A siphon hazard in moving water is most likely caused by which feature?

• A. Undercut rocks, sucking current
• B. Submerged rock overhang
• C. Strong wind gusts
• D. Sudden drop-offs

Answer: (A)

In moving water, a siphon hazard shows up when a rock is undercut, leaving a hollow behind it. Water is funneled through a narrow space and around the rock, speeding up as it passes. This fast, accelerated flow creates a low-pressure region at the entrance and can pull surface water and anything near the cavity into the hollow, much like a siphon. A kayaker or a limb can be drawn toward the cavity and become entrapped or swept into the hole, with the downstream current making release difficult. That pull is the classic siphon effect associated with undercut rocks. Other hazards—like wind gusts affecting balance or sudden drop-offs causing a fall—pose danger in moving water too, but they don’t create this specific suction channel that draws you into a hollow behind a rock. The key idea is recognizing that the hollow behind an undercut rock acts like a siphon, drawing water and objects into the cavity.