyroclastic surges • stratigraphy • radiocarbon ages • paleomagnetism