Conditions for bubble elongation in cold ice-sheet ice

Highly elongated bubbles are sometimes observed in ice-sheet ice. Elongatio n is favored by rapid ice deformation, and opposed by diffusive processes. We use simple models to show that vapor transport dominates diffusion excep t possibly very close to the melting point, and that latent-heat effects ar e insignificant. Elongation is favored by larger bubbles at pore close-off, but is nearly independent of bubble compression below close-off The simple presence of highly elongated bubbles indicates only that a critical ice-st rain rate has been exceeded for significant time, and provides no informati on on possible disruption of stratigraphic continuity by ice deformation.