Vandalism is a huge problem at US National Parks. While most visitors stick to the principles of leave no trace, a few feel the need to make their mark for others to see. Carving initials into trees causes permanent damage, and graffiti on rocks can often only be removed with harsh chemicals or sandblasting, both of which can kill plants and insects while causing environmental damage.
Grand Prismatic, the most famous geothermal spring at Yellowstone is uniquely vulnerable, and its colorful bacterial mats can be seriously damaged by visitors walking on the surface or using sticks to draw in the surface, possibly thinking it is 'only mud'.
