Sedimentary Rocks
Sedimentary rocks are formed by the accumulation of sediments, like fragments of older rocks, organic remains (shell, bones), and minerals that eventually compact and harden to rocks over a long period. Sediments accumulate in layers on earth’s surface or at the bottom of lakes, rivers and oceans. As the sediments lose water they cement and harden to create a rock.
Properties & Characteristics: Crumbles easily, can be scratched by fingernails; grainy texture due to layers of sand, silt or gravel; varying sizes of crystals.
Examples: Limestone and Sandstone
Image Source: BBC Bitesize
Stancliffe Stone
Liverpool Cenotaph is made from Stancliffe Stone a coarse grained durable Carboniferous Sandstone that is quarried from Derbyshire, although a strong sandstone Stancliffe Stone naturally contains tiny pore holes, bedding planes and hairline fractures and joints.
It is considered a moderately porous stone which is one of the reasons it is widely used in buildings and memorials.
After nearly a century of being exposed to Liverpool's industrial and busy city environment has left clear signs of weathering on the Cenotaph and its location will have played a part in the type of weathering it has suffered.
Weathering
Weathering is the in-situ breakdown of rocks, minerals or soil on earth, through physical, chemical or biological processes, it happens slowly over time.
Key Types of Weathering
1. Physical/Mechanical Weathering
Weathering caused by physical factors breaks down rock without changing its chemical composition. One example is thermal expansion and contraction: when rocks are heated by the Sun, they expand, and when they cool, they contract. Repeated cycles of heating and cooling create stress in the rock, which can eventually cause it to crack.
Another example is freeze–thaw weathering. Where rainwater can enter small cracks or holes in the rock. Temperatures drop, this water freezes and expands, because ice takes up more volume than liquid water, it forces the cracks wider. Over many cycles of freezing and thawing, the cracks grow until pieces of rock eventually break off.
Image Source: BBC Bitesize
2. Chemical Weathering
Rainwater absorbs carbon dioxide from the atmosphere, forming a weak acid called carbonic acid, so rainfall becomes slightly acidic. Some rocks are more vulnerable to this type of chemical weathering than others. Sandstone like Stancliffe Stone, is made up of sand grains (mainly quartz) that are often held together by a cementing material such as clay, iron oxides, or calcium carbonate. While quartz itself is very resistant to chemical weathering, the cement binding the grains together can be weakened or dissolved by acidic rainwater.
When this happens, the bonds holding the sand grains together break down, causing the rock to become weaker. Over time, grains can be released and washed away, gradually wearing down the surface of the sandstone.
Image created via AI
3. Biological Weathering
Tree roots, plants or animals may shatter and/or crumble the stones as a result. Damage from lichens, moss or other organisms growing on the surface of rocks is also frequent. The surface of some rock types provide the nutrients that lichen need. The rocks may become weaker due to changes in their composition.
Image Source: BBC Bitesize
The Cenotaph’s weathering patterns are also influenced by its location on the exposed raised ground of St George’s Plateau. Different sides of the memorial experience varying levels of wind, rainfall, pollution and shelter from nearby buildings, creating noticeable differences in how the sandstone has weathered over time.
TO LOG THIS CACHE
As this is an EarthCache there is no physical box at the location, instead you must visit the marked location and answer the following questions. Please send your answers to me via email or the Geocaching message centre.
1) Looking at the rock directly below the bronze panel on the side that faces the road, describe the condition of the stone surface. Does it appear smooth, rough, cracked, grainy or worn? What type of weathering do you think has caused these features ?
2) Now examine the rock below the bronze panel on the side facing St George’s Hall. Compare the weathering on this side with the road-facing side. Which side appears more weathered or stained, and what environmental factors do you think may have caused the difference ?
3) Why do you think this type of stone has used for this memorial at this location instead of another sedimentary rock such as Limestone ?
4) Optional photos are always nice to see in logs, but they are not required. If uploading photos, please avoid revealing answers to the EarthCache questions.