MILLIONS of small fire-blackened stones in Ireland and Scotland are giving support to the theory that northern parts of the British Isles were depopulated by a nuclear winter-style disaster almost 3,200 years ago.

Archaeologists believe the disaster was caused by a huge volcanic eruption in Iceland in 1159 BC.

An examination by John Barber, of the Scottish Historic Buildings and Monuments Directorate, and other archaeologists, of these piles of burnt stones has led to the conclusion that hunting, as a major part of the prehistoric economy, declined rapidly after the mid twelfth century BC.

The stones were used in the cooking of meat and other food. Now normally referred to as 'potboilers', they were the main method of boiling water when metal cauldrons were rare and pottery not strong enough to withstand great heat.

Modern tests have shown that normally it would have taken around three such stones, deposited into the pit of water over a 15- minute period, to bring the water to the boil. Many stones were retrieved, reheated and reused.

However, it is the distribution and dating of these fire-blackened mounds of stones which lends support to claims that an environmental catastrophe struck upland areas of the British Isles.

The earliest burnt mounds date from 2,100BC and for most of the second millennium BC can be found in permanent settlement sites and temporary hunting camp sites. But in upland areas, as from the mid twelfth century BC, burnt mound material persists only in settlement sites.

Hunting camp sites ceased to occur and archaeologists believe this is linked to the volcanic eruption, which probably destroyed much of upland Britain and led to the demise of many game species and, consequently, to a massive move away from hunting.

Research by Dr Michael Baillie and Dr Martin Munro, of the Palaeoecology Centre at Queens University, Belfast, paved the way for the development of the catastrophic depopulation theory.

They discovered, through an examination of tree-ring data, that tree growth slowed dramatically at times of major northern hemisphere volcanic eruptions - including that of Mount Hekla in Iceland in 1159 BC.

It is thought that the eruption, which spewed at least 12 cubic kms of volcanic dust into the atmosphere, and the ensuing environmental problems, reduced the population of northern Britain by as much as 90 per cent.