Introduction:
Temple Church in Bristol, a 12th-century structure, is well known for its leaning tower, a fascinating example of how natural geological forces shape human structures. This EarthCache focuses on subsidence, a geological process where the ground sinks due to changes in the underlying sediments. At this location, you’ll explore the relationship between the local geology, human activity, and the impact these forces have had on this historic building.
Geological Context:
Temple Church is built on alluvial deposits, layers of clay, silt, sand, and gravel deposited by the River Avon over thousands of years. These sediments are highly compressible and can compact unevenly when subjected to heavy loads, such as the weight of a stone tower. This uneven compaction has caused the tower to lean, making it an excellent case study of subsidence.
Subsidence is influenced by several factors:
- Soil composition: Clay-rich soils shrink and swell with moisture changes, while sand and gravel tend to settle differently.
- Groundwater changes: The construction of Bristol’s Floating Harbour altered the local water table, exacerbating the instability of the sediments beneath the church.
- Load distribution: The weight of the church tower concentrated on specific areas of the soil caused uneven settling.
Weathering and Observations:
As you explore the site, look for clues in the church’s stonework. Weathering is the breakdown of rock due to physical, chemical, and biological processes. Examples of weathering you may observe include:
- Surface discoloration (chemical reactions with rainwater).
- Cracks or flaking (caused by freeze-thaw cycles).
- Moss or lichen growth (biological processes breaking down the stone).
Revised Logging Tasks
To log this EarthCache, visit the location and answer the following questions. Use the information provided in the description and your observations on-site to complete the tasks:
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Subsidence Evidence:
- Observe the leaning tower from different angles. In your own words, describe how the tower's lean reflects uneven settling of the ground. Which side of the tower appears to have settled more, and what might this suggest about the underlying sediments?
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Weathering Features:
- Closely examine the church’s stone walls. Identify one visible feature that indicates weathering (e.g., cracks, flaking, discoloration). Based on what you’ve learned in the description, explain what type of weathering might have caused this.
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Geology in Action:
- Reflect on the relationship between the local geology and human activity. How might changes in the water table caused by the Floating Harbour have contributed to the subside
Additional Notes:
- The site offers a rare chance to observe subsidence in action. Consider how this geological process affects not just this tower, but other buildings worldwide.
- Be respectful of the ruins and do not climb or disturb the structure.
- Photos are aloud