A municipality is generally not liable for injuries which result from the "natural causes" of snow and ice on city sidewalks. Three recent Alaska decisions held that pedestrian and vehicular traffic which caused rough surfaces on sidewalks and crosswalks were also "natural causes."
Alaska Case Law,
Torts—Municipal Liability—"Natural Causes"—Climatic Conditions and Vehicular Traffic,
40 Wash. L. Rev.
Available at: https://digitalcommons.law.uw.edu/wlr/vol40/iss2/24