Question

How do natural disasters contribute to genetic drift?

Answer 1

Drastic changes in environmental conditions can sometimes cause drastic changes to the gene pool of the population.

Answer 2

Genetic drift is a random change in allele frequencies that occurs in a small population.  Because there are so few parents in small populations, the frequencies in the offspring produced may differ from allele frequencies in the parents. This can result in certain genes disappearing as individuals die, or do not reproduce. Natural disasters can wipe out certain individuals (or whole parts) of a population. When this happens, genetic drift is the result.