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Geomorphology across the Maltese Islands

The resultant geological rock strata of these marls and limestones have a marked effect on the coastal morphology giving the coast a diverse range of characteristic features.

Rifting in the vicinity of the Maltese Islands has resulted in alternate uplifting of various regions of the Maltese Islands. This has given the archipelago a tilt towards the north-east thus creating two main types of coasts. The low indented shoreline of the north east is contrasted with the sheer, rectilinear coasts of south west Malta. Here the highest point (253m) on the islands can be found at Dingli cliffs in south western Malta; while the eastern coastlines are drowned. This tilt of the archipelago is also responsible for the predominant north-eastern trend of drainage channels on Malta, Paskoff (1985).

Malta is crossed by two main fault systems representing the effects of two separate rifting episodes in the vicinity of the archipelago. The older of the two, the Great Fault, trends SW to NE, while the Maghlaq Fault system trends approximately NW to SE along the southern coast of the island and has been responsible for the down throw of Filfla to sea level. A system of horst and graben structures of east-northeast trend gives rise to a series of rifts and valleys north of the Great Fault. No well-defined horst and graben systems occur south of the Great fault. Several circular subsidence structures are distributed throughout the islands. The origins of these structures are various, but are mainly associated with solution of limestone by percolating acidified ground water leading to roof collapse of subterranean or submarine caverns.

Trenhaile (1987), Paskoff (1985) and Pedley et al (2002) mention various types of karstic landforms that give the relatively short coastline of the Islands a variety of geomorphic features. The presence of partially or totally submerged karst caves influences the development of coastal scenery around the islands. Paskoff and Trenhaile (1987) mention semicircular coves or circular subsidence structures (see opposite figure) that are distributed throughout the islands. The origins of these structures are various, but are mainly associated with solution of limestone by percolating acidified ground water leading to roof collapse of subterranean or submarine caverns. Wave action during storms can also provoke roof collapse hence forming such coves. These are evident in the southern coast of Malta. The many inlets found are partially drowned valleys of subaerial erosion. Calanques mentioned by Paskoff (1985) are ‘coastal inlets which can be of a gorge-like’ nature. According to Paskoff and Sanlaville (1978) these calanques are fault controlled.

Cliffs of two types can be found along the Maltese archipelago. Vertical plunging cliffs are formed from Lower Coralline limestone and Upper Coralline Limestone. These lack shore platforms at their feet due to the absence of mass movement processes and are probably tectonic in origin (Magri, 2002 and Paskoff, 1985). The rdum or coastal scree cliffs occur when marls of Blue Clay formations are overlaid by upper coralline limestone. The unconsolidated Blue Clay are easily eroded by wave action. After torrential rains water percolates through the overlying limestone fissures resulting in the saturation of the clay. This causes the clay to become plastic and mudslides may occur. The Upper Coralline Limestone on top is undercut and rock falls also occur. A gradual cliff retreat occurs as a result of this. The rdum cliffs are common in the north western side of Malta due to the extensive Upper Coralline Limestone plateau found (Magri, 2002).

The north-east side of Malta and north of Gozo are lacking in cliff formations. The coasts here are more stable as the geological structure is mainly composed of Globigerina Limestone and Lower Coralline Limestone. Long tracts of low, rocky coastlines of corrosion are found instead. Pools and Lapis characterise this landscape of low lying rocky shoreline. The platforms are jagged especially when cut in Coralline Limestone. Paskoff (1985) mentions the two most significant weathering processes, chemical and biological, that prevail in the area. The physical process of abrasion seems to be mostly absent.

Several coastal platforms rising to different levels are found on this type of coast. Platforms in northern Gozo form where Globigerina limestone crops out. Large boulders dislodged by storm waves can be seen scattered on platforms only on exposed coasts. Notches are also found. Beach formation is restricted to the northern shores of the Malta. The lack of beaches means concentrated tourism threats to the rare ecosystems found on the pocket beaches of the Islands.

Quaternary age deposits lie upon the Upper Coralline Limestone surface. This dips down to the North of the Comino graben. Such deposits represent relic landforms and old beach deposits that contain shells of land snails and also the characteristic irregular shapes that are formed by hardened sediment around the roots of various plants. The original root structure is no longer preserved.

The above information has been compiled by the Euro-Mediterranean Water Information System (EMWIS)