Abstract
The aim of this paper is to investigate Jökulhlaups: outbursts of ice-dammed lakes. The governing equations of unsteady water flow through straight, circular conduits, as derived by the authors in a previous paper, are compared with the equations of Nye, and for the steady state situation with Röthlisberger's theory. The dynamic theory is treated numerically by a finite-difference technique. Run-off simulations are illustrated for a model of the Grimsvötn Jökulhlaup, a periodic outburst of a subglacial lake beneath the Vatnajökull in Iceland. We study how various parameters, such as the friction coefficient of the conduit, and constants in the flow law of ice, influence the evolution of the outburst. In particular, we compute discharge hydrographs both incorporating and neglecting the rate of change of internal energy. It is shown that this term is not negligible and that the lake temperature, as a boundary condition, strongly influences the time-discharge relation and might explain the abrupt end of the outburst well before the lake has been emptied.
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