Eresztvény Quarries Educational Trail: Family-friendly geological formation with extras

Itinerary

• From Eresztvény we follow the ZT sign of the educational trail to the fork before Salgóbánya.
• At the fork we turn right onto the S◼ sign.
• From the center of Salgóbánya we follow the Z sign going straight ahead.
• We climb up to Salgó Castle via the PL and then the branching P▲ signs.
• Descending from the castle, we turn left onto the PL sign, which we follow to the Dornyai Tourist House.
• From the tourist house we follow the P sign northwards to the border of Eresztvény.
• At the asphalt road running along the border of Eresztvény we turn right onto the P+ sign, which leads back to the starting point.

Detailed tour description

Beautifully named Eresztvény, located along the road towards Salgóbánya, is the gateway to the Medves Plateau. Here you can find the modern and cozy visitor center of the Novohrad-Nógrád Geopark, where you can rest in a pleasant café after the tiring journey, while the children can run around in the excellent playground. But be careful not to let the kids burn too much energy; there will be places to hold on to during the walk!

Previously, the stone was ‘brought down’ from the notable basalt quarries of the surroundings to here by horse-drawn carriage, later by a funicular built for this purpose, where it was transferred to the narrow-gauge stone transport railway starting here, which carried the valuable stone to the stone crusher in Somoskőújfalu and to the national railway network. Eresztvény is located on the edge of the Medves Plateau formed by a basalt volcano that operated intermittently 2-3 million years ago - at the place where mining was most economical. At the beginning of volcanic activity, fine-grained debris was first scattered from the vent known today as Medves Peak, then several large lava flows created one of Europe's largest basalt plateaus. Although the largest mines were in what is now Slovakia, there was a time when ten mines operated simultaneously around Eresztvény. Our rich, especially family-friendly educational trail passes through the most important of these, starting from the visitor center with the P+ sign towards Somoskő, quickly entering the forest.

Eresztvény Great Quarry

Initially along the edges of weekend houses, then among visibly moss-covered rock spoil heaps, our winding but very well-marked educational trail with many signs leads to the first quarry. At the overview sign, where you can see the really large quarry yard, you learn that this quarry was founded by Jakab Hofbauer in the 1890s and operated until the mid-1980s. The cobblestones carved here once had great prestige. Until the 1930s, they were transported by wagon, then by a funicular built for this purpose down to Eresztvény, where they were transferred to the stone transport railway that carried the stone all the way to Somoskőújfalu. From there, the cobblestones reached not only Budapest but also Vienna, other cities of the monarchy, and even Paris. Later, with declining interest in cobblestones, the crushed stone produced by the stone crusher was transported from here.

Another sign describes the geological structure of the Medves Plateau and the structure of the lava flows, and at the bottom of the quarry yard, you can even find sheet-structured spherical stones that - believe it or not - formed as a result of sunlight even after mining ceased. The excellently cleavable, uniformly abrasive yet highly durable basalt that forms the former lava flows sometimes wears strongly and flakes off in layers (sometimes even after installation). This process, not yet fully understood today, produces these spherical stones. This phenomenon also puzzled famous stonemasons, the ritzers, since it was impossible to separate the durable stone from the lower quality freshly during mining. Let's look around carefully in the quarry yard, study the signs, then cautiously climb out along the steep path on the far side of the quarry yard!

Margit Quarry

A few steps later we arrive at the nearby Margit Quarry, where the information boards explain fascinating knowledge mainly related to human presence. A special fact is that the Medves narrow-gauge railway mentioned earlier was built twice, essentially on the same route. It was first established around 1870, transporting coal from the Medves coal mines to Somoskőújfalu railway. Then the vanished viaduct and an industrial-history curiosity tunnel under Eresztvény were built. After a few decades of operation, the tracks were dismantled, but with the boom of stone quarrying, they were relaid carefully on embankments. The approximately 10 km long stone transport narrow-gauge railway, reaching the quarry yards via branches, operated between 1923 and 1963. Margit Quarry started operation rather late; it is not mentioned in the 1930 descriptions but appears on maps from the 1960s. We also learn that stone blocks were initially separated from the wall by hand using wedges and later by blasting. Then came the ritzers, highly skilled craftsmen who did not have to ‘break’ the stone with huge hammers but split smaller and larger blocks with surprisingly easy movements based on sound. The ritzers sorted the blocks suitable for carving and paving cobblestones and split the basalt into various sizes in covered workstations called ritzer stands. Unsuitable raw materials for cobblestones were taken to a crusher and sold as crushed stone. Near the quarry, you can also see the ruins of a former ritzer house. Considering that daily commuting was impossible then, workers worked on the mountain in 10-day, later one-week shifts, resting and cooking in simple barracks and carrying water from nearby springs as a relaxing exercise.

Middle Quarry (Tavas Quarry)

Although this is one of the oldest quarries in Medves, it owes its fame more to the lake filling the quarry yard, which transforms the site into a very picturesque place and can compete with the category-winning mountain lake on Megyer Hill. The quarry also opened at the end of the 1800s and was used until the 1970s. Water is found here because mining reached a huge water lens at the bottom of the basalt layer. Regarding the famous basalt organ pipes of the area (e.g., Somoskő), we learned (or can learn at Salgó Castle) that quickly cooling basalt lava shrinks into regular, mostly pentagonal or hexagonal shapes. Shrinkage is less visible at the surface, but partly due to contemporary mining results, we can see columnar basalt trapped in vents, such as at Somoskő or Salgó. In the thus-formed rock fissures, water seeps deep under the surface and gets trapped where sediment layers under the former lava flow act as waterproof barriers. This is how the large water body in the basalt, reached during mining in this quarry, formed. Water was pumped out and later intended to be drained into former coal mines, but this plan was never realized. Besides the lake's picturesque beauty, it is known as a habitat for the freshwater jellyfish (Craspedacusta sowerbyi). These harmless, wonderful, polyp-like water creatures can sometimes be seen with the naked eye, but we should not touch them.

Another sign mentions water's important role in the ritzers' work. Blocks separated from the quarry face were often sprayed with water because cracks in the rock slowed the drying process. These cracked, so-called ‘feverish’ stones were split into various sizes for paving stones, and unsuitable material was also transported from here by narrow-gauge railway for crushing. Due to the rock decay phenomenon known from the Great Quarry, carved stones were not exposed to direct sunlight, which would have worsened their quality.

Small Quarry

Despite its name, it was the second largest quarry in the historical area of today's Hungary, where stone was split between 1920 and 1960. At one point in the quarry, it is clearly visible that among basalt from lava flow, slaggy, crumbly rock also settled in. This was called ‘trocka’ (the term derived from local coal mining), which made production quite difficult. We also learn that in 1940, during the peak of quarrying, about 500 workers were employed in the then 5-7 Hungarian quarries, but by 1960 only 227 remained, and naturally, the extracted quantity continuously decreased. Moreover, a map shows all the former quarries of Medves, which can be very useful, especially if you intend to visit the geopark’s Slovak side as well.

New Quarry

The adjacent New Quarry's signs explain the phenomenon already encountered in several places: how hard, angular basalt blocks become rounded, plate-peeling spherical stones, even within a few decades after mining ceased. The ritzers called such basalt ‘sunburnt’ rock. The main cause is daily temperature fluctuations affecting the surface-exposed rock during mining. This causes weathering along cracks, rounding the corners.

The István Tunnel Air Shaft

Our visit tracing the origin of cobblestones ends at the New Quarry; our last stop relates to coal mining. The thickest parts of brown coal deposits which formed during the Miocene under the basalt were mined at the eastern plateau (currently in Slovakia) through István Tunnel near the edge of Salgóbánya. They literally tunneled under the basalt plateau. Coal mining partly stopped in the 1960s partly because the mine entrance reached the Slovak border. However, the István Tunnel still operates, currently ‘mining’ spring water at the tunnel's end, supplying nearly 300 liters of water per minute to the surrounding residential areas. The visible air shaft on the surface was established for mine air supply.

From the wide dirt road arriving from the Medves Plateau, turning right onto the Z sign, let's glance left to enjoy views of the Medves Plateau's - not infinite but extensive and beautiful - fields. After about 100 meters on the Z sign, we turn right again, this time onto the S◼ sign that leads straight to the House of Geowonders. Definitely visit the visitor center, where you'll find further attractions and a buffet.

Conquering Salgó Castle

If taking a circular route, you can visit perhaps the most iconic location of the entire Medves region: the nearby Salgó - Kis-Salgó (Boszorkány-kő) range, where you literally get a glimpse inside a volcano, as the conical mountains are another typical volcanic form created by the basalt volcanism that formed the Medves Plateau. From the House of Geowonders we walk through Vár Street through the village to the parking lot under the castle, from where we first take the Z sign to a fork, then turn right onto the PL sign, and after about 100 meters change onto the P▲ sign to reach the castle (a sign marks the route).

Believe it or not, the Salgó - Kis-Salgó (Boszorkány-kő) range was formed along a fault, so it was not as characteristically prominent as it is today. What we see today is essentially the negative imprint created by millions of years of erosion. After volcanism ended, various rocks with different hardness weathered at different rates under external forces, mainly water, wind, and frost: terrain covered with hard basalt eroding slower than looser volcanic debris or marine sediments formed before volcanism. This transformed valleys and fissures into mountains (tectonic processes also played a role). Moreover, Salgó is one of the most characteristic domestic examples of volcanic vent fillings, meaning the cone visible today is the gradually cooled magma trapped in the former volcano, of which the surrounding tuff ring has eroded. The well-preserved castle also offers fantastic panoramic views of the Medves Plateau, Somoskő, Karancs, Salgótarján, and even the Mátra ridge looking north. Descending back to the PL sign, turning left and a short walk brings you to the once more beautiful Dornyay tourist house, from where you can return to nearby Eresztvény either on the asphalt road or via the initially asphalt road-following P sign that cuts the corner.