Equilibrium State of Jakobshavns Isbræ, West Greenland

Abstract

Jakobshavns Isbra;, located at 69°10′ Ν on the west coast of Greenland, is the world’s fastest known glacier. Measurement of surface velocities at the calving front in July of 1964, 1976, 1978, 1985, and 1986 yielded a mean velocity of 20.6 m/d. Variation in mean velocity from year to year is less than 1 m/d. Velocity measurements 10 km behind the calving front indicated mean annual velocities of 17.1 m/d compared to mid-summer velocities of 17.6 m/d. The maximum possible decline in winter velocity is then 7%. Calculation of the volume flux into the fjord is 3.72 × 10¹⁰ m³ a⁻¹ ± 10%. The surface balance of Jakobshavns Isbræ is 3.37 × 10¹⁰ m³ a⁻¹ ± 12%. The agreement between these balance calculations, the long-term stability in glacier velocity, and the reasonably stable glacier front indicate that Jakobshavns Isbræ is in a state of near equilibrium, with probably a small negative balance.