Geologic hazards are often interrelated. This is especially true for unstable slopes. Slopes may become unstable for a variety of reasons such as the character of a geologic formation or the occurrence of earthquakes, rain, fire, melting permafrost, or rapid deglaciation. In addition, rapid down slope movement of large quantities of material into or under water can generate tsunamis. Surficial and engineering geologic maps and geologic hazard reports often contain information about landslides in an area.