Rhakotis Found

Rhakotis existed about 700 years before Alexander even came to that site. Geoarchaeologist Jean-Daniel Stanley was doing some core samples off the coast of Alexandria, hoping to shed some light on the seismic failure of certain structures in the area. What he found were remnants of human habitation in that area more than 3000 years old.
He's discovered bits of human waste, iron, pottery shards, and stone building material from various parts of Egypt. This article pretty much says it all. Archaeologists have been searching for Rhakotis for some time. How exciting this is! For years it was discarded as nothing more important than a small fishing village on the shores of the bay Alexander the Great would later choose for his capital.
These new core samples, however, are telling a different story of a flourishing urban cultural center rich with trade. Future research here may shed some light on the lifestyle of ancient mariners and their day to day.

Here's a bit more.

The logic now is not that Alexander built his city on the same site as Rhaktosis, but that he used an already flourishing city and simply expanded upon it!

Alain Véron from the Paul Cézanne University in Aix-en-Provence, France, and colleagues made the discovery by measuring the variations in lead concentration in a mud core from Alexandria's ancient harbour. They determined how lead levels had changed over time by carbon-dating seashells found in the core.

Clear pulses of lead contamination occurred between 2686 and 2181 BC and then again from 1000 to 800 BC. The researchers conclude that these peaks were associated with human activities such as plumbing, fishing, building and ship-building. This is supported by ancient texts, which mention a settlement named Rhakotis existing around the same time Alexander would have arrived.

It sounds like earthquakes then were in part to do with the fall of dynasties in old Egypt ?

No doubt we can assume tsunamis too. I wonder if anybody has ever thought to look inland for tsunamis debris fields from the Old kingdom ?

Originally posted by sy.gunson
It sounds like earthquakes then were in part to do with the fall of dynasties in old Egypt ?

No doubt we can assume tsunamis too. I wonder if anybody has ever thought to look inland for tsunamis debris fields from the Old kingdom ?

This has been thought about. Most recently, the crusade on this has been take up by theorists who hypothesize that the Santorini eruption might have been responsible for the plagues of Egypt portrayed in the book of Exodus. An eruption the size of Santorini would surely have caused several Tsunamis, as well as earthquakes and other natural disasters. Evidence of this has been found in North Sinai.

After 10 years of digging in Horus road, where remains of several military forts, granaries, dormitory and temples were found, Egyptian archeologists of the Supreme Council of Antiquities (SCA) came upon 20 pumice stones or solidified lava inside a pit at Tel Habuwa from Santorini Volcano which erupted in 1500 BC, killing 35,000 people and demolishing several coastal cities in southwest Turkey, Crete, north of the Saudi Arabia, Palestine and the Sinai.

The pumice, which was found among several 18th Dynasty clay vessels that date back to the Hyksos era, was probably brought to Sinai by a tsunami caused by the volcano.

You can find more in this article. I think the fall of the Old Kingdom was more likely to do with the collapse of the central power structure toward the end of the sixth dynasty, rather than natural disasters. And as always, Egypt found a way to get by.