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Generally, the ages on a well-preserved moraine surface show unimodal normal distribution.Frequently, erosion, exhumation and boulder toppling are blamed for the younger outliers.

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Due to the geomorphic complications after deposition, such as degradation, exhumation, bedrock erosion, snow cover and toppling of boulders, several (n1-2 m) samples should be dated to obtain a reliable age distribution.

These particles interact with atoms in atmospheric gases, producing a cascade of secondary particles that may in turn interact and reduce their energies in many reactions as they pass through the atmosphere.

By the time the cosmic ray cascade reaches the surface of Earth it is primarily composed of neutrons.

Assuming a constant rate of production, the number of atoms of Be-10 and Al-26 that accumulate in a rock surface will be proportional to the length of time the rocks were exposed to cosmic ray bombardment and the respective rates of radioactive decay for each isotope.

An age determined by measurement of the amount of each nuclide would be an estimate of the age of the surface exposure, that is, the surface could have been exposed for much longer than the minimum calculated age.