Geology of Malta

The cliffs along the southern side of Gozo are both amazingly beautiful and very old. This Lower Coralline Limestone was deposited around 30 million years ago!

UPDATED: 2/5/2023

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When Lindsey and I traveled to Malta, I had only just begun to study the unique geology of this island nation. During our trip I was fascinated by what I learned and upon returning home spent time investigating how the geologic processes that shaped the land also affected the island’s ecology as well as the ancient people of Malta. These slow, inexorable processes persist even to this day and continue to shape the Maltese islands.

The island nation of Malta is roughly 122 square miles, less than half the size of New York City, and is located in the Mediterranean Sea, about 100 miles south of Sicily. The three islands of Malta, Gozo, and Comino are the largest and most often referenced in descriptions of the country; however, there are also dozens of tiny islands of varying sizes. While most of these islands are too small to be inhabited, a few others are. Cominotto is a popular tourist destination, and Manoel Island, located between Valletta and Sliema, has long been inhabited and currently features several modern day yacht clubs and also a large fort dating back to the 1700s. The formation and evolution of these islands dates to about 35 million years ago (relatively recently when you consider the dinosaurs went extinct about 60 million years ago) and are, much like the archaeological history of Malta, inexorably tied to the sea.

Quick Facts About Malta’s Geology

Malta is entirely sedimentary rock, mostly calcium carbonate rock deposited from marine life – a massive carbon sink.
The landmass of Malta rose out of the Mediterranean due to geologic forces.
Malta has been connected to mainland Europe at various points in the past when the height of the Mediterranean was lower.
There are no natural year-round rivers or lakes on Malta.

Check out this link for a great map showing the surface rocks of Malta, pink being the oldest, green the youngest in age.

As you look out in wonder at the beauty of Malta, take a moment to consider how it formed.

Origin of the Island of Malta

So why are there islands here anyway and what interesting geologic clues can you see while traveling to Malta? The first thing to remember is that rock layers are put down in order with (generally) the oldest rock on the bottom and the youngest at the top. Thus, the deeper we dig into the Maltese rock layers the farther back in time we go. The second point to consider is the height of ocean has changed (and continues to change) over the history of the Earth and the ground also rises and falls over time due to geologic forces, and this is especially true for Malta. There are five rock layers found on Malta, and each is identified and discussed briefly below.

layer 1: Malta’s Lower Coralline Limestone

Roughly 30 million years ago Malta did not exist. Around this time the oldest and deepest rock found on Malta started to deposit under the surface of the Mediterranean along a shallow extension of the continental shelf. What is now known as the Lower Coralline Limestone was formed by deposition from marine life. Coral skeletons and the shells of other organisms built up over time, and they fused together to form this thick layer of carbonate rock.

We were able to see beautiful examples of this when we took our hike along the huge cliffs near Xlendi Bay. We can recommend an amazing hike that leaves right from Xlendi, Gozo which will give you a chance to witness some amazing Lower Coralline Limestone cliffs (you can read more about it on our blog post here). Something interesting to point out is that each rock layer weathers and erodes at different rates due to their varying properties. As such, we found that in some places along our hike, the underlying rock layers were eroding faster than those on top resulting in a relatively thin overhang. I have no idea how strong these overhangs are so to be safe, don’t get too close to the edge! This limestone is very hard and while it was used throughout history (some of the megalithic structures are made of this stone), ancient people had no effective tools with which to cut or shape it so use was (and still is) more limited than many of the other rock types found on Malta.

Looking at the cliffs of Xlendi Bay, Gozo you are able to see millions of years of Lower Coralline Limestone deposited layer after layer.

Layer 2: Malta’s Globigernia Limestone

Above the Lower Coralline Limestone sits the Globigerina Limestone. This is a very important layer of rock because of its soft and uniform nature which makes it an excellent building material. Roughly 14-23 million years ago Malta would have been found deeper underwater since this limestone forms deep under the surface of the ocean. Tiny marine organisms called Globigerina form calcium carbonate shells. When they die, they settle to the bottom of the ocean to form a thick ooze. Much of the ocean floor today is covered with a similar ooze and is still being deposited to this day. Over time, the ooze thickens as the Globigerina die and the pressure from above begins to compact lower levels. The microscopic shells chemically bind together, transforming into Globigerina Limestone. This soft rock has a beautiful honey-like color and can be seen everywhere on Malta as a building and sculpting material. Due to the work-ability of the rock, the Maltese have been using it for millennia to create beautiful structures.

The megalithic temples like those found at Tarxien, seen here, were crafted from a mix of rock types, but the surfaces seen by ancient people were carved from Globigerina Limestone because it was soft enough to sculpt with the tools they had.

Layer 3: Malta’s Blue Clay

On top of the Globigerina Limestone is a layer called Blue Clay. This layer was deposited between 10-25 million years ago. While called Blue Clay, this layer is actually formed of blue, yellow, green, and gray clay. This layer has very fine clay-sized rock grains which would have been eroded by wind and rain from the nearby land, probably Italy. At this time geologic forces had begun pushing the sea floor upward to a depth that Globigerina could not thrive, so we cease finding Globigerina in this layer.

This layer of clay would become instrumental for the ancient people of Malta in two ways: pottery and drinking water. Clay deposits the world over have long been used for pottery, and having a local source for clay was very beneficial to the ancient Maltese. The use for drinking water stems from the characteristic of clay that makes it great for pottery: clay is impermeable to water. This clay layer traps rainwater as it passes through the permeable upper layers and creates areas of fresh groundwater (aquifers) that people have long relied upon. Malta has no natural year-round rivers or lakes so this underground water was essential to early people. However, as the population of Malta has grown in recent years desalination plants are employed to bridge the gap between natural freshwater supplies and the needs of the population.

Layer 4: Malta’s Greensand

Atop the layer of blue clay sits the Greensand layer, which formed from about 7-10 million years ago. This layer of rock formed from sand particles fusing together into a rock type aptly named sandstone. This layer helps trap water above the underlying Blue Clay later to form the natural aquifers we discussed in the previous paragraph.

Contrast between Upper Coralline and Globigerina Limestone.

Layer 5: Malta’s Upper Coralline Limestone

The youngest rock on Malta is the Upper Coralline Limestone. This rock looks similar to the significantly older Lower Coralline Limestone but was formed only between seven and five million years ago. It is a little strange to use the word “only” to describe something that happened FIVE MILLION years ago… but, well… geology is weird that way.

The upper rock layers have been eroded away in a large portion of Malta. In fact, if you never get out of the major metropolitan area around Valletta you will likely only see Globigerina Limestone under your feet. However, if you head into the hills of the western part of Malta or if you take a ferry over to Gozo, you can ascend into the younger layers.

In the image to the right (or above if on mobile), you can see the hard rock of the Upper Coralline Limestone bedrock upon which The Cittadella (Il-Kastell) of Gozo was built. Above the deep mustard color of the Coralline Limestone, you can see lighter and much softer bricks made from Globigerina Limestone. Two types of brick are present: the original and much weathered blocks and newly laid blocks from just a few years ago. The stark contrast in the speed at which the Upper Coralline Limestone compared to the Globigerina Limestone weathers and breaks down is on full display here.

Il-Kastell is an amazing structure build from Globigerina Limestone and pearched atop the much younger Upper Coralline Limestone.

Geologic Forces at Work on Malta

Of course, the development of rock layers is not the only factor of interest on Malta. The geology of this island is also largely affected by other forces at work. Here are a few of the major impacts that can be seen on Malta.

Uplift and Subsidence

Malta owes its place above the Mediterranean surface in part due to uplift of the continental shelf it is attached to. The Mediterranean is the meeting place of the Eurasian and African tectonic plates. The interactions between these throughout the ages have given rise to the Alps, both opened and closed the strait of Gibraltar (resulting in the near evaporation of the Mediterranean) and around 5 million years ago near the end of the Miocene and the beginning of the Pliocene, geologic forces thrust the floor of the Mediterranean where Malta sits up above sea level.

This process is ongoing - currently Malta is slowly sinking (this is separate from the rise of global sea levels). However, the southeastern side of the island is sinking faster resulting in the formation of cliffs on the northwestern section of the island and deep harbors on the southeast as the island tilts on its axis. For amazing cliff views check out the coasts of Gozo and northwestern Malta.

Erosion

Throughout human occupation of Malta, erosion has helped to grow the size of the country as rock from the higher elevations broke down and filled in the ocean around the edges of the island. So much rock has eroded in the past several thousand years that the coastline has changed considerably. This can be seen in the ruins of several ancient megaliths which are sometimes literally falling into the ocean. There are also ruins of a Roman harbor about a kilometer away from the present day shoreline. Both of these show clear evidence that the shorelines are not what they once were, both shrinking and growing.

Evidence indicates that Malta would have been covered in forests when humans first landed some 5,000 years ago. As seen throughout the world, harvesting lumber for fire and buildings drastically reduces the size of forests and on Malta this virtually eliminated forests from the island. To exasperate the situation, tilling the ground for agriculture loosens the soil and further increases erosion. This is especially problematic on Malta which has a dearth of arable land. Farmers now take extra care to prevent soil erosion and you can see walls and berms around fields which help contain the soil throughout Malta.

Earthquakes

While the island of Malta is in a fairly active tectonic zone large earthquakes rarely strike the island. Sometimes cave structures below the surface collapse, propagating tremors at the surface, but Malta is generally free from major earthquakes. This is interesting because there are several active volcanoes surrounding Malta and the region is tectonically active, but Malta is largely insulated from these events.

Remains of ocean life can often be seen embedded within the Limestone of Maltese buildings. Can you spot them?

Malta is a wonderful country full of rich human and geologic history. Knowing a little about how Malta originated will let you better appreciate what you see when you visit. If nothing else, you can tell your friends why there are seashells embedded within the walls of important buildings and ancient castles!

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