Differential glacio-isostatic uplift of crustal blocks at Glen Roy, Scotland

Detailed measurements of the altitudes of the shorelines of former ice-dammed lakes in Glen Roy and vicinity in the Scottish Highlands prove erroneous the conventional view that former shorelines in areas affected by glacio-isostatic uplift are uniformly tilted and/or gently warped. The measurements demonstrate differential uplift of blocks of the earth's crust. The surfaces of some blocks have no detectable tilt whereas others have gradients up to at least 4.6 m/km and are tilted in different directions. In three areas 0.7–2.0 km long, shorelines are distorted by crustal movements; all these areas have landslides attributed to earthquakes that accompanied the release of stress. In the area of greatest local distortion three shorelines rose about 3 m above their average altitudes for the immediately surrounding area, and a fault scarp was produced. Possibly these local distortions accompanied catastrophic lake drainage by jökulhlaup, analogous to crustal movements associated with man-made lakes. A relationship between crustal movement and the limit of a glacial advance is demonstrated. These findings have implications for other parts of the world affected by glacioisostatic uplift.