A frozen record of density-driven crustal overturn in lava lakes: the example of Kīlauea Iki 1959

Lava lakes are found at basaltic volcanoes on Earth and other planetary bodies. Density-driven crustal foundering leading to surface renewal occurs repeatedly throughout the life of a lava lake. This process has been observed and described in a qualitative sense, but due to dangerous conditions, no data has been acquired to evaluate the densities of the units involved. Kīlauea Iki pit crater in Hawai`i houses a lava lake erupted during a 2 month period in 1959. Part of the surface of the Kīlauea Iki lake now preserves the frozen record of a final, incomplete, crustal-overturn cycle. We mapped this region and sampled portions of the foundering crust, as well as overriding and underlying lava, to constrain the density of the units involved in the overturn process. Overturn is driven by the advance of a flow front of fresh, low-density lava over an older, higher density surface crust. The advance of the front causes the older crust to break up, founder, and dive downwards into the lake to expose new, hot, low-density lava. We find density differences of 200 to 740 kg/m³ between the foundering crust and over-riding and under-lying lava respectively. In this case, crustal overturn is driven by large density differences between the foundering and resurfacing units. These differences lead, inevitably, to frequent crustal renewal: simple density differences between the surface crust and underlying lake lava make the upper layers of the lake highly unstable. Work originally presented at the American Geophysical Union Fall Meeting in San Francisco, California on December 11, 2007.     

The anatomy of exhumed river-channel belts: Bedform to belt-scale river kinematics of the Ruby Ranch Member,Cretaceous Cedar Mountain Formation,Utah, USA

Many published interpretations of ancient fluvial systems have relied on observations of extensive outcrops of thick successions. This paper, in contrast, demonstrates that a regional understanding of palaeoriver kinematics, depositional setting and sedimentation rates can be interpreted from local sedimentological measurements of bedform and barform strata. Dune and bar strata, channel planform geometry and bed topography are measured within exhumed fluvial strata exposed as ridges in the Ruby Ranch Member of the Cretaceous Cedar Mountain Formation, Utah, USA. The ridges are composed of lithified stacked channel belts, representing at least five or six re-occupations of a single-strand channel. Lateral sections reveal well-preserved barforms constructed of subaqueous dune cross-sets. The topography of palaeobarforms is preserved along the top surface of the outcrops. Comparisons of the channel-belt centreline to local palaeotransport directions indicate that channel planform geometry was preserved through the re-occupations, rather than being obscured by lateral migration. Rapid avulsions preserved the state of the active channel bed and its individual bars at the time of abandonment. Inferred minimum sedimentation durations for the preserved elements, inferred from cross-set thickness distributions and assumed bedform migration rates, vary within a belt from one to ten days. Using only these local sedimentological measurements, the depositional setting is interpreted as a fluvial megafan, given the similarity in river kinematics. This paper provides a systematic methodology for the future synthesis of vertical and planview data, including the drone-equipped 2020 Mars Rover mission, to exhumed fluvial and deltaic strata.     

Witches, children and Kiva-the-research-dog: striking problems encountered in the field

This paper examines how power, privilege and vulnerability can surface in unexpected ways during fieldwork. Drawing from my experiences working with indigenous women and children who beg and sell on the streets of Ecuador, I suggest that researchers do not always hold as much power as we might assume. By positioning myself within stories about witches and children, I discuss how multiple research identities can shift power dynamics in unsettling and unexpected ways. In this paper, I also reflect upon a particularly unorthodox research method: using my dog as a research assistant. My dog inadvertently became instrumental in providing access to children's life stories; however, her presence also highlighted some of the dramatic incongruities between their life experiences and my own.     

Vesiculation of high fountaining Hawaiian eruptions: episodes 15 and 16 of 1959 Kīlauea Iki

The 1959 summit eruption of Kīlauea volcano produced the highest recorded Hawaiian fountain in Hawai‘i. Quantitative analysis of closely spaced samples from the final two high-fountaining episodes of the eruption result in a fine-scale textural study of pyroclasts and provide a record of postfragmentation processes. As clast vesicularity increases, the vesicle number density decreases and vesicle morphology shifts from small and round to larger and more irregular. The shift in microtexture corresponds to greater degrees of postfragmentation expansion of clasts with higher vesicularity. We suggest the range of clast morphologies in the deposit is related to thermal zonation within a Hawaiian fountain where the highest vesicularity clasts traveled in the center and lowest traveled along the margins. Vesicle number densities are greatest in the highest fountaining episode and therefore scale with intensity of activity. Major element chemical analyses and fasciculate crystal textures indicate microlite-rich zones within individual clasts are portions of recycled lava lake material that were incorporated into newly vesiculating primary melt.     

Spring flux as an indicator of source geomorphology,substrata, and temperature conditions in springs

Hydrogeology Journal - Spring flux (m/s), defined as spring flow (m3/s) divided by the area over which groundwater emerges (m2) at a spring, provides a meaningful way to distinguish between...     

Community structure and dynamics in climate networks

We consider climate networks constructed from observed and model simulated fields of three climate variables and investigate their community structure. We find that for all fields the number of effective communities is rather small (four to five). We are able to trace the origin of these communities to certain dynamical properties of climate. Our results suggest that the complete complexity of the climate system condenses beyond the ??weather?? time scales into a small number of low-dimensional interacting components and provide clues as to the nature of the climate subsystems underlying these components.     

Historical channel narrowing along the Rio Grande near Albuquerque,New Mexico in response to peak discharge reductions and engineering: magnitude and uncertainty of change from air photo measurements

Over the last century, geomorphic processes along the Middle Rio Grande have been altered by flood control and bank stabilization projects, intensified land and water use, and climate change. In response to potential risks to infrastructure and ecological integrity, recent (1985–2008) adjustment was investigated and historic (1918–1985) changes in Rio Grande channel planform through the Albuquerque, New Mexico, area were reviewed, especially in relation to changes in annual peak discharge and river engineering measures. Using a GIS, channel characteristics were digitized from georeferenced photographs and analyzed with particular attention to quantifying potential measurement error and its propagation. Error associated with average channel widths and channel area ranged between 4 and 13%. For smaller polygons, e.g. islands, error was higher (11 to 40% for width and >200% for area) because width error is large relative to polygon width. Between 1918 and 1963, average channel widths decreased 8 m/yr, from 516 ± 67 m to 176 ± 7 m, mostly due to decreasing peak flows and the implementation of flood control and other engineering measures. From 1985 to 2008, widths decreased 0·7 m/yr, from 176 ± 23 m to 146 ± 5 m, accompanied by an increase in vegetated island area which largely coincided with low flow periods. Narrowing was concentrated at tributary inputs and in the upstream part of the reach, where bedload trapping by Cochiti Dam has caused degradation. Bank protection structures and dense vegetation limit bank erosion in the reach, but erosion is significant where expanding islands, incision, and increased meandering force water against banks. Copyright © 2010 John Wiley & Sons, Ltd.     

Eruption dynamics of Hawaiian-style fountains: the case study of episode 1 of the Kīlauea Iki 1959 eruption

Hawaiian eruptions are characterized by fountains of gas and ejecta, sustained for hours to days that reach tens to hundreds of meters in height. Quantitative analysis of the pyroclastic products from the 1959 eruption of Kīlauea Iki, Kīlauea volcano, Hawai‘i, provides insights into the processes occurring during typical Hawaiian fountaining activity. This short-lived but powerful eruption contained 17 fountaining episodes and produced a cone and tephra blanket as well as a lava lake that interacted with the vent and fountain during all but the first episode of the eruption, the focus of this paper. Microtextural analysis of Hawaiian fountaining products from this opening episode is used to infer vesiculation processes within the fountain and shallow conduit. Vesicle number densities for all clasts are high (10⁶–10⁷ cm⁻³). Post-fragmentation expansion of bubbles within the thermally-insulated fountain overprints the pre-fragmentation bubble populations, leading to a reduction in vesicle number density and increase in mean vesicle size. However, early quenched rims of some clasts, with vesicle number densities approaching 10⁷ cm⁻³, are probably a valid approximation to magma conditions near fragmentation. The extent of clast evolution from low vesicle-to-melt ratio and corresponding high vesicle number density to higher vesicle-to-melt ratio and lower vesicle-number density corresponds to the length of residence time within the fountain.     

Recent Ostracoda from Port Pegasus,Stewart Island,New Zealand

Sixty‐one species are listed from 19 stations in the Port Pegasus area of Stewart Island, New Zealand. A chart showing bottom sediment characteristics for all samples is included. Because of the sparseness of the sampling stations no attempt was made to evaluate ostracod distribution in terms of depth zonations or assemblages. It is hoped, however, that the information presented will aid in the interpretation of the broader provincial aspect of ostracod distribution. This paper is the first to present scanning electron micrographs to illustrate a New Zealand ostracod fauna.