📋 Logging Tasks (Answer to log your find):
Please visit the summit area and observe the rock formations near the trig point. Then send me answers to the following:
1. At the summit near the trig point please describe the colour and texture of the large rock formation. Can you identify any layers, fragments, or embedded materials?
2. Based on what you observe, which type of volcanic rock (e.g., lava flow, tuff, agglomerate) do you think it might be? Please describe why this might be.
📸 Optional but appreciated: Post a photo of yourself or an item at the trig point or with the rocks (no spoilers of your answers, please).
🏔 About the Summit & Trig Point
At the highest point of Black Fell, you’ll see a concrete pillar — this is a trig point (short for triangulation point). These were built by the Ordnance Survey during the 1930s–60s to create accurate maps of Britain. Surveyors used them to take angular measurements between hills using theodolites, helping create a network of fixed points across the country.
This trig point is built directly into the Borrowdale Volcanic bedrock, which provides a stable foundation — both physically and geologically.
🪨 Geological Story of Black Fell
The summit of Black Fell is part of the Borrowdale Volcanic Group (BVG), a complex of ancient volcanic rocks that form the central highlands of the Lake District. These rocks formed in a subduction zone volcanic arc, similar to modern-day Japan or the Andes.
🧱 Key rock types here include:
- Andesite & Dacite Lava Flows
Solidified molten lava from explosive eruptions. Fine-grained, dark-grey to greenish in colour.
- Volcanic Tuffs
Formed from layers of compacted volcanic ash. Often banded and finer in texture.
- Agglomerates or Breccias
Made from larger, angular volcanic fragments (bombs, blocks) embedded in a finer matrix.
The volcanic activity occurred around 450 million years ago (Ordovician period), and the resulting rocks have since been uplifted, folded, fractured, and shaped by glacial erosion. The Ice Age carved out valleys and exposed these formations — some of which you can touch at this very summit.
🌬 Weathering & Glacial Effects:
- Glacial action may have polished some of the exposed rocks and left striations (scratches) in places.
- Look out for blocky fractures caused by frost shattering — water freezing and expanding in cracks over time.
- Lichen-covered surfaces may obscure some features but are part of the weathering story.
🧭 Access Notes
- A popular route ascends from Tarn Hows, with well-marked footpaths.
- The terrain is moderate, with occasional rocky and steep sections near the top.
- Respect this fragile upland environment — take only memories, leave only footprints.
📚 Learn More
- British Geological Survey: https://www.bgs.ac.uk
- “The Lake District – Landscape and Geology” by Paul Gannon
- OS Explorer Map OL7 – The English Lakes: South-eastern Area