Slurry flows are typically a mixture of water and solid particles (such as soil, sediment, or other debris) that can move down slopes due to gravity. They are often associated with certain types of mass wasting or slope failures. Based on the options provided, the most fitting statement about slurry flows would be:
are a special type of slope failure.
Slurry flows can indeed be considered a form of slope failure in specific geological and hydrological contexts. The other options do not accurately represent the nature of slurry flows.