What are oscillatory waves in inland bodies of water called?

• A. Tides
• B. Tsunamis
• C. Seiches
• D. Swells

Answer: (C)

Seiches are standing, oscillatory waves that form in inland bodies of water such as lakes, reservoirs, or bays. When a disturbance—like strong wind, changes in atmospheric pressure, or a ground shake—shakes the water, energy is trapped and reflects back and forth between opposite shores. This sets up a back-and-forth sloshing, rather than a moving wave traveling across the surface.

The period of a seiche depends on the basin’s size and depth; larger or deeper basins have longer oscillation periods, often ranging from minutes to hours. A simple way to think about it is that the water is trying to slosh from one end of the basin to the other and back, with the basin acts like a resonant cavity for gravity waves.

This phenomenon is different from tides, which are caused by the gravitational pull of the Moon and Sun and produce regular, global daily patterns; tsunamis, which are long-wavelength waves generated by submarine earthquakes traveling across oceans; and swells, which are waves generated by storms at sea that propagate across large distances and are not confined to inland waters. Seiches are unique to enclosed or semi-enclosed basins and are characterized by this standing-wave, back-and-forth motion.