Answer :
Primary succession is one of the two types of ecological succession of the life of plant. This type pertains to that which occurs after a place is devoid of vegetation. From the given choices, the phenomenon or happening that would cause a loss of vegetation is a lava flow. Thus, the answer is the second choice.
A. Lava flow. Primary succession takes place when the structure of an ecosystem changes drastically in such a way that it can no longer support organisms. In this case of primary succession, lava flow completely alters the ecosystem and it occurs in such a way that this change is not caused by 'pioneer' organisms being edged out by better adapted organisms.
