Everyone has at some time thrown a stone into water and stood mesmerized, watching the ripples spreading effortlessly outwards and onwards. Whenever we contemplate the sea or ocean, we see the surface stirred by waves. These surface waves are oscillations in the water’s surface, most commonly generated by the wind. Strong, long lasting winds blowing over great distances create the biggest waves.

Waves provide a means of transmitting energy through water with relatively small displacement of the water particles in the direction of the energy flow. The water particles move in orbital fashion. For oscillations to exist and grow they must have a returning force and in the case of surface waves the returning force is gravity, the pull of the Earth. In deep water, waves move freely through the water but as the wave approaches shallow coastal waters its base catches on the sea bed and slows down while the top carries on, curls over and crashes down and breaks.

Other waves exist within the ocean and these have various causes such as interactions with waves, tides and atmospheric disturbances.

Tidal waves are large incoming waves which are caused by high wind or spring tides, whilst tsunamis (Japanese for “harbour wave”) are caused by disturbances associated with undersea earthquakes, seabed slides, or large volcanic eruptions (such as Krakatoa in 1883,) and are therefore usually impossible to predict. Tsunamis are formed by a sudden massive uplift or subsidence of the sea bottom, as if a large plunger was suddenly moved up or down. They travel at exceptionally high speed (in deep water they can reach speeds of more than 600 miles per hour) and are extremely long in length and duration. As tsunamis enter the shallow waters of the coastline, their velocity decreases and their height can increase to more than 100 feet so that they strike with devastating force causing wide spread destruction to shoreline life and facilities.

More on tsunamis:

The Lisbon Earthquake, 1755
Killer tidal waves - fact or fiction?