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Discovering the Ionian Islands and Exploring the Geodiversity of Zakynthos

This blog explores the geodiversity of Zakynthos (in Greek: Ζάκυνθος), also called Zante one of the seven islands of Greece’s western Eptianissa archipelago or the Ionian Islands. From north to south the once Venetian ruled Ionian Islands include Corfu, Ithaca, Kefalonia, Kythira, Lefkada, Paxi and Zakynthos.

Navagio Beach and its shipwreck in Zakynthos - Image by Diego Allen
Navagio Beach and its iconic shipwreck in Zakynthos - Image by Diego Allen

Living your best life is surely balancing the trifactor of family, work and downtime. Nothing says this more than multi-tasking by scribbling down this blog whilst experiencing the indulgence of eating a plate of Dolmadakia or freshly stuffed vine leaves, sipping a glass of locally produced wine whilst your partner catches those last minute sun rays in Zakynthos before returning homewards to Devon.

Zakynthos is the third largest of the Ionian Islands and covers an area of over 405 Km2. More traditionally known for its iconic ship wreck at Navagio Beach, the Blue Caves a coastal karst system and the National Marine Park of Zakynthos (N.M.P.Z.) on the southern shores at Laganas Beach ranked amongst the most important sites for protecting the critically endangered Loggerhead Sea Turtle (Caretta caretta) and also one of the most endangered seal species on Earth called the Mediterranean Monk Seal (Monachus monachus).

It was the Ionian islands that inspired Homer's Iliad and many of the characters and places in the Iliad have connections to the Ionian Islands and the surrounding regions. Given that this epic 156,000 word poem (in original Ancient Greek text) recounts the ten year Trojan War the Ionian Islands now face a different kind of battle to its environment. Whether that is from a dramatic increase in tourist developments, uncontrolled, unplanned construction and threats posed to the Ionian marine ecology from continued oil exploration, overfishing, marine litter, and climate change.

In 2022 research was published exploring the sensitivity of Zakynthos to both coastal erosion and flooding caused by climate change-induced hazards using the standard Coastal Sensitivity Index (CSI). The CSI investigates the impact of six physical variables of geology, geomorphology, coastal slope, rate of long-term shoreline erosion or accretion, relative sea-level change rate, mean wave height and mean tidal range.

The outcome indicated that nearly 14.1 Km or 7.4% of the entire coastline of Zakynthos had a high and very high sensitivity to climate change due to its low regional coastal slope and the presence of highly erodible sandy and coble beaches.

Rocky Shoreline of Zakynthos - Image by Joel H
Rocky Shoreline of Zakynthos - Image by Joel H

Zakynthos, also known as Zante, is one of the Ionian Islands located off the west coast of Greece. This island is not only famous for its stunning beaches and vibrant nightlife but also for its intriguing geological features that have shaped its landscape over millions of years.

The geology of Zakynthos provides a fascinating glimpse into the tectonic processes, sedimentary formations, and karst landscapes that define the region.

The rural landscape of Zakynthos is an embroidery of olive groves, lemon trees, pines and vineyards bordered by dramatic cliffs, hidden coves and white-sandy beaches washed by a temperate sea whose marine sediments grow ribbon-like meadows of Neptune Seagrass (Posidonia oceanica).

Fresh Lemons from Zakynthos
Fresh Lemons from Zakynthos

In some parts the shallow waters have naturally occurring assemblages of pipes, disc's and doughnut's from Pliocene Epoch (5.33 - 2.58 million years) aged fossilised authigenic mineral concretions.

Initially these concretions were thought to be underwater ‘archaeological remains’ of a long-lost Greek city but after research by the Ephorate of Underwater Antiquities of Greece, National and Kapodistrian University of Athens and the University of East Anglia.

They were established to have been created by a rare shallow water naturally occurring geological phenomenon and their composition acts as a natural indicator of historic seawater chemistry.

These mineralised assemblages are of Dolomite calcium magnesium carbonate mineral formed by bacteria in the shallow marine sediments. The bacteria utilise the carbon in subsurface methane escaping from the faults and fissures from deeper hydrocarbon reservoirs and change the chemistry of the sediment to form a cement-like structure or concretion.

As a result this phenomenon of in-situ inorganic precipitation on the seafloor occurs within the sediment column rather than the water column.

Doughnut Shaped Concretion from Zakynthos - Image Archaeology Wiki
Doughnut Shaped Concretion from Zakynthos - Image Archaeology Wiki

The coast is washed by the temperate and iridescent peacock-blue waters of the Ionian Sea named after Io (meaning Moon) the first priestess of Hera, the wife of Zeus and also his lover - it didn’t end well for Io!

Loggerhead Sea Turtle (Caretta caretta)
Loggerhead Sea Turtle (Caretta caretta)

The island of Zakynthos is located at the head of the present-day The Hellenic Arc a subduction zone and trench system formed along the convergent zone and plate boundaries between the subducting African tectonic and the overriding Eurasian tectonic plate. Zakynthos is actually located in one of the most seismically active regions of Greece.

This subduction zone has given rise to significant seismic activity and the release of stress from slow slip events. Over time the slow slip events can build to trigger large-magnitude earthquakes, earthquake swarms and fault interactions that deform the surrounding rock.

The island's frequent tectonic activity is recorded on Earth Quake Tracker and has played its role in shaping the Ionian Island's geomorphology, topography, hydrology and geological faults and fractures.

Zakynthos is also located at the transition between the Pre-Apulian and Ionian Zones areas of Mesozoic – Cenozoic aged marine carbonate depositions.

The Pre-Apulian zone on the island of Zakynthos is characterised Late Cretaceous to Pleistocene sediments, while the Ionian zone is represented by Triassic Period breccias and gypsum.

These zones have been extensively influenced by the mountain building of the Alpine orogeny dating back between 65 - 2.5 million years ago - though still active. This was a time when the Alps, Pyrenees and Carpathian Mountains in Europe were formed.

The Alpine orogeny created multiple episodes of large scale deformation including the Hellenides fold-and-thrust belt and interestingly also the the tilted and folded rocks known as the "Lulworth Crumple" at Lulworth Cove along the Jurassic Coast over 1,000 miles from Greece.

There are three major areas of Zakynthos including the central north-to-south mountain range with Mount Vrakhiónas the highest peak in the west. A flat fertile central plain and in the east the Vassilikos peninsula and its beaches - geology of Zakynthos shown below.

Geological Map of Zakynthos - Image by Issaak Parcharidis & LEKKA
Geological Map of Zakynthos - Image by Issaak Parcharidis & LEKKA

The geological history of Zakynthos and diverse rock formation stratigraphy is dominated by sedimentary rocks, primarily limestones, and marls. The western part of Zakynthos is dominated by limestones that both act as important natural ground water resource for the islands water supply and the soluble properties of limestone has overtime formed an unique karst landscape of caves, sinkholes or dolines, and underground rivers.

To the north of the island are The Blue Caves renowned for their stunning blue waters achieved by the refraction of the light as it changes direction and speed passing into the water having bounced off the white limestone.

The Blue Caves are a series of naturally eroded limestone caves and arches. The larger cave is called Megali Spilia and the smaller cave is named Mikri Spilia.

These sea caves are a testament to the erosive power of waves and the dissolution processes that have sculpted the island's coastline.

Blue Caves of Zakynthos - Image by Max van den Oetelaar
Blue Caves of Zakynthos - Image by Max van den Oetelaar

In the south and south east of Zakynthos, the geodiversity changes from the brilliant white limestone to expose a succession of post Alpine orogenic formations of evaporites, clay-marl beds, sandstones, calcitic sandstones, marl intercalations, shale, silt, sand and pebbles.

There are many features to these formations of interest but two stand out. Firstly, the prevalence of unconformities. For example, and based upon additional research, this coastal exposure below shows that the marls are underlain by the alternations of a sandstone and marls formation and a red sandstone formation overlays on top with an angular unconformity.

A Succession of Post-Orogenic Deposits at Cliffs at Bouka Beach (also known as Gaidaros Beach)
A Succession of Post-Orogenic Deposits at Cliffs at Bouka Beach (also known as Gaidaros Beach)

The other interesting feature of these formations and specifically the evaporites that were formed by the precipitation of minerals from evaporating water. The evaporites of Zakynthos help to explain the Messinian Salinity Crisis (MSC) a relationship between regional tectonics, climate, and oceanography.

The Messinian Salinity Crisis (MSC) was a geological event that influenced the Mediterranean Basin in the Late Miocene where the Mediterranean Sea dried up for approximately 640,000 years between 5.97–5.33 million years ago. The Messinian Salinity Crisis (MSC) was caused when the connection between the Atlantic Ocean and Mediterranean Sea became gradually isolated by the shifting tectonic activity of the African and Eurasian tectonic plates closing the Strait of Gibraltar.

USGS Landsat 5 satellite of Iran’s Dasht-e Kavir, or Great Salt Desert.
USGS Landsat 5 satellite of Iran’s Dasht-e Kavir, or Great Salt Desert.

This dramatic event created a significant drop in sea level and the evaporation of vast quantities of water leading to the deposition of an extensive halite-dominated evaporite layer of Messinian salt on the Mediterranean seafloor. The Mediterranean Sea evaporated faster than rivers could supply more water and a thick layer over 1.5 Km deep of evaporite was formed of gypsum and salt over the entire Mediterranean Sea basin. 

The Messinian Salinity Crisis (MSC) was a profound environmental crisis leading to widespread biodiversity loss due to the harsh hypersaline conditions and dry climate. In some ways a similar environmental story to Iran’s Dasht-e Kavir, or Great Salt Desert (as shown above) a once ancient salt-rich ocean that has experienced evaporation leaving behind a layer of salt as much as 6-7 Km in depth. 

The end of the Messinian Salinity Crisis and the restoration of the Mediterranean Sea would start with the Zanclean mega-flood into Mediterranean basin when the Atlantic Ocean breached the natural barrier at the Strait of Gibraltar. The volume and speed of the water flow would have been immense reshaping the landscape. The refilling restored Mediterranean sea levels and reinstated a habitable marine environment once again.

Makai Resto Bar to enjoy Mojito looking out over the Ionian Sea
Makai Resto Bar to enjoy Mojito looking out over the Ionian Sea

Zakynthos is undoubtedly known as a holiday destination less than four hours flight from the UK. Maybe as you lay back comfortably on your resort sun bed sipping your Mojito this blog may go someway to encouraging you to explore this small islands natural credentials and coastal scenery.

Zakynthos does offer a fascinating window into the geological history and high seismic risk of the Ionian Islands and knowing more about this geodynamic setting may contribute towards preserving this delicate ecosystem for future generations. 

The Fossil Coast Drinks Co Team travelled to Zakynthos from Exeter Airport with Tui Blue and stayed at the Caravel.


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