The level of the Grímsvötn subglacial lake, Vatnajökull, Iceland, monitored with SPOT5 images

The uplift map of Grímsvötn shows that 10.9 (± 1) km2 of ice was floating between 11 and 16 August 2004. The ice shelf rose by 1.7 (± 0.6) m indicating that the volume of liquid water in the lake increased by 0.018 (± 0.007) km3. Our field observations show that surface melting due to meteorological processes contributed 70% of the accumulated water, hence, the rest originated from ice melted by the subglacial geothermal activity. The power required to melt 0.005 km3 (water equivalent) of basal ice in 5 days is 4000 MW. The applicability of the technique can be extended to volcanology and seismology, and even landslides or subsidence, when finer-resolution optical images become available. Applied to two pairs of images, it could solve for the 3-dimensional displacements of the Earth's surface.