Pumice on south Mediterranean - remnant of the Thera eruption?

On the Mediterranean coast west of the city of Alexandria, in Egypt, there is a belt of pumice embedded in the sedimentary stone that covers the landscape there. This article describes this belt and its possible origins.

Introduction:

On the Mediterranean coast west of the city of Alexandria, in Egypt, there is a belt of pumice embedded in the sedimentary stone that covers the landscape there.

As a youngster, I used to spend summers in Agami Abou Youssef, a resort area 18.5 km West of Alexandria, and I remember with curiosity wondering what this belt was.

Pumice is an unusually light rock due to the many bubbles inside it. Most pumice floats on water. It is formed by volcanic eruptions when molten lava is shot in the air with many bubbles of gas in it. As it cools, it solidifies into pumice.

Description:

The belt is about one meter or less wide, and is parallel to the coast line. It is about 600 meters away from the present coast line.

The pumice is visible on the surface, and is not covered by layers of any depth of the said sedimentary stone.

The pumice pieces are small, most being about 5 cm in diameter. Most are round or oblong. The color is mustard brownish.

The sedimentary stone that the pumice is embedded in is made of the exact same kind of sand that is on the coast there, hardening over the ages and composing this rock.

The width of the belt is unknown, and probably goes on for tens or hundreds of miles.

The area is now built up and the exact places where I saw this belt are now under gardens and villa foundations. However, there are still exposed areas a bit west of the original place. Perhaps on a future visit, I can try to find another area and get pictures and more exact measurements.

Origin:

Since the belt lies parallel to the sea coast, the pumice must have floated over the water, and then pushed by the waves to the shore. As the sand was transformed into stone, the pumice became embedded into it. Since pumice originates from volcanic eruptions, it is certain that an event like the Thera volcanic eruption is the source of this pumice.

Questions:

Some questions need to be answered in order to date this pumice correctly and identify its source:

• Is the type of pumice in this belt identical to the pumice present today in Santorini?
• Is the type of pumice in this belt identical to the pumice present today in Crete, with the origin being the Thera eruption?
• Is the type of pumice in this belt identical to the pumice found in Tell El Dab'a exacavations?
• Can the shore line recede by 600 meters in 3500 or so years?
• Can any exact dating be done on the pumice belt that would help narrow the dating of the Thera eruption (provided the type of pumice is identical)?
• Are there any other known volcanic eruption in the eastern Mediterranean that this pumice can be traced to?

All this is material for future research. Anyone interested?

Responses from Specialists

Since I was interested in this topic, I did some searching on the internet for people who may have the answers to this puzzle. I initially contacted Sturt Manning, who is now in Tornoto teaching History of Fine Art, since he wrote a book A Test of Time, when at Reading in the UK.

He said that this is outside his are of speciality, but referred me to two other people, including Max Bichler in Vienna, Austria.

Max kindly wrote back in January 2005 saying:

Dear Khalid,
This sounds actually highly interesting!

To your questions:

The provenience of the pumice can be easily detemined by chemical analysis. My working group is running an analytical database on all relevant pumice producing eruptions in the Eastern Mediterranean for the last million years.

We also checked the Tell el Daba finds for their volcanic source and it turned out, that most of them were Santorinian, But other sources like Nisyros, Kos and Giali were present, too.

Our database comprises presently 3 eruption cycles at Milos, 6 at Santorini, 2 at Nisyros, 2 at Giali and 1 at Kos (all Greece).
Additionally, there are also included 6 of the biggest Kappadokian eruptions in Turkey.

Changes in the coastline in the order of magnitude you describe are absolutely possible for such geological time spans.

I would be highly interested to receive samples from your pumice belt for analysis. A set of samples covering the whole width of the belt at one place would be interesting.

Best regards from Vienna,
Max Bichler

So, perhaps the mystery of this pumice belt will solved at some point, and we may have a more exact date for Thera and other eruptions.