The geology of the White Mountains (text: Dr. G. Fasoulas, “Φουρόγατος” Magazine, Issue 54, Saturday, July 10, 2004).
The White Mountains are white indeed! This is obvious to everyone gazing the mountain range of western Crete from a distance. Regardless the orientation of approaching the region, or the season of the year, white is the color of the mountain peaks. In the winter, of course, there is the shining white of the snow that coats the summits. When this is absent, the summits seem white, again, because of the greyish-white marble that outcrops bare of vegetation in the horizon.
The White Mountains is the largest mountain range of Crete and is formed in total from marble, limestone and dolomite - rocks whose main component is calcium carbonate. In total, they were formed million years ago, in the sea from the dissolved calcium carbonate which was swept away from the earth’s rocks by rainfall.
The picture of the mountain range gives the dynamic impression of a fist that pierces the earth and sticks up in the sky – a characteristic that is due to the geological forces that lifted violently the rocks, some million years ago and continue today. In the last 5 million years this uplift, compared to the current sea level, was over 1.500 meters.
The vertical route of the rocks of the White Mountains carved deeply by the flow of surface water created large gorges, as the impressive Samaria, and large caves like Gourgouthakas which reaches 1.100 meters depth from the earth’s surface. All these are the result of the karstic erosion and the tectonic uplift of the land.
The region’s rocks
The geology of the region could have been monotonous, considering the fact that compared to the rest of Crete, the rocks present are not diverse. However, the processes that acted on them were so variable and intense, that their final result, the current terrain, is impressive.
In total, the core of the mountain range is comprised primarly of two main groups of rocks: Plattenkalk limestone and Tripali. The most important and the one that occupies the largest volume, is Plattenkalk limestone. These are the rocks that form the ridge (backbone) on which all the other groups of rocks are found, and in addition, they are the deepest rocks that are known in Crete, since we do not know what lays underneath them. Although in Crete the age of this group of rocks dates from approximately 300 million years ago, on the White Mountains only the upper parts of the group are present. Therefore, on the edge of the mountain range, greyish dolomite and limestone, of 200 million years, are present, while on the core, younger rocks appear.
One of the most characteristic rocks is stromatolitic dolomite, a dark colored rock with banded iron deposits strips, created by stromatolithes - organisms living in anoxic waters. These organisms that absorb the dissolved iron oxides and release oxygen, played a key role in the appearance of oxygen in the earth’s atmosphere 2 billion years ago. Parts of these rocks are found inside the Gorge of Samaria, mainly in the upper and western part and in the form of boulders in the riverbed.
In many parts of the mountain range, and particularly, on the top of Gkigkilos, yellowish shales with thin sandstone layers, cover the stromatolitic dolomite. These layers that are named after this characteristic summit, mark a major geological event, 160 million years ago. At that time, the ocean bed, where these rocks were formed, started to deepen at a fast rate, as a result of the removal of the lithospheric plates of Africa and Europe. The result of this phenomenon was the formation of the typical group of rocks that dominates in the mountain range, and inside the Gorge of Samaria, the squamous, greyish-blue limestone, with the distinctive white stripes or parts of cherts.
This limestone which was considered for centuries a fine construction material on the island has on its base spherical or elliptical parts of white pyrite, which according to some researchers, could be due to sponges living on the seabed, while this was relatively shallow. On the upper parts, the rock is comprised of thinner plates that can be easily separated from each other, and are alternated with stripes (ταινίες) and complex, in design, shapes of white pyrites. Both the limestone and the pyrites were formed from dissolved calcium and silicon salts in deep water.
On top of the Plattenkalk limestone, at some certain parts of the mountain range, there are very small flysch layers, deposited 30 million years ago, closing (ending) the formation process of the Plattenkalk limestone rocks.
Apart from the Plattenkalk limestone rocks, there are some other groups of rocks in the White Mountains. These are the recrystallised limestone of Tripali, the shale, mainly, rocks of the Phyllite-Quartzite group, and the Tripoli limestone. The Tripali rocks appear only in western Crete and are the distinctive white limestone of the peaks of the White Mountains that cover the Plattenkalk limestone, or the brecciated limestone with the cavities encountered from the village of Lakkoi until Omalos, or at Mount Tripali, on the east of the mountain range. Their age is between 200 and 140 million years.
The rest of the rocks, also cover the Plattenkalk limestone, but are rarest, found mainly on the east and west margins of the mountain range, even though they cover larger areas in other parts of Crete.
The route through Samaria Gorge starts from the rocks of Trypali at Xyloskalo, at the lower rocks of the Plattenkalk limestone group. In addition to the plattenkalk limestones, we encounter the schists of Gigilos and the stromatolite dolomite at the end of the steps. The rocks from about the halfway point of the Gorge until the exit at Ayia Roumeli are made up only of Plattenkalk limestone.
History and formation of the Gorge
The limestone, and generally all the rocks of calcium carbonate are very hard and resistant, but are easily dissolved by rainwater, like heated butter. This is the process of karstic erosion, where the acids of the surface water erode (melt and destroy) the limestone, releasing the calcium carbonate they contain. Through this procedure the plateaus, caves and gorges are formed, together with the other smaller shapes on the earth’s surface. Of course, the process of the formation of the karstic shapes in the White Mountains, including the gorges, was not so simple.
From the moment the rocks were formed in the sea until today, they were affected by complicated processes that started with the collision of the African and the European plate. Those were compressed, folded and uplifted, creating mountain ranges.
The rocks of the White Mountains, however, and particularly, the plattenkalk limestone, were covered, initially, from a large volume of rocks exceeding 40 km in thickness. Due to the pressure and heat developed, they were transformed into marbles, became lighter, and then suddenly sprang to the surface scattering the other rocks. Great cracks fragmented the continuity of the rock and defined the current form (shape) of the White Mountains.
The uplift of the rocks in their current place began 13 million years ago, but was more intense in the last 5. The movement of the rocks took place on the cracks, like the crack of Xiloskalo, on top of which the path meanders, which uplifted the area on the north of the gorge, or the Palaiochora-Sfakia crack that uplifted the total region of the White Mountains and triggered the development of all the area’s gorges.
Therefore, the tectonic movements continued uplifting the land against the sea, forcing the water of the streams to dig deeper into the rocks, eroding them at the same time, resulting in the creation of gorges perpendicular to the direction of the cracks. The impression that the gorges follow along and in depth older cracks is false, and this can be seen clearly from the narrow parts of the area’s gorges (e.g. Imbros, Samaria), where the rocks continue undisturbed on both sides of the gorge.
The fluctuations of the sea, however, controlled the behavior of the surface water. Therefore, when the sea level increased, which occurred many times during the interglacial periods, the stream water instead of digging, deposited material on the bank of the gorges, creating the terraces. These can be encountered around the old village of Samaria, and at the exit of the gorge, as well. There, probably during the last interglacial period, the water deposited gravel and pebbles staring from the Iron Gates until the coast. The last rise of the land (or drop of the sea level) forced the water to dig again its deposits and to create a smaller gorge, of approximately 6 meters in depth, and 1 meter wide that can be seen clearly after the kiosk at the gorge exit.
Charalampos G. Fasoulas, Ph. D.
(This is the text of the presentation of Charalampos G. Fasoulas, Ph. D. researcher of the Natural History Museum of Crete, at the Seminar on the White Mountains and its Gorges, organized by the Ecological Initiative of Chania in collaboration with the Department of Environmental Education, Directorate of Primary Education of Chania, on the 7th of February 2004, at the 16th-17th Primary School of Chania, in the frames of the Program “Volunteerism and Environment”, implemented by the Ecological Initiative of Chania, for the monitoring, protection, and promoting of the gorges of Dictamos and Machairi, the lakes Agia and Kournas, and the coasts of the northern axis of Chania).