This was primarily due to the study of ice cores from Greenland and Antarctica, together with remote sensing using satellite data and aerial photography.

A study of the ice dynamics and thermal regimes in Greenland and Antarctica today enables us to understand better the behaviour of the ice cap which once covered North and Mid Wales.

The study of isotopes in Antarctic ice cores has given us an accurate indication of temperature variations over the last 400 000 years. It shows that we are at present in an ice age which has exhibited a series of cold glacial periods with intervening warmer interglacials showing a clear 100 000 year cyclicity in which temperatures fall slowly to a low during glacials and rise quickly into warm interglacials (One of which we are enjoying at the present time.)

On a much longer geological time scale, apart from a small number of cold periods like the present one, the planet has generally been in a warm (greenhouse) condition for the last 4 billion years.

Remote sensing from satellites, using radar, visual and gravity data, enables ice sculpted landforms and lineations to be identified. For example, in North America drumlins and lineations can be picked up in which there are cross-cutting relationships which are evidence of multiple glacial episodes.

In Antarctica radar images enable the study of the dynamics of ice drainage from ice domes in the interior to the floating ice shelf and the sea. There are a number of ice domes within which the ice velocity is low, of the order 5 metres per year, with sharp margins to fast moving ice streams with velocities of some 500 metres per year. The paths and convergence of these streams can be studied as ice moves from ice domes, through ice streams and eventually to the ice shelf.

Landforms related to ice margins, including drumlins, lineations and the distribution of erratics can be related to the beds of former ice sheets, including in Britain structures on the sea floor, off the coast.

Welsh Ice

Such studies can be applied to the ice caps which once covered Mid and North Wales, in that the landforms and lineations they left behind can be used to deduce the original positions of ice caps and their associated ice streams.

In the accepted model the last glacial maximum occurred about 18 000 years ago when northern Britain was ice covered with a major outlet through the Irish sea and a lobe along the east coast over East Anglia.

The representation of data for this study comprised a digital terrain relief map with simulated shading as if from low solar radiation from the north-west with a visible plus near infra-red false colour satellite image “draped” over it.

Traces of fast moving “ice streams” could be identified from the aligned drumlins and lineations. The direction of flow is confirmed by reference to the actual shapes of drumlins. From these the location of ice masses can be deduced.

These findings enable glaciologists to make deductions about the behaviour and configuration of former ice sheets. Two events or phases can be identified.

The earlier event 1 was centred on a slow moving ice dome over the high North and Central Wales mountains, extending to the Wrexham area. Over the high mountains it was frozen to the ground and left little geomorphological trace. This was a distribution centre for ice streams generally in a NE and SW direction to the Irish Sea and Cheshire.

Event 2 was marked by a divide along a north-south orientated axis with major fast-moving ice streams in the eastern part of the ice cap. It was related to the deglaciation of the ice cap when the ice thickness was reduced and ice streams were controlled by the topography. At least four major ice streams are identified, the Conwy, Bala, Four Crosses and Severn Ice Streams, all of which followed topographical troughs.

The second event corroborates recent studies of the widespread outwash gravels in North Shropshire, which massive flows are also the result of the north easterly ice streams resulting from deglaciation.

Mid Wales Geology is an amateur club, affiliated to the G.A.. The last meeting in the "Land of My Fathers" season is on Thursday 20th March, 7.15 p.m. at Plas Dolerw, when Colin Humphrey will talk on "A Fateful 1834 Welsh Journey". The story of a great Victorian controversy. Contact Bill Bagley 01686 412679 and 413967. www.mwgeology.members.beeb.net