The safety of geological repositories has to be assured over very long time spans; whether such long-term performance can be achieved is assessed by safety analyses.
These analyses have to be based on an adequate understanding of system behaviour, which can be obtained in part from studies of so-called natural analogues - processes and situations similar to those occurring in a geological repository and its surroundings can also be found in nature. The information obtained from these studies improves our understanding of the long-term behaviour of radioactive waste repositories. Compared to short-term laboratory experiments, processes that have extended over thousands of years can be studied in nature.
During the span of a human lifetime, it is not possible to directly witness many geological processes as they occur very slowly. This lack of possibilities for direct observation can be made up by drawing conclusions from interpretations of natural phenomena.