What type of landslide movement is characterized by a turning moment about a point above the center of gravity?

The type of landslide movement described as having a turning moment about a point above the center of gravity is best characterized as a rotational slide or slump. This type of movement occurs when a mass of soil or rock moves down a slope along a curved surface, leading to a rotation of the material about a pivot point.

In a rotational slide, the failure surface is typically curved concavely upward, and as the material slips downwards, it rotates backward about a point located above the center of gravity. This is in contrast to translational slides, which involve movement along a relatively planar surface without rotation.

Debris flows and silt flows are characterized by more fluid movement, often involving the mixture of soil and water, but they do not exhibit the rotational aspect that is central to a slump. Therefore, the precise nature of the rotational movement and its distinction from other types of landslide behavior firmly supports the identification of a rotational slide or slump as the correct answer.