Rift valleys can form when fractures in the Earth's crust widen. The valley walls slowly move at a rate of only a few millimeters a year. Which of these best describes the types of tectonic activity that forms rift valleys?
a.)
b.)
c.)
d.)

Rift valleys can form when fractures in the Earths crust widen The valley walls slowly move at a rate of only a few millimeters a year Which of these best descr class=