Kulanaokuaiki Tephra (ca. A.D. 400-1000): Newly recognized evidence for highly explosive eruptions at Kilauea Volcano, Hawai'i

Abstract

Kīlauea 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 Kīlauea, commonly regarded as a gentle volcano, was the site of energetic pyroclastic eruptions and indicate the volcano is signifi cantly 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 chiefl y on a marker unit that contains unusually high values of TiO 2 and K 2 O and on paleomagnetic signatures of associated lava fl ows, which show that the Kulanaokuaiki deposits are the time-stratigraphic equivalent of the upper part of a newly exhumed section of the Uwēkahuna 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 Uwēkahuna at the base of the caldera wall. Collectively, these fi ndings justify the elevation of the Uwēkahuna Ash to formation status; the newly recognized Kulanaokuaiki Tephra to the south, the chief focus of this study, is defi ned as a member of the Uwēkahuna Ash. The Kulanaokuaiki Tephra is the product of energetic pyroclastic falls; no surge-or pyroclastic-fl ow deposits were identifi ed with certainty, despite recent interpretations that Uwēkahuna surges extended 10-20 km from Kīlauea's summit.

Variation of lithium isotope geochemistry during basalt weathering and secondary mineral transformations in Hawaii

“…All sites are near 1200 m elevation, receive 2500 mm annual rainfall, and have a mean annual temperature of 15°C. The two youngest sites (0.3 ka; Thurston (Th) and Ola'a (Ol)) are in Keanakakoi tephra derived from phreatomagmatic eruptions of tholeiitic composition at the summit of Kilauea (McPhie et al, 1990;Fiske et al, 2009), while the older sites (P20 ka) are composed of alkali basalt, such as hawaiite, mugearite, and their associated tephra (MacDonald et al, 1983;Wright and Heltz, 1986;Wolfe and Morris, 1996). The soils exhibit a general trend of increasing crystallinity of secondary minerals with age (Chorover et al, 1999(Chorover et al, , 2004.…”

“…Soils were collected from hand-dug pits to about 1 m depth except for the youngest soil; Thurston (Th) is about 40 cm deep and overlies unweathered pahoehoe lava, and Ola'a (Ol) is about 70 cm deep and overlies a buried soil on the $1000 year old Kulanaokuaiki tephra (Fiske et al, 2009; Fig. 1).…”

Tephrochronology and its application: A review

“…(3) incompleteness of stratigraphic records of tephra-erupting episodes against which to attempt correlation (e.g., Alloway et al, 1994;Davies et al, 2004a;Newton et al, 2007;Fiske et al, 2009); (4) paucity or inadequacy of characterization data of potential correlatives, especially in proximal areas where the deposits may be compositionally complex such as in preHolocene eruptives in Iceland (e.g., Larsen and Eiríksson, 2007), or in New Zealand where, for example, many proximal tephras from Egmont/Taranaki volcano have not been characterized geochemically (Shane, 2005);…”

“…Partly the issue boils down also to how the constituent tephras are defined as stratigraphic units. For example, a series of thin tephra layers deposited incrementally over many years but appearing as a "seamless" non-differentiated unit, such as at Sakurajima, does represent an isochronous unit that spans 55 years -not quite "instantaneous" but nevertheless exactly the same 55-year time-span wherever it occurs because the base marks year- Extending beyond the present to the recent geological past, Fiske et al (2009), in evaluating the eruptive history of Kilauea volcano for the past several thousand years, identified a sequence of previously unrecognised basaltic tephras dated between ca. 400 and 1000 AD.…”

Aeolian processes on the terrestrial planets

“…Gooding (1982) analyzed some of the materials in this area and determined that the sand was derived largely from the Keanakako'i tephra formation, which is a sequence of ash and tephra that has been deposited from periodic phreatic eruptions that Kilauea volcano has experienced over the last 2000 years (Fiske et al, 2009). Gooding (1982) suggested that the material in the dunes he sampled were too well-sorted to have been emplaced directly from a base surge (Christiansen, 1979).…”