Why is there less chance for genetic drift if the population is large?
Changes in a small population have a large effect. The same changes in a large population will have a smaller effect
Blonde hair is a genetic mutation a loss of the genetic information that causes color in the hair. In a small population like Iceland the small the recessive genetic mutation has better chance of being expressed by people having the double recessive gene.
Blonde hair is considered attractive in Icelandic Culture so those with Blonde hair have a better chance of reproducing and passing on the gene, creating genetic drift.
In a larger population the gene for blonde hair will rarely be expressed. The gene will be lost and there is less chance that the blonde gene will affect the larger population.