It's one thing to deal with human moral evil. We know that God has allowed us the free exercise of our agency, and there is no way for us to be genuinely free if we are not at liberty to do evil as well as good. Accordingly, moral evils are to be expected in this life. "It must needs be that offences come; but woe to that man by whom the offence cometh!" (Matthew 18:7).
Natural evils, however, pose a different kind of problem. Why have horrific plagues killed so many people? Why are Boy Scouts sometimes hit by lightning? Why do crops fail, leading to famines? Why must tectonic plates intersect in such a manner as to cause massive earthquakes and tsunamis? Are such things really necessary to our mortal probation?
A Latter-day Saint believer will be inclined to answer yes. Faith isn't merely or even principally agreement with a checklist of historical and doctrinal assertions. Faith is trust — trust in a person. Even if we can't now understand, our trust in a loving and incomprehensibly wise Heavenly Father teaches us to believe that there are necessary and sufficient reasons for him to permit natural evils. (We now know, in fact, that active tectonic plates are vital to the origin and continuation of life on earth; among other functions, they maintain the proper level of acidity in the oceans.)