Which phenomenon describes waves spreading behind obstacles?

• A. Waves bounce off vertical surfaces
• B. Oscillation of water in enclosed basin
• C. Waves spread behind obstacles
• D. Underwater earthquake, landslide, eruption

Answer: (C)

Diffraction is the bending and spreading of waves as they meet an obstacle or pass through a gap, so energy and motion can appear behind the obstacle even when the direct path is blocked. This explains why waves wrap around rocks, breakwaters, or other barriers and continue to affect the water behind them, which is especially important to anticipate while paddling near obstacles. The other descriptions refer to different wave behaviors—waves bouncing back from a surface (reflection), standing wave patterns created in enclosed basins, and tsunamis generated by submarine events—so they describe other phenomena rather than how waves spread behind obstacles.