Limestone and the Karst Landscape of Apokoronas The first ride in Reading the Landscape took me down to the coast and the salt pans cut into the rock beside the sea. Today the route went in the opposite direction, away from the coast and into the broken limestone country of Apokoronas. The subject was not difficult to find. Stone was everywhere. The ride started in Kokkino Chorio and ran through Drapanos, Paleloni and Kefalas before entering the Enchanted Forest. From there I followed the Dry Stone Wall Track onto Litsarda Ridge, descended through Cold Valley to Vryses, and then began the return by the Riders Church Climb. The route continued across Vamos Ridge to Xerosterni, then through Drapanos and back to Kokkino Chorio. The ride covered 33.5 kilometres with 710 metres of ascent and 710 metres of descent. Moving time was 2 hours 2 minutes, with an average moving speed of 16.4 km/h and a maximum speed of approximately 52 km/h. The highest point was approximately 350 metres, with the lowest at around 60 metres. Maximum recorded gradients were 13.8% uphill and 13.8% downhill. This was familiar country, but today's subject required me to look at it differently. Stone Across this part of western Crete, exposed limestone is such a common part of the landscape that it is easy to stop noticing it. It appears beside tracks, breaks through fields and hillsides, forms ridges and outcrops, and sometimes dominates the ground completely. In places there is barely enough soil to cover it. Trees and scrub grow between the rocks, taking advantage of fissures and pockets where soil and moisture have accumulated. On today's route there were places where the limestone became particularly prominent. Large irregular formations stood above the surrounding vegetation, some broken into sharp projections, others deeply fissured and weathered. They looked almost chaotic. They are not. What can be seen on the surface is the result of a very long process involving the nature of the rock, the movement of water and the gradual development of a karst landscape. Limestone and Water Limestone consists principally of calcium carbonate. It is particularly susceptible to chemical weathering by slightly acidic water. Rainwater absorbs carbon dioxide as it passes through the atmosphere and, more importantly, as it moves through soil containing decaying organic material. This produces a weak carbonic acid. It is not dramatic. Nothing happens quickly enough to be observed during a ride. But over long periods the water slowly dissolves the limestone. Existing joints, cracks and fractures provide routes into the rock. Water enters them and gradually enlarges them. Small openings become larger fissures. Surface depressions develop. Drainage can increasingly disappear underground. The collective result is what geologists call karst. Crete contains extensive areas of karst terrain, and western Crete provides some particularly clear examples. Today's photographs show the process on a relatively small scale. The limestone is fractured and irregular. Some sections have been reduced into narrow projecting forms while other, more resistant masses remain standing. Hollows and fissures separate individual blocks. Vegetation has established itself wherever sufficient soil and moisture have accumulated. This is not simply loose stone lying on a hillside. It is the exposed structure of the landscape. Where the Water Goes One of the more interesting consequences of limestone geology is the relationship between the amount of rain that falls and the amount of water visible on the surface. Western Crete can receive substantial winter rainfall, particularly over the higher ground, yet much of the limestone landscape becomes extremely dry during summer. Part of the explanation lies beneath the surface. Where limestone is heavily fractured, water can penetrate through joints and fissures rather than remaining above ground. As those openings are gradually enlarged by dissolution, underground drainage systems can develop. Water that disappears into the limestone may eventually emerge elsewhere as a spring. This is why caves, springs, seasonal watercourses and apparently dry limestone country can all form parts of the same hydrological system. What appears dry on the surface does not necessarily mean that water is absent. It may simply be underground. Stone and Vegetation The photographs from today's ride show particularly well how geology affects vegetation. The ground is not uniformly covered. There are extensive areas of exposed limestone separated by patches of dry grass, scrub and trees. Some of the larger trees appear almost to grow directly from the rock. They do not, of course. Their roots are exploiting the fractures and pockets within it. Soil accumulates in depressions and fissures. Organic material gathers there. Water is retained for longer than it is on the exposed rock surface. Plants become established and their roots penetrate still further into existing weaknesses. The distribution of vegetation is therefore partly controlled by the stone beneath it. Once that relationship is recognised, the hillside begins to make considerably more sense. The rock determines where soil can accumulate. The soil influences where vegetation can become established. Vegetation affects the movement of water and contributes organic material to the ground. What appears at first to be a random mixture of rock, grass, scrub and trees is the visible result of several connected processes. Stone Beneath the Wheels For a mountain biker, there is another way of understanding limestone. You ride across it. On an E-MTB, the geology is transmitted directly through the tyres, suspension and handlebars. Where sufficient soil has accumulated, a track may be relatively smooth. A few metres later the soil can disappear and the underlying limestone becomes the riding surface. The character of the track changes immediately. Exposed rock produces edges, steps and irregular wheel lines. Fractured limestone creates loose material. Water erosion can expose still more stone. On steeper ground, the combination of fixed rock and loose fragments requires careful choice of line. The geology therefore affects far more than the appearance of the landscape. It affects movement through it. The old tracks across this country were not laid out independently of the terrain. They had to negotiate ridges, depressions, steep slopes, exposed rock and natural passages through broken ground. Modern machinery can cut routes where earlier generations could not, but many older tracks still reflect the limitations imposed by the landscape. Riding them provides a different way of seeing those limitations. A line that appears perfectly reasonable on a map can look very different when the ground itself is reached. The White Mountains The most striking photographs from today's ride look beyond the immediate limestone outcrops towards the Lefka Ori — the White Mountains. That view puts the stone beside the track into a much larger setting. The White Mountains dominate western Crete. Their pale mass can be seen from much of Apokoronas, and their name is generally associated with their light-coloured limestone and, during winter and spring, snow on the higher summits. They are themselves heavily affected by karst processes. Across the range are caves, sinkholes, enclosed depressions, gorges and extensive areas where surface water rapidly disappears into the limestone. At high altitude there are landscapes in which exposed rock dominates almost completely. The mountains also demonstrate the scale on which geological processes have operated in Crete. The limestone formations visible today began as sediments deposited in ancient marine environments. Those sediments were eventually transformed into rock and subsequently caught within the enormous tectonic processes that created the mountains and islands of the eastern Mediterranean. Crete continues to occupy an active geological setting associated with the convergence of the African and Eurasian tectonic systems. The landscape is therefore not simply the result of erosion acting upon an ancient, motionless island. Uplift, faulting, fracturing, erosion and dissolution have all contributed to the ground we see today. Reading the Ground There is a tendency when travelling through a familiar landscape to concentrate on destinations. The village. The climb. The ridge. The descent. The next junction. Mountain biking reinforces that tendency because attention is necessarily directed towards the track immediately ahead. But occasionally it is worth stopping and looking at what the track is actually crossing. Today's ride crossed limestone country for much of its length. The stone determined the shape of the hillsides. It influenced where water travelled. It affected where soil accumulated and where vegetation could grow. It helped determine where tracks could be made and how those tracks have subsequently weathered. Further south, the same broad relationship between geology, water and erosion has helped create the much greater landscape of the White Mountains. The individual formations photographed beside today's route are therefore only the most visible part of something much larger. The landscape begins beneath them. And for much of today's ride, it was immediately beneath my wheels. Reading the Landscape is 50 Rides, 50 Encounters Part 1 — The Salt Pans Part 2 — Stone The next encounter will come from the next ride.