Student's work reveals when Anglesey became an island

Mike Roberts gained a first class honours in Ocean Sciences

New research has revealed Anglesey was still connected to the mainland less than 6,000 years ago.

Hunter-gatherer humans were giving way to settled farmers when the Menai Strait became a permanent fixture between 5,800 and 4,600 years ago.

Mike Roberts, a mature student from Amlwch, discovered this while completing a PhD at Bangor University's School of Ocean Sciences.

"About 14,000 years ago the entire region of the Menai Strait was dry land and both humans and animals could easily cross from one side to the other," said Mike, who did not embark on his academic career until his late 30s, having previously worked as a plasterer and fisherman.

"Over the next few thousand years the climate warmed and melting ice caused sea levels to rise which, in turn, caused the coastline of Wales to take on its familiar shape and flooded the Menai Strait from either end.

A drilling rig located in the Menai Strait faciltated the research

"Then one day sometime between 8,800 and 8,400 years ago, a high spring tide actually separated Anglesey from the mainland for the first time."

For the next 4,000 years humans could cross from the mainland at low tide via a causeway in the vicinity of Ynys Gorad Goch in the Swellies.

But Mike discovered that some 5,000 years ago there came a moment when even the lowest of the low spring tides failed to reveal any dry land and the tidal strait as we know it today was first formed.

He was able to discover the evidence for these developments by taking advantage of a drilling rig in the Strait.

It had been set up in 2002 to build a mooring for the university's new research vessel.

"What you need to reconstruct sea levels is to get really deep down under the sea bed," said Mike.

"So we asked them to drill down and bring up a sediment core.

Ice sheets

"Part of that sediment was laid down when the Menai was dry land. You can date at which depth this occurred by carbon-dating the plant matter.

"There's a clear change between stuff laid down when it was land and when it was part of the sea."

This newly-discovered history of changing sea levels in north Wales has also revealed information about the size of the ancient ice sheets that used to cover Snowdonia, plus when and how fast they disappeared.

Professor James Scourse, one of Mike's PhD supervisors, said: "Mike's study not only unlocks the recent geological history of the region in which we work, it also demonstrates that the NE Menai Strait is one of the most important localities for sea-level reconstructions in the whole of Europe.

"The amount of data from this single locality is unprecedented".

The research was supported by the Cemlyn Jones Trust and the Countryside Council for Wales.