I was walking back towards Victoria Station on way way home from London Calling 2025, when I noticed these pillars. There has been some remedial work with some of them being replaced, but some have been affected very badly from weathering.
Tall buildings may affect GPS signal. You should be standing on the Ebury Road side , near the pedestrian crossing looking West along the bigger road towards the large green road sign.
1) Look at the pillars - describe the one in poorest condition. Based on your answer, what type of weathering has caused this?
2) Are there any other types of weathering present here?
3) Do you think all the weathered pillars come from the same bed? Why do you say that?
4) Take a photo of yourself at GZ, or an identifying item with the blue plaque just around the corner on Ebury Street (beside no 32) in the background.
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.
Differing permeability of rocks
Sedimentary rocks are typically composed of particles that are loosely packed together. These particles, such as sand, silt, and clay, settle and accumulate over time through processes like erosion and deposition. Due to their loose arrangement, sedimentary rocks often have higher permeability, allowing fluids like water to flow more readily through their pores and fractures. However, this also means they are easier to carve, which makes them a popular choice for more ornate flourishes on buildlings, such as these pillars.
Sedimentary stone of the same type can weather at different rates due to a combination of physical and chemical factors. Here are some ways this can happen:
Cement Type and Strength: Sedimentary rocks are held together by natural "cement" (like silica, calcite, or iron oxide). Some cements are stronger and more resistant to weathering than others. For example, silica cement is much more durable than calcite.
Grain Size and Sorting: Rocks with finer grains and well-sorted particles tend to weather more slowly because they are more compact. Coarser or poorly sorted rocks have more spaces between grains, allowing water and air to enter and cause weathering faster.
Porosity and Permeability: If the rock has more pores (tiny holes) or allows water to pass through easily, it will weather more quickly. Water brings in acids and oxygen, which break down the minerals.
For example, two limestones from the same quarry may look similar, but one with more clay seams and small pores may crumble much faster in a damp climate.
Weathers Effect on Rocks
Weathering is exactly that - the effect the wind and rain has on rocks. Rain can permeate rocks where the particles are loosely packed together, washing grains away. The repetition of this over time can be seen on the surface of the stone, the type of stone and the location it is placed in affect the speed this takes place.
Often in statues or carvings, one of the effects of weathering can be seen where the carvings are - what started out when the statue was new as a sharp edge becomes softer as the grains of the fine, sharp edge are removed by weather - think of a drawing with a blunt rather than a sharp pencil. Sometimes the stone can become stained by other chemicals in the air or water.
Whole sections can break off by strong wind or by water entering gaps, freezing and expanding, causing gaps to get wider and wider and eventually break over time.
More information on the various types of weathering is below.
Types of weathering
Physical
Caused by changing temperature. Temperature causes rock to expand and contract as it gets warmer and colder. Repetition of this action can cause cracks and breaks. Freeze-thaw weathering also affects sandstone. When water seeps into the pores of sandstone and freezes during cold weather, it expands, exerting pressure on the rock. This expansion can cause the sandstone to crack and fragment over time. When the ice thaws, the water contracts, further stressing the rock. Over many freeze-thaw cycles, this gradual weakening and fragmentation can lead to the disintegration of sandstone into smaller pieces.
Chemical
Chemical weathering can significantly impact sandstone over time. When certain chemicals, such as acids from rainfall or organic acids from decaying vegetation, interact with the minerals in sandstone, they can cause chemical reactions that break down the rock. More porous limestone weathers faster this way.
Biological
Biological weathering involves the breakdown of sandstone by living organisms. One common mechanism is root wedging, where plant roots grow into cracks and crevices of the rock. As the roots expand, they exert pressure, causing the rock to fragment over time. Another form of biological weathering is caused by burrowing organisms like ants or worms, which create tunnels and crevices within the sandstone, facilitating the infiltration of water and further weathering processes. Additionally, organisms such as lichens and mosses can release acids that chemically weather the minerals in sandstone. Biological weathering, driven by the activities of organisms, plays a significant role in shaping landscapes and contributing to the erosion of sandstone formations over extended periods.