Glacial Lake Origins - Icy Histories

Delaney, Catherine ORCID: https://orcid.org/0000-0002-5846-2377 (2024) Glacial Lake Origins - Icy Histories. In: Lakes in Ireland - Mirrors of Change. Marine Institute, Ireland, Dublin, Ireland, pp. 38-63. ISBN 9781902895871

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Abstract

It has been over 11,000 years since a glacier last existed on the island of Ireland. Nevertheless, the impact of former glaciations on our lakes is inescapable and almost every lake in Ireland has a glacial legacy. During the last glaciation, ice covered the entire island. As the ice retreated onshore, vast quantities of meltwater were released, forming lakes along the ice margin wherever bedrock, ice or moraines formed a barrier. Some of these lakes have vanished completely, but many remain. Glacial lakes with dams formed largely of bedrock continue to exist in both upland and lowland glaciated landscapes today, whereas lakes dammed by moraines and ice drained more easily and have mostly disappeared or are much smaller than in the past. As the last ice sheet melted, the meltwater carried sediments from the glacier that were then deposited in the lakes and these glacial lake deposits continue to affect our environment and society today. Sand and gravel deposited where meltwater streams entered the glacial lake form groundwater aquifers in many areas, while the finer silt and clay carried further into deeper parts of the lake basins controls local hydrology by acting as an impermeable seal, causing waterlogging and the growth of peat in raised bogs across lowland Ireland. Glacial lake sediments can provide a record of meltwater discharge and ice sheet retreat, useful for understanding future retreat patterns in modern ice sheets. Deltas and outwash fans deposited in glacial lakes are an important source of aggregates for the construction industry. This chapter examines the glacial origins of modern and ancient lakes in Ireland.