The Heinsohn Horizon: 21st July 912

Numerous academic articles acknowledge Alexandria has been “hit” by two destructive tsunamis.

Alexandria was hit by a number of tsunamis in the course of the history (see Papadopoulos et al. 2007 ; Salamon et al. 2007), two of which have flooded the city with destructive effects, namely the 21 July 365 A D and the 8 August 1303 Crete tsunami events.

Scenario-based assessment of buildings damage and population exposure due to earthquake-induced tsunamis for the town of Alexandria, Egypt
G Pagnoni, A Armigliato and S Tinti – University of Bologna

The later Alexandrian tsunami of 8th August 1303 CE is well documented.

The 1303 Crete earthquake occurred at about dawn on 8 August.

It had an estimated magnitude of about 8, a maximum intensity of IX (Violent) on the Mercalli intensity scale, and triggered a major tsunami that caused severe damage and loss of life on Crete and at Alexandria.

Detailed information is available from reports made by representatives from Heraklion (then Candia) to the controlling Venetian administration, written on the day of the earthquake and twenty days later.

In Alexandria the city walls were mostly destroyed and the lighthouse was badly damaged.

The earlier Alexandrian tsunami of 21st July 365 AD is also well documented.

The 365 Crete earthquake occurred at about sunrise on 21 July 365 in the Eastern Mediterranean, with an assumed epicentre near Crete. Geologists today estimate the undersea earthquake to have been a magnitude eight or higher.

The Crete earthquake was followed by a tsunami which devastated the southern and eastern coasts of the Mediterranean, particularly Libya, Alexandria and the Nile Delta, killing thousands and hurling ships 3 km (1.9 mi) inland.

On 21 July 365, Alexandria was devastated by a tsunami (365 Crete earthquake), an event annually commemorated years later as a “day of horror.”

Much of the royal and civic quarters sank beneath the harbour due to earthquake subsidence in AD 365, and the rest has been built over in modern times.

Alexandrea Ad Aegyptum – Ev. Breccia – 1922

But there are a couple of issues with the earlier Alexandrian tsunami of 21st July 365 AD.

The primary source doesn’t date the 21st July tsunami using the Julian calendar.

The Roman historian Ammianus Marcellinus described in detail the tsunami that hit Alexandria and other places in the early hours of 21 July…

While this usurper [Procopius] yet lived, whose various deeds and whose death I have described, on 21 July in the year in which Valentinian was consul for the first time with his brother… Ammianus Marcellinus 26.10.15-19

Ammianus and The Great Tsunami – Gavin Kelly [Peterhouse, Cambridge]
The Journal of Roman Studies – Vol. 94 – 2004

The Julian calendar, proposed by Julius Caesar in 46 BC (708 AUC), was a reform of the Roman calendar. It took effect on 1 January 45 BC (AUC 709), by edict. It was the predominant calendar in the Roman world, most of Europe, and in European settlements in the Americas and elsewhere, until it was refined and gradually replaced by the Gregorian calendar, promulgated in 1582 by Pope Gregory XIII.

The 21st July 365 AD tsunami doesn’t appear in the scientific catalogue.

Luckily, sediment cores from Alexandria’s East Harbor can help date the 21st July tsunami.

Historic records refer to Rhakotis as a settlement on Egypt’s Mediterranean coast before Alexander the Great founded the famous Mediterranean port city of Alexandria in B.C. 332.

Little is known of Rhakotis, however, because the site has yet to be clearly identified beneath the modern city.

This problem motivated a geoarchaeological investigation of sediment cores from Alexandria’s East Harbor, from which radiocarbon-dated sections of pre-Alexander age (>2300 yr B.P.) have been obtained for study.

Alexandria, Egypt, before Alexander the Great: A multidisciplinary approach yields rich discoveries – Jean-Daniel Stanley, Richard W. Carlson, Gus Van Beek, Thomas F. Jorstad and Elizabeth A. Landau – GSA Today: v. 17, no. 8 – August 2007

Six of the cores were extracted from quayside locations in the “submerged ports”.

The quayside AL19 core [blue dot – above] clearly reveals two outlier events in the Heavy Mineral trace which are very suggestive of the two destructive tsunamis.

Upper Sand (V) and Upper Mud (IV) sections in this and other East Harbor cores comprise the most abundant and diverse suites of archaeological material.

These upper two units contain potsherds, pebble-size rock clasts, and high concentrations of heavy minerals, lead, organic matter, quartz, and crystalline and aggregate limestone, when compared to the three older facies (I–III).

Alexandria, Egypt, before Alexander the Great: A multidisciplinary approach yields rich discoveries – Jean-Daniel Stanley, Richard W. Carlson, Gus Van Beek, Thomas F. Jorstad and Elizabeth A. Landau – GSA Today: v. 17, no. 8 – August 2007

The AL21 core [red dot] is more interesting as it’s not from a quayside location.

The tsunami of 1303 CE is clearly identified in the AL21 core as a distinctive step which is [remarkably] accurately dated to 1310 CE by uncalibrated radiocarbon dating.

The earlier 21st July tsunami is also easily identified by its distinctive step shape.

Unfortunately, radiocarbon dating of the earlier 21st July is impractical because it’s associated with a significant “carbon-14 spike” and a change in the radiocarbon regime.

“The Δ14C values in a chronology can clearly be used to identify catastrophic gaps and catastrophic rises in carbon-14.”

The first four gaps have a jump up in 14C with a fairly quick return to the calibration curve shown in the figure on the second left.

However, from about 2000 b2k there is a steady rise in the Δ14C values.

The 993–994 carbon-14 spike was a rapid increase in carbon-14 content from tree rings, and followed the 774–775 carbon-14 spike.

Wikiversity – Geochronology/Radiocarbon dating

However, the 21st July tsunami is dated to 921 CE based upon the deposition rate.

In other words:

The AL21 sediment core from Alexandria’s East Harbor shows the 21st July tsunami of 921 CE physically marks the Heinsohn Horizon.

Personally, I favour dating the 21st July tsunami to 912 CE because the retro-calculation of Comet Halley’s orbital track indicates a perihelion occurred on the 18th July 912 CE.…62Y

Either way, the Alexandrian sediments send their seasonal greetings to Gunnar Heinsohn!

The Alexandrian sediments also send their seasonal greetings to the Radiocarbon Calibration Crew with the sincere wish they remember their Δ14C values in the New Year.

This entry was posted in Catastrophism, Comets, Dendrochronology, Heinsohn Horizon, History, Radiocarbon Dating. Bookmark the permalink.

5 Responses to The Heinsohn Horizon: 21st July 912

  1. Carsten says:

    Very very interesting. For just a couple of years now I’ve been acquainted with the works of Heinsohn; interestingly the history of Denmarks seems to coincide with the Heinsohn horizon as it is broadly accepted that the ruling Danish monarchy came to power in 935 CE. Efforts are being made to track the history of royalty farther back but very little specific is known.
    Norway too saw a new king come to power during 934 CE and the Piast’s of Poland entered the scene around 960 CE.

  2. Thx1138 says:

    Published October 2017

    Dim red aurora at low magnetic latitudes is a visual and recognized manifestation of geomagnetic storms. The great low-latitude auroral displays seen throughout East Asia on 16-18 September 1770 are considered to manifest one of the greatest storms. Recently found 111 historical documents in East Asia attest that these low-latitude auroral displays were succeeding for almost 9 nights during 10-19 September 1770 in the lowest magnetic latitude areas (< 30°). This suggests that the duration of the great magnetic storm is much longer than usual. Sunspot drawings from 1770 reveals the fact that sunspots area was twice as large as those observed in another great storm of 1859, which substantiates this unusual storm activities in 1770. These spots likely ejected several huge, sequential magnetic structures in short duration into interplanetary space, resulting in spectacular world-wide aurorae in mid-September 1770. These findings provide new insights about the history, duration, and effects of extreme magnetic storms that may be valuable for those who need to mitigate against extreme events.

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