Nial Peters

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.

The absolute sensitivity of digital colour cameras

A new and improved method to obtain the average spectral pixel responsivity and the quantum efficiency of Digital Single Lens Reflex (DSLR) cameras is outlined. Two semi-professional cameras, the Nikon D300 and the Canon 40D, are evaluated. The cameras red, green and blue pixel responsivities and quantum efficiency are retrieved by illuminating an integrating sphere with a wavelength tunable monochromator. 31 intensity calibrated monochromatic spectral lines from 4000 to 7000 A, with a bandpass of approximately 12 A, were used as a library to solve the main equations of observation for the cameras. Both cameras have peak sensitivity in the blue and minimum sensitivity in the red. The Canon 40D has blue and green channel sensitivity close to the Nikon D300. The Canon red channel has half the sensitivity of the Nikon camera.

A CO2‐gas precursor to the March 2015 Villarrica volcano eruption

We present here the first volcanic gas compositional time-series taken prior to a paroxysmal eruption of Villarrica volcano (Chile). Our gas plume observations were obtained using a fully autonomous Multi-component Gas Analyser System (Multi-GAS) in the 3 month-long phase of escalating volcanic activity that culminated into the March 3 2015 paroxysm, the largest since 1985. Our results demonstrate a temporal evolution of volcanic plume composition, from low CO2/SO2 ratios (0.65-2.7) during November 2014-January 2015 to CO2/SO2 ratios up to ≈ 9 then after. The H2O/CO2 ratio simultaneously declined to <38 in the same temporal interval. We use results of volatile saturation models to demonstrate that this evolution toward CO2-enriched gas was likely caused by unusual supply of deeply sourced gas bubbles. We propose that separate ascent of over-pressured gas bubbles, originating from at least 20-35 MPa pressures, was the driver for activity escalation toward the March 3 climax.

Numerical analysis of rapid water transfer beneath Antarctica

We use a simple energy-conservation model and a model based on Rothlisbergers theory for steady-state water flow in a subglacial conduit to model water movement between lakes in the Adventure subglacial trench region of East Antarctica during a 1996-98 jokulhlaup. Using available field evidence to constrain the models suggests that water flow would likely be accommodated in a tunnel with a cross-sectional area of 36 m 2 and a value for k (the reciprocal of Mannings roughness parameter) larger than the 12.5 m 1/3 s -1 previously calculated. We also use Nyes theory for time-dependent conduit water flow to model the temporal evolution of conduit discharge, cross-sectional area, water pressure and lake draining and filling during the flood. We initially assume one source and one sink lake. We perform sensitivity tests on the input parameter set, matching modeled source- and sink-lake depth changes with measured surface elevation data. Using a simple function for vertical ice deformation in which surface deformation scales linearly to the lake depth change, we find the scaling factor is of the order 4 × 10 -3 of the ice thickness. The most likely value of k lies in the range 55-68 m 1/3 s -1 , and the ratio of source to sink-lake radii is approximately 1:1.4. Finally, we experiment using Nyes theory to model water movement between one source and three sink lakes. The model fails to produce the observed patterns of water movement as indicated by the surface deformation data.

Plumetrack: Flux calculation software for UV cameras

Abstract Ultraviolet (UV) cameras are increasingly employed to map and measure SO2 abundances in volcanic emissions to the atmosphere. The main purpose of this is to estimate mass fluxes of SO2, which requires estimation of the transport velocity of the plume. In this paper, we present Plumetrack, open-source Python based software for computing SO2 fluxes from calibrated UV camera images. Designed to be the final component in UV camera processing toolchains, Plumetrack provides functionality for velocity estimation using optical-flow, flux calculation and error estimates. It can be used interactively via a graphical user interface or for batch processing via a commandline interface. We discuss the features and implementation details of Plumetrack, describe in detail a new flux calculation algorithm and demonstrate its performance on a set of synthetic UV camera images. The new algorithm is found to out perform the established flux calculation method, especially for highly spatiotemporally variable plumes. Furthermore, we show that the Plumetrack software may be successfully used with data from other imaging systems such as standard video cameras.

Ion velocity filter effect observed in dayside hydrogen aurora

[1] Observations of dayside auroral hydrogen emissions of H α (A656.3 nm) were carried out using spectrometers on Svalbard at Ny-Alesund (NYA: 76.3°N, 111.0°E CGM) and Longyearbyen (LYR: 75.3°N, 111.9°E CGM). Using a Monte Carlo model, simulated Doppler profiles were fitted to the spectra to estimate precipitating proton energy. A difference in energy was found between the sites for approximately 45 minutes. When combined with measurements of antisunward convection, the energies are consistent with the inverse variation of ion energy with latitude observed by satellites in the cusp region, known as the ion velocity filter. This is the first measurement of the ion velocity filter effect in the dayside aurora using ground-based optical instrumentation. The increasing difference in energy observed is interpreted as a measure of the decreasing merging rate at the magnetopause.