The most distinctive part of Landscape Park Strunjan are its cliffs, up to 80 metres high, which have been, together with their bosky edges and the 200-metre-wide sea belt underneath, declared a nature reserve.

This is also the longest stretch of natural seashore in the entire 130 kilometre coastline between Grado, Italy, and Savudrija, Croatia, which circumscribes the Gulf of Trieste.

The precipitous faces and the pebbly beach at the foot of the cliffs are entirely left to natural processes, which constantly mould the friable layers of rock, finely chiselling their features.

Off to the Cliffs

The term cliff denotes a high, steep or overhanging rock face composed of solid rock or unbounded, aggregate sediments, in addition to its place along and above, in this case, the seashore.

The Cliffs of Strunjan, like most of the Slovene littoral region and the entire area of Landscape Park Strunjan, are composed of Middle Eocene flysch rock. Flysch is a heterogeneous formation characterised by rhythmically repeated sequences of various types of rock, which accumulated 40 million years ago in deep marine waters. Underwater avalanches of mud and sand provoked by earthquakes, violent storms or tsunamis slid down steep slopes and deposited in the deep sea with upward fining of the material. The accumulated sediments compacted and cemented into hard strata of flysch rock. Due to subsequent tectonic uplifts the sea basin narrowed, the sea receded and the flysch rocks wrinkled, crumpled and rose to the surface, where they can be studied and admired today.

At the bottom of each cycle in the flysch are coarse conglomerates, which usually evolve upwards into sandstone and fine-grained mudstone or marlstone. The individual beds in the flysch differ in depth, in Slovenia they are commonly thin (a few centimetres to several dozen centimetres).

A peculiarity of the flysch facies in the Slovene coast, however, is that the sequences are occasionally intercalated with up to a few metres thick limestone layers, also termed megabeds due to their extent.

The appearance of the Cliffs of Strunjan is constantly changing. Its configuration was determined in its formative era by tectonic activity, which created picturesque faults, folds and fractures, most noticeable in Cape Strunjan in the west and Cape Kane in the east, while the changes that we are actually able to witness result from the processes of weathering and erosion. These produce gullies, rills and other landforms typical of cliffs.

A fracture is an interval in the continuity of a layer of body of rock caused by stress, which caused the rock to crack open while showing little or no visible movement. There are two primary types: tensile and shear fractures.

Tensile fractures or joints are normally perpendicular to the load axis and can measure between a few centimetres and several hundred meters. They are open-mode fractures providing flow paths for aqueous solutions with varying amounts of dissolved minerals. The minerals precipitated out of the saturated solution fill the fractures and create veins. In Slovenia, the veins are most frequently infilled with calcite and flint.

Shear fractures run parallel to the load axis, they are closed and without veins.

There are also joint systems, consisting of several intersecting joint sets, which are families of parallel, evenly spaced joints that can be identified on the basis of orientation, spacing and physical properties.

A different type of discontinuity in a volume of rock is a fault, which divides a rock into two planes across which there occurred visible displacement. Almost all vertical or cross-layer faults in the Cliffs of Strunjan are calcite-mineralized.

Weathering is the physical and chemical breakdown of rocks caused by atmospheric phenomena and biological organisms. The weathered material, combined with organic material, creates soil. Erosion, on the other hand, is the fragmentation, fretting and flushing away of rocks due to the natural agencies of water, wind and ice, and their transportation and deposit in a different location.

The speed of erosional processes in flysch rock is largely dependent on the thickness and structure of its composing layers. Mudstone and marlstone beds are softer and less resistant to weathering and the wave action of the sea than sandstone and limestone strata, so wave-cut notches form at the base of flysch cliffs, identifiable as compact overhanging rock. Continued erosion under this overhang eventually leads to sandstone and limestone layers breaking off and falling onto the shore underneath.

As flysch is friable, susceptible to changing shape due to the atmospheric conditions as well as the actions of sea waves and currents, the Slovene coast and sea bottom are characterised by gradual, rather than steep inclination.

At the point of contact between land and sea an abrasion shelf of various breadth can form, continuing under the water table into a submerged marine terrace and ending at several metres of depth in a steep declivity. The height and gradient of the rock face, the presence and width of the abrasion terrace and the sea depth vary from cliff to cliff. Cape Ronek features the rock face with the steepest incline (around 70°) and at the same time the shelf-terrace formation with the minimum gradient in the Slovene coast. The shore runs at right angles to the orientation of the flysch layers, which classifies it as a ria-type coast.

The larger and mostly fairish rocks on the shore and in the shallows originate in the thicker limestone beds in the flysch; the grey or brown stones that cover the major part of Slovene shorefront and shallow seabed derive from sandstone strata, while marlstone is more susceptible to decay and together with the remains of sea organisms builds the silty substrate. The latter, combined with the shallowness of the sea and a relatively large number of small tributaries into the Gulf of Trieste, is a major factor influencing the turbidity of seawater in this area.

The giant blocks of limestone (formerly part of higher-lying cliff strata, which broke off and fell into the sea) that can be seen on a walk on the beach are perfect for observing fossils. Among the most easily detectable are the calcareous shells of marine plankters (the so-called foraminifera), portions of broken off spines and tests of sea urchins and red algae remains.

Although infrequently, the fossilised remnants of living organisms visible to the naked eye, such as portions of tree trunks, sometimes plant leaves, can also be found in the sandstones on the seashore. More often, though, these preserve the marks left behind by the organisms while they were alive. Such stones are called ichnofossils or trace fossils. Most traces reflect the behaviour of their makers (crawling, creeping, resting, eating…), but not their biological affinity

Trace fossils can easily be discovered by simply turning around the gravel stones lying on the beach. However, it is important that you not take them away or reposition them after observation; please put them back where you found them, as they are home to marine organisms that hide under them during low tide.

Did You Know that the Cliffs Are Receding?

The processes of erosion, which on the Cliffs of Strunjan occur quite rapidly, cause the surface to lower and the slopes to retreat inland. That is why we say that the cliffs are receding, about one centimetre a year on average.

Due to the action of sea, rain, sun and wind the flysch rock cracks, crumbles and falls down. On a visit to the seashore you should therefore avoid the bald, exposed and steep slopes of the cliffs.

Utilisation of Flysch Rock

Two flysch rock components – sandstone and marl – have a long tradition of use in building construction.

There used to be quite a few sandstone quarries in the littoral area – on the Milje Hill (Jelarji, Premančan, Debeli rtič, Valdoltra), near Puče, in Boršt and in the environs of Prešnica – but only those near Jelarji, Puče and Boršt have remained active to date. The grey to brown fine- to medium-grained stone extracted there is used primarily in the production of stone pavers, while in the past, it was commonly utilised in house construction. Most of the old Istrian houses are in fact built with blocks of flysch sandstone.

Marl, on the other hand, the rock with the largest content share in the composition of flysch, is the primary raw material in the production of cement. It has also been utilised in the Anhovo cement factory.

Nature on the Cliffs

Sub-Mediterranean Deciduous Forest

The Mediterranean climate and soil formed on flysch bedrock favour the growth of a sub-Mediterranean deciduous forest, which is the prevalent association of plant species in Slovene Istria.

The steep northern and western faces and the upper edges of the cliffs in the Strunjan Nature Reserve are covered by a typical European hop-hornbeam and downy oak community, with the autumn moor grass (Sesleria autumnalis) as the most widespread undergrowth species. In the warmest locations, the understory also includes typical Mediterranean taxa, such as the evergreen rose (Rosa sempervirens), wild madder (Rubia peregrina), wild asparagus (Asparagus acutifolius), osyris (Osyris alba) and rough bindweed (Smilax aspera).

In the shadowy positions, the composition of the forest changes and the stand expands to include the somewhat more mesophile Turkey oak (Quercus cerris). The proximity of the settlements and the long-term human action manifest in the large number of non-native species in the area, such as bay laurel (Laurus nobilis), laurustinus (Viburnum tinus), Aleppo pine (Pinus halepensis), Turkish pine (Pinus brutia), European black pine (Pinus nigra), holm oak (Quercus ilex), Italian cypress (Cupressus sempervirens), and others.

The sub-Mediterranean wood species present on the cliffs are (listed by frequency): European hop-hornbeam (Ostrya carpinifolia), manna ash (Fraxinus ornus), downy oak (Quercus pubescens), hawthorn (Crataegus monogyna), a variant of scorpion senna (Coronilla emerus subsp. emeroides), Spanish broom (Spartium junceum), Oriental hornbeam (Carpinus orientalis), smoke bush (Cotinus coggygria), wild service tree (Sorbus torminalis), service tree (Sorbus domestica), Christ’s thorn (Paliurus spina-christi), field elm (Ulmus minor), field maple (Acer campestre).

Mediterranean Vegetation

The living conditions in Slovene Istria are unfavourable for most genuine Mediterranean plant species, which is why we see these more frequently planted in parks and gardens, but still, due to the proximity of the sea and the warm climate some of them can flourish in the natural environment, too. The most particular among these are the strawberry tree and the common myrtle, whose northernmost autogenous habitat in the Adriatic is precisely in the Strunjan area.

The strawberry tree (Arbutus unedo) is a shrub or small tree with reddish bark that is typically flaking in older plants. The leaves are evergreen, ovate and elongated, with a serrated margin. The strawberry tree flowers in September and October. The tiny bell-shaped flowers are white and produced in pendent panicles. The fruit is an orange to reddish berry with a rough surface. A peculiarity of the strawberry tree is that its berries take almost a year to mature, so the flowers often appear while the previous year’s fruit is ripening. The berries are edible, often used to make jams and liqueurs.

The common myrtle (Myrtus communis) can also grow as a shrub or a small tree. Its long lanceolate leaves are evergreen, with an entire margin and a characteristic smell, reminiscent of eucalyptus. The flowers are white, with five petals in a stellate arrangement and many stamens. The fruit is a blue-black berry, in Sardinia and Corsica used to make a sweet liqueur.

Two other flowering plants native to the Mediterranean which flourish in Slovene Istria both wild and cultivated, are bay laurel (Laurus nobilis) and laurustinus (Viburnum tinus). The birds feeding on their fruits spread their seeds, which in favourable conditions germinate and develop into shrubs or even several metre high trees.

Cliffs’ Buglife

The forests, shrublands and meadows, along with the agricultural and cultural landscapes, which extend over the 65 hectares of the cliffs in the form of various habitat types, are also home to numerous animal species. At present, the best studied class of animals inhabiting Landscape Park Strunjan is that of insects, and within them the orders of moths and butterflies, mantises, grasshoppers and katydids.

A peculiarity from the latter group is the recently observed Andreiniimon nuptialis, only recorded three times previously in Slovenia. Based on the data in scientific literature this insect species is widespread in the southern Balkans and central Italy. A. nuptialis is a member of katydids, also known as bush crickets, which represent one of the rare insect groups where the general means of communication is sound. The males especially are well-known for their loud shrills during the mating period.

The numerous moth and butterfly varieties inhabiting the cliffs’ area also include three alien invasive species unintentionally introduced to Slovenia in recent years as a result of globalisation.

The box tree moth (Cydalima perspectalis) is native to Asia, its homeland stretching across the territories of Japan, Taiwan, China, Korea, the Russian Far East and India. The caterpillars, which feed on the leaves and shoots of the host plant, are causing great damage in Europe, as their natural regulation has not yet been established in this new environment. Synthetic insecticides and, for the males, pheromone traps, are used to protect the box tree shrub, while the most natural weapon against this pest is birds.

The geranium bronze (Cacyreus marshalli) is the first allochthonous species of butterfly discovered in Slovenia. It originates in South Africa and was introduced to Europe, initially to the Balearic Islands, in 1987 via Pelargonium geranium bedding plants, the primary hosts of the caterpillars of this animal. The caterpillars feed largely on the flower buds and leaves, but also make burrows into the stem, completely destroying the plant. This small butterfly species from the Lycaenidae family was first recorded in Slovenia in 2008 and can now be found primarily in the Primorska region. Since the continental climate seems not to agree with this insect, and given that adult individuals develop quite late in the year and have a low survival rate in winter conditions, the spread and proliferation of geranium bronze in other areas of Slovenia is questionable.

The tomato leafminer (Tuta absoluta) is one of the major tomato crop pests. This moth from the family of Gelechiidae, which started spreading over South America in the 1960s, was introduced to Europe in 2006 with international trade in tomato fruits. It took only three years for it to reach Slovenia. The primary host of the tomato leafminer, as it name reveals, is the tomato, but the insect also attacks the potato and other nightshades, causing the vermiculation of their fruits. In warmer geographical areas it can rapidly destroy large quantities of crops, as up to 12 generations can occur in a single year and the insect is capable of survival in all its developmental phases