No rivers, no lakes... yet this is how waters shaped Malta as we know it today
Surface and underground waters - as well as sea and climate action - all contributed to shaping the Maltese Islands
The Maltese archipelago was created through an uplift of sedimentary rocks that happened in the late Miocene and Pliocene periods, some 5 million years ago. Before it lifted above sea level, the sedimentary rock, that’s up to 25 million years old, was already being eroded when the shelf was situated in shallow waters. Afterwards, surface and underground waters, as well as sea and climate action, including the Ice Age, all contributed to shaping the Maltese Islands as they appear today.
Surface waters
The Pliocene (5.333 million years ago - 2.58 million years ago) and early Pleistocene (2,580,000 to 11,700 years ago) were marked by the Pluvial periods coinciding with the Ice Age. River tributaries coming from the north, when Malta was still attached to the continent, have eroded land to create valleys such as Wied il-Ghasel (Mosta), Wied il-Kbir (Qormi) and Wied Dalam (Birzebbuga) in Malta and Wied il-Ghasri (Iz-Zebbug) in Gozo. These present different characteristics to, say, Mgarr ix-Xini valley (Wied Hanzira) in Gozo which was formed due to fault lines.
Today, there are no permanent rivers on the islands but heavy rainfall continues to contribute to the erosion of the valleys. In addition, as waterlogged soil causes water carrying clay, soil and sand to run towards the sea, a delta may form by the precipitating coarser materials as the stream meets the sea. When clay becomes waterlogged, its viscosity causes landslipping, fracturing the overlying greensand and upper coralline limestone and causing it to slide; meanwhile, running water forms the characteristic grooves in the clay slopes.
Underground water
The porous limestone and the permeable greensand strata in the Maltese Islands allows rainwater to percolate through rock fissures to the impermeable clay strata. Perched water tables can be found at Pwales, Marfa and Comino.
Sometimes, the carbon dioxide and other gasses present in rainwater make it acidic enough to dissolve rock to form watercourses and caverns. Natural springs occur when the water finds its way to the surface through faults or the greensand and blue clay transition, otherwise it may cause a cave-in such as that at the Maqluba sinkhole in Qrendi and the many sinkholes at Dwejra, Gozo. Caves caused by subterranean water erosion include Ghar Hasan (Zurrieq), Ghar Dalam (Birzebbuga) and Chark El Hamien (St George’s Bay) in Malta and the Alabaster Caves (Xaghra) in Gozo.
Dissolved carbonate in the water percolating to the cave eventually redeposits in the crystalline form of calcite as stalagmites, stalactites or encrustation of the walls and fissures. Alternatively, water action can create conical holes in the cave roof or wall, as seen in Ghar Dalam, Ghar Hasan and Ghar il-Friefet (Girgenti).
Effects of the Ice Age
From 800,000 to 20,000 years ago, temperatures dropped to create ice ages with intermittent milder periods. Although ice advanced from the north over most of the north European plain, the Mediterranean region did not suffer directly from glaciation but experienced a series of pluvial periods that caused considerable denudation by both surface and underground water. Apart from the large number of valleys and caves that flowing, freezing and expanding waters in joints and fissures created on the islands, the increased rate of denudation also saw the development of the soil cover.
Sea action
Wave action is the main erosive factor on the coastline. It’s not just the hydraulic forces - far more powerful is the impact of sand, gravel, stones and rocks being hurled by the water, sometimes undercutting cliffs to cause great chunks to fall from above. Wave action can also create caves and when coming from two sides, natural arches are formed. The Blue Grotto with its natural arch (Qrendi) is an example. With continued erosion, a collapse arch may leave a stack such as that at Il-Mara (Birzebbuga).
Any stretch of coastline is either eroded or accumulates deposits. Hard stones whirled about in circles by surf in rough weather cause underwater potholes in the soft globigerina limestone. When these rise above sea level, the same action continues to eat away at the base. The harbours and inlets in the southeast of Malta were created in this way, due to the tilt of the Malta graben bringing the top layer of soft globigerina limestone to sea level to be easily eroded.
On the other hand, as rock fragments roll against one another, they cause rounded boulders, pebbles and sand. The colour and size of the sand particles depend on their originating bed-rock. For example, Ghajn Tuffieha Bay in Malta and Ramla Bay in Gozo share a fine golden sand, Mellieha Bay has coarser grey sand and the Blue Lagoon has thick white sand.
Climatic factors
Sea water spray and rain also have an erosive action on the softer limestone. Rain and sea water spray erosion is distinct in that it produces uneven weathering resembling a honeycomb, compared to the smooth wearing of the globigerina limestone face by wind action. Wind action also produces the sand dunes and contributes to the formation of conical hills with a flat top, such as those in Gozo.
So that's how the Maltese Islands, which were created underwater and rose to be surrounded by water, were ultimately also shaped by water.