Which of the following describes a cause-and-effect relationship with Washington's geography

1. Erosion of mountain ranges resulted in huge valleys and mountain passes that connected the two halves of the state
   
2. The breakup of Pangaea increased the amount of rainfall in the eastern region of Washington
   
3. The melting of glacial ice dams led to floods that created a massive erosion on the Columbia Plateau
   
4. Volcanic activity resulted in the creation of fjords, such as Puget Sound
   
   

I think the answer is 3 just not so sure though