Answer:
Sand dunes and strong winds (~90 mph)
Step-by-step explanation:
Primary succession occurs in lifeless areas. That eliminates lava flow and bare rock. Sand dunes are also formed by this mode.
Secondary succession occurs in areas where an existing ecology has been wiped out by some disaster, such as a blowout in a dune.
A blowout is a steep sided valley in a sand dune caused by strong winds. They blow the beach sand inland and cover up existing vegetation, so the stages of succession must begin anew.