Select the two options that are true. view available hint(s) select the two options that are true.

a. the angle of repose is the same value for all types of rocks, sediment, or soil.
b. material, sediment for example, fails when it comes to rest below its angle of repose.
c. existing structural weakness zones cannot promote landsliding.
d. mass wasting can occur gradually over time or in sudden catastrophes.
e. external geologic events such as earthquakes or volcanoes can trigger sudden mass-wasting events.

D. Mass wasting can occur gradually over time or in sudden catastrophes.

E. External geologic events such as earthquakes or volcanoes can trigger sudden mass-wasting events.

Explanation:

D) mass wasting such as mudflows can move at a rate of 1cm to 1m per second due to the angle and the addition of high volumes of water. However, soil creep can move as little as 0.1mm-1cm per year.

E) Earthquakes create seismic waves and transient stress on a slope. These waves can cause a slope to lose its shear strength, its ability to hold up the slope. During a volcanic eruption, the motion of the eruptions to the addition of falling debris to a slope might add to the shear stress, the force acting on the slope to cause a mass-wasting event.