The active layer thaws and freezes seasonally. The annual freeze–thaw cycle of the active layer causes significant surface height changes due to the volume difference between ice and liquid water. We estimate the subsidence rate and active-layer thickness (ALT) for part of northern Alaska for summer 2017 to 2022 using interferometric synthetic aperture radar and lidar. ALT estimates range from ~20 cm to larger than 150 cm in area. Subsidence rate varies between close points (2–18 mm per month).

In Antarctica, supraglacial lakes often form near grounding lines due to surface melting. We model viscoelastic tidal flexure in these regions to assess its contribution to lake drainage via hydrofracturing. Results show that tidal flexure and lake-water pressure jointly control drainage near unconfined grounding lines. Sensitivity analysis indicates the importance of the Maxwell time of ice in modulating the tidal response.