Final answer:
Overpressurized pore water causes slope failure by decreasing friction, leading to reduced stability and potential landslides.
Step-by-step explanation:
Overpressurized pore water in a pile of sediments can cause slope failure because it leads to decreased friction among the sediment particles.
This decrease in friction reduces the ability of the slope material to stay in place, contributing to reduced stability of the slope.
Factors such as erosion by rivers, heavy rains, earthquakes, volcanic eruptions, and excess weight due to various reasons can all contribute to overpressurization of pore water in sediments, thus increasing the likelihood of slope failure or landslide.