In the past two decades, mass loss from the Greenland ice sheet has accelerated, partly due to speedup of glaciers. However, uncertainty in speed derived from satellite products hampers detection of inland changes. In-situ measurements using stake surveys or GPS have lower uncertainties. To detect inland changes, we repeated in-situ measurements of ice-sheet surface velocities at historical locations first measured in 1959. Here, we show ice velocities have increased 5-15% across all deep inland sites. Several sites show a northward deflection of 3-4.5° in their flow azimuth. The recent appearance of a network of large transverse surface crevasses, bisecting historical overland traverse routes, may suggest a fundamental shift in local ice dynamics. We suggest that creep instability - a coincident warming and softening of near-bed ice layers - may explain recent acceleration and rotation, in the absence of a change in local driving stress. This mechanism, if included in simulations may improve projections of future ice loss.
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