Rock massifs are subject to long-term deformations, as well as to environmental effects. Decades of precise crack gauging have led to a series of qualified results of practical importance to geotechnical engineering. Slow deep-seated rock slope movements have been observed and monitored in cases where long-term stability was anticipated. In addition to movement trends, specific events of acceleration were detected and impulse periods determined. Examples in the field of geotechnics are given, which include an observed rock massif response to prestressed anchors, a history of slope instability affected by human interference, and evaluation of fault-controlled stability in a railway cutting affected by long-term rock weathering.