Peat Bog Course with Richard Lindsay August 16th 2013- notes from a field visit to UradalePart 2
5. Peat slip -A smaller peat slip to the north of the main slip of August 22nd 2012. S. capillifolium and s. subnitens are present. Peat depth was 1.85m
|measuring peat depth|
Taking peat cores peat cores – 0.0-0.5m depth shows uniform peat formation, Von Post score H3. An invertebrate found in the core at 20cm depth will date from 200 years ago. The cores had sphagnum visible in them, the hyaline cells were visible under Richard’s field microscope.
The second core from 0.5-1.0 m was also sphagnum rich and showed no indications of any dramatic events, Von Post score H4.
The cores taken illustrate rich steady growth of sphagnum in this area for over 1000 years.
6. Peat face
The bare peat face has been exposed for a year so oxidation has occurred and obscured some of the detail of the peat face section. Some banding is visible, for instance a pale brown layer at the base of the section. Some pockets of s. capillifolium survive just back from the edge but the bare face presents an impossible steep water gradient making it vulnerable to the 3 processes of primary consolidation, secondary compression and thirdly, oxidative wastage. The peat will shrink and sphagnum will vanish.
Light bands of pure compressed sphagnum visible in the peat face. The distortions in the bands are due to the drying that has occurred since the bog burst.
7. Destructive Peat pipes
2 processes are needed for a “bog burst”- lubrication and weakness. Cracks in the peat can extend to the peat base so that water can get down to the base of the peat or to a weak layer in the peat. Several “peat pipes” are exposed at the base of the visible edge of the slip. During heavy rain peat pipes can get so full of water that the peat above is lifted away from the base. During torrential rain water under pressure is forced through the underground peat pipes and the subsequent hydrostatic pressure lifted the peat and carried it away down the hill. It is possible to detect vulnerable areas from air photos (look for drainage lines that mysteriously disappear) or possible using ground penetrating radar.
Richard has his arm up one of the peat pipes at base of exposed edge of peat slide.
8. Constructive Peat Pipes
Constructive peat pipes can form where peat growth rapidly overcomes a stream course
“puddling” a classic sphagnum cuspidatum pool