Which of the following is a reason the Gros Ventre rockslide took place?
-A sandstone bed acted as a layer of slip, upon which all of the overlying sediments moved downslope.
-The sedimentary strata were dipping at a very high angle.
-A large earthquake triggered this event.
-Much of the tree cover from the mountain flank was removed, thereby decreasing slope strength.
-Because the river eroded material at the valley base, there was no support of the material upslope.