I've often looked at the limestone used to form the sea defences around Morecambe to see if I could spot any fossils. On a recent wander along the jetty, I didn't find any fossils, but I did see traces of a limestone pavement from the rock's origin.
There is no need to climb the rocks to answer the questions for this earthcache - you can make much better observations from the footpath on the jetty.
Use the image below to find the correct rock - we're looking at the one behind the red rectangle.
1) How many grooves can you see on the rock covered by the red rectangle?
2) How wide are the grooves? (roughly - if you don't have a way of measuring, are they as thick as your finger, or your arm?)
3) Do you think this is rinnenkarren or a rillenkarren?
4) Take a photo of yourself at GZ, or an identifying item near GZ.
Please submit your answers via message though the Geocaching website or by sending me an email - there is no need to wait for a response before logging your find.
Limestone Pavement Formation
Limestone pavement forms over thousands of years where a layer of limestone bedrock has been exposed at the surface, usually after glaciers scraped away the soil and other looser rocks during the last Ice Age. Limestone is a type of rock made mostly of calcium carbonate, which actually dissolves quite easily in rainwater. Over time, the slightly acidic rain eats away at the rock, especially along natural cracks and joints in the limestone, creating the patterns and features we see.
Rinnenkarren vs Rillenkarren
Rinnenkarren Formation
Rinnenkarren are a type of karren that show how flowing water shapes limestone. They form on sloping surfaces of the limestone pavement where rainwater runs off. As the slightly acidic water flows consistently along particular paths, it slowly dissolves the limestone in those specific lines, carving out elongated, shallow grooves or channels. Over time, these channels deepen and become more defined, often appearing as parallel or branching lines that follow the direction of water flow down the slope.
Rinnenkarren near Ribblehead Viaduct
Rillenkarren Formation
Rillenkarren are small, parallel grooves that form on exposed limestone surfaces as rainwater flows over them. The rain dissolves the rock, carving channels that are typically a few centimetres wide. These features are a type of karst landform and often appear on sloping ground.
An example of Rillenkarren
Differences
Generally, rinnenkarren are larger than rillenkarren, with channels that can be several centimetres wide and deep. Rillenkarren, on the other hand, are much smaller, typically only a few millimetres wide and just a few millimetres deep. The scale of the feature depends on the rock type, the slope of the surface, and the amount of water flowing over it.