A NEW PERSPECTIVE ON THE 19TH-CENTURY GOLDEN PUMICE DEPOSIT OF KīLAUEA

The golden pumice represents one of the latest episodes of Hawaiian fountaining in the Keanakāko‘i Tephra and is the product of the first fountaining eruption at Kīlauea summit in ca. 300 years. The deposit has been observed by many authors but has never been studied in detail from a volcanological perspective, resulting in little knowledge regarding its dispersal or eruptive sequence. We present a new physical characterization of the deposit based on the field study of over 200 sites detailing stratigraphic and structural relationships. Due to the absence of any overlying deposit of significant thickness, the field mapping is complicated by severe surface erosion, alteration and silicic encrusting of the deposit.

Our sites lie in an area of 20 km², extending 6 km N-S, and reaching 4.5 km west of Kīlauea caldera. Basic componentry analyses reveal a dominance of pumice lapilli and bombs associated with achneliths, Pele’s hair and, in proximal areas, dense outgassed clasts. The isopach map for the entire deposit, elongate both in a dominant SW dispersal direction associated with trade winds and in an atypical NNW direction, is difficult to resolve with only one fountain. Proximal sections reveal at least two episodes of fountaining from one or more sources in the present caldera. Fountains must have been sufficiently high to deposit outgassed bombs with diameters up to 30 cm on the caldera rim. Stratigraphic relationships reveal intense syn-eruptive erosion, suggesting major rainfall events during deposition of the tephra.

We view the golden pumice deposit as produced by an eruptive sequence including several high fountaining episodes and probably multiple vents. The timing of the activity can be framed by i) its occurrence above the phreatic and phreatomagmatic deposits erupted in 1790 and ii) the first observations of probable golden pumice by Ellis in 1823. This new characterization of the golden pumice increases the knowledge of the Keanakāko‘i stratigraphy and contributes to a better understanding of the explosive history of Kīlauea prior to the renewal of dominantly effusive