The last great ice age, the Pleistocene, began two million years ago, and ended ten thousand years ago. During this time much of Ireland was covered in glacial ice.
When snow first falls it is light and fluffy because the ice crystals contain lots of air. Further snowfalls compress the ice, this drives out most of the air and turns it into a more dense layer called firn. Over many years, further compression forces even more air out from the firn and turns it eventually into blueish-coloured glacial ice.
Glacial ice builds up in zones of accumulation; places where snowfall accumulates faster than it melts. Where melting is faster than snow falls, these area areas are called zones of ablation. Glacial ice melts and retreats from these places.
During the Pleistocene many zones of accumulation existed on mountains where temperatures were extremely low. Glaciers were formed in the mountains. These glaciers moved downslope and eventually joined together to create vast ice sheets that covered entire lowlands. Parts of Ireland lay under one kilometer of ice.
There is much to learn and understand about glaciation - how the ice moves, processes of erosion, landforms of glacial erosion how load is transported, features of glacial deposition ... Memories of secondary school geography are popping to mind no doubt! Information for another earthcache another day…
The purpose of this earthcache is to learn the basics about how the Curragh was formed.
Fluvio-Glacial processes were common during the Ice Age. (Fluvio from the Latin fluvious meaning river). These processes were not carried out by the ice itself but rather by the meltwater streams and rivers that flowed under and out from under melting ice sheets and glaciers. These processes are very similar to river processes with hydraulic action, abrasion, attrition, and deposited materials being sorted and stratified.
All rock and boulder clay that is transported by a glacier is called moraine. There are a number of types of moraines: lateral, medial, and terminal.
Lateral moraine is deposited on the sides of glaciers, where rocks of all sizes fall onto the glacier edges (usually caused by freeze thaw action in the valley above).
Medial moraine forms when the lateral moraine of two glaciers meets, and is now carried along in the centre.
Terminal/ end moraine was deposited when glaciers stopped for a long period of time during interglacial or warm spells. This moraine was deposited unstratified, in crescent-shaped ridges of material across valleys and plains. It marks the furthest point reached by the glacier. The forward movement of the glacier was balances as the front was being melted, the front therefore became stationary, even though the glacier itself continues to carry deposits of marine towards it. Ice sheets also carried terminal moraine forward. The Midlandian Ice Sheet(70,000 years ago) deposited a terminal moraine all across Ireland from Wicklow to the mouth of the Shannon (see diagram).
When temperatures rose, melting increased and the front of the glacier began to retreat. This retreat was not constant as temporary cooler periods paused the retreat. Moraine deposited during these periods formed recessional moraines.
And back to the Curragh…
Fluvio-Glacial processes
An outwash Plain is a low-lying area of sand and gravel that is usually found close to a large terminal moraine.
Towards the end of the Ice Age, vast amounts of water flowed from a melting ice front due to increasing temperatures. The meltwater flushed gravel, sand and clay out through the nearby terminal moraine. The fine clay was carried far away by the water but the heavier gravel and sand were deposited close to the terminal moraine in the form of an outwash plain.
Outwash plains made up of outwash deposits are characteristically flat and consist of layers of sand and other fine sediments, generally well drained.
In order to log a find for this earthcache, please send me the answers to the following questions via messages.
1 At Stage 1 what characteristics of an Outwash plain are evident?
2 At Stage 2 describe the soil type.
3 Please compare the soil type at Stage 1 and stage 2.
4 Based on the small amount of information in this earthcache, why do you think horseracing became popular in this area?
5 An optional photo of you somewhere on the vast Curragh Plain would be nice :)