Firstly this cache is nothing to do with the Simpsons episode with Moe in the Stonecutters. However I thought it amusing to get a picture of the Simpsons on an EarthCache
The listed coords will bring you to the beach at Cromer just in front of the Pier. You don't need to go on the beach to answer the questions so is wheel chair friendly.
The learning element of this Cache is to learn about the Mohs hardness scale of Rocks and how it is an important factor in determining which rocks / building materials to use for RipRaps.
Below is an example of one of the many types of a Riprap
What is a Riprap?
Riprap is a layer of large, broken stones or boulders placed on shorelines, riverbanks, or other embankments to prevent erosion and scour from water, waves, or ice. It works by absorbing and dissipating the energy of water, protecting the underlying soil and structures from being washed away. Riprap can be made of natural rock or concrete, and is used for everything from armoring streambeds to supporting bridge abutments.
Cromer Beach
Cromer beach can have strong waves, especially during storms or high tide, which can make it challenging for some beachgoers. The strongest waves are typically found during the winter months, but strong winds and large swells can occur at other times of the year. The strong waves can cause erosion of the coast line but on the plus side the waves are enjoyed by surfers. At GZ you will notice Cromer Pier. This has been damaged many times by stormy seas.
Mohs scale of Hardness
The Mohs scale of hardness is a relative scale of scratch resistance for minerals, ranking them from 1 (softest, talc) to 10 (hardest, diamond). It was developed by geologist Friedrich Mohs in 1812 and is based on the principle that a harder substance will scratch a softer one. A mineral with a higher rating can scratch any mineral with a lower rating.
Materials used for Ripraps:
The two main materials used for Ripraps are Reinforced Concrete and Rock/ Stone.
Reinforced Concrete:
The Mohs hardness of reinforced concrete ranges from 5 to 7, with the exact value depending on factors like its compressive strength, age, and specific aggregates used. This hardness is typically determined through a scratch test, which is used to select appropriate tooling for grinding and polishing the concrete surface
Sedimentary Rock
Sedimentary rocks don't have a single Mohs hardness because their hardness varies depending on the minerals they are made of. For example, limestone, which is composed mainly of soft calcite (Mohs 3), is relatively soft, while sandstone, which is primarily made of hard Quartz (Mohs 7), is harder and more resistant to weathering.
Igneous and Metamorphic Rocks
Most igneous and metamorphic rocks contain much feldspar, quartz, pyroxenes and amphiboles. Their hardness is thus going to be between 6 and 7.
An example being Granite
Metamorphic rocks also don't have a single hardness value on the Mohs scale because they are made of different minerals. However, metamorphic rocks are often harder than their parent rock and typically range between a hardness of 6 and 7, primarily due to the presence of minerals like quartz and feldspar. The specific hardness depends on the minerals that compose the rock, with harder rocks like quartzite (mainly quartz) resisting scratches more than softer ones like slate, which can have a hardness of around 1 to 2.
UK 2025 costs for reinforced concrete and Granite:
The cost of reinforced concrete per cubic meter (m⊃3;) varies significantly, but on average, you can expect to pay approximately £110 to £130 per m⊃3; for a standard mix in the UK, although it can range from about £90 to £195+ per m⊃3; depending on factors like the concrete grade, location, and additives.
The cost of granite per cubic metre in the UK varies significantly depending on the product type (e.g., aggregate, setts, or polished slabs for worktops). It can range from approximately £100 to over £1,400 per cubic metre, with higher prices for finished products.
Finally something relevant to this EarthCache:
Biological Growth
- Red Algae (specifically Trentepohlia species): This is a very common cause of orange or rusty-red powdery deposits or films on hard outdoor surfaces, including Granite.
So to the questions:
Please send me your answers to the following questions via the messaging or email. You may log the the EarthCache as soon as you have done this.
1. In your own words please tell me what a Riprap is?
2. Describe the Riprap you see in front of you on the beach in terms of material used and shape and size.
3. Give 3 reasons why you think this material has been used ? Would you have used this material or a common alternative?
4. What is causing the discolourations of the material used?
5. Post a photo of yourself or a piece of paper with your caching name with the pier behind you. Please do not give away any of the answers.
Thanks for visiting the EarthCache