Answer:
A) Remaining populations will have reduced genetic diversity
Step-by-step explanation:
A random mating population allows for genetic diversity as each individual have equal chance of been mated to and it allows for perpetuation of frequently occurring genes.
For a small population the frequency of allele is mostly fix with virtually all loci having the same genotype because mating is within small individual and genes whose frequency is few will be drifted out of the population.
Hence, after the eruption due to a small random population diversity will be reduced as diversity occur more in a large random mating population.