The purpose of this brief note is to draw the attention of historians interested in the ancient Erythraean Sea world to a short excerpt from Agatharchides of Cnidus’ treatise entitled On the Erythraean Sea1. To my knowledge, this text has not elicited any particular comments from commentators on Agatharchides, with the exception of D. Woelk (see below). In this passage, Agatharchides recounts in a few lines a myth that was common among the Ikhthyophagoi (“Fish-Eaters”), a people living on the African coast of the Red Sea (an area also known as Trôgodytikê). There is little doubt, as we shall see, that this ancestral myth refers to a tsunami that struck the coastline inhabited by some of these Ikhthyophagoi.
1. Introductory remarks
a) What is a tsunami ?
A tsunami is a maritime phenomenon whose true power is visible on the coastline but whose causes often originate in the open sea. To summarize what a tsunami is in a few lines, I reproduce below the essential elements of the article from Britannica Academic2.
“Tsunami, (…) also called seismic sea wave or tidal wave: catastrophic ocean wave, usually caused by a submarine earthquake, an underwater or coastal landslide, or a volcanic eruption. (…). After an earthquake or other generating impulse occurs, a train of simple, progressive oscillatory waves is propagated great distances over the ocean surface in ever-widening circles, much like the waves produced by a pebble falling into a shallow pool. In deep water a tsunami can travel as fast as 800 km (500 miles) per hour. The wavelengths are enormous, sometimes exceeding 500 km (about 310 miles), but the wave amplitudes (heights) are very small, only about 30 to 60 cm (1 to 2 feet). The waves’ periods (the lengths of time for successive crests or troughs to pass a single point) are very long, varying from five minutes to more than an hour. (…). As the waves approach the coast of a continent, however, friction with the rising sea bottom reduces the velocity of the waves. As the velocity lessens, the wavelengths become shortened and the wave amplitudes (heights) increase. Coastal waters may rise as high as 30 metres (about 100 feet) above normal sea level in 10 to 15 minutes. The continental shelf waters begin to oscillate after the rise in sea level. Between three and five major oscillations generate most of the damage, frequently appearing as powerful “run-ups” of rushing water that uproot trees, pull buildings off their foundations, carry boats far inshore, and wash away entire beaches, peninsulas, and other low-lying coastal formations. (…) Much like any other water waves, tsunamis are reflected and refracted by the topography of the seafloor near shore and by the configuration of a coastline. As a result, their effects vary widely from place to place. Occasionally, the first arrival of a tsunami at a coast may be the trough of the wave, in which case the water recedes and exposes the shallow seafloor . Such an occurrence took place in the bay of Lisbon, Portugal, on November 1, 1755, after a large earthquake; many curious people were attracted to the bay floor, and a large number of them were drowned by the wave crest that followed the trough only minutes later.”
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