Final answer:
Estinger, Riecken, and Schachter identified two significant aspects of the members' behavior prior to the flood date: preparations made by the members and changes in behavior within the group.
Step-by-step explanation:
Estinger, Riecken, and Schachter observed two significant aspects of the members' behavior during the weeks prior to the flood date. One aspect they noted was the preparations made by the members. This could include actions like stockpiling supplies, reinforcing structures, or making evacuation plans.
The second aspect observed was the change in behavior within the group. This could involve increased collaboration, cooperation, or cohesion among the members to handle the impending flood.