This Earthcache
In September 2022 I visited Derrynane Beach and headed out to Abbey Island as part of the nearby multi. That doesn't bring you far enough out onto the island to see all of the views though, so I went investigating. I found lovely vistas there, as well as something I could make into an earthcache.
You might see a "Wading Required" attribute here... at high tide the sand connecting Abbey Island to the mainland is under water. But at most times of the day, you'll be fine. Just keep an eye out.
Derrynane at low tide
Limestone and baby bullauns
These aren't sinkholes in the true sense of the word, but they are an interesting little feature of limestone that I hadn't noticed nor really thought about before.
Limestone (calcium carbonate) is a type of sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of CaCO3. Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life.
Most limestone is formed by the activities of living organisms near reefs, but the organisms responsible for reef formation have changed over geologic time. Organisms precipitate limestone both directly as part of their skeletons, and indirectly by removing carbon dioxide from the water by photosynthesis and thereby decreasing the solubility of calcium carbonate.
Limestone is relatively soft, with a Mohs hardness of 2 to 4, and can easily be eroded by rainwater and water flow. The Burren is the best example of this "karst" landscape, but you can see a little bit of this process in action on the ground at the cache co-ordinates. You will see some rock beneath your feet, with tiny little holes in it, often filled with pebbles. These are tiny Bullauns.
A bullaun is the term used for the depression in a stone which is often water filled. Natural rounded boulders or pebbles may sit in the bullaun. The size of the bullaun is highly variable and these hemispherical cups hollowed out of a rock may come as singles or multiples with the same rock.
Questions
Answer the following questions and send them to me via the Messenger or via an email. Feel free to log the cache before you send them, but please send them within a reasonable timeframe. Sending no answers may result in your log being deleted, with fair warning. Optional questions are just that, optional, they are for the earthcache nuts (like me) who enjoy looking that bit more closely.
At the given co-ordinates you'll see a feature beneath your feet with lots of holes in it.
- What rock do you think this feature is made of?
- Speculate how the little holes formed.
- Why do you think they have pebbles in them?
- Measure the size of three different holes. Are they all the same depth?
- Do you think this feature will become "karst-like" similar to the Burren?
- Optional: Why do you think they are all the same depth but not the same radius?
- Optional: Count the holes!
References:
- https://en.wikipedia.org/wiki/Limestone
- https://en.wikipedia.org/wiki/Bullaun