Travelers should always be aware of their surroundings when exploring the outdoors, but Yosemite National Park is warning summertime visitors about something they may not expect: falling tree branches.

In a recent post on Instagram, the park explained that Summer Branch Drop is “a seasonal occurrence when a seemingly healthy tree suddenly loses a limb, oftentimes without warning.”

The Northern California park says it’s most common among its black oak trees, “on particularly hot, calm afternoons when there is no wind.”

Unlike branches broken by wind, the park says these limbs usually break along a horizontal line, away from the tree trunk, even though the branches “appear to be quite sound.”

“There is no way to know exactly when Summer Branch Drop is going to occur, but there are a few things you can do to prevent injury,” the park said.

It shared the following safety tips for Yosemite visitors:

• Don’t sit or pitch a tent below black oak trees on hot days.
• Don’t leave anyone with mobility issues under the trees.
• Avoid already damaged trees and report new damage to park officials.
• If you hear a crack overhead, quickly get away.