Final answer:
Curved tree trunks, tilted fences, and broken retaining walls indicate a landslide, which is a form of mass movement caused by gravity on over-steepened slopes and can be exacerbated by factors like water saturation and geologic conditions such as faults.
Step-by-step explanation:
Curved tree trunks, tilted fences, and broken retaining walls are often signs of a type of mass movement known as a landslide. Landslides embody a range of ground movement, including rock falls, deep failures of slopes, and shallow debris flows. The usual trigger for a landslide is gravity acting on an over-steepened slope; however, several other factors contribute to this geological phenomenon, such as the saturation of slope material with water resulting in a debris flow or mud flow. When this happens, the mixed slurry of rock and mud can entrain various objects in its path, including trees, houses, and cars, often blocking structures like bridges and causing flooding.
Other factors contributing to landslides include geological conditions, like the types of faults present. For example, normal faults and reverse faults, including thrust faults, represent instances of Earth's crustal movement that can destabilize slopes. Erosion processes such as meandering, where rivers erode on the outer bend and deposit sediment on the inner bend, can also undercut slopes and contribute to their failure.