Sand dunes of Derrynane EarthCache
Hidden : 5/29/2009
Difficulty:
1.5 out of 5
Terrain:
2 out of 5

Size: Size: other (other)

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Geocache Description:

This is an EarthCache about sand dunes so there's no box or logbook to find. Easy to combine with your ring of Kerry trip!



Sand dunes of Derrynane
In Europe 20% of the coastline is backed by sand dunes. Within Ireland, County Kerry has a significant proportion of the Nation's sandy beaches and dune systems and fien examples are evident throughout the country.
Generally, maximum dune development occurs on windward coasts, which explains why the majority of sand dune systems occur along the west/southwest coast of Ireland.

The formation of sand dunes
An abundant sand supply, strong offshore winds and well-adapted vegetation are important prerequisites for extensive dune development. The beach is the area of transport between the submarine and deposits and the growing sand dunes. It is probably the more frequent but less powerful prevailing winds that are the most important in dune development.

Sand entrapment
The sand carried by the wind is deposited in a streamline form around obstacles such as dried seaweed, beach debris and pieces of wood. Plants such as san twich and, to a lesser extent, sea lyme grass colinise the small mounds of sand that accumulate around the flotsam of the high water mark. As sand deposition proceeds their foliage creates even more deposition and their root networks binding the sand together into low "embryo dunes".
As they grow, the foredunes are often called "yellow dunes" due to the amount of bare sand yet to be colonised. The effect of vegetation cover on sand deposition means that these dunes grow rapidly in height from modes 1-2m foredunes into dunes about 10m high.

Colonisation and succession
As the dunes grow higher, the wind blows sand over the crest and deposits it in the lee. The dune therefore builds upwards and landwards until it reaches a height where he stronger wind remove as much as they deposit. The sans is still mobile so the dominant species of plant is marram, although grasses such as red fescue and sand sedge invade.
As the influence of salt and mobile sand decreases inland, so different species invade and dominate and the soil develops.
Landwards of this dune ridge, there may be older dune ridges separated by dune slacks. These older or "grey dune" are lichens of the genus Cladonia, along with mosses, grasses and low shrubs such as see bucktom. The most vigorous of the species that stabilise dune is marram grass, whose growth and vigour is directly related to the rate of influx of sand.

Human factors of dune erosion
Natural processes of dune erosion are being accelerated by human activities such as removal of sand, burning and cutting of vegetation, grazing by animals and recreational use.

Erosion of the sand dunde system
Virtually all dune systems are subject to erosion usually a combination of several different types. The most common type of erosion is the occurrence of "blow-outs".

Formation of "Blow-outs"
Wind gains access to the sand beneath the vegetation cover close to the ridge crest and rapidly erodes the surface, causing a depression or "blow-out". As the wind is channelled into it the "blow-out" grows, the eroded sand inundating adjacent "grey" dunes revitalising clumps of previously moribund marram grass.
The "blow-out" expands laterally until its width reduces the channelling effect of the wind and vertically until it reaches the water table or pebble besement.
Erosion of the "grey" dune system results in an amorphous, low-lying, rolling dune pasture (called Machair). Machair lands form an important grazing area for livestock.
Frequently the front edge of the foredunes are cut back by storm waves. The entire seaward face of the dunes system moves landwards marked by a steep slope of loose sand and slipping clumps of crestal vegetation. Cumulative pressure of grazing, cars, pedestrians and caravans have resulted in serious erosion in many Irish dune systems.

How to log this Earthcache?
To log this cache just answer these two simple questions and email these answers to us!

- Name four human factors in dune erosion.
- Goto N 51°45.607' W010°07.939' and make a picture on this sand dune holding your GPSr and add this picture (see example) to your log (optional).
- Estimate the height of this sand dune and email us your answer.

Note: Logs from teams or logs emailing incorrect answers will be removed without further notice! If you think your answers are correct, feel free to log a 'Found'.

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