I see migrations as part of Catastrophism as major catastrophic events inspire people, out of fear of their safety, and that of their loved ones, to get the hell out of where they are living. Safe havens have often been the Egyptian delta for example, with birds and fish in abundance. However, migrations can be inspired for purely economic reasons, as occurred during the Middle Kingdom period (lots of foreigners entered Egypt in order to enjoy a better standard of living). This was not necessarily inspired by Catastrophism. However, the two examples below appear to have a clear Catastrophist trigger – in the first instance it was the end of the Ice Age that brought life back into those parts of Europe formerly buried beneath an ice sheet, and in the second example it was in response to the collapse of the Late Bronze age world.
At www.reading.ac.uk/news-and-events/releases/PR647509.aspx … Reading University claims they have found human activity in Scotland in 1240BC, at Rubha Port an t-Scilich on Islay. Pigs foragining along the Islay coast uprooted Mesolithic flints which led to the start of the excavations. They belong to the Ahrensburgian Culture which flourished in Europe (we were still attached at that time) towards the end of the Ice Age n- known mainly from Denmark and Sweden.
One interesting point to note is that the archaeologists are thinking in terms of these people as coastal huggers using skin boats (like kayaks), living on marine life (fish, seals and shellfish etc). In other words, these people had sea faring skills, even as early as the Late Pleistocene. However, this should not be altogether surprising as during the Ice Age itself, Solutrean culture people living in Iberia, are thought to have had the ability to hug the ice sheet and make their way across the Atlantic.
Stone tools, animal bones, plant remains, and a hearth were discovered and there is clearly a lot more still to be dug out of the ground in future seasons. Steven Mithen and Karen Wicks led the excavation and the dates produced fall within what is known as the Younger Dryas event, a cool period of climate when glaciers are thought to have covered the mountains of the Highlands. There was continuous land stretching from the Hebrides to Scandinavia – the North Sea did not exist at this time (although this does not take into account possible sea level oscillations in the Younger Dryas).
The finds are dated by tephrachronology – a new technique based on grains of ash from known volcanoes – in this instance, Icelandic volcanoes.
The second migrations is more startling in some ways – but not entirely unsuspected. At http://phys.org/print363598618.html … and concerns people moving from Western Asia (presumably Arabia and the southern Levant) into the Horn of Africa – 3000 years ago. This is the end of the Late Bronze Age when civilisations across western Asia and in Egypt collapsed, with great loss of life, followed by epidemics and drought conditions (as a result of changes in the monsoon track). When the fog of obsurity disappears we find we have a Saba in Africa (modern Sudan region) and Sa'ba (Sheba) in what is now the Yemen. Clearly people moved from one region to the other but in this report the migration is confirmed by DNA research. Various people over the years have made some astounding claims for migrations from western Asia into Africa, some of them too obviously outlandish. It seems there is a modicum of truth in the theory – and taking the migration further, south into East Africa, the newcomers appear to have been caught up in another migration shift, this time the movement of Bantu tribes from West Africa to East Africa (and subsequently into southern Africa). However, we also have to bear in mind that 'sand dwellers' or bedouin, were located in the desert to the east of Egypt long before the end of the Late Bronze Age.