Rogue waves are huge, abnormal waves that occur unexpectedly. The waves are large compared to the state of the sea and pose a great danger to even the largest ships as they appear without warning with a great force. Sometimes rogue waves may appear from the direction opposite that of the prevailing normal waves in the vicinity. The waves are also referred to as monster waves, freak waves, extreme waves, or episodic waves. Rogue waves can easily wreck a ship by exerting great pressure in spite of the design of the ship. The appearance of rogue waves is likened to a wall of water.
Causes of Rogue Wave
There is no distinct documented cause of rogue waves because they are uncommon. However, when a combination of forces such as strong currents is accelerated by high winds, small waves merge to form an unexceptionally strong wave. Another thesis explains that the highest predictable risks occur where a robust current run to counter the basic direction of the normal wave. Other hypotheses that lead to the formation of rogue waves are:
Diffractive focusing is a hypothesis suggesting that the seabed shape directs a number of several small waves which meets in phases. The minor waves combine to give rise to one freak wave.
Focusing on Currents or Wave Energy
Numerous waves from one current are forced into an opposing normal current. The result is shortening of wavelength leading to the increase in the height of the wave after several waves dynamically join in. The oncoming waves compress together to form a rogue wave. Such waves clast for a longer period of time.
Rogue waves can be caused by modulation instability. It is hypothesized that such a natural nonlinear process leads to “sucking” of energy from adjacent waves hence grow into a near vertical wave. The model equation is the Nonlinear Schrödinger equation (NLS). The NLS model states that one normal wave may soak energy from other waves within its vicinity reducing their ripple and increasing itself. The NLS model is applicable mostly in deep water set up.
This hypothesis states that small swells in an ocean travel at different speeds and directions. As the swells pass through each other, their troughs, lengths, and crests collide or alternatively reinforce each other. Such a process can lead to the formation of towering waves. If the swells are moving in the same direction, then rogue waves form. Such waves last a short time.
Freshwater Rogue Waves
In rare instances, rogue waves have occurred in freshwater bodies such lakes. One of the disastrous shipwrecks of the 20th century is believed to have been caused by rogue waves. The Edmund Fitzgerald was wrecked on Lake Superior in North America. The 729-foot ship and the 29 crew members were lost.
Regions Prone to Rogue Waves
The Bermuda Triangle is believed to have the most ships wrecked by rogue waves. The triangular region in the Atlantic Ocean stretches off the coast of Bermuda, Florida, and Puerto Rico. Despite the theory of human error, there are high chances of rogue waves, especially in the 20th century. The tip of South Africa is also prone to rogue waves at Cape Agulhas near the southern tip of the African continent. The waves form from the Indian Ocean, South Atlantic Ocean, and the Southern Ocean. The Gulf Stream in the North Atlantic Ocean is also prone to rogue waves.