The coordinates will bring you to the beautiful area of Donard Forest where you find the River Glen. The river is 2 miles (3.2 km) long and flows down from the foot of Slieve Commedagh and Slieve Donard into Dundrum Bay.
Beautiful River Glen but no spoiler (filter on the pic)
This earthcache makes you look a bit closer at the formation of the river in the area of Donard Forest. What you notice first when standing at the given coordinates is a waterfall.
You might have always asked the question, what exactly is a waterfall?
A waterfall is a river or other body of water's steep fall over a rocky ledge into a plunge pool below. The process of erosion is important for the formation of the waterfall but it also plays a part to erosion itself. They form as streams flow from soft rock to hard rock.
All clear? Ok, let's have a deeper dig into the erosion part: How is a waterfall formed?
A stream always carries sediment which can be microscopic silt, pebbles or even boulders. It erodes the stream bed which is made of soft rock until the channel cuts so deep into the bed that only harder rock remains. A waterfall develops as hard rock formations form cliffs. Water flows over the ledge and falls into a plunge pool in the soft rock below. As the water hits the plunge pool it will erode the rock by both hydraulic action (= force of the water against the bedrock)and by abrasion (= water acting like sandpaper as it carries sediment in the riverbed). Eventually the overhang will collapse due to the erosion of the soft rock beneath it. In result the waterfall retreats upstream.
So we've established how soft and hard rock can influence the transformation of a waterfall. The bedrock of River Glen is composed of granite and shale.
What is granite and shale, you ask?
Granite - Hard igneous rock rich in quartz and feldspar which is formed by the cooling of magma. Granite can be mainly white, pink or gray in color, dependent on the minerals it contains.
Shale - Soft rock type which typically tends to split into thin layers. The colour is mainly dependent on its composition. Hydrated ferric oxide gives a reddish and purple colour to the shale while mineral components rich in ferrous iron causes it to be blue, green and black. Calcareous shales are light gray or yellowish.
Sources:
https://education.nationalgeographic.org/resource/waterfall/
https://www.alevelgeography.com/waterfalls/
https://www.britannica.com/science/shale
https://en.wikipedia.org/wiki/Granite
Before you log a find on this earthcache do the following:
- Read the description.
- Have a look at the waterfall and the rocks around you (but watch your steps as it can be slippery).
- Answer the questions below and send them to me via email or via the Geocaching Message Center. The questions can be answered in English or German language. Found logs without sending the answers will be deleted.
- While log pictures are appreciated please don't post photos which will give away the answers to the questions.
Q1) Look at the rocks that make up the riverbed (not the path!) while you're walking up to waypoint 2. Is it soft or hard? What colours can you primarily see? Based on your answers what rock type is it?
Q2) Given the collected information from the previous question and the information given above what do you think will happen long-term with the riverbed?
Q3) Looking upstream at the given coordinates you see a big boulder. Do you think the river moved it there or was it there before?
The last step is the most important one. Have fun and enjoy the surrounding nature while doing this earthcache!