MINERALOGICAL STUDY OF VOLCANIC SUBLIMATES FROM HALEMA UMA U CRATER, KILAUEA VOLCANO

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1 MINERALOGICAL STUDY OF VOLCANIC SUBLIMATES FROM HALEMA UMA U CRATER, KILAUEA VOLCANO Ryan A. Bishop College of Arts and Sciences University of Hawai i at Hilo Hilo, HI ABSTRACT Halema uma u Crater has been the center of eruptive activity in Kilauea Caldera for the past 150 years. Due to degassing and the presence of boiling groundwater, sublimates and precipitates have formed inside and on the rim of the crater. Samples have been collected from the solfataras around the rim and from ejecta that were recently erupted out of the crater. By studying these precipitates and sublimates we can better understand what they are composed of and how they were formed. These deposits show similarity to those that have been found on Mars. By understanding how they are formed at Halema uma u Crater, we can better understand how they might have formed on Mars. A complicated mineral assemblage exists at this location with sulfur and gypsum being the prominent minerals present at the core of fumaroles with opal and anatase forming at a distance. The presence of alunite in an ejected block suggests there is intense acid alteration occurring at depth. SUBLIMATE DEPOSITS AT RIM OF HALEMA UMA U CRATER Kīlauea s summit magma chamber has been degassing at Halema uma u Crater for the last 87 years, since the 1924 collapse. This degassing, combined with boiling groundwater, has produced significant solfataric alteration in a number of areas around the rim of Halema uma u; directly correlated to areas around the crater rim that had elevated temperatures. Surprisingly, there have not been systematic mineralogical studies conducted in this region since the advent of modern equipment. Macdonald (1955) mapped this area, but did not include the strong solfataric alteration, which indicates these areas began forming after this time but prior to 1978 (Casadevall and Hazlett, 1983). This is corroborated by comparing a 1954 aerial photograph of Halema uma u with a recent Google Earth image showing the altered areas (Figure 1). These temporal changes allow the placement of important time constraints on the formation of the acid sulfate sublimates. The goal of our research was to build a framework for a more comprehensive understanding of how volcanic gases interact with basaltic rocks to produce a wide variety of sublimates and acidic alteration products. Under a National Park Service research permit, 60 samples were collected by Dr. Ken Hon and Lopaka Lee of the Hawaiian Volcano Observatory, from the solfataras around the rim of Halema`uma`u Crater in May The locations from which these samples were gathered were carefully documented and mapped (Figure 2). During the March 2008 eruption, altered rock was ejected and deposited on the rim of the crater. Dr. Hon and others also

2 collected about 15 samples of the ejecta. Samples collected from the Northeast rim of the crater (near the 1982 fissure site) were the primary focus of this project; 10 of the sublimate samples and one ejecta sample were selected and analyzed. Figure 1: Halema uma u Crater comparison. White solfataras can be seen around and within the crater in the present day image (right) but are not present in the aerial photograph from 1954 (left). Figure 2: Sample collection sites along the rim of Halema uma u Crater (Kilauea Caldera).

3 SUBLIMATE SAMPLES The ten sublimate samples I selected to analyze were: HM-1, HM-3, HM-5, HM- 10, HM-13, HM-14, HM-15, HM-16, HM-18, and HM-20. The ejected block sample selected to be analyzed was HMB-2. The samples were initially photographed in hand sample and under the microscope as references and for visual identification. A Bruker D- 8 X-ray Diffractometer (XRD) was used to identify minerals present in the samples. A Quantx EDXRF (Energy Dispersive X-ray Florescence) was first used to identify elements present in bulk sample. This step made it easier to identify minerals with the XRD once the compositions were known. I was briefly granted access to a scanning electron microscope (SEM) to identify minerals present in six of the sublimate samples and the block sample. HM-1 was a sample of the most common crust where alteration had been occurring. Sulfur, gypsum and opal CT were identified in this sample by use of the XRD (Figure 3). Samples were collected from active fumaroles near the crater rim (Figure 4a). Samples taken from the core of these fumaroles were found to be gypsum (HM-13 and HM-16) and sulfur (HM-5 and HM-20). Away from the fumaroles we find an opaline crust (HM-14) that contains gypsum (Figure 4b). It is important to note that this opaline material was not formed by standing liquid water; it was formed by fumarolic alteration. This is significant because I have not found any documented case where basalt has been altered into opal by a vapor process this quickly HM Lin (Counts) Theta - Scale HM 1 - File: HM-1 origional_1.raw - Type: 2Th/Th locked - Start: End: Step: Step time: 96. s - Temp.: 25 C (Room) - Time Started: 6 s - 2-Theta: Theta: Chi: 0.0 Operations: Strip kalpha Background 1.000,1.000 Import (I) - Sulfur, syn - S (*) - Gypsum - Ca(SO4)(H2O)2 Figure 3: XRD graph shows the presence of Gypsum, Sulfur, and Opal CT in sample HM-1

4 Figure 4: a) (Left) Fumarole with gypsum and sulfur concentrated at its core. b) (Right) Opaline crust; sample HM-14 collection site. Away from the fumaroles, on the 1971 rampart, there was a patch of altered spatter (HM-15) (Figure 5). The spatter had been almost completely altered into opal and anatase (Figure 6). Similar opaline material was found in the Gusev Crater on Mars. The presence of opaline silica was also identified by the Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars (Milliken et al., 2008). The deposits in the Gusev Crater were interpreted to have been formed under hydrothermal conditions (Squyres et al., 2008); this analog offers a potential alternate explanation for the formation of opals by means of vapor alteration. Sample HM-18 was a Salmon colored clayey material found beneath the crust that had also undergone very acidic alteration to form silica spheroids that were mostly opal with some anatase and cristobalite. Sample HM-3 contained pickeringite, cristobalite, gypsum, and metavoltine (the presence of metavoltine in the sample could not be confirmed due to small amount in sample). Sample HM-10 was altered lithic ash from the 1924 eruption that was composed of minerals with high silica contents. Figure 5: Left: Patch of altered spatter from 1971 rampart (HM-15 collection site). Right: Curve on graph produced by XRD indicates the presence of opal in HM-15.

5 Figure 6: Left: SEM image of HM-15. Right: Graph produced by SEM indicates an abundance of Si and Ti in HM-15. An eruption in 2008 at Halema uma u Crater ejected rock from deep within the volcano. These ejecta samples are some of the only samples that depict what kind of acid alteration we have going on inside an active volcano. The sample HMB-2, which is one of the volcanic bombs collected at the site, gives us a unique look at what processes are occurring at depth. Underground we have a complicated mineral assemblage including natroalunite, alunite, melanterite, and pickeringite found in HMB-2 (Figure 7). The presence of alunite indicates extreme acid alteration occurring at depth. Figure 7: SEM image and data for HMB-2. Graphs depicting minerals natroalunite (top left), melanterite (bottom left), alunite (top right), and pickeringite (bottom right). FINDINGS AND CONCLUSIONS At the core of fumaroles surrounding Halema uma u Crater there is a concentration of sulfur and gypsum. An opaline crust with sulfur and gypsum is the most common altered surface in the immediate area surrounding the fumaroles. Some areas have been almost completely altered to opal and anatase. The opal has replaced the basalt rapidly by a vapor process (without the presence of standing liquid water). Due to strong acid leaching, Si and Ti are all that remains of the original basalt. This offers a

6 potential explanation for the formation of opaline materials found on Mars which makes Halema uma u Crater a good analog site. Data collected from SEM and XRD show a complicated mineral assemblage exists underground including alunite. Evidence from the ejected block indicates that acid steam alteration intensifies at depth. Further investigations of these blocks may give us a clearer understanding of what alteration processes are going on inside the volcano. ACKNOWLEDGEMENTS I would like to thank Dr. Steven Lundblad for assistance with the EDXRF, Dr. Gary Huss for SEM assistance, Dr. Ken Morris and Rahul Haware for XRD assistance, and Dr. Jeff Taylor for being my co-advisor. I would also like to thank NASA and the Hawaii Space Grant Consortium for giving me the opportunity to gain valuable experience doing research in science. Most of all, I would like to thank my advisor, Dr. Ken Hon for all his guidance and advice during the course of my project. REFERENCES Casadevall, T J and Hazlett, R W., 1983, Thermal areas on Kilauea and Mauna Loa Volcanoes, Hawaii. Journal of Volcanology and Geothermal Research. Volume 16, Issues 3-4, p Macdonald, G. A., 1955, Distribution of areas of pneumatolytic deposition on the floor of Kīlauea caldera: Volcano Lett., 528, p Milliken, R. E., and 11 others, 2008, Opaline silica in young deposits on Mars: Geology, v.36, p , doi: /G24967A.1 Squyres, S.W., and 17 others, 2008, Detection of silica-rich deposits on Mars: Science, v. 320, p , doi: /science