Neolithic and Bronze Age Landscapes of North Mayo: Report 2011

isen. Due to greater isostatic rebound to the east due to its proximity to the centre of Ice
accumulation relative sea level has changed less in this area. According to these models, at
approximately 4000 BC, relative sea level at Killala Bay was about -3m and in Belmullet -5m.
Intertidal peats at Blacksod Bay and Killala Bay demonstrate the innundation of ancient landscape by
the rising sea.
The impact of this vertical sea level rise on the location of the coast line is harder to assess, as
erosion and shoreline migration are hard to reconstruct. In areas of hard coast – the high rocky cliffs
that dominate much of the North Mayo coast for example – the sea level change will have made no
difference to the location of the shoreline, beyond the impact of thousands of years of cliff erosion.
However, in areas of soft sediment, sea level rise will have also involved coastal erosion and,
potentially, the redeposition of material, making the precise reconstruction of prehistoric shorelines
very difficult. In areas such as the Mullet peninsula the comparatively gentle topography means that
small sea level rises could have drowned comparatively large areas and ancient shore lines may lie
some distance off the modern coast.
River processes
This coast line includes a number of significant rivers. The extensive Glenamoy basin includes two
main rivers: the Glenamoy and the Muingnabo which trend west. Further east, the rivers of the
North Mayo coast flow south to north: the Belderg River, Glenlassra River and Glenulra River. The
Glenlassra and Glenulra rivers are hanging valleys, exiting on high cliffs. At Ballycastle, the Ballinglen
River flows into Banatrahir Bay, along with the Bellananaminnaun River at the west of this Bay. To
the east the Cloonalaghan River flows into Lackan Bay, overlooked by Lackan Hill. Killala bay is
primarily fed by the River Moy, and the estuary is associated with complex shifting sand banks, bars
and islands.
In keeping with many parts of Ireland, little is known about the details of river development in the
case study area (Brown et al. 2007, Turner et al. 2010). The Glenamoy River is associated with
significant alluvial deposits and small scale investigations carried out by Davis, Warren and Turner
near the mouth of the Belderg river have indicated that c4.8m of sediment has been deposited since
375-175 cal BC (UBA-8287, 2195±35 bp). This suggests that, in some places at least, significant
landscape change may have taken place in terms of river activity. A deeper understanding of how
rivers have changed over time would be extremely helpful.
Soils
The modern soils of the region are dominated by high and low level blanket peat which extends
along most of the North Mayo coast. This has a very limited range of potential agricultural uses, and
today they are dominated by rough grazing (Gardiner and Radford 1980). This blanket peat has been
extensively used for peat cutting, mainly by hand, but with significant recent use of mechanised
extrusion technologies in recent years. Some small pockets of wet and dry podzols are also present
in river valleys in these extensive peat lands (Associations 155/185p) (??) and these support slightly
more intensive grazing.
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