The most likely reason for the changes you described, including cracked and moved earth materials, flooding, and extreme erosion near a coastline, is:
A: Both an earthquake and a tsunami caused the damage.
This option recognizes that earthquakes can trigger tsunamis, which are known to cause significant coastal damage, leading to the effects you've described. While a tsunami alone could cause damage, the combination of both an earthquake and subsequent tsunami is a common cause of such extensive geological and hydrological alterations in coastal areas.