Twentieth-century changes in Norwegian glaciers have been pronounced, but the different geometries and dynamics of the glaciers have caused different responses to similar climatic changes. Close to the Arctic Circle, all the glaciers of Svartisen, the largest ice-covered area of northern Scandinavia, have retreated since the beginning of the century. However, several of the smaller glaciers which end at relatively high altitude have experienced both periods of advance and periods of retreat since the mid-1960s. The mass balance of Engabreen, the largest of the West Svartisen glaciers, was positive in 21 of the 27 years to 1995–96. The sizes of most of the glaciers of the Okstindan area, 60 km south-east of Svartisen, have also decreased throughout the twentieth century, but Corneliussens Bre, a small glacier at the eastern side of the massif, has been advancing since 1970. The areas supplying some of the southern glaciers of Okstindan have been reduced as a result of changes in ice thickness at high altitude. Studies of glacier change are aided by the use of digital terrain models (DTMs). Triangular irregular network DTMs of the surface and bed topography of the largest of the Okstindan glaciers, Austre Okstindbreen, have been used in studies of mass-balance variations and changing surface flow patterns between 1976 and 1995.