We came across this sight on our coastal walk from Marsalforn to Wied Il-Mielaħ, a walk full of geological interest. Please keep to the path here and do not stray too near the edge. All the information you need for this Earthcache can be seen from the path or is in the cache description.
The terrain in this area, above the cliffs, is full of holes, cracks, fissures and sharp points, these are features of Karst. It has been formed by the action of acidic rainwater on the upper coralline Limestone. Upper Coralline is a sedimentary rock, it is quite hard and is white and/or grey coloured. It was the last to form and is the youngest rock found on the Maltese Islands. It is also porous, which means that it lets water pass through it. Approximately 15 percent of the Earth’s land surface is karst.
In order to form a sea cave, the host rock must first contain a weak zone. In igneous or metamorphic rock, this is generally either a fault or a dike. In sedimentary rocks such as limestone, this may be a bedding-plane parting or a contact between layers of different hardness. When carbon dioxide dissolves in the rainwater it forms a mild acid that causes erosion along the fissures of the bedrock. Since the mineral composition of the rock varies it does not erode evenly and so the typical karst landscape is formed.
Over time, these fractures enlarge as the bedrock continues to dissolve. Openings in the rock increase in size, and an underground drainage system begins to develop, allowing more water to pass through the area, and accelerating the formation of underground karst features.
Amongst the most common types of karst are:
- Sinkholes (a closed depression draining underground)
- Caves
- Turloughs (a type of disappearing lake)
- Limestone pavement (a flat, incised surface of exposed limestone that resembles an artificial pavement)
- Springs (a spring emerging from karst, originating a flow of water on the surface)
- Dry valleys
- Karst Fenster ("karst window"), a feature where a spring emerges briefly, with the water then immediately disappearing into a nearby sinkhole
In order to log this Earthcache
Please send your answers to the following questions by message or email. You do not need to wait for a reply before logging, we will contact you if there is a problem but please note, logs without answers being sent will be deleted.
- Name the TYPES of karst mentioned above that you can see here?
- What FEATURES of karst do you see in the terrain here, above the cliffs?
- Standing at the posted coordinates , how many caves do you see and, in your own words, how do you think they were formed?
- Updated guidelines June 2019 re photos confirm it is once more acceptable to request a photo. Please therefore attach a photo of you or your GPS or any personal item which will show you have visited GZ but not reveal any of the other answers.