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Related Concept Videos

Kinetic and Potential Energy of a Wave01:10

Kinetic and Potential Energy of a Wave

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All forms of waves carry energy; this is directly visualized in nature. For instance, the waves of earthquakes are so intense that they can shake huge concrete buildings, causing them to fall. Loud sounds can damage nerve cells in the inner ear, causing permanent hearing loss. The waves of the oceans can erode beaches. 
In mechanical waves, the amount of energy is related to their amplitude and frequency. In the context of the above examples, large-amplitude earthquakes produce large...
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Standing Waves01:17

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Sometimes waves do not seem to move; rather, they just vibrate in place. Unmoving waves can be seen on the surface of a glass of milk kept in a refrigerator, which is one example of standing waves. Vibrations from the refrigerator motor create waves on the milk that oscillate up and down but do not seem to move across the surface. These waves are formed or created by the superposition of two or more identical moving waves in opposite directions. The waves move through each other, with their...
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Wave Parameters01:10

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The simplest mechanical waves are associated with simple harmonic motion and repeat themselves for several cycles. These simple harmonic waves can be modeled using a combination of sine and cosine functions. Consider a simplified surface water wave that moves across the water's surface. Unlike complex ocean waves, in surface water waves, water moves vertically, oscillating up and down, whereas the disturbance of the wave moves horizontally through the medium. If a seagull is floating on the...
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Shock Waves01:16

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While deriving the Doppler formula for the observed frequency of a sound wave, it is assumed that the speed of sound in the medium is greater than the source's speed through it. When this condition is breached, a shock wave occurs.
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Interference and Diffraction02:18

Interference and Diffraction

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Interference is a characteristic phenomenon exhibited by waves. When two electromagnetic waves interact with their peaks and troughs coinciding, a resulting wave with enhanced amplitude is produced. This is known as constructive interference. In this case, the two waves interacting are in phase with each other.
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Travelling Waves01:04

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A wave is a disturbance that propagates from its source, repeating itself periodically, and is typically associated with simple harmonic motion. Mechanical waves are governed by Newton's laws and require a medium to travel. A medium is a substance in which a mechanical wave propagates, and the medium produces an elastic restoring force when it is deformed.
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Related Experiment Video

Updated: Feb 20, 2026

Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing
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Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing

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Hafgerðingar and giant waves.

Siebren van der Werf

    Applied Optics
    |October 20, 2017
    PubMed
    Summary

    The King's Mirror describes sea fences, a phenomenon explained as a superior mirage. This study extends the analysis, showing periodic changes in atmospheric inversion layers explain the illusion of giant waves.

    Area of Science:

    • Atmospheric optics
    • Oceanography
    • Historical meteorology

    Background:

    • A 13th-century Norse text, The King's Mirror, describes 'sea fences' (hafgerðingar) in the Greenland Sea.
    • This phenomenon involves a raised horizon and the appearance of three giant waves.
    • Previous research by Lehn and Schroeder proposed a superior mirage explanation.

    Purpose of the Study:

    • To extend the superior mirage explanation for 'sea fences'.
    • To investigate the role of time-dependent atmospheric properties.
    • To explain the illusion of incoming waves and perceived danger.

    Main Methods:

    • Analysis of optical phenomena in the Greenland Sea.
    • Mathematical modeling of atmospheric inversion layers.

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  • Incorporation of periodic time dependence into optical models.

    • Main Results:

    • The study supports the superior mirage hypothesis for 'sea fences'.
    • Periodic variations in the inversion layer's properties can create the illusion of waves.
    • This model explains the visual characteristics and perceived threat of the phenomenon.

    Conclusions:

    • Superior mirages, influenced by dynamic atmospheric conditions, can explain historical accounts of 'sea fences'.
    • The illusion of dangerous, incoming waves is a plausible consequence of these optical effects.
    • This research provides a scientific basis for understanding a historical maritime observation.