Stratigraphic and Tectonic Structures
Gulf of Gera Fault
Ophiolite Tectonic Nappe
Olympos Tectonic Window
Aghia Paraskevi Fault
Tria Marmaria – Kryfti Gorge
The Geopark of Lesvos is a unique place as here are revealed important evidence of the geological history of the Aegean basin for the last 300 million years. Particularly beautiful landscapes and landforms which were formed through the passage of time are witnesses of the complex geohistorical evolution.
Lesvos Geopark provides information even for the early stages of evolution of the Aegean, when at that time there was a big ocean, the Tethys. The Tethys was an ocean for hundreds of millions of years. The ocean of Tethys closed and was completely destroyed 45 million years ago.
At the same time, in the central Aegean there was a mythical land area called Aegiis, which was united with both the Asia Minor hinterland and continental Greece. The Geopark of Lesvos was part of this single land area which was covered by dense tropical – subtropical forests. 21,5 to 16,5 million years ago in the northeastern Aegean, intense volcanic activity created the major volcanic centers and the impressive volcanic structures in Lesvos Geopark, which led to the creation of the Petrified Forest of Lesvos.
Impressive geosites dominate in every corner of Lesvos Geopark, enigmatic edifices that stand proudly, forming a unique dreamlike setting, where even a single humble rock, in the land of Theophrastus, the first scientist who taught the distinction and classification of the stones, has a story to tell.
Tria Marmaria - Kryfti Gorge - Nappe
An important geosite is in the area of Kryfti, which is typical for the formation of the rocks and provides evidence on the presence of tectonism in the North Aegean.
The area showcases impressive images of tectonic mixtures (mélange), geological formations that show a chaotic structure, as smaller or larger pieces of rocks are found mixed within the matrix. They consist mainly of crystalline limestone, quartzite-mica schist, prasinites and ophiolites.
The ophiolites are rocks formed from magma rising to the bottom of the Tethys ocean as it opened and was in the process of creation. About 150 million years ago the geological conditions changed. The large landmasses of Laurasia and Gondwana began to converge. The rocks that formed the ocean floor of Tethys were pressed, spun and overthrusted on the continental margin of Eurasia, hundreds of kilometers away from their original position, overcoming other rocks which are currently below the ophiolitic rocks of the ocean floor of Tethys.
The tectonic mixtures were created during the placement of the ophiolitic mass on the continental margin. The basement limestones (like the mountain of Panaghia Kryfti), were detached from the continental margin during the placement of the ophiolites and mingled with them. Today they dominate in the area as they appear enclosed within the tectonic mixtures.
The rocks of the area have been strongly influenced by a large strike-slip fault with a NE-SW direction, showing the impressive vertical gradients of tectonic mixtures in a zone hundreds of meters wide. The fault is responsible for the creation of the gorge and the hot springs that flow in the area. The geological structure (type of rock, fault, etc.) is responsible for the creation of caves that characterize the area, one of which has been used for the building of the chapel of Panaghia Kryfti.
The Antissa Fault runs through the volcanic rock of the Skamiouda hill. The fault plane creates a steep bluff. It is one of the most distinctive faults on Lesvos and serves as a reminder of the enormous geological changes which have shaped the Lesvian landscape of today.
The fault was created by mounting pressure in the earth’s crust which at some point exceeded the strength of the rocks and broke them apart. The rocks on either side of the fault shifted, with one side shifting downwards.
The fault plane, meaning the rock surface where the fracture occurred, creates a sharp step in the landscape. Its surface is marked by visible friction lines called slickenlines which indicate the direction of the fault movement, evidence of the seismic activity in the region. These slickenlines were caused by the friction of rocks (quartz grains, pebbles etc) being dragged across the fault surfaces when the two sides slid past each other in opposing directions. Along the fault, one can see a zone of crushed and fragmented rocks which were a result of the grinding between the two fault blocks.
The Antissa Fault is part of the deformed structures which are linked to the great Anatolian Fault and the intense seismic activity in the North Aegean.
Aghia Paraskevi Fault
The fault of Aghia Paraskevi is one of the most characteristic faults of Lesvos and it is a unique testimony of major geological changes which shaped the present landscape of the island. It is a right-lateral fault with an impressive fault scarp (the surface where one side of a fault has moved vertically with respect to the other). On this surface appear successive generations of tectonic lines, indicative of successive strong earthquakes. These characteristic lines show that the movement was horizontal. The traces were formed as a result of friction of hard materials (quartz grains, etc.), due to the sliding of the two fragments on both sides of the fault. There are indications of its activation during the major earthquake of 1867 with seismic magnitude of 6.8 degrees on the Richter scale.
The fault of Aghia Paraskevi is part of the big Central Lesvos fault zone crossing Lesvos with a NNE-SSW direction. It runs through the central part of the island with a direction North – South, and probably continues underwater in Kalloni Gulf. This fault zone is compatible with the active stress field in the area which is affected by the major tectonic structure of the region, the North Anatolia fault, the southern branch of which runs north of Lesvos.
Mt.Olympus Tectonic Window
The bare peak of Olympus represents one of the most impressive geological spectacles of Lesvos: a tectonic half-window.
Intense tectonic forces, active during the breakup of the ancient Tethys Ocean, placed ophiolitic ocean rocks on top of the metamorphic rocks which originated from marine sediments of the oceanic plate. This rock sequence was placed on top of the carbonate rocks of Mount Olympus which was once part of the edge of an old continent.
Today in the region, lower tectonic rocks have risen up to the surface through the ophiolites and metamorphic rocks. Forming the peak of Mount Olympus, these tectonic rocks shaded in hues of white, ash grey, and rose are recrystallized limestones.
All around the perimeter of the main peak of Mount Olympus grows lush vegetation including chestnut forests, black pine forests and groves of apples, walnuts as well as olives. The mountain is part of the Natura 2000 Network and the area has been characterized as a botanical garden of the Aegean because of the great variety of endemic plants.
The limestone hill in the area of Larsos, in the gulf of Gera looks like as if it was cut by the knife of the giant Engeladus. The Larsos fault is one of the most active faults on Lesvos, a testimony of major geological changes that shaped the landscape of the island with deep gulfs and peninsulas.
Characteristic is the steep terrace and the impressive fault scarp containing polished surface areas on which are engraved the traces of the tectonic movement of the hanging wall. They were formed due to the sliding of the two fragments on either side of the fault’s surface, by the friction of hard materials (quartz grains etc). Along the fault line there is a scree zone containing angular limestone fragments.
It is a normal active fault, compatible with the active stress field. The Larsos fault scarp has a more or less east – west direction and forms a large geomorphological step, causing the sinking of the region located on the southwest side (left) forming the Evergetoulas river delta and the protected wetlands of Ntipi – Larsos.
On Larsos fault scarp during the Roman period was carved a water transport channel, which is part of the Roman aqueduct transporting water from the Mt Olympus area to Mytilene, parts of which are the Roman aqueduct of Moria and Lampou Milli.
Gulf of Gera Fault
The Gulf of Gera is a closed tectonic basin with a narrow opening. Ιt was created by large conjugate geological faults with NW-SE direction, at the eastern and western side of the gulf.
The continuous reactivation of the faults created tectonic steep scarps and terraces on the east side of the bay, extending south to the village of Loutra and northwards to the village of Pigi. Similar structures can be observed in the village of Ippios on the western coast of the gulf.
The faults of the Gulf of Gera are of particular importance because of their proximity to the city of Mytilene. Their maximum seismic potential reaches 6,5 on the Richter scale.
Along these faults, hot spring water gushes at the area of Therma in the Gulf of Gera. The water temperature is 39,7oC and the springs are defined as sodium chloride springs. The water contains ammonium chloride, sodium bromide, potassium nitrate, calcium chloride, magnesium chloride, etc.
A major geological fault with E-W direction appears in the area of Agrilia, at the end of Amali peninsula. It affects ophiolitic rocks and creates the steep southern coast of the peninsula.
Ophiolite Tectonic Nappe
The presence of ophiolitic rocks in Lesvos is a testimony of great geological changes in the Mediterranean region. They are characteristic rocks of the oceanic crust of the Tethys Ocean, an ocean that existed between Europe and North Africa 180 million years ago.
Tethys, according to Greek mythology, was the daughter of Uranus and Gaia. Tethys’ consort was Oceanus and from their union came the ocean nymphs, also referred to as the three-thousand Oceanids, and all the rivers of the world, fountains, and lakes.
The word “ophiolites” has derived from the Greek words ophis (=snake) and lithos (=rock) because of their usually dark green color (serpentinites) that resemble to the skin of a snake.
These ophiolitic rocks were formed when rising magma coming from the mantle of the earth, was solidified at the bottom of the Tethys Ocean. 150 million years ago these rocks were compressed and overthrusted at the edge of Eurasia, hundreds of kilometers away from their original position.
In Amali peninsula and in the central part of Lesvos vast areas are covered with ophiolitic rocks. Today, on the ophiolitic rocks of Lesvos grows a pine forest. Characteristic is the change of vegetation at the contact of the different rock types, changing from pine forest to olive groves that grow on the older rocks.
An important geological fault with E-W direction appears in the site of Fykiotrypa and creates the northern coast of the islet of the castle of Mytilene.
Typical is in the area the emergence of lake sediments. They are Pliocene freshwater limestones, in which are identified fossils of invertebrates such as gastropods, lamellibranches and shells. Today these freshwater rocks are found on land and are witnesses of the presence of the great lake of Mytilene, which covered the area of today’s sea channel between Lesvos and the coast of Asia Minor.
At the end of the Pliocene, early Pleistocene, about 1.8 million years ago, when Lesvos was part of a single continental area, the sea withdrawed to the south and lakes were formed in the northern and central Aegean, one of which was Lake Mytilene. In the rocks are strongly marked also the signs of marine erosion.
At the top of the rock there is the lighthouse of Fykiotrypa, which is a typical example of lighthouse of the north Aegean and the coast of Asia Minor. It is one of the few surviving lighthouses built during the eighth decade of the 19th century, in order to facilitate the approach to the port of Mytilene and the navigation in the strait between the island and the coast of Asia Minor.
It was included in the Greek lighthouses network in 1915 and the Ministry of Culture has declared it as a monument to be preserved.
Tabakaria Lacustrine Sediments of Mytilene
The Tabakaria lacustrine sediments of Mytilene are lake sediments from a large lake which once existed in the current sea channel between Lesvos and the Asia Minor coast.
These Pliocene sediments consist of freshwater marly limestones, with intercalations of sandstones, conglomerates, whitish marl and clays in which invertebrate fossils such as gastropods, lamellibranch and ostracods have been identified. The total thickness of these deposits exceeds 60m. Bearing witness to the presence of the great lake of Mytilene, these freshwater rocks are now found on dry land.
These sediments were formed when Lesvos was part of a unified landmass. During this period the sea receded southwards and lakes formed in the northern and central Aegean, among them the lake of Mytilene.