Glacio‐isostatic crustal movements caused by historical volume change of the Vatnajökull Ice Cap, Iceland

Measurements of the lake level of Lake Langisjór at the SW edge of the Vatnajökull ice cap indicate a tilt of 0.26 ± 0.06 μrad/year away from the ice cap in the years 1959–1991. The tilt is too large to be explained as an elastic Earth response to ice retreat this century, or to be caused by change in the gravitational pull of the ice cap, but it can be explained by sub‐lithospheric viscous adjustment. Regional subsidence in historical times in SE Iceland can similarly be attributed to viscous adjustment resulting from the increased load of Vatnajökull during the Little Ice Age. The inferred sub‐lithospheric viscosity is 1 × 10¹⁸ − 5 × 10¹⁹ Pa s.