Porthleven Cliffs East

Site of Special Scientific Interest · 50.0812, -5.3184

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Also within

Cornwall County Cornwall Scenic Area King Charles Way - Penzance to St Mawes National TrailSouth West Coast Path National Trail

Condition (Natural England)

Favourable (4) Part Destroyed (1)
UnitFeatureConditionArea (ha)Assessed
SW626254 — Favourable 8.46 2024-02-21
SW627254 — Favourable 8.46 2024-02-21
SW628253 — Favourable 8.46 2024-02-21
SW629253 — Favourable 8.46 2024-02-21
SW636247 — Part Destroyed 5.51 2024-02-21

Climate exposure

This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.

Coastal

Coastal habitats are exposed to sea-level rise and storm erosion. Where hard sea defences sit behind them, there's nowhere landward to retreat to — a squeeze that keeps compressing the habitat no matter how well it's managed.

Habitats

Coastal vegetated shingle

Geology & landscape

Rock Type: Flint, Slate

Landscape processes: Coastal, Volcanic / Igneous

Description

Porthleven Cliffs East˙ SSSI Description Porthleven Cliffs East comprises a 1.5 kilometre stretch of coast immediately to the east of Porthleven, three kilometres south-west of Helston. The cliffs and beach are of particular interest for their geology and coastal morphology. Porthleven beach is an integral part of the classic coastal landform which includes Loe Bar to the east. The beach system is an essential member of a suite of major beaches formed and maintained by predominantly south-west wave regimes. The beach comprises mainly flint shingle and coarse sand. Inputs from adjacent cliffs are small, and overall the beach is in deficit. The geology interest of Porthleven Cliffs includes both intrusive igneous rocks and complex Variscan structures. The igneous interest is confined to the north-western half of the site. Although generally regarded as the type area of the Mylor Series sediments of West Cornwall, this section of coast also exhibits many small high-level intrusive greenstone bodies. The main interest lies in their contact relationships which indicate intrusion into wet sediments and thus were penecontemporaneous with sedimentation, unlike some of the larger intrusive bodies in south-west England. The Variscan structures extend along the entire section of cliff. This locality provides an outstanding illustration of the interplay of the three main regional phases of deformation which affect South Cornwall. There are three generations of folds and associated cleavages cut by a series of steep northeast-southwest extensional faults. The section lies at right angles to the dominant north-easterly strike of the structure. Exposures of thin-bedded Mylor slates show an eastwards transition to more proximal Gramscatho turbidites. The stratigraphy is cut up into a number of fault-bound packages which probably contain repetitions of parts of the sequence. Within some slices there is a suggestion of fining up from slate to greywacke. The ‘Carrick Thrust’, which supposedly marks the Mylor-Gramscatho boundary, is not evident in the exposures and if it exists, it has been cut out by normal faulting. First generation folds are especially well represented in the striped Mylor slates. Folds and thrusts marking the second regional deformation phase are intermittently developed throughout the section but are more prominent towards Loe Bar. Recumbent third generation folds overprint the earlier deformation phases giving rise to spectacular fold interferance patterns. The latter phase is associated with the emplacement of the Cornubian batholith.

Plant communities

MC6 — Coastal vegetated shingle, Hard cliff and cliff slope

Atriplex prostrata-Beta vulgaris ssp. maritima sea-bird cliff community

Daucus carota, Sonchus oleraceus, Taraxacum officianalis, Tripleurospermum maritimum, Cochlearia officinalis, Silene uniflora, Spergularia rupicola, Atriplex hastata, Malva arborea, Plantago coronopus, Armeria maritima, Polygonum aviculare, Rumex crispus, Bromus hordeaceous, Catapodium marinum, Dactylis glomerata, Festuca rubra

SD1 — Coastal vegetated shingle, Sand dune

Rumex crispus-Glaucium flavum shingle community

Solanum dulcamara, Crithmum maritimum, Cirsium arvense, Cirsium vulgare, Helminthotheca echioides, Hypochaeris radicata, Jacobaea vulgaris, Lactuca serriola, Leontodon saxatilis, Senecio viscosus, Sonchus arvensis, Sonchus asper, Tripleurospermum maritimum, Crambe maritima, Cerastium fontanum, Honckenya peploides, Sagina apetala, Silene uniflora, Atriplex prostrata, Sedum acre, Euphorbia paralias, Lathyrus japonicus, Geranium robertianum, Glaucium flavum, Plantago coronopus, Plantago lanceolata, Rumex crispus, Potentilla anserina, Ammophila arenaria, Arrhenatherum elatius, Elytrigia atherica, Elytrigia juncea, Festuca rubra, Holcus lanatus, Lolium perenne

SD2 — Coastal vegetated shingle, Sand dune

Honkenya peploides-Cakile maritima strandline community

Salsola kali, Achillea millefolium, Cirsium arvense, Eryngium maritimum, Hypochaeris radicata, Senecio vulgaris, Sonchus arvensis, Tripleurospermum maritimum, Cakile maritima, Cerastium diffusum, Honckenya peploides, Silene uniflora, Stellaria media agg., Atriplex glabriuscula, Atriplex laciniata, Atriplex littoralis, Atriplex patula, Atriplex prostrata, Sedum acre, Polygonum oxyspermum subsp. Raii, Rumex crispus, Potentilla anserina, Agrostis stolonifera, Ammophila arenaria, Arrhenatherum elatius, Elytrigia juncea, Elytrigia repens, Festuca rubra, Leymus arenarius, Poa annua

SD3 — Coastal vegetated shingle, Sand dune

Matricaria maritima-Galium aparine strandline community

Bolboschoenus maritimus, Juncus bufonius, Juncus gerardii, Ligusticum scoticum, Matricaria discoidea, Sonchus arvensis, Sonchus asper, Tripleurospermum maritimum, Mertensia maritima, Cakile maritima, Cochlearia officinalis, Honckenya peploides, Stellaria media agg., Atriplex glabriuscula, Atriplex patula, Atriplex prostrata, Triglochin maritimum, Plantago maritima, Armeria maritima, Rumex crispus, Glaux maritima, Galium aparine, Agrostis stolonifera, Elytrigia repens, Festuca rubra, Holcus lanatus, Leymus arenarius, Poa annua