Geology topics

William B. Durham

Publications and source records attributed to William B. Durham.

5 recordsLinked to original sources

USGS2018

Inhibition of grain boundary sliding creep in fine-grained ice by inter-granular particles: Implications for planetary ice masses

Ice in both terrestrial and planetary settings often contains rock particles. Here we present an experimental investigation of the influence of intergranular particles on the rheological behavior of ice. Experiments were performed on samples fabricated from 10‐μm ice powders +1‐μm graphite or 0.8‐μm alumina particles and subjected to elevated confining pressures. A critical particle fraction, ∼6%, was observed, below which samples behave like pure ice and deform by both grain boundary sliding (GBS) and dislocation creep, and above which GBS creep is impeded. Above this critical fraction, ice grains occur in particle‐free clusters surrounded by bands of particles mixed with fine‐grained ice, resulting in the impedance of GBS in the bands as well as sliding between the ice clusters. Our results imply that South Polar Layered Deposits and midlatitude lobate debris aprons on Mars must contain >94% ice and that the shallow subsurface of Ceres could contain >90% ice.

Geophysical Research Letters↗

USGS2006

Methane Hydrate Dissociation Rates at 0.1 MPa and Temperatures above 272 K

We performed rapid depressurization experiments on methane hydrate under isothermal conditions above 272 K to determine the amount and rate of methane evolution. Sample temperatures rapidly drop below 273 K and stabilize near 272.5 K during dissociation. This thermal anomaly and the persistence of methane hydrate are consistent with the reported recovery of partially dissociated methane hydrate from ocean drilling cores.

Annals of the New York Academy of Sciences↗

USGS1999

Steady-state flow of solid CO2: Preliminary results

To help answer the question of how much solid CO 2 exists in the Martian south polar cap, we performed a series of laboratory triaxial deformation experiments at constant displacement rate in compression on jacketed cylinders of pure, polycrystalline CO 2 . Test conditions were temperatures 150 < T < 190 K, hydrostatic confining pressures 5≤ P ≤40 MPa, and strain rates 4.5×10 −8 ≤ ε ≤4.3×10 −4 s −1 . Most of the measurements follow a constitutive law of the form ε = Aσ n exp(−Q/RT), where σ is the applied differential stress, R is the gas constant, and the other constants have values as follows: A = 10 3 86 MPa −n s −1 , n = 5.6, and Q = 33 kJ/mol. Solid CO 2 is markedly weaker than water ice. Our results suggest that the south polar cap on Mars is unlikely to be predominately solid CO 2 , because the elevation and estimated age of the cap is difficult to reconcile with the very weak rheology of the material.

Geophysical Research Letters↗

USGS1996

Peculiarities of methane clathrate hydrate formation and solid-state deformation, including possible superheating of water ice

Slow, constant-volume heating of water ice plus methane gas mixtures forms methane clathrate hydrate by a progressive reaction that occurs at the nascent ice/liquid water interface. As this reaction proceeds, the rate of melting of metastable water ice may be suppressed to allow short-lived superheating of ice to at least 276 kelvin. Plastic flow properties measured on clathrate test specimens are significantly different from those of water ice; under nonhydrostatic stress, methane clathrate undergoes extensive strain hardening and a process of solid-state disproportionation or exsolution at conditions well within its conventional hydrostatic stability field.

Science↗

USGS1987

Inelastic properties of several high pressure crystalline phases of H2O: Ices II, III, and V

We have performed deformation experiments on cylinders of polycrystalline H 2 O at temperatures from 178 to 257 K at pressures to 500 MPa in the stability fields of ices II, III, and V. Ice II is the strongest of the phases, having a strength under laboratory conditions roughly comparable to that of ice I h . Ice V is somewhat weaker than ice II. Ice III is extremely weak and over geologic times must behave essentially as a liquid bounded below by ice V and above by ice II or I h . Phase relationships are complicated by a number of phase metastabilities, the most important of which is the existence of ice III in the ice II field for extended periods of time. Even under deformation at temperatures as low as 211 K (over 30 K below the ice III field), the transformations from III to II can not be made to happen in the laboratory.

Journal de Physique Colloques↗