Philip R. Kyle

Real‐time data received from Mount Erebus Volcano, Antarctica

Internal and eruptive volcano processes involve complex interactions of multi-phase fluids with the solid Earth and the atmosphere, and produce diverse geochemical, visible, thermal, elastic, and anelastic effects. Multidisciplinary experimental agendas are increasingly being employed to meet the challenge of understanding active volcanoes and their hazards [e.g.,Ripepe et al., 2002; Wallace et al., 2003]. n nMount Erebus is a large (3794 m) stratovolcano that forms the centerpiece of Ross Island, Antarctica, the site of the principal US. (McMurdo) and New Zealand (Scott) Antarctic bases. With an elevation of 3794 m and a volume of ∼1670 km3, Erebus offers exceptional opportunities for extended study of volcano processes because of its persistent, low-level, strombolian activity (Volcano Explosivity Index 0–1) and exposed summit magma reservoir (manifested as a long-lived phonolitic lava lake). Key scientific questions include linking conduit processes to near-field deformations [e.g., Aster et al., 2003] ,explosion physics [ e.g., Johnson et al., 2003], magmatic differentiation and residence [e.g., Kyle et al., 1992], and effects on Antarctic atmospheric and ice geochemistry [e.g., Zreda-Gostynska et al., 1997]. The close proximity of Erebus (35 km) to McMurdo, and its characteristic dry, windy, cold, and high-elevation Antarctic environment, make the volcano a convenient test bed for the general development of volcano surveillance and other instrumentation under extreme conditions.

Mineralogy and glass chemistry of recent volcanic ejecta from Mt Erebus, Ross Island, Antarctica

Abstract Bombs erupted in 1972 and recent flows of anorthoclase phonolite from Mt Erebus both contain phenocrysts of anorthoclase and microphenocrysts of olivine (Fa46Te3Fo51), clinopyroxene (Wo48Fs15En37), titanomagnetite (USP70), pyrrhotite, and apatite; the associated glass is peralkaline (agpaitic index = 1.06). The composition of glass inclusions in large anorthoclase (Ab65An16Or19) phenocrysts, which form a lag gravel on the summit cone of Mt Erebus, is generally more evolved than that from the groundmass of recent flows and bombs. Glass inclusions from between the core and rim of anorthoclase phenocrysts represent variations with time and show a small and systematic increase of Al2O3 and decrease of FeOT (total iron as FeO), possibly owing to reaction of the glass with the anorthoclase after entrapment. In contrast, whole rock-groundrnass trends show decreasing Al2O3 and increasing FeOT. The whole rock compositions of recent flows and ejecta are similar to older (up to 1 m.y.) anorthoclase phonolit...

Rare earth element geochemistry of Late Cenozoic alkaline lavas of the McMurdo Volcanic Group, Antarctica

Abstract Rare earth element (REE) concentrations were determined in 16 Ross Island and northern Victoria Land alkaline lava samples which were representative of four lava lineages of the McMurdo Volcanic Group, Antarctica. A kaersutite and two feldspar mineral separates were also analysed. Two of the lava lineages, a basanite to nepheline benmoreite and a basanite to phonolite, have similar chondrite-normalized REE fractionation patterns, with a continuous enrichment of light and heavy REE and depletion of middle REE. The patterns result from the fractionation of olivine, clinopyroxene, spinels, feldspar, kaersutite and apatite. Kaersutite is an important fractionated phase responsible for the middle REE depletion. Another of the lava lineages is mildly potassic with trachyandesite to peralkaline K-trachyte lavas which have partly overlapping REE fractionation patterns. There is a depletion in REE from tristanite to K-trachyte. Fractionation of olivine, clinopyroxene, feldspar and apatite probably control the REE chemistry of the lineage, greater degrees of apatite fractionation deplete the K-trachyte in REE relative to the tristanite. Feldspar fractionation in the genesis of the peralkaline K-trachyte is shown by a large negative Eu anomaly (Eu/Eu∗ = 0.10). A nepheline hawaiite to anorthoclase phonolite lava lineage from the Erebus Centre shows enrichment of REE, although minor overlapping in the middle REE does occur. Anorthoclase phonolite has a positive Eu anomaly (Eu/Eu∗ = 1.31), indicating possible accumulation of anorthoclase. The lineage resulted from fractionation of olivine, clinopyroxene, magnetite and apatite.

Contributions to quaternary geology of Cape Crozier, White Island and Hut Point Peninsula, McMurdo Sound region, Antarctica

Abstract Rocks of the McMurdo Volcanics from Cape Crozier, White Island and Hut Point Peninsula can be correlated with the Melania Basalt, Aurora Trachyte, Nubian Basalt and Trachyte Hill Formations of Black Island. The volcanic cones of Cape Crozier comprise an alternating sequence of basalt and trachyte lavas which rest upon the lower flanks of Mt. Terror. Advances of glacier ice have formed extensive moraine covered beaches up to 300 m high between the volcanic cones. White Island is comprised of two basalt shield volcanoes, with younger basalt cones aligned north-south across them. Five glacial benches on the north coast have been found and pebble types on them suggest that they were probably formed by an expanded Ross Ice Shelf, rather than an enlarged Koettlitz Glacier. The basalt volcanoes of Hut Point Peninsula are aligned NNE. Trachytes occur at the southern end of the lineation at Observation Hill, and autoclastic breccias at the northern end at Castle Rock.

Correlation of cycles in Lava Lake motion and degassing at Erebus Volcano, Antarctica

Several studies at Erebus volcano have recorded pulsatory behavior in many of the observable properties of its active lava lake. A strong correlation between the variations in surface speed of the lake and the composition of gas emitted has previously been noted. While previous studies have shown that the SO2 flux and the surface elevation exhibit pulsatory behavior with a similar period to that of the surface speed and gas composition, suggesting they are linked, a lack of overlap between the different measurements has prevented direct comparisons from being made. Using high time-resolution measurements of surface elevation, surface speed, gas composition, and SO2 flux, we demonstrate for the first time an unambiguous link between the cyclic behavior in each of these properties. We also show that the variation in gas composition may be explained by a subtle change in oxygen fugacity. The cycles are found to be in-phase with each other, with a small but consistent lag of 1–3 min between the peaks in surface elevation and surface speed. Explosive events are found to have no observable effect on the pulsatory behavior beyond the ∼5 min period required for lake refill. The close correspondences between the varying lake surface motion, gas flux and composition, and modeled oxygen fugacity suggest strong links between magma degassing, redox change, and the fluid dynamics of the shallow magmatic system.

Tephra and debris layers in the Skelton Neve And Kempe Glacier, South Victoria Land, Antarctica

Abstract Basanite tephra layers have been found in glacier ice at several places on the Skelton Neve and Kempe Glacier, South Victoria Land. They are coarse to fine moderately well to poorly sorted, mainly essential vitric to vitric crystal ash. similar to that produced in strombolian (or hawaiian) eruptions. They were probably erupted from a cinder cone or cones located between the Koettlitz Glacier and the Royal Society Range. Grain size analysis of the ice enclosing the tephras suggests that deposition occurred between 1000 and 10000 years ago. Other dirt layers in these areas are composed of local rock material such as dolerite and Beacon Supergroup debris. They sometimes contain tephra as well. Such layers were formed after wind deposition.

Geology of Northern Evans Névé, Victoria Land, Antarctica

Abstract Geological examination of previously unmapped parts of the Northern Evans Neve,and detailed re-examinationof other outcrops in the are, form the basis for a revised geological map.Sedimentary rocks (Robertson Bay and Bowers Group) and intrusives (Admiralty Intrusive Group, Ferrar Group and basic dikes of unknown affinity)are described. They range in age from Late Preccambrian to Jurassic. A new radiometric date of 330 m.y. on granodiorite exposed in the Southern Salamander range confirms that the pluton forms part of the Admiralty Intrusives. A detailed examination was carried out on the Camp Ridge Quartzite (Bowers Group) which was widely exposed in the area.The upper part of the formation was deposited by a river flowing to the north-west or north-north-west.The trace fossil assemblage in the lower part suggests that it formed the marine portion of a delta.