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Earth Science Conservation Review
| Tamnagh - site of local interest | Londonderry |
| Site number: | 752 | ||
| Locality Type: | Inland exposure, Valley | Status: | local interest |
| Grid Reference: | C591025,C604000 End(s) of linear site | ||
| Google maps: | 54.86719,-7.07951 | ||
| County: | Londonderry | Council area: | Derry City & Strabane District Council |
| Period: | Quaternary | ||
| Site Description | |
|---|---|
| Highlights: | |
The site is a 5km long valley drained by the Sluggda Burn and is located between the slopes of Learmount and Sawel in the northern foothills of the Sperrin Mountains. It contains poorly exposed dissected cross-valley streamlined ridges bordered by flat-topped alluvial terraces. Further up-valley, two cross-valley ridges pass laterally and vertically into peat-covered diamict. Bordering the ridges to the south is a steep-sided ridge of well-sorted planar cross-bedded sand and cobble gravel. Directly across the valley at a lower altitude, 9m of stratified sediments are exposed in a valley-side wedge-shaped remnant. The Tamnagh valley is interpreted as a complex of cross-valley moraines, deltaic valley fill and eskers. | |
| Description: | |
The site is a 5km long valley drained by the Sluggda Burn and is located between the slopes of Learmount and Sawel in the northern footslopes of the Sperrin Mountains. In the lower section of the valley, 1.25km southeast of Park, poorly exposed dissected cross-valley streamlined ridges form several topographic highs bordered by flat-topped alluvial terraces. Further up-valley two cross-valley, 7m high ridges pass laterally and vertically into peat-covered diamict. Bordering the ridges to the south is a steep-sided ridge of well-sorted planar cross-bedded sand and cobble gravel. Directly across the valley at a lower altitude, 9m of stratified sediments are exposed in a valley-side wedge-shaped remnant. 500m further up-valley, at 30m higher elevation, three distinct steep-sided sub-parallel bedded ridges approximately 20m across by 15m high, run 200m cross-valley from a mound 30m in diameter 40m above the ridge tops. | |
| Importance: | |
The site is of scientific significance as it exposes a complex of cross-valley moraines, deltaic valley fills and eskers. | |
| Interpretation: | |
The Tamnagh valley is interpreted as a complex of cross-valley moraines, deltaic valley fill and eskers. The steep sided ridge section represents part of a glaciolacustrine valley fill including foresets of a glaciolacustrine delta prograding at 120° north into a waterbody ponded at 256m O.D. The steep slope was possibly formed in ice-contact and represents the ice-front position at the time of the deltas progradation. The poor exposure of the features in the upper-valley leaves interpretation based largely upon morphology. Small-scale bedding structures and sharp vertical contacts (interpreted as representing rapid, channelised, cross-cutting avulsion) lead to the interpretation of the slopes as primarily depositional in character and the features as eskers. | |
| Notes: | |
See also ESCR Key Site 503 - Faughan and Dungiven Basins - Tamnagh [Sand and Gravel Landscapes Block]. | |
| Keywords | |
|---|---|
| Rocks: | Diamict, Gravel, Sand |
| Relations: | Deltaic sediments, Glaciolacustrine deposit |
| Geomorph: | cross-valley moraine, delta, esker, ice-marginal lake |
| Measurements | |||||
|---|---|---|---|---|---|
| Length: | 5km | Width: | Height: | ||
| Depth: | Area: | ||||
| Access | |
|---|---|
| Approach: | This site is a 5km valley drained by the Sluggda Burn located between the slopes of Learmount and Sawel in the northern foothills of the Sperrin Mountains. |
| Uses | |
| Educ. Level: | The site is of educational value to researchers and students of glaciology. |
| Record type: | SLNCI Report | ||
| Entered by: | E M Porter | ||
| Last updated: | 09/10/03 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Tamnagh - site of local interest, County Londonderry, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=752. Accessed on 2026-11-08. |
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