The coastal cliffs of the Maltese Islands are characterised by vertical or near-vertical rock faces rising from the sea to heights of up to 70-130m above mean sea level and continuing below it down to depths of 80m in places. Steep slopes which are often terraced and which have been under cultivation for hundreds of years cap parts of these cliffs whereas spectacular boulder screes (known locally as rdum) dominate others.
Coastal rdum landscapes typically consist of an Upper Coralline Limestone block overlying Blue Clay. Erosion and recession of the latter causes the cliff edges to collapse under their own weight resulting in massive boulders which then move downslope over the mobile clay, particularly when this is wet and plastic. A boulder scree thus results at the foot of the escarpment and, where the rdum is close to sea level, extends downslope to the sea where it may form a boulder shore in places. A perched aquifer is present in the permeable Coralline Limestone, supported by the Blue Clay aquiclude. Seepage from this, in the form of scarp-foot springs, results in the slopes below the rdum receiving abundant water during the wet season and beyond.
Because of their relative inaccessibility both the vertical cliffs rising from the sea and the rdum with their boulder screes provide important refuges for many threatened and/or specialised species of Maltese flora and fauna, including many endemics.
Within the cliff systems are found examples of many unusual central Mediterranean coastal habitats, including clay slopes, boulder screes, and rocky ledges on the cliff faces and karstic limestone plateaux beyond the cliff edge. Gorges cut by extinct streams interrupt the cliffs in places and where these dry valleys (known locally as widien) open on the coast, they occasionally give rise to saline marshlands and sandy and shingle beaches. Away from the mouth of these valleys are found characteristic watercourse and spring habitats. With these habitats are associated rupestral, steppic, garigue and maquis assemblages, as well as those of temporary rainwater rock-pools that form on the karstic rock, and those of watercourses and freshwater wetlands. Because of the heterogencity of the terrain, mosaics of assemblages form, giving rise to a very rich biodiversity
The fauna of the coastal cliffs includes some of the rarest of Maltese animals. For example, the endemic snail Lampedusa melitensis occupies a very precarious habitat of a few tens of square metres on a small area of boulders on the south-west cliffs of Malta, while two other rare, endemic snails (Lampedusa imitatrix and Trochoidea gharlapsi) are found in just a few cliffside localities. The cliffside vegetation is dominated by shrubs and is especially important due to the presence of a large number of endemic plant taxa, including the Maltese Rock Centaury (Palucocyanus crassifolius - the National Plant of Malta), the Maltese Salt Tree (Darniella melitensis) and the Maltese Cliff-Orache (Cremnophyton lanfrancoi). Other important cliff-side plants include species with a restricted Mediterranean distribution, such as the Egyptian St. John's Wort (Hypericum aegypticum), the Rock Crosswort (Crucianella rupestris) and the Cliff Carrot (Daucus rupestris). Several of these ecologically important shrubs often form associations that are exclusive to the Maltese Islands such as that known phytosociologically as the Triodeno-Chilindenietum bocconei.
The vegetation of the boulder screes is also interesting in that it is often a mosaic of different vegetation types including rupestral, garigue, maquis, watercourse and coastal elements and is best termed an rdum assemblage.
The coastal cliffs, especially particularly inaccessible areas, are also important bird-breeding sites, often supporting large colonies of seabirds (e.g. Filfla, Ta' Cenc and L-Irdum tal-Madonna) some of which are important on a Mediterranean scale.
The coastal cliffs are also important from a geological and geomorphological point of view. One particular feature of regional importance is the Upper Coralline Limestone outlier (an outcrop of rock occurring in a detached location from the main body of similar rock), located in the Ghar Lapsi-Mnajdra area on the southwestern coast of mainland Malta. In the case of the Ghar Lapsi-Mnajdra outlier, the nearest outcrop of Upper Coralline Limestone occurs some 1km to the northwest. This outlier is, apart from Filfla islet, the only part of the extensive central Mediterranean Pantelleria Rift system that is currently exposed above sea level and as such it provides a unique opportunity for study of the syntectonic depositional processes associated with rift development. Additionally, the younger parts of the deposit record a Late Miocene emergence of the Maltese Islands better than that seen in any other Maltese locality.
Some cliff faces are also the only sites that exhibit all the local lithostratigraphical sequence. Moreover, specific cliffs have been designated as the type localities for several local geological strata, e.g. the Qammieh beds, Gebel Imbark member, Il-Mara member, Rdum il-Hmar beds, Tal-Pitkal member, Ghajn Melel member, Xlendi member and Ghajn Znuber beds.
Geomorphologically, the Maltese coastal cliffs present a magnificent complex of coastal land-forms including massive limestone faces rising from depths of around 100m below sea-level to a maximum height of 150m above; raised/submerged shore platforms incorporating emergent and submerged sea-caves, natural tunnels and slicken-sided faults, escarpments, boulder screes, shoreline platforms extending offshore into shoals, arches, stacks and blowholes.
Some areas are also of palaeontological importance. Features include the transitional strata between the Lower Coralline Limestone and the overlying Lower Globigerina Limestone formation, in which beds are found especially numerous remains of the echinoid Scutella subrotunda; the phosphate nodule beds and hardgrounds that separate the various Globigerina Limestone members, and Quaternary deposits which are relatively abundant in some cliff areas.
The landscape of coastal cliffs has also evolved organically over the years with several types of human uses or adaptations. These include troglodytic dwellings, agricultural terracing of unknown antiquity and their associated dry stone walling, salt pan construction, archaeological sites such as Bronze-Age villages, megalithic temples, tombs and other such features, and even relict landscapes where cliff-side agriculture and other activities have been abandoned, and where the natural vegetation is regenerating.. This superimposition of natural and cultural elements make these coastal cliffs even more important as they illustrate the evolution of the Maltese society and settlements over time under the influence of the physical constraints and opportunities presented by the natural environment, and also by successive social, economic and cultural forces. This has resulted in a sustainable land management system, which has not only maintained the landscape, but also helped in supporting the biological diversity of the area.
The coastal cliffs also assume an important role in in-situ biodiversity conservation especially for several endemic plant and animal species. Some of the endemic plants of the islands are relics from the pre-glacial Mediterranean flora (these are called palaeoendemics) and have no close relatives anywhere else in the world. The principal palaeoendemics are Maltese Cliff-Orache (Cremnophyton lanfrancoi), Maltese Rock-Centaury (Palucocyanus crassifolins, the national plant of Malta), Maltese Salt-tree (Darniella melitensis), Maltese Fleabane (Chilindenus bocconei), Maltese Hyoseris (Hyoseris frutescens), and Maltese Dwarf Garlic (Allium lojaconei). The genera Cremnophyton and Palueocyanus are monotypic, that is, represented by a single species only, and therefore, these are also endemic to the Maltese Islands. Palucocyanus is most closely related to the genus Centaurea but is more primitive than this and related genera. Cremnophyton is related to the ancestors of Atriplex. These species are therefore of interest from the evolutionary point of view since they throw light on the evolution of certain important plant groups. Other endemic plants evolved more recently, following final separation of the Maltese Islands from the Sicilian and European mainland (these are called neoendemics). The neoendemics include Maltese Sea lavender (Limonium melitense), Zerapha's Sea lavender (Limonium zeraphae), Maltese Pyramidal Orchid (Anacamptis urvilleana), and Maltese Sea-camomile (Anthemis urvilleana). These are closely related to mainland species but differ due to their reproductive isolation. Such species therefore illustrate evolutionary processes at work.
Kemmuna and adjacent islets
The whole coastline of Kemmuna and its adjacent islets is of considerable geomorphological value in view of the uniquely rich concentration of marine erosional features in various stages of formation that they display. In addition, both islands were, until recently, spared from the environmental pressures to which Malta and Gozo had been subjected and therefore still support a relatively rich ecology and a relatively unspoilt coast which also harbours some distinct features.
The islets along the western side of Kemmuna constitute by far the best agglomeration of stacks in the whole Maltese archipelago (the largest being 70-feet n1etres high); superimposed onto these features are several other geomorphological features.
The northeastern cliffs of the islet display one of the best concentrations of marine erosional features, including low-lying stacks, the submerged stumps of former stacks, natural arches and inlets formed by cave collapse combined with faulting.
The same stretch of coastal cliffs extends southwards and supports fine examples of cliff habitats that vary from high, sheer cliffs (sisien) to scree-dominated rdamijiet. and is also an important breeding site for cliff-dwelling birds including the National bird of Malta, the Blue Rock-trush Monticola solitarius.
The probable remnant of a subsidence doline survives as a shallow but steep-sided semicircular depression on the south-eastern side (the remainder having been destroyed by marine erosion or downfaulted below sea level). Further marine erosional features such as a shallow blowhole, a natural arch, and a conical stack are present below the depression.
Remarkably abundant Quaternary deposits are present along the western coast of the island and they could provide detailed information on Quaternary processes in the area. The submerged channel between Kemmuna and Kemmunett (sometimes erroneously referred to as a "lagoon") and the islets in the same area of sea are the spectacular result of a complex combination of valley formation, land submergence, faulting, and the collapse of dolines together with marine erosional features. Kemmunett itself is a large stack (the second largest in the Maltese Islands, after the islet of Selmunett off mainland Malta). A "tombolo" (double-sided sandy beach) known as Ir-Ramla ta' Kemmunett, linking two parts of the islet which are otherwise only bridged by a natural arch, is the only known feature of its type in the Maltese archipelago.
The islet of Kemmunett supports one of the best garigue habitats due to the limited human disturbance of this uninhabited islet. Interesting shrubs present include the endemic Maltese Spurge Euphorbia melitensis, the Olive-leaved Bindweed Convolvulus oleifolius, the Shrubby Kidney-vetch Anthyllis hermanniae and the subendemic Maltese Toadflax Linaria pseudoluxiflora. A colony of the Mediterranean Shearwater Puffinus puffinus yelkouan also occurs here.
Kemmunett also supports a lizard population that presents some colour variation from populations found on the other islands of the archipelago and may therefore be a distinct subspecies.