The Fallout from the Thera Eruption

By: Nicholas Hartmann

Originally Published in 1987

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The effects of the Thera eruption on the island itself were devastating. Estimates of the amount of volcanic material (tephra) ejected during the eruption range from 3 to 28 cubic kilometers. Much of this volume fell back directly onto the island, burying parts of it under 30 meters of debris. Thera would also have suffered violent earthquakes before and during the eruption, and was repeatedly raked by white-hot avalanches of volcanic gas and dust called “base surges.”

The eruption’s effects on the rest of the Aegean and the Mediter ranean have been the subject of lively debate among geologists and archaeologists. The evidence is sparse and equivocal, and scholars are by no means unanimous even now, but these statements are probably accurate:

—The noise of the first explosion was heard all over the eastern Mediterranean. Although the total power released by the eruption was comparable to that of a multi- megaton thermonuclear bomb, the volcanic event released its energy over a much longer period of time, so that outside the island itself, there were none of the “blast effects” associated with nuclear weapons.

—An unknown proportion of the tephra released from the crater was carried away by winds at low and high altitudes. Sea-floor soundings have detected ash from the Thera eruption throughout the Aegean and eastern Mediterranean, with a distribution indicating that winds were from the northwest. Tephra may have reached as far as north western Cyprus (800 km away), and portions of the island of Crete were covered with ash, to depths estimated at between 5 millimeters and 10 centimeters. The most noticeable effect was darkness: complete blackness over the island for a period of days to weeks, and perceptible darkening for days over the entire Aegean area. If sufficient quantities of ash were propelled into the upper atmosphere and circulated around the globe by high-altitude winds, the amount of sunlight reaching the Earth’s surface would have decreased, and there would have been effects on climate worldwide for a period of years after the eruption.

—When the magma chamber beneath the island finally collapsed to form a caldera, the result was an underwater shock wave called a tsunami, a Japanese word far what is often inaccurately called a tidal wave. Tsunamis are unlike ordinary sea waves: they travel at up to 750 kilometers per hour across open sea, and contain a huge amount of energy. One calculation indicates that the collapse of the Thera caldera generated a tsunami that was 11 meters high when it struck the north coast of Crete near Herakleion. Such a wave might have penetrated some distance inland. This assumes, however, that the collapse occurred essentially all at once; if the process was slower, the sequence of smaller tsunamis would have been much less destructive.

This is an excerpt from, Atlantis Lost and Found.

Cite This Article

Hartmann, Nicholas. "The Fallout from the Thera Eruption." Expedition Magazine 29, no. 2 (July, 1987): -. Accessed February 29, 2024.

This digitized article is presented here as a historical reference and may not reflect the current views of the Penn Museum.

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