Mudslide

The hillside lets go all at once, and the land itself becomes the enemy.

Starts with a soil-heavy slope stripped by over-grazing, fire, drought, too much rain, or traffic, then triggered by sudden heavy rain or fools crossing the unstable ground. It sweeps people, stones, and trees away, buries victims, crushes them, deprives them of air, and leaves a slick muddy swath behind.

Kind Environmental or Procedural Threat